Thesis_Biomems by Keng Sukcharoenchoke

REUSABLE BIO MICROELECTROMECHANICAL SYSTEMS (bioMEMS): INTRAOCULAR DRUG DELIVERY DEVICE AND MICROFLUIDIC INTERCONNECTS by RONALEE LO

A Dissertation Paper Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (BIOMEDICAL ENGINEERING)

June 2009

Table of Contents List of Tables ..............................................................................................................xi List of Figures ...........................................................................................................xiii List of Equations .....................................................................................................xxix Abstract: Modular bioMEMS ...................................................................................... 1 1

Introduction .......................................................................................................... 2

MEMS Based Drug Delivery Devices ................................................................. 7 2.1 Introduction .................................................................................................. 7 2.1.1 Ocular Drug Delivery Methods............................................................ 8 2.1.1.1 Topical and Oral Medications.......................................................... 8 2.1.1.2 Intraocular Injections ....................................................................... 9 2.1.1.3 Implants............................................................................................ 9 2.2 A MEMS Approach to Drug Delivery: Manually-Actuated Device ......... 11 2.2.1 Design ................................................................................................ 14 2.2.2 The Components ................................................................................ 15 2.2.2.1 Refillable Reservoir and Refill Guides .......................................... 15 2.2.2.2 Cannula and Check Valve.............................................................. 17 2.2.2.3 Support Posts.................................................................................. 19 2.2.2.4 Suture Tabs .................................................................................... 19 2.2.3 Device Fabrication ............................................................................. 19 2.2.3.1 The Silicon and Acrylic Masters.................................................... 20 2.2.3.1.1 Silicon Masters......................................................................... 20 2.2.3.1.2 Acrylic Master.......................................................................... 22 2.2.3.2 Layer Fabrication ........................................................................... 23 2.2.3.2.1 The Bottom Layer .................................................................... 24 2.2.3.2.2 The Middle Layer..................................................................... 27 2.2.3.2.3 The Top Layer.......................................................................... 29 2.2.3.3 Device Assembly ........................................................................... 31 2.2.3.3.1 Cleaning ................................................................................... 32 2.2.3.3.2 Oxygen Plasma Bonding.......................................................... 33 2.2.3.3.3 Bonding Top Layer to Middle and Bottom Layers.................. 34 2.2.3.3.4 Reinforcing Layer .................................................................... 34 2.2.3.4 Dimensions of Assembled Device ................................................. 35 2.2.4 Benchtop Experiments- Methods and Results ................................... 36 2.2.4.1 PDMS Bonding .............................................................................. 36 2.2.4.1.1 Oxygen Plasma Bonding Method ............................................ 38 2.2.4.1.2 Wet Chemical Bonding Method............................................... 39 2.2.4.1.3 Results ...................................................................................... 39 2.2.4.2 Check Valve ................................................................................... 41 ii

2.2.4.2.1 Benchtop Operation ................................................................. 41 2.2.4.2.2 Characterization ....................................................................... 42 2.2.4.2.2.1 Check Valve Opening and Closing Pressures................... 42 2.2.4.2.2.1.1 Methods...................................................................... 42 2.2.4.2.2.1.2 Results ........................................................................ 45 2.2.4.2.2.2 Check Valve Closing Time Constant................................ 47 2.2.4.2.2.2.1 Methods...................................................................... 47 2.2.4.2.2.2.2 Results ........................................................................ 48 2.2.4.3 Refillability .................................................................................... 51 2.2.4.3.1 Needle Determination .............................................................. 51 2.2.4.3.1.1 Methods............................................................................. 51 2.2.4.3.1.2 Results ............................................................................... 51 2.2.4.3.2 Maximum Puncture Events and Leakage After Puncture ........ 53 2.2.4.3.2.1 Methods............................................................................. 53 2.2.4.3.2.2 Results ............................................................................... 55 2.2.4.3.3 Benchtop Refill and Dispensation............................................ 57 2.2.4.3.3.1 Methods............................................................................. 57 2.2.4.3.3.2 Results ............................................................................... 57 2.2.5 In Vivo and In Vitro Experiments- Methods and Results................... 58 2.2.5.1 Device Placement........................................................................... 58 2.2.5.1.1 Methods.................................................................................... 58 2.2.5.1.2 Results ...................................................................................... 59 2.2.5.2 Device Functionality ...................................................................... 60 2.2.5.2.1 In Vitro Delivery ...................................................................... 60 2.2.5.2.1.1 Methods............................................................................. 60 2.2.5.2.1.2 Results ............................................................................... 60 2.2.5.2.2 Device Refill ............................................................................ 61 2.2.5.2.2.1 Methods............................................................................. 61 2.2.5.2.2.2 Results ............................................................................... 61 2.2.5.2.3 In Vivo Delivery ....................................................................... 62 2.2.5.2.3.1 Methods............................................................................. 62 2.2.5.2.3.2 Results ............................................................................... 63 2.2.6 Summary ............................................................................................ 63 2.3 Electrically-Actuated Device with Dual Check Valve Device .................. 65 2.3.1 Device Design .................................................................................... 66 2.3.1.1 The Components ............................................................................ 66 2.3.1.1.1 Check Valve and Cannula........................................................ 66 2.3.1.1.1.1 Design ............................................................................... 68 2.3.1.1.1.2 Theory ............................................................................... 74 2.3.1.1.1.3 Finite-Element Modeling .................................................. 76 2.3.1.1.1.4 Valve Fabrication.............................................................. 77 2.3.1.1.1.4.1 SU-8 Valve Seat and Pressure Limiter ...................... 77 2.3.1.1.1.4.2 SU-8 Spacer Plate ...................................................... 80 2.3.1.1.1.4.3 Silicone Valve Plate ................................................... 81 iii

2.3.1.1.1.4.3.1 Simple Valve Plate: No Bossed or Overhang Features 81 2.3.1.1.1.4.3.2 Valve Plate with Bossed Feature and Valve Plate with Bossed and Overhang Features .............................................. 82 2.3.1.1.1.5 Valve Heat Shrink Packaging ........................................... 83 2.3.1.1.1.6 Benchtop Experiments- Methods and Results .................. 86 2.3.1.1.1.6.1 Valve Plate Deflection ............................................... 86 2.3.1.1.1.6.1.1 Methods............................................................... 86 2.3.1.1.1.6.1.2 Results ................................................................. 87 2.3.1.1.1.6.2 Heat-Shrink Packaging Characterization ................... 88 2.3.1.1.1.6.2.1 Methods............................................................... 88 2.3.1.1.1.6.2.2 Results ................................................................. 90 2.3.1.1.1.6.3 Packaged Valve Characterization .............................. 91 2.3.1.1.1.6.3.1 Finite-Element Analyses Results ........................ 91 2.3.1.1.1.6.3.2 Benchtop Operation ............................................ 92 2.3.1.1.1.6.3.3 Packaged Valve Opening and Closing Pressures 93 2.3.1.1.1.6.3.3.1 Methods........................................................ 93 2.3.1.1.1.6.3.3.2 Results .......................................................... 94 2.3.1.1.1.6.3.4 Packaged Check Valve Closing Time Constant . 96 2.3.1.1.1.6.3.4.1 Methods........................................................ 96 2.3.1.1.1.6.3.4.2 Results .......................................................... 96 2.3.1.1.2 Electrolysis Pump and Pump Chamber.................................... 98 2.3.1.1.2.1 Theory ............................................................................... 98 2.3.1.1.2.2 Design ............................................................................... 99 2.3.1.1.3 Refillable Reservoir ............................................................... 100 2.3.1.1.3.1 Design ............................................................................. 100 2.3.1.1.3.2 Fabrication ...................................................................... 100 2.3.1.1.3.2.1 Silicone Reservoir .................................................... 100 2.3.1.1.4 Cannula .................................................................................. 102 2.3.1.1.5 Baseplate ................................................................................ 104 2.3.1.1.6 Suture Tabs ............................................................................ 104 2.3.1.1.7 Refill Port ............................................................................... 104 2.3.1.1.7.1 Port Material ................................................................... 104 2.3.1.1.7.2 Refill Port Placement ...................................................... 105 2.3.1.2 Assembled Device........................................................................ 105 2.3.2 Summary .......................................................................................... 108 2.4 Surgical Shams......................................................................................... 110 2.4.1 Solid Surgical Shams ....................................................................... 110 2.4.1.1 Design .......................................................................................... 110 2.4.1.1.1 Solid Sham Timeline.............................................................. 113 2.4.1.2 In Vivo Experiments .................................................................... 114 2.4.1.2.1 Implantation ........................................................................... 114 2.4.1.2.1.1 Methods........................................................................... 114 2.4.1.2.1.2 Results ............................................................................. 115 2.4.1.2.2 Refill Ring.............................................................................. 116 iv

2.4.1.2.2.1 Results ............................................................................. 116 2.4.2 Hollow Surgical Shams.................................................................... 117 2.4.2.1 Design .......................................................................................... 118 2.4.2.1.1 Needle Stop ............................................................................ 118 2.4.2.1.1.1.1 Needle Ring Guide................................................... 119 2.4.2.1.1.1.2 Rigid Device Baseplate ............................................ 120 2.4.2.1.2 Hollow Sham Timeline .......................................................... 121 2.4.2.1.3 Fabrication ............................................................................. 125 2.4.2.1.3.1.1 Reservoir .................................................................. 125 2.4.2.1.3.1.2 Base .......................................................................... 126 2.4.2.1.3.1.3 Device Assembly ..................................................... 126 2.4.2.1.3.1.4 Benchtop Verification .............................................. 127 2.4.2.2 Acute and Chronic In Vivo Refill and Dispensation ................... 129 2.4.2.2.1 Methods.................................................................................. 129 2.4.2.2.1.1 Acute In Vivo Dispensation ............................................ 129 2.4.2.2.1.2 Chronic In Vivo Study .................................................... 131 2.4.2.2.2 Results .................................................................................... 132 2.4.2.2.2.1 Acute In Vivo Results ..................................................... 132 2.4.2.2.2.2 Chronic In Vivo Results.................................................. 134 2.4.3 Summary .......................................................................................... 138 2.4.4 Additional Applications ................................................................... 138 2.4.4.1 Rat Retinitis Pigmentosa Drug Delivery Device ......................... 139 2.4.4.1.1 Design and Fabrication .......................................................... 139 2.4.4.1.2 In Vivo Testing ....................................................................... 142 2.4.4.1.2.1.1 Methods.................................................................... 142 2.4.4.1.2.1.2 Results ...................................................................... 143 2.4.4.2 Cancer Treatment Device............................................................. 143 2.4.4.2.1 Design and Fabrication .......................................................... 144 2.4.4.2.1.1 Diffusion Device ............................................................. 144 2.4.4.2.1.2 Electrolysis Delivery Device........................................... 144 2.4.4.2.2 In Vivo Testing ....................................................................... 150 2.4.4.2.2.1 Methods........................................................................... 150 2.4.4.2.2.2 Results ............................................................................. 150 3

Microfluidic Interconnects ............................................................................... 152 3.1 Introduction .............................................................................................. 152 3.2 Single Interconnect .................................................................................. 157 3.2.1 Interconnect Design ......................................................................... 157 3.2.1.1 Proof-of-Concept ......................................................................... 158 3.2.1.2 SU-8 Anchors............................................................................... 159 3.2.1.3 Septum ......................................................................................... 161 3.2.1.4 Interconnect Integration ............................................................... 161 3.2.2 System Fabrication........................................................................... 162 3.2.2.1 Test Interconnect.......................................................................... 162 3.2.2.2 Integrated System......................................................................... 164 v

3.2.2.3 Septum Formation........................................................................ 166 3.2.3 Experimental Methods and Results.................................................. 168 3.2.3.1 Coring vs. Non-coring Needle Tip Type...................................... 168 3.2.3.1.1 Methods.................................................................................. 168 3.2.3.1.2 Results .................................................................................... 169 3.2.3.2 Pull-out Force and Reusability..................................................... 169 3.2.3.2.1 Theory .................................................................................... 169 3.2.3.2.2 Methods.................................................................................. 171 3.2.3.2.3 Results .................................................................................... 172 3.2.3.3 Maximum Operating Pressure...................................................... 179 3.2.3.3.1 Methods.................................................................................. 179 3.2.3.3.2 Results .................................................................................... 181 3.2.3.4 Prolonged Pressure Operation...................................................... 182 3.2.3.4.1 Methods.................................................................................. 182 3.2.3.4.2 Results .................................................................................... 183 3.2.3.5 Failure Modes .............................................................................. 183 3.2.3.5.1 Delamination .......................................................................... 183 3.2.3.5.2 Needle Misalignment ............................................................. 184 3.2.4 Summary .......................................................................................... 185 3.3 Multiple Interconnects ............................................................................. 186 3.3.1 Design .............................................................................................. 186 3.3.1.1 Septa Design ................................................................................ 187 3.3.1.1.1 Septa Shape ............................................................................ 188 3.3.1.1.2 Septa Spacing ......................................................................... 189 3.3.1.2 Needle Guides .............................................................................. 190 3.3.1.3 Side Ports ..................................................................................... 191 3.3.1.4 Microchannels .............................................................................. 194 3.3.1.4.1 SU-8 Microchannels .............................................................. 194 3.3.1.4.2 Parylene C Microchannels ..................................................... 195 3.3.1.4.3 Converging Microchannels .................................................... 196 3.3.1.5 Metal Structures ........................................................................... 197 3.3.1.5.1 Electrolysis............................................................................. 197 3.3.1.6 Arrayed Interconnect Permeations............................................... 198 3.3.1.7 Fabrication ................................................................................... 199 3.3.1.7.1.1 Arrayed Interconnect, SU-8 Microchannel without Metal 200 3.3.1.7.1.2 Arrayed Interconnect, SU-8 Microchannel with Metal... 206 3.3.1.7.2 Parylene C Microchannel....................................................... 211 3.3.1.7.2.1 Arrayed Interconnect, Parylene C Microchannel without Metal 211 3.3.1.7.2.2 Arrayed Interconnect, Parylene C with Metal................. 215 3.3.1.8 Needle Array ................................................................................ 223 3.3.1.8.1 Shared Input Needle Arrays ................................................... 223 3.3.1.8.2 Separate Input Needle Array.................................................. 224 3.3.1.9 Experimental Methods and Results.............................................. 226 vi

3.3.1.9.1 FEM Analysis of Stress Distribution ..................................... 226 3.3.1.9.1.1 Methods........................................................................... 227 3.3.1.9.1.2 Results ............................................................................. 228 3.3.1.9.2 Photoelastic Stress.................................................................. 230 3.3.1.9.2.1 Methods........................................................................... 230 3.3.1.9.2.2 Results ............................................................................. 231 3.3.1.9.3 Insertion Test.......................................................................... 233 3.3.1.9.3.1 Theory ............................................................................. 233 3.3.1.9.3.2 Methods........................................................................... 235 3.3.1.9.3.3 Results ............................................................................. 241 3.3.1.9.4 Pressure Test .......................................................................... 248 3.3.1.9.4.1 Maximum Leakage Pressure ........................................... 248 3.3.1.9.4.1.1 Methods.................................................................... 248 3.3.1.9.4.1.2 Results ...................................................................... 249 3.3.1.9.4.2 Prolonged Pressure.......................................................... 253 3.3.1.9.4.2.1 Methods.................................................................... 253 3.3.1.9.4.2.2 Results ...................................................................... 254 3.3.1.9.5 Electrolysis Pressure Generation............................................ 254 3.3.1.9.5.1 Theory ............................................................................. 254 3.3.1.9.5.2 Methods........................................................................... 255 3.3.1.9.5.3 Results ............................................................................. 255 3.3.1.9.6 Sideport Functionality............................................................ 256 3.3.1.9.6.1 Methods........................................................................... 256 3.3.1.9.6.2 Results ............................................................................. 257 3.3.1.9.7 Parylene C Microchannel Functionality................................. 258 3.3.1.9.7.1 Methods........................................................................... 258 3.3.1.9.7.2 Results ............................................................................. 259 3.3.2 Summary .......................................................................................... 262 4

Conclusion ....................................................................................................... 264

References ........................................................................................................ 265

Appendices....................................................................................................... 270

Appendix A- Fabrication Process for Silicon Masters ........................................... 270 Appendix B- Steps to Mount Silicon Master to Glass Substrate ............................. 271 Appendix C- Fabrication Steps for Creating Acrylic Master................................... 272 Appendix D- Mask Used to Fabricate Bottom Layer Silicon Master...................... 273 Appendix E- Fabrication Steps for Creating Bottom and Middle Layers................ 274 Appendix F- Mask Used to Fabricate Middle Layer Silicon Master ....................... 275 vii

Appendix G- Fabrication Process for Creating Top Layer from Acrylic Master .... 276 Appendix H- Pattern to Cut PDMS Reservoirs ....................................................... 277 Appendix I- Cleaning Process for Device Layers Prior to Oxygen Plasma Treatment .................................................................................................................................. 278 Appendix J- Oxygen Plasma Treatment Process for Bonding Bottom and Middle Layers....................................................................................................................... 279 Appendix K- Process for Making PDMS Members of a Certain Thickness ........... 280 Appendix L- Mask Used to Make Metal Alignment Marks for All of the Modular Valve Processes........................................................................................................ 281 Appendix M- Mask Used to Pattern First Layer of SU-8 Valve Plate/ Pressure Limiter ...................................................................................................................... 282 Appendix N- Mask Used to Pattern Second Layer of SU-8 Valve Plate/ Pressure Limiter...................................................................................................................... 283 Appendix O- Fabrication Process for SU-8 Valve Seat and Pressure Limiter ........ 284 Appendix P- Mask Used to Pattern SU-8 Spacer Plate............................................ 287 Appendix Q- Fabrication Process for SU-8 Spacer Plate ........................................ 288 Appendix R- Mask Used to Pattern SU-8 Mold for Silicone Valve Plate ............... 290 Appendix S- Fabrication Process for SU-8 Mold to Create PDMS Valve Plate ..... 291 Appendix T- Mask Used to Pattern SU-8 Mold for Silicone Valve Plate with Optional Bossed Feature .......................................................................................... 293 Appendix U- Fabrication Process for SU-8 Mold to Create Silicone Valve Plate with Bossed Feature ......................................................................................................... 294 Appendix V- Mask (1 of 3) Used to Pattern SU-8 Mold for Silicone Valve Plate with Optional Bossed and Overhang Features ................................................................. 297 Appendix W- Fabrication Process for SU-8 Mold to Create Silicone Valve Plate with Bossed and Overhang Features ................................................................................ 300 Appendix X- Assembling Second Generation Heat Shrink Valve SOP .................. 303 Appendix Y- Procedure to Test Heat-Shrink Packaged Valve ................................ 308 viii

Appendix Z- File Used To Make Custom-Designed Cut Puncture Jig.................... 310 Appendix AA ........................................................................................................... 311 Appendix BB- Laser File for Making the Molds for Possible Layouts for Version 1 of the Solid Surgical Shams. .................................................................................... 312 Appendix CC- Laser File User to Create Solid Surgical Sham v2_large and v2_small .................................................................................................................................. 313 Appendix DD- Laser File Used to Create Solid Surgical Sham Mold v3_1 ........... 314 Appendix EE- Laser File Used to Create Hollow Surgical Sham Molds v3_2, v3_2, and v4_1 ................................................................................................................... 315 Appendix FF- Laser File Used to Create Hollow Surgical Sham Molds v5_1 and v6_1.......................................................................................................................... 316 Appendix GG- Laser File Used to Create Hollow Surgical Sham Mold v7............ 317 Appendix HH- Fabrication Process for Making Hollow Shams.............................. 318 Appendix II- Surgical Protocol for In Vivo Implantation of Hollow Surgical Shams .................................................................................................................................. 319 Appendix JJ- Fabrication Process to Create the Interconnect Test Structure .......... 320 Appendix KK- Fabrication Process to Create Integrated Interconnect System ..... 322 Appendix LL- File for Creating a Layer of the Parylene C Deposition Holder ...... 324 Appendix MM- Masks Used to Fabricate the Single Interconnect Designs............ 325 Appendix NN- Wafer Level Pictures of Arrayed Interconnect ............................... 329 Appendix OO- Mask Used To Fabricate Arrayed Interconnect SU-8 Wafer 1....... 331 Appendix PP- Masks Used to Fabricate Arrayed interconnect SU-8 Wafer 2 ........ 332 Appendix QQ- Masks Used to Fabricate Arrayed interconnect Parylene C Wafer 1 .................................................................................................................................. 335 Appendix RR- Masks Used to Fabricate Arrayed interconnect Parylene C Wafer 2 .................................................................................................................................. 338 Appendix SS- Fabrication Process for Arrayed Interconnects with SU-8 Microchannels .......................................................................................................... 343 ix

Appendix TT- Fabrication Process for Arrayed interconnects with SU-8 Microchannels and Metal Components.................................................................... 344 Appendix UU- Fabrication Process for Arrayed Interconnects with Parylene C Microchannels .......................................................................................................... 346 Appendix VV- Fabrication Process for Arrayed Interconnects with Parylene C Microchannels with Metal Components .................................................................. 348 Appendix WW ......................................................................................................... 350

List of Tables Table 2-1 Dimensions of Drug Delivery Device....................................................... 35 Table 2-2 Summary of Results from In Vivo Delivery using the Manually-Actuated Drug Delivery Device.................................................................................. 63 Table 2-3 Summary of values used in theoretical calculations of large deformations in uniform thin plates................................................................................... 75 Table 2-4 Dimensions of valve components, including the three valve designs (hole, straight arm, s-shape arm). All components are 900 Îźm in diameter......... 77 Table 2-5 Summary of heat-shrink tube characterization results for two tube gauge sizes (22 AWG and 18 AWG) ..................................................................... 91 Table 2-6 Summary of the FEM results for displacement and stress on an assembled valve............................................................................................................. 92 Table 2-7 Summary of closing time constants for the packaged valve..................... 97 Table 2-8 Dimensions of Fabricated Version 1 Surgical Shams............................. 112 Table 2-9 Solid sham timeline and description of solid sham characteristics......... 113 Table 2-10 Timeline for hollow surgical sham, including major device characteristics. ........................................................................................... 124 Table 2-11 Summary of Results from In Vivo Delivery using Hollow Surgical Sham ................................................................................................................... 133 Table 2-12 Summary of endothelial cell density at the conclusion of the 6 month study for eyes that were implanted and refilled 6 times during the course of the study and an implant were the refills were terminated 2 months prior to the end of the study at month 4.................................................................. 136 Table 3-1 Comparison of Connector Design Options ............................................. 154 Table 3-2 Values used for theoretical pull-out force calculation. ........................... 173 Table 3-3 Summary of Connector Parameters for Published Connectors............... 176 Table 3-4 Summary of Leakage Pressure Results.................................................. 181 Table 3-5 Summary of fabricated arrayed interconnect combinations. .................. 198 xi

Table 3-6 Summary of the SU-8 microchannel arrayed interconnects which were fabricated. These interconnects do not have any metal structures............ 203 Table 3-7 Summary the SU-8 microchannel arrayed interconnects with metal, which were fabricated........................................................................................... 209 Table 3-8 Summary of the Parylene C microchannel arrayed interconnects which were fabricated. These interconnects do not have any metal structures... 214 Table 3-9 Summary of the Parylene C microchannel arrayed interconnects with metal structures, which were fabricated. ................................................... 220 Table 3-10 Summary of relationship between insertion and removal forces and the needle type (coring vs. non-coring), needle gauge (27G or 33G), number of needles (1, 4, or 8), and rate of insertion (0.5 or 1 mm/sec) (mean Âą SE, n=4)............................................................................................................ 247 Table 3-11 Summary of failure pressure and failure locations for all septa designs. Arrows indicate failure points. .................................................................. 251

xii

List of Figures Figure 2-1 Illustration of device functionality A) Device is comprised if 3 molded silicone layers. B) Layers are assembled and bonded to form device which contains a refillable reservoir, flexible cannula, suture tabs, support posts, and check valve. C) Device is sutured to the sclera. D) Flexible cannula is inserted into the anterior or posterior segments of the eye via a scleral tunnel; device is covered by the conjunctiva (no shown). E) The patient manually-actuates the device by pressing on the reservoir with their finger. F) The change in device volume causes an internal pressure to build up until the check valve opens and fluid is expelled from the device into the eye interior. G) After several dispensing events, the device is depleted. H) A surgeon can, in a minimally invasive manner, refill the device using a 30G (O.D. 305 Îźm) non-corning needle. Figure adapted from images courtesy of Tun Min Soe............................................................................................ 13 Figure 2-2 Exploded view of the drug delivery device. The device is comprised of three layers (bottom, middle, and top) which define the components of the device........................................................................................................... 15 Figure 2-3 Placement of the drug delivery device. Note, conjunctiva is not shown. Figure adapted from image courtesy of Tun Min Soe................................. 16 Figure 2-4 Illustration of the refill ring used to prevent the needle from penetrating through the base of the device. .................................................................... 17 Figure 2-5 Image of several ring guides placed along a 30 gauge needle. For application, only one ring guide per need is necessary. .............................. 17 Figure 2-6 Check valve operations for forward and reverse pressure....................... 18 Figure 2-7 Image of the assembled check valve. Dyed liquid is used to provide contrast......................................................................................................... 19 Figure 2-8 Cross-section of fabrication process to create silicon masters. ............... 21 Figure 2-9 Image of a silicon mold used to create the (a) bottom and (b) middle layers for the drug delivery device. The silicon masters were coated in Parylene C to facilitate mold release of the PDMS layer from the master.. 21 Figure 2-10 SolidWorks image of the three layers that comprise the drug delivery device. The entire device is 17 mm in length. Note, suture tabs are not shown........................................................................................................... 24 xiii

Figure 2-11 SolidWorks image of the bottom layer. Dimensions of the bottom layer are given [mm]. Note, suture tabs are not shown. ...................................... 25 Figure 2-12 Cross-sectional image of the fabrication process for the bottom layer silicon master and individual silicone layer. The cross-section is taken through the line of symmetry (line indicated on Figure 2-13)..................... 26 Figure 2-13 Red line indicates location of cross-section image for Figure 2-12. ..... 27 Figure 2-14 SolidWorks image of the middle layer. Dimensions of the bottom layer are given [mm]............................................................................................. 27 Figure 2-15 Cross-sectional image of the fabrication process for the middle layer silicon master and individual silicone layer. The cross-section is taken through the line of symmetry of the middle layer (line is indicated in Figure 2-16)............................................................................................................. 28 Figure 2-16 Red line indicates location of cross-section image for Figure 2-15. ..... 29 Figure 2-17 SolidWorks image of top layer. The interior cavity of the top layer defines the reservoir volume. Dimensions are indicated [mm]. ................. 30 Figure 2-18 Process for making drug delivery device reservoirs. A) Use epoxy to affix acrylic squares onto a glass slide, B) Pour PDMS prepolymer onto acrylic mold and half-cure PDMS, C) Cut reservoirs from molded PDMS piece. D) Remove reservoirs from mold, E) Reservoirs are ready for assembly. ..................................................................................................... 31 Figure 2-19 Illustration of how the three layers are fabricated and assembled to form the manually-actuated drug delivery device. ............................................... 32 Figure 2-20 Placement of pairs of pieces on glass slide to facilitate placement and alignment of layers after oxygen plasma treatment. .................................... 33 Figure 2-21 Adding reinforcing layer to drug delivery device. A) Device is placed on an inclined glass slide, B) PDMS prepolymer is poured around the device, covering the edge of the device but not occluding the check valve opening, C) The device is removed from the slide and excess PDMS is cut from the device. ........................................................................................... 35 Figure 2-22 Procedure used to qualitatively determine bond strength after oxygen plasma or wet chemical treatment. .............................................................. 37 Figure 2-23 Testing setup used to quantitatively measure bond strength after oxygen plasma or wet chemical treatment. .............................................................. 38 xiv

Figure 2-24 A) Implanted in vivo device (plasma bonded) with bond failure location due to surgical handling identified. B) Reinforcing layer added to bonded device in order to provide more mechanical robustness to the device. C) Excess silicone was removed from the device to create the desired device outline, ruler divisions measure 1 mm......................................................... 41 Figure 2-25 Time-lapsed photographs of dyed DI water being dispensed from the check valve under manual actuation............................................................ 42 Figure 2-26 Typical Diode Current versus Voltage Curve ....................................... 43 Figure 2-27 Typical Check Valve Pressure versus Flow Rate Curve. ...................... 43 Figure 2-28- A) Exploded SolidWorks view of the custom-made laser-machined jig to characterize the check valve operation. B) Pressure setup used to open the valve with pressurized water.................................................................. 45 Figure 2-29 Flow Rate vs. Pressure curve for check valve (mean ± SE, N=4)......... 47 Figure 2-30 Check valve control of dosing under 250 mmHg and 500 mmHg of applied pressure. Duration of applied pressure was varied using a solenoid valve controlled using a 50% duty cycle square waves............................... 49 Figure 2-31 A representative graph depicting the volume dispensed after the applied pressure (250 mmHg and 500 mmHg) is removed from the valve. The dashed lines indicate when the accumulated volume reached 63.2% of the final value, the time at which this point occurred was defined as the closing time constant for the valve........................................................................... 50 Figure 2-32 Refill needle determination, A) Coring versus non-coring 30 gauge (305 μm OD) needle illustration and SEM images, B) Top view of needle track through punctured PDMS slab using each needle, C) Side view of needle track through PDMS slab............................................................................. 52 Figure 2-33 Exploded SolidWorks image of the custom-made laser machined jig used ensure multiple puncture events pierce the membrane in the same location for worst-case scenario testing....................................................... 54 Figure 2-34 A) Exploded SolidWorks view of the custom-made laser-machined jig to apply pressure to punctured membranes. B) Setup used to provide measure leakage pressure of punctured membranes.................................... 55 Figure 2-35 Leakage pressure for 250 μm and 673 μm thick membranes punctured 8, 12 and 24 times through the same location with a 30G non-coring needle (n = 4). ......................................................................................................... 57 xv

Figure 2-36 Surgical verification of liquid delivery in vitro using the drug delivery device........................................................................................................... 60 Figure 2-37 Surgical verification of drug device refill was completed in vitro using a commercially-available, standard 30 gauge non-coring needle. ................. 62 Figure 2-38 A MEMS ocular drug delivery device, which is sutured to the eye, contains a refillable drug reservoir, contoured morphology, cannula, and modular valve. The valve comprises four stacked disks (valve seat, valve plate, spacer plate, and pressure limiter. The cannula is inserted into the anterior or posterior segments of the eye for targeted delivery of drugs..... 69 Figure 2-39 Heat-shrink packaged valve integrated into a silicone surgical sham device. Drug reservoir with metal ring indication refill port location, heatshrink tubing, and valve are indicated. Ruler divisions are 1 mm.............. 70 Figure 2-40 Valve operation (from left to right): initially normally-closed, valve opens under forward pressure that exceeds cracking pressure, excessive pressures close the valve, and valve remains closed under reverse pressure. ..................................................................................................................... 71 Figure 2-41 Photo of the valve components (valve seat, valve plate, spacer plate, and pressure limiter), pre-shrink heat–shrink tube, and fully assembled valve. 72 Figure 2-42 a) Side view and b) top view of the packaged valve in a FEP heat-shrink tube. The valve was placed inside the tube with a custom jig. The entire fixture was heated to 215 ºC at 1.5 ºC/min and cooled at the same rate to room temperature......................................................................................... 73 Figure 2-43 a) Parylene C cannula integrated with a drug delivery pump, b) clogging of Parylene C cannula after ex vivo testing.................................................. 74 Figure 2-44 Three different valve plate designs a) hole, b) straight arm, and c) sshape arm; and the corresponding fabricated valve plates d) hole (through holes are indicated by the arrows), e) straight arm, and f) s-shaped arm. ... 77 Figure 2-45 Fabrication process for the valve seat and pressure limiter plates. Fabrication steps are cross-section views at the A-A’ line.......................... 80 Figure 2-46 Fabrication process for the SU-8 spacer plate. Fabrication steps are cross-section views at the A-A’ line............................................................ 81 Figure 2-47 Fabrication process for the valve plate using an SU-8 master mold. Fabrication steps are cross-section views at the A-A’ line. Straight arm valve is shown; hole and s-shaped arm valves are fabricated in an identical manner. ........................................................................................................ 82 xvi

Figure 2-48 Illustration of the additional features (bossed and/or overhang) which can be added to the simple valve plate designs. .......................................... 83 Figure 2-49 Top and side views of valve assembly. a) valve seat, b) valve plate added to valve seat, c) spacer plate placed on valve plate, d) pressure limiter added to assembled valve. ........................................................................... 84 Figure 2-50 a) Heat-shrink jig setup. Teflon base and top each contains a centering pin. The top and base are aligned with machine screws. Nuts set the top and base distance. b) Close up view of an assembled valve with pre-shrink heat-shrink tube surrounding the valve........................................................ 85 Figure 2-51 Process steps to package assembled valve. a) FEP heat-shrink tube is placed around bottom centering pin, assembled valve is placed on centering pin, b) jig top is added, valve is clamped between top and bottom centering pins, FEP tube is lifted around valve, c) jig and valve assembly is placed in vacuum oven, and d) packaged valve is removed from jig. ........................ 86 Figure 2-52 Valve plate deflection setup. ................................................................. 87 Figure 2-53 Comparison of measured valve plate deflection to the theoretical values for a flat plate............................................................................................... 88 Figure 2-54 Pre and post heat-shrink tubing. Solid disk packaged in heat-shrink tubing to test robustness of the adhesiveless packaging method................. 89 Figure 2-55 Visualization of flow rate through a packaged valve using Rhodamine B................................................................................................................... 93 Figure 2-56 Test setup to determine valve operating characteristics. ....................... 94 Figure 2-57 Flow profiles from 4 runs on same valve, valve was kept hydrated in double distilled water between runs to prevent valve from drying out. The hole valve plate was used in this packaged valve........................................ 95 Figure 2-58 Accumulated volume measurements to determine closing time constant. Closing time constants were calculated by determining the amount of time for 63.2% of the total accumulated volume to exit the valve. ..................... 97 Figure 2-59 Top and side views of the molds used for fabrication the second generation drug delivery device reservoir. ................................................ 102 Figure 2-60 Fully integrated electronically-actuated drug delivery device. Device includes a refillable reservoir, electrolysis pump, separate refill area, refill ring, PEEK baseplate, silicone cannula, heat-shrink packaged dual check valve, and suture tabs................................................................................. 108 xvii

Figure 2-61 Definition of major and minor axes on surgical sham devices. .......... 111 Figure 2-62 First version of the implanted solid surgical shams and the dimensions. ................................................................................................................... 113 Figure 2-63 Implanted surgical shams, A) 2 mm x 12 mm x 15.9 mm and B) 1 mm x 13 mm x 29.4 mm...................................................................................... 115 Figure 2-64 Mold used to fabricate version 2 of the surgical shams. Dimensions are the same as version 1 with additional sutures on the 1mm thick sham (v2_large) and the sutures removed from the silicone cannula from both shams. ........................................................................................................ 115 Figure 2-65 Implanted solid surgical sham with stainless steel ring visible through the conjunctiva. The surgeon was able to simulate refill by targeting the center of the stainless steel ring using a commercially available 30 gauge needle. The stainless steel ring is outlined in this image to help indicate its location. ..................................................................................................... 117 Figure 2-66 Illustration of the hollow surgical sham. A refill needle access the sham interior by piercing the refill port location (designated by a refill ring). A PEEK baseplate prevents the needle from piecing through the entire device. ................................................................................................................... 118 Figure 2-67 Illustration of the application of a refill ring on the refill needle. ....... 120 Figure 2-68 Image of the PEEK baseplate to limit refill needle insertion depth. ... 121 Figure 2-69 Top and side view of the initial reservoir design for the integrated drug delivery device. The reservoir body is separated from the refill port to prevent the pump chamber and Parylene C bellows from accidentally being punctured by the refill needle. ................................................................... 123 Figure 2-70 Illustration of acrylic molds used to fabricate the hollow surgical sham. ................................................................................................................... 125 Figure 2-71 Fabrication steps for making the hollow surgical sham. ..................... 127 Figure 2-72- Hollow surgical sham being filled on benchtop................................. 128 Figure 2-73 Benchtop demonstration of manual dispensation of dyed liquid from within a hollow sham device. .................................................................... 128 Figure 2-74 Illustration of the hollow sham placement in the eye.......................... 129 Figure 2-75 Images of hollow sham device implantation for acute and chronic in vivo studies................................................................................................. 131 xviii

Figure 2-76 Still images of surgical video taken during device refill in a chronic in vivo study. A) Transillumination of the eye helps locate and identify the target refill area. B) A 30G needle is inserted through the center of the refill area. Needle insertion stops when the needle tip encounters the rigid baseplate embedded in the device base. C) Trypan blue dye is injected into the device; the dye can be observed spreading through the device. .......... 132 Figure 2-77 Transilluminated eye with implanted hollow sham device. The device and stainless steel ring outlines are clearly visible through the eye tissue (i.e. conjunctiva) covering the device........................................................ 134 Figure 2-78 Images of in vivo device refilling and dispensing. First, the refill site is checked for any damage, infection, or scarring from previous refills. Next, the eye is transilluminated to help identify the refill ring location (the refill ring appears as a darker shadow). The refill needle (30G non-coring) is inserted through the center of the refill ring until the needle progressing is stopped by the device baseplate. Trypan blue dye is injected into the device; dye can be seen spreading through the device as a dark plume. The dye exits the cannula and into the anterior chamber. Finally, the puncture site is inspected for damage or leakage. .................................................... 135 Figure 2-79 Assembled device with bone screws used to secure device to rat skull. ................................................................................................................... 140 Figure 2-80 Image of proposed device superimposed on a image of a rat skull..... 140 Figure 2-81 Laser file to create molds for the rat retinitis pigmentosa drug delivery device......................................................................................................... 141 Figure 2-82 Image of a) curing stand to prevent suture tabs from becoming sealed during assembly, b) device assembly on curing stand............................... 142 Figure 2-83 Laser file to create molds for mouse cancer drug delivery device. ..... 147 Figure 2-84 Image of the components to fabricate the rat cancer drug delivery device (device body and electrolysis actuator). .................................................... 148 Figure 2-85 Fully assembled rat cancer drug delivery device with electrolysis actuator. Heat-shrink wrapping on wires not shown. ............................... 149 Figure 3-1 Microfluidic system with integrated circular interconnects. 33 gauge non-coring needles were inserted into the input and output septa. Rhodamine was introduced into the system to demonstrate system functionality. PDMS septum is outlined to indicate its location. ............. 156

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Figure 3-2 Exploded view of the setup used to demonstrate horizontal interconnect proof-of-concept. ....................................................................................... 158 Figure 3-3 Images showing fluid progression in proof-of-concept setup. .............. 159 Figure 3-4 A) Image of an assembled circle septum interconnect. B) Top view of three different septum connector shapes (circle, barbed, and square) that were designed and integrated into the test microfluidic system. Needle, PDMS septum, SU-8 housing, and microchannel in the designs are indicated. C) Side view of the needle piercing the PDMS septum. Image is not drawn to scale. ..................................................................................... 160 Figure 3-5 Integrated interconnect with microfluidic system. System contains SU-8 layer which defines the septum housing, microchambers, and microchannel. Electrolysis structure and flow sensors are fabricated with a Ti/Pt metal layer. PDMS septum and glass cover plate are not present...................... 161 Figure 3-6 Cross-sectional fabrication steps for the test interconnect. Cross-section is taken through the microchamber............................................................ 164 Figure 3-7 Simplified fabrication process for the microfluidic chip with integrated interconnect. Cross section views are through the PDMS septum and microchamber with interdigitated electrodes for an electrolysis pump..... 166 Figure 3-8 Edge view of the needle insertion location. The 33 gauge non-coring needle pierces the PDMS septum through the edge of the system, creating an in-plane connection............................................................................... 168 Figure 3-9 Pull-out test setup. Connector is held perpendicular to the ground by placing the microfluidic device in the Plexiglas test fixture. Weights are added to a container attached to the luer lock portion of the needle. Pull-out force is determined by multiplying gravity by the combined mass of the weights, needle, and container. Image is not drawn to scale.................... 172 Figure 3-10 Pull-out force of the interconnects are compared to the calculated theoretical values. ...................................................................................... 173 Figure 3-11 Comparison of the interconnect (circular, square, and barbed) and that of other published connectors of the first pull-out force with respect to contact length............................................................................................. 175 Figure 3-12 Comparison of the interconnect (circular, square, and barbed) and that of other published connectors of the first pull-out force with respect to contact area. ............................................................................................... 175

Figure 3-13 Comparison of the pull-out force for our interconnects (circle, square, barbed) compared to other published connectors. Pull-out force varies over subsequent pull-outs and is dependent on contact area. ............................ 178 Figure 3-14 Comparison of normalized pull-out force with respect to contact area. ................................................................................................................... 178 Figure 3-15 Test setup for leakage pressure test and prolonged pressure test using pressurized water. Output needle is blocked using an Upchurch plug. .... 180 Figure 3-16 Test setup for leakage pressure test using pressurized N2. Leakage is visualized by N2 bubbles escaping from the submerged the microfluidic chip. ........................................................................................................... 181 Figure 3-17 Interconnect failure at the PDMS septum and stainless steel needle interface. A) Water surrounds the needle shaft as PDMS is debonded from the needle and B) seeps from the needle insertion point. .......................... 182 Figure 3-18 Interconnect failure due to Parylene C delamination. Dyed water can be seen spreading between the Parylene C and substrate layers. ................... 184 Figure 3-19 Schematic indicating key features of our interconnect technology. Here, interconnects with surface micromachined Parylene C channels are shown. Needle guides to help align the needle arrays to the septa. Additional features which can be added to the arrayed interconnect include sideports and interdigitated electrodes for electrolysis or electrochemical sensing. 188 Figure 3-20 Septa configurations used in the arrayed interconnect designs. .......... 190 Figure 3-21 Illustration of the needle guides designed to align the trajectory of the needle for the arrayed interconnect design. ............................................... 191 Figure 3-22 Parallel sideport structures integrated into arrayed interconnect designs that have A) individual septum, and B) combined septa. .......................... 192 Figure 3-23 Illustration of the perpendicular sideports in the arrayed interconnect design......................................................................................................... 194 Figure 3-24 Converging microchannel designs of A) 4 rectangular, B) 8 rectangular, and C) 4 oval overlapping septum designs. ............................................... 197 Figure 3-25 Fabricated arrayed interconnect with Parylene C microchannels and sideports. Salient features of the arrayed microfluidic system with integrated interconnects are highlighted. External access via needles is not shown in these photographs....................................................................... 198 xxi

Figure 3-26 Fabrication steps for the SU-8 wafer that contains interconnect designs that do not require metal structures. The cross-section is taken horizontally along the microchannel. The SU-8 is lighter in color at step D because after SU-8 patterning, no SU-8 exists along the cross-section line. However, the lighter SU-8 represents the SU-8 material remaining surrounding the needle guide and microchannel in order to better visualize the process flow after step D. This process flow is used for designs shown in Figure 5-37A..... 201 Figure 3-27 Fabrication steps for the SU-8 wafer that contains interconnect designs that do not require metal structures. The cross-section is taken horizontally along the microchannel. The SU-8 is lighter in color at step K because after SU-8 patterning, no SU-8 exists along the cross-section line. However, the lighter SU-8 represents the SU-8 material remaining surrounding the needle guide and microchannel in order to better visualize the process flow after step D. This process flow is used for designs shown in Figure 5-37B..... 208 Figure 3-28 Process flow for Parylene C microchannel arrayed interconnect designs. The cross-section line is taken along the microchannel. Translucent SU-8 represents SU-8 which surrounds a component but not within the crosssectional line. The translucent SU-8 is included to aid in illustrating the fabrication process. This fabrication process is used for designs shown in Figure 5-38A.............................................................................................. 213 Figure 3-29 Time-lapsed images of the working electrolysis structures prior to packaging. 0.3 mA of current was applied to the electrodes. Bubble formation was visually confirmed. ............................................................ 217 Figure 3-30 Process flow for Parylene C microchannel arrayed interconnect designs. The cross-section line is taken along the microchannel. Translucent SU-8 represents SU-8 which surrounds a component but not within the crosssectional line. The translucent SU-8 is included to aid in illustrating the fabrication process. This fabrication process is used for designs shown in Figure 5-38B.............................................................................................. 219 Figure 3-31 Needle arrays which provide shared or separate input capabilities to needles and thus microchannels. a) 4 shared 4 needles, 1 mm spacing, b) 4 shared needles, 2.54 mm spacing, c) 8 shared needles, 1 mm spacing, d) 4 separate needles, 1 mm spacing, and e) 8 separate needles, 2.54 mm spacing. The scale bar represents 10 mm. ................................................ 223 Figure 3-32 Custom-made laser machined molds for creating an array of needles (4 or 8). All layers are made of acrylic and are color coded to illustrate assembly. ................................................................................................... 226 Figure 3-33 Centerline of FEM analysis of needle insertion induced stress in arrayed interconnect. .............................................................................. 228 xxii

Figure 3-34 FEM images of stress distribution within septa during needle insertion, a) pre-puncture, b) partial puncture, and c) complete insertion................. 229 Figure 3-35 Experimental setup to visualize photoelastic stress............................. 231 Figure 3-36 Photoelasic stress in PDMS from needle insertion for a single (18G) and needle array (four 27G). Yellow arrows indicate areas of stress.............. 232 Figure 3-37 Illustration of membrane behavior during pre-puncture, puncture, and post-puncture stages of needle insertion.................................................... 234 Figure 3-38 Custom-made laser-machined jigs used to measure insertion force through PDMS using a A) 4 or B) 8 needle assembly............................... 237 Figure 3-39 Illustration of needle tip displacement relative to the PDMS membrane for frictional force measurements.............................................................. 239 Figure 3-40 Generic results from insertion force tests. a) needle touches surface of the PDMS sample, b) material being pierced by needle (combination of stiffness and puncture forces), c) needle moving through PDMS material (friction force), d) needle stops moving and material relaxes, e) needle in process of being removed from material (max removal force), f) needle fully removed from material. Inset: needle displacement over time ........ 242 Figure 3-41 Relationship of post-puncture insertion forces (friction and cutting forces) and removal forces with respect to the number of insertion needles. ................................................................................................................... 244 Figure 3-42 Illustration of â&#x20AC;&#x153;tentingâ&#x20AC;? effect. ............................................................ 250 Figure 3-43 Common failure modes of the arrayed interconnect. a) Leakage through needle insertion path between needle and septa, b) leakage at output septa through needle track, c) delamination between the septa and Parylene C coated substrate, d) delamination between the Parylene C coating and the substrate. Examples of needle misalignment are shown in c) and d). ...... 253 Figure 3-44 Internal pressure change due to electrolysis. Pressure increases when current (0.3 mA) is applied to the interdigitated electrodes, pressure decreases when current is turned off and the oxygen and hydrogen gas recombine into water. ................................................................................ 256 Figure 3-45 Experimental setup for sideport testing............................................... 257 Figure 3-46 Time lapse images of sideport function: a) dyed water introduced in the main septum and un-dyed water through the sideport, b) close up image of the laminar flow within the microchannel. ................................................ 258 xxiii

Figure 3-47 Time-lapsed images of IPA evaporating from within the arrayed interconnect Parylene C microchannel. ..................................................... 260 Figure 3-48 Time-lapsed images of Rhodamine B moving through the arrayed interconnect Parylene C microchannel via capillary action. Scale bar is 1 mm. ............................................................................................................ 261 Figure 3-49 Time-lapsed images of Rhodamine B moving through the arrayed interconnect Parylene C microchannel in a partially packaged device. Scale bar is 1 mm. ............................................................................................... 262 Figure 5-1 6 mm x 6 mm acrylic squares to form the acrylic mold of the device reservoir. Note, image is not shown true to scale. .................................... 272 Figure 5-2 Mask used to create silicon master for the bottom layer of the drug delivery device. The white sections are etched 100 Îźm into the silicon substrate to create a negative of the desired structure. .............................. 273 Figure 5-3 Mask used to create silicon master for the middle layer of the drug delivery device. The white sections are etched 250 Âľm into the silicon substrate to create a negative of the desired structure. .............................. 275 Figure 5-4 Pattern used to cut uniform reservoirs from molded PDMS sheet........ 277 Figure 5-5 Mask used to create the metal alignment marks. This mask patterns a photoresist layer. Metal is then deposited on the photoresist; the photoresist is removed using acetone, isopropyl alcohol, and water. .......................... 281 Figure 5-6 Mask used to pattern the bottom layer of the SU-8 valve seat and pressure limiter. SU-8 is a negative resist, therefore, the white areas indicate locations where SU-8 structures will remain, while the black areas will be removed. ........................................................................................ 282 Figure 5-7 Mask used to pattern the top layer of the SU-8 valve seat and pressure limiter. SU-8 is a negative resist, therefore, the white areas indicate locations where SU-8 structures will remain, while the black areas will be removed. .................................................................................................... 283 Figure 5-8 Mask used to pattern the SU-8 spacer plate. SU-8 is a negative resist, therefore, the white areas indicate locations where SU-8 structures will remain, while the black areas will be removed.......................................... 287 Figure 5-9 Mask used to pattern the SU-8 mold used to cast the silicone valve plate. SU-8 is a negative resist, therefore, the white areas indicate locations where SU-8 structures will remain, while the black areas will be removed. ....... 290 xxiv

Figure 5-10 Mask used to pattern the optional second layer for an SU-8 mold used to cast the silicone valve plate with bossed feature. SU-8 is a negative resist, therefore, the white areas indicate locations where SU-8 structures will remain, while the black areas will be removed.......................................... 293 Figure 5-11 Mask used to pattern the first layer for an SU-8 mold used to cast the silicone valve plate with bossed and overhang feature. The thickness of this layer determines how far the overhang will extend beyond the valve plate. SU-8 is a negative resist, therefore, the white areas indicate locations where SU-8 structures will remain, while the black areas will be removed. ....... 297 Figure 5-12 Mask used to pattern the second layer for an SU-8 mold used to cast the silicone valve plate with bossed and overhang feature. This layer defines the bossed structure. SU-8 is a negative resist, therefore, the white areas indicate locations where SU-8 structures will remain, while the black areas will be removed. ........................................................................................ 298 Figure 5-13 Mask used to pattern the third layer for an SU-8 mold used to cast the silicone valve plate with bossed and overhang feature. This layer is used to define the thickness of the valve plate and the shape of the valve plate arms (i.e. through-holes). SU-8 is a negative resist, therefore, the white areas indicate locations where SU-8 structures will remain, while the black areas will be removed. ........................................................................................ 299 Figure 5-14 Three valve plate types: a) hole, b) straight arm, c) s-shaped arm...... 303 Figure 5-15 Steps to prepare valve plate................................................................. 304 Figure 5-16 Items needed to packaging valve......................................................... 304 Figure 5-17 Front and side views of SU-8 pieces ................................................... 305 Figure 5-18 Aligning pieces (top view) : valve plate only, valve plate with valve seat, valve plate & valve seat & spacer plate, valve plate & valve seat & spacer plate & pressure limiter .................................................................. 305 Figure 5-19 Aligning pieces (side view) : valve plate only, valve plate with valve seat, valve plate & valve seat & spacer plate, valve plate & valve seat & spacer plate & pressure limiter .................................................................. 305 Figure 5-20 Process needed to shrink FEP tubing around valve ............................ 306 Figure 5-21 Assembled valve in heat shrink prior to placing in the oven .............. 306 Figure 5-22 Side and top view of a packaged valve ............................................... 307 Figure 5-23 Testing setup to apply pressure to packaged valves or solid disks...... 308 xxv

Figure 5-24 The three custom-designed laser-machined layers that are stacked to form the puncture jig. ................................................................................ 310 Figure 5-25 Corel Draw files to create puncture force jigs. Jig assembly is also shown. The colors are just used to indicate corresponding layers and are not present in the laser file......................................................................... 311 Figure 5-26 Corel draw files used to create custom-made, laser-machined molds of various shapes and sizes for the first version of the solid surgical shams. The 0.75 mm to 2 mm labels indicate the thickness of the sham. ............. 312 Figure 5-27 File used to fabricate the redesigned solid surgical sham molds (v2_large and v1_small). The dimensions are the same as in version 1 with additional sutures on the 1 mm thick sham and the sutures removed from the silicone cannula from both shams........................................................ 313 Figure 5-28 Drawing used to create solid sham mold v3_1. The mold is a convex dome which was filled with silicone, leveled, and cured to create a solid sham........................................................................................................... 314 Figure 5-29 Drawing used to create hollow sham molds v3_2, v3_3, and v4_1. Shaded portions are etched to create domes or flat surfaces. .................... 315 Figure 5-30 Drawing used to create hollow sham molds v5_1 and v6_1. Shaded portions are etched to create domes or flat surfaces. ................................. 316 Figure 5-31 Drawing used to create hollow sham mold v7. Shaded portions are etched to create domes or flat surfaces. ..................................................... 317 Figure 5-32 Corel Draw file to create Parylene C deposition holder. 6 layers using this pattern were cut. The assembled holder is modular and can be placed in the Parylene C deposition chamber with up to all six layers in place. The Parylene C deposition holder layers are separated using plastic standoffs. ................................................................................................................... 324 Figure 5-33 Mask used to pattern photoresist to create a metal liftoff layer for the single interconnect design.......................................................................... 325 Figure 5-34 Mask used to pattern photoresist to create an etch mask for the Parylene C and expose the metal electrodes and electrolysis structure on the single interconnect deign...................................................................................... 326 Figure 5-35 Mask used to pattern SU-8 layer to create a 300 Îźm channel. This produces a structure that is compatible with using a 33 gauge needle to pierce the septum. ...................................................................................... 327 xxvi

Figure 5-36 Mask used to pattern SU-8 layer to create a 500 Îźm channel. This produces a structure that is compatible with using a 30 gauge needle to pierce the septum. ...................................................................................... 328 Figure 5-37 Wafers with SU-8 microchannels, A) which do not contain metal structures, and B) microchannels integrated with electrolysis and conductance structures. The blue areas identify the septum locations. .... 329 Figure 5-38 Wafers with Parylene C microchannels, A) that do not contain metal structures, and B) microchannels integrated with electrolysis and conductance structures............................................................................... 330 Figure 5-39 Mask used to pattern SU-8 layer for the SU-8 microchannel arrayed interconnects found in Figure 5-37A......................................................... 331 Figure 5-40 Mask used to pattern photoresist to create a metal liftoff layer for the SU-8 microchannel arrayed interconnects found in Figure 5-37B............ 332 Figure 5-41 Mask used to pattern photoresist to create an etch mask for the Parylene C and expose the metal electrodes and electrolysis structure on the SU-8 microchannel arrayed interconnects found in Figure 5-37B. .................... 333 Figure 5-42 Mask used to pattern SU-8 layer for the SU-8 microchannel arrayed interconnects found in Figure 5-37B. ........................................................ 334 Figure 5-43 Mask used to pattern photoresist to create a sacrificial photoresist structure that defines the microchannel interior for the Parylene C arrayed interconnect designs found in Figure 5-38A. ............................................ 335 Figure 5-44 Mask used to pattern photoresist to create an etch mask for the Parylene C covering the microchannel opening of the Parylene C microchannel designs found in Figure 5-38A. ................................................................. 336 Figure 5-45 Mask used to pattern SU-8 layer for the Parylene C microchannel arrayed interconnects found in Figure 5-38A............................................ 337 Figure 5-46 Mask used to pattern photoresist to create an etch mask which etches the Parylene C for the Parylene C microchannel arrayed interconnects found in Figure 5-38B. The etched areas will allow the electrodes of the metal structure to come into direct contact with the glass substrate. .................. 338 Figure 5-47 Mask used to pattern photoresist to create a metal liftoff layer for the Parylene C microchannel arrayed interconnects found in Figure 5-38B... 339

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Figure 5-48 Mask used to pattern photoresist to create a sacrificial photoresist structure that defines the microchannel interior for the Parylene C arrayed interconnect designs found in Figure 5-38B.............................................. 340 Figure 5-49 Mask used to pattern photoresist to create an etch mask for the Parylene C covering the microchannel openings, electrodes, and electrolysis structures for Parylene C microchannel designs found in Figure 5-38B... 341 Figure 5-50 Mask used to pattern SU-8 layer for the Parylene C microchannel arrayed interconnects found in Figure 5-38B ............................................ 342 Figure 5-51 Corel Draw file used to create custom-made, laser-machined, jigs to measure insertion force of 4 and 8 needles arrays. Jig assembly is also shown......................................................................................................... 350

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List of Equations Equation 2-1 Large deflection in a homogenous, thin film plate......................... 75 Equation 2-2 Flexural rigidity equation to determine deflection in thin film plate............................................................................................................. 75 Equation 2-3 Electrochemical reaction during electrolysis of water................... 99 Equation 2-4- Volume of an Ellipsoid .................................................................. 111 Equation 2-5- Volume of a Dome.......................................................................... 111 Equation 3-1 Adhesion Force................................................................................ 170 Equation 3-2 Frictional Pull-Out Force ............................................................... 170 Equation 3-3 Frictional Pull-Out Force Independent of Pressure .................... 170 Equation 3-4 Total Pull-Out Force....................................................................... 171 Equation 3-5 Critical width to prevent stiction in cantilevers ........................... 195 Equation 3-6 Phase difference due to stress ........................................................ 230 Equation 3-7 Insertion Force of a Needle into a Membrane.............................. 233 Equation 3-8- Stiffness Force of a Membrane Deflecting................................... 233 Equation 3-9- Frictional Force of a Needle Through a Membrane................... 234 Equation 3-10- Cutting Force of a Needle Piercing a Membrane ..................... 235 Equation 3-11 Insertion force equation ............................................................... 238 Equation 3-12 Removal force equation ................................................................ 238 Equation 3-13 Volume of gas generation during electrolysis............................. 254

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Abstract: Modular bioMEMS The field of bioMEMS (bio Microelectromechanical Systems) has seen a dramatic increase in research and applications in recent years. The merging of traditional MEMS fabrication techniques with unique medical needs has helped this field grow. Though bioMEMS devices have proven useful in research and real-world situations, many bioMEMS devices are designed for a single application, and because of their complete wafer-level process, are difficult to alter without requiring an entirely new fabrication process.

Additionally, non-modular designs lack the flexibility and

versatility to allow MEMS designs from being easily adapted to new applications. Modular devices provide several advantages such as creating interchangeable parts, allowing flexibility in designed operation range and principle, simply â&#x20AC;&#x153;plug and playâ&#x20AC;? components which are easily replaced, and rapid prototyping. Presented in this work are two devices, an ocular drug delivery device with a dual-regulation check valve, and an arrayed, horizontal microfluidic interconnect; both contain modular components, which can be altered to increase the functionality of these devices.

1 Introduction Microelectromechanical Systems (MEMS) have many advantages over traditional manufacturing processes. First, MEMS devices can be fabricated with a high degree of precision (micron scale, 10-6 m). Additionally, due to their miniature size, many devices can be batch fabricated on a single wafer during the fabrication process. However, fabrication processes can be costly, and small modifications to a component within the device often require an entire redesign of the entire process.

MEMS fabrication processes are costly in finances, time, and resources.

In a

research setting, a process run may require several masks, each can cost a couple hundred dollars, whereas, commercial processes may require masks which are several thousands of dollars apiece.

Additional costs may also include device

materials, especially of parts, components, or devices cannot be reused in the new design, as well as the additional use and time in cleanroom facilities. Furthermore, redesigning masks and re-characterizing changes to the process run are very time consuming tasks, which can affect research or delivery deadlines. Finally, additional man-hours and equipment availability must be considered. Modular designs, which allow for increased flexibility and versatility of designs, can mitigate some of the additional time and cost requirements. Modular designs provide opportunities to accommodate component changes, extend device applications, and aid in device assembly.

Modularity can be defined in a number of ways. It can refer to replacing an entire component within a device, similar to a â&#x20AC;&#x153;plug and playâ&#x20AC;? model, or it can mean replacing a part within a component. Modular devices can also be defined as scaling the design by repeating a design feature or altering the dimensions of a feature or part. Each of these definitions is not mutually exclusive and has a common theme of increasing device functionality and adaptability.

Device designs which allow entire components to be easily replaced allows for quick repairs without having to fabricate an entirely new device. Additionally, once a working device is established, components can be swapped for to verify specific component functionality, which can be used to help debug and identify faulty components.

Replacing a part within a component has several advantages.

First, MEMS

fabrication lends itself to creating multiple identical copies of a specific part. These parts are all interchangeable; interchangeable parts are essential to the assembly-line fabrication process, which allows for inexpensive mass production of reliable devices. Changing a single part, which is different in dimensions, shape or materials, from the replaced part can result in a component with a different operation. This change results in a new component, which can be tailored to fit a separate application, without having to redesign the entire device. Rapid prototyping of new devices can be accomplished by changing small parts within device components.

Finally, modular designs may scale the current design either by changing the dimensions of a component or part, or repeating a desired element. Scaling by scaling either by increasing a part/componentâ&#x20AC;&#x2122;s dimensions can shift the operating range of a device. Additionally, trade-offs based on need and available resources can be optimized when the dimensions can be scaled. For example, a more robust design may require more space; however, there is a finite amount of real-estate, available. Therefore, once the space constraint is determined, the component can be scaled up to fill all of the available space, resulting in the strongest device possible. The second version of scaling modulation is to repeat elements. Repetition of specific design elements means that a design can be extended from a single device to an arrayed device, or even vice versa, where an arrayed device can be reduced to a single device, as desired functionality dictates. Presented in this work are two different bioMEMS designs that contain modular systems. The first is an ocular drug delivery system (Section 2). Current drug delivery systems include 1) biocompatible matrices infused with drugs and 2) membrane coated reservoirs that release drugs upon membrane rupture. Modular designs, including interchangeable parts, redesigned parts, and replaceable components allowed for rapid prototyping and testing of designs in order to accommodate physiological needs. Presented here is a manually-actuated prototype device containing a refillable reservoir, a microchannel or cannula for targeted drug delivery, a valve to control fluid flow, and suture tabs to secure the device in place. Each component was tested on benchtop; the integrated device was tested using 4

acute in vitro and in vivo studies to demonstrate the proof-of-concept of a refillable drug delivery device. The results from the manually-actuated device were used to design and fabricate an electrically-actuated system with a refillable reservoir, refill port, flexible cannula, modular dual regulation check valve, suture tabs, electrolysis pump, and separate drug and pump chambers. Surgical shams were created to refine the surgical protocol. Chronic in vivo tests (6 month studies) were conducted to determine long-term biocompatibility of the device, and to demonstrate dispensation and refill in vivo.

The second project is a device that can be used to connect the microfluidic world to the macro or benchtop world (Section 3). Applications of microfluidic devices are found in the biological and chemical research areas as well as lab-on-a-chip and micro total analysis systems (ÂľTAS). The connections (or interconnects) used to access microsystem are generally custom-made solutions which are single-use, require precision alignment, additional and complex fabrication steps, have increased dead volume, and utilize adhesives to secure them in place. These challenges limit interconnects from being batch fabricated or easily integrated into microfluidic devices, thus lowering device yield and wide-spread implementation. A modular interconnect, which can be incorporated into a wide variety of existing devices was created. The design, fabrication, testing, and advantages of a reusable horizontal interconnects is presented.

Single interconnect versions were fabricated to

demonstrate proof-of-concept. The horizontal interconnect design was scaled and extended to create an arrayed interconnect where multiple connections can be made 5

simultaneously.

Finite element analysis of the insertion stresses as well as

experimental determination of insertion and removal forces were conducted. Operating ranges of both the single and arrayed interconnect were determined and a discussion of interconnect design improvements is presented.

2 MEMS Based Drug Delivery Devices 2.1 Introduction Targeted and precisely controlled delivery of therapeutic compounds into the body is an ongoing challenge in many areas of drug delivery. Drug delivery to ocular tissues is particularly difficult due to several factors including physiological barriers and trauma to the eye during invasive therapies. Furthermore, drug delivery devices need to be small in order to fit within the spatial limitations in and surrounding the eye. Ocular drug delivery has been investigated as a treatment method for chronic eye diseases such as glaucoma, age-related macular degeneration (AMD), diabetic retinopathy, and retinitis pigmentosa.

These diseases are the leading causes of

irreversible blindness (Geroski and Edelhauser 2000). Lifelong treatment in the form of therapeutic medications and surgical procedures are necessary to slow or prevent disease progression. Current methods of treatment include topically and orally administered medications, intraocular injections, surgical intervention, and biodegradable implants. However, limitations in current methods suggest a need for a new solution to ocular drug delivery.

A manually-actuated drug delivery prototype device presented here is a first generation device which is used to demonstrate the feasibility of a MEMS refillable ocular drug delivery device. This prototype is capable of targeted delivery, refill, and fluid flow control. It also allows individual device components to be quickly integrated into a system where device components can be tested in vitro and in vivo. 7

These results will be used to design a second generation device (electrically-actuated device with dual check valve) capable of targeted delivery, device refill/reusability, fluid flow control under operating parameters, and precise dosage control.

2.1.1 Ocular Drug Delivery Methods Current ocular drug delivery methods are categorized as, 1) topical or oral, 2) intraocular injections, and 3) implants (Lee, et al. 2004). Concerns such as patient compliance, invasive therapies, resulting side-effects, targeted delivery, and dosage control must be considered when choosing a treatment method.

2.1.1.1 Topical and Oral Medications Drug delivery to the anterior and posterior segments of the eye is especially difficult due to physiological barriers. Non-invasive methods of delivery, including eye drops and oral medications, must permeate through the modified mucosal membrane of the cornea, or the blood-retina barrier, respectively. For eye drops, it has been reported that only 5% of the dispensed drug may reach the anterior intraocular tissues through the cornea (Geroski and Edelhauser 2000).

Furthermore, drug dilution due to

lacrimation, tear drainage, and turnover limit the drug contact time with the cornea. Oral medications can be used to treat diseases that affect the posterior ocular tissues; however the blood-retina barrier significantly impedes the penetration of drugs. Larger doses need to be administered in order to obtain therapeutic levels, however, this may result in serious systemic side effects (Fraunfelder 1977, 1979, 1980, 1990, Fraunfelder and Meyer 1984, Fraunfelder 2004, Fraunfelder and Fraunfelder 2004).

While topical and oral medications are the simplest and least invasive method of treatment, they rely on patient compliance and self-dosing.

2.1.1.2 Intraocular Injections Intraocular injections directly bypass physiological barriers and are an effective method for delivering precise dosages into the ocular space. However, the limited half-life of drugs in the vitreous cavity necessitates frequent injections (1-3 per week) for disease management (Lee, et al. 2004). This method of treatment is a viable solution for bacterial infections, such as endophthalmitis, but is not suitable for chronic diseases such AMD or cytomegalovirus (Mamalis, et al. 2002). In addition, patient acceptance of this method is poor. Frequent injections also may result in trauma to the eye tissues that can lead to cataracts, vitreous hemorrhage, and retinal detachment (Ambati, et al. 2000).

2.1.1.3 Implants Due to the limitations of currently available drug delivery methods, there is a need for advanced drug delivery systems that can provide both accurate and targeted dosing.

Ideal drug delivery devices are biocompatible, minimize trauma and

inflammation, provide localized delivery with minimal exposure to other tissues, provide sustained therapy (i.e. can be refilled), and are placed to facilitate medical inspection without impeding the vision of the patient (Metrikin and Anand 1994). The system should have broad drug compatibility and have a small, minimallyinvasive form factor; limited real-estate exists for comfortable placement of the device within the ocular orbit. The device must be able to reliably dose medication 9

under normal intraocular pressure (IOP) conditions (15.5 Âą 2.6 mmHg (mean Âą SD)) (Ritch, et al. 1989), elevated conditions caused by diseases such as glaucoma (IOP > 22 mmHg) (Wilensky 1999), and transient conditions of fluctuating pressures due to outside influences such as patient sneezing, eye rubbing, or changes in altitude (e.g. flying). Existing drug delivery devices can be categorized as (1) biodegradable or nonbiodegradable (2) implantable pump systems, and (3) atypical implantable systems. Biodegradable and non-biodegradable systems typically consist of a polymer matrix infused with drug or a reservoir containing drug, respectively. The drug is released as the matrix dissolves or as the drug diffuses from the non-biodegradable reservoir. This form of drug delivery is dependent on drug load within the polymer and in vivo polymer degradation; this method has limited volume and cannot be refilled. Implantable pump systems provide control over delivery rate and volume by using an active pumping mechanism to dispense drug from an internal reservoir. Five types of implantable pump systems have been investigated: infusion pumps, peristaltic pumps, osmotic pumps, positive displacement pumps, and controlled release micropumps. Atypical systems provide targeted delivery at a constant rate and reduce the amount of drug necessary for treatment (Dash and Cudworth 1998). For example, hydrogel systems consisting of a polymer matrix infused with drug swell due to the absorption of biological fluids. Drug release occurs proportionally to the rate of swelling. Existing ocular drug delivery devices fall into the first or last category, while implantable pump systems have been successfully executed for other 10

drug delivery needs (e.g. insulin delivery, neurological compounds) (Grayson, et al. 2004, Razzacki, et al. 2004, Ziaie, et al. 2004). Two commercially available devices, Vitrasert® and Retisert™, distributed by Bausch and Lomb utilize this method of delivery. The Vitrasert® and Retisert™ have a reported lifetime of 5-8 and 30 months, respectively. However, commercial sustained ocular drug delivery implants require repeated surgical interventions to implant and replace the device resulting in similar side effects to those found in injection therapies.

2.2 A MEMS Approach to Drug Delivery: Manually-Actuated Device A drug delivery device capable of providing targeted and precisely controlled delivery to intraocular tissues can be fabricated using microelectromechanical systems (MEMS) techniques. This device will be an improvement over current sustained-delivery devices because a MEMS device (1) utilizes techniques that can miniaturize the system to fit within the space constraints, (2) may contain valving and electronics which are able to control the dosage and provide custom drug regiments, and (3) can be refilled. The polymer MEMS delivery device consists of a refillable drug reservoir, transscleral cannula, check valve, support posts, and suture tabs. This is the first MEMS drug delivery device to feature a refillable reservoir (Lo, et al. 2006). A refillable reservoir provides several advantages over existing ocular drug delivery systems: (1) it extends the usable lifetime of the device without increasing the device size; (2) it can be replenished without significant surgery as opposed to sustained implant devices that need to be removed and re-implanted; and (3) it can take advantage of newly available pharmaceutical solutions simply by 11

changing the drug solution within the reservoir.

Additionally, the device is

assembled using interchangeable parts. Interchangeable parts allow all of the parts to be fabricated in parallel and then assembled. The device is surgically implanted with the reservoir placed underneath the conjunctiva, a membrane surrounding the eye (Figure 2-1C). The cannula is inserted through the eye wall with the drug dispensing tip terminating in either the anterior or posterior segment depending on the site of treatment (Figure 2-1D). A specific dose of medication is dispensed from the device when the reservoir is mechanically actuated by the patientâ&#x20AC;&#x2122;s finger (Figure 2-1E). The increase in pressure within the reservoir forces the drug to travel down the enclosed microchannel within the transscleral cannula.

A flow-regulating check valve (one-way valve) was

incorporated near the tip of the cannula. The check valve responds to the pressure increase and opens, allowing drug to flow out of the device but prevents back flow of bodily fluids into the device (Figure 2-1F). Support posts are contained within the microchannel and the reservoir to prevent stiction following the collapse of the device walls when the drug is depleted. When the reservoir has been depleted, medical personnel can, in a minimally invasive manner, refill the device using a standard needle and syringe (Figure 2-1G,H).

Figure 2-1 Illustration of device functionality A) Device is comprised if 3 molded silicone layers. B) Layers are assembled and bonded to form device which contains a refillable reservoir, flexible cannula, suture tabs, support posts, and check valve. C) Device is sutured to the sclera. D) Flexible cannula is inserted into the anterior or posterior segments of the eye via a scleral tunnel; device is covered by the conjunctiva (no shown). E) The patient manually-actuates the device by pressing on the reservoir with their finger. F) The change in device volume causes an internal pressure to build up until the check valve opens and fluid is expelled from the device into the eye interior. G) After several dispensing events, the device is depleted. H) A surgeon can, in a minimally invasive manner, refill the device using a 30G (O.D. 305 Îźm) non-corning needle. Figure adapted from images courtesy of Tun Min Soe.

2.2.1 Design The

drug

delivery

device

formed

from

three

layers

molded

polydimethylsiloxane, PDMS, (Sylgard 184, Dow Corning, Midland, MI) (Figure 2-1A, Figure 2-2). The bottom layer defines the base of the device and includes suture tabs through which sutures are threaded to secure the device to the eye. This layer also contains support posts to prevent stiction of device walls when the drug has been depleted. The final support post at the tip of the cannula also serves as the check valve seat. The middle layer forms a portion of the cannula and the check valve orifice. The topmost layer completes the refillable reservoir and defines the maximum drug volume that can be housed. Multiple identical copies of each layer can

fabricated

simultaneously,

providing

interchangeable

components.

Additionally, alternate top layer pieces can be fabricated to increase or decrease the interior volume without requiring new bottom or middle pieces.

Figure 2-2 Exploded view of the drug delivery device. The device is comprised of three layers (bottom, middle, and top) which define the components of the device.

2.2.2 The Components 2.2.2.1 Refillable Reservoir and Refill Guides The total device size and the reservoir volume, is limited by the available subconjunctival area and the space in between the rectus muscles (Figure 2-3). Patient comfort must also be considered. The internal volume is defined by the desired volume per dose and frequency of the dosage. Ophthalmic surgeons estimate that the entire device should measure no more than 2-3 mm in thickness to maximize patient comfort.

Figure 2-3 Placement of the drug delivery device. Note, conjunctiva is not shown. Figure adapted from image courtesy of Tun Min Soe.

When the drug contained within the reservoir is depleted, the reservoir can be refilled with a non-coring needle. Device refill is aided by the addition of a needle refill guide. The refill guide limits the needle insertion depth to prevent the needle from penetrating the entire device and entering the eye and to prevent the needle tip from becoming embedded into the bottom wall of the reservoir (Figure 2-4). If the tip becomes embedded in the reservoir wall, the needle lumen may be occluded and prevent the drug from being dispensed into the reservoir. The refill guide is a PDMS ring affixed to the needle shaft (Figure 2-5). The ring is set at the maximum depth the needle can penetrate into the device. The maximum depth is determined by the combined values of the reservoir wall thickness and the height of the interior reservoir volume.

Figure 2-4 Illustration of the refill ring used to prevent the needle from penetrating through the base of the device.

Figure 2-5 Image of several ring guides placed along a 30 gauge needle. For application, only one ring guide per need is necessary.

2.2.2.2 Cannula and Check Valve The cannula and integrated check valve cross the eye wall and enable targeted delivery to intraocular tissues either in the anterior or posterior segment.

The

cannula dimensions are determined by both ocular anatomy and surgical considerations. The cannula tip must not obscure the visual pathway (i.e. pupil) and the cannula should not come into contact with the cornea. These constraints limit the length of the cannula. The width and height of the cannula should be no more than 1 mm (0.04 inches) which corresponds to the maximum incision size the eye is able to self-seal. The cannula measures 10 mm x 1 mm x 1 mm (0.4’’ x 0.04’’ x 0.04’’). The internal dimensions of the cannula were chosen so as to minimize flow resistance (cross-section of 0.5 mm x 0.1 mm or 0.02’’ x 0.004’’).

A check valve is a microfluidic component that serves as a flow restrictor within the system.

The integrated check valve is a normally-closed one-way valve.

normally-closed valve remains closed until enough pressure is generated to open the valve. This opening pressure is known as the cracking pressure for the valve; the valve opens when the applied pressure exceeds the cracking pressure. If the external pressure on the valve is higher than the internal pressure, the valve remains closed (Figure 2-6). This prevents bodily fluids from entering the device and contaminating the drug. A check valve directs one-way flow, preventing backflow in a system.

Figure 2-6 Check valve operations for forward and reverse pressure.

A post located at the tip of the cannula serves as the valve seat. The check valve is formed by aligning a 203 Îźm diameter orifice over the valve seat at the end of the cannula (Figure 2-7).

Figure 2-7 Image of the assembled check valve. Dyed liquid is used to provide contrast.

2.2.2.3 Support Posts Support posts resembling extruded square pillars (0.4 mm x 0.4 mm x 0.1 mm), are located along the interior length of the cannula and in the reservoir. The support posts prevent PDMS stiction within the cannula and reservoir.

2.2.2.4 Suture Tabs Four suture tabs provide surgeons a means for anchoring the device to the eye. Suture tabs are circular in shape (O.D. 2 mm) and placed at each corner of the reservoir so that the anchoring sutures will not accidentally occlude or damage the cannula (Figure 2-2).

2.2.3 Device Fabrication The device was fabricated by combining three separate layers of molded PDMS. The PDMS was molded using either a silicon or acrylic master. Once the pieces were fabricated and separated, the individual layers were assembled and bonded to create the final device.

2.2.3.1 The Silicon and Acrylic Masters 2.2.3.1.1 Silicon Masters The master molds for the bottom and middle layers were constructed from silicon wafers. Silicon was used as the substrate because etching fine structures into the silicon is well understood and controllable using available etching techniques. First, 4” silicon wafers were dehydration baked at 100 °C for at least 30 minutes (Figure 2-8A). The wafers were vapor coated with hexamethyldisilazane (HMDS) adhesion promoter. Photoresist (AZ 4620, AZ Electronic Materials, Branchburg, NJ) was spin coated at 2 krpm for 40 seconds to obtain a 10 μm layer (Figure 2-8B). After the photoresist is exposed and patterned, native oxide (SiO2) was removed with a 10% hydrofluoric acid (HF) dip (Figure 2-8C). 100 and 250 μm etch depths for the bottom and middle molds, respectively, were achieved using deep reactive ion etching (DRIE) (PlasmaTherm SLR-770B, Unaxis Corporation, St. Petersburg, FL) (Figure 2-8D). Photoresist was removed using acetone, isopropyl alcohol (IPA), and deionized (DI) water (Figure 2-8E). Then the wafers were cleaned using oxygen plasma (400 mTorr, 400 W, 4 minutes) (PEIIA, Technics Plasma, Kirchheim, Germany).

Figure 2-8 Cross-section of fabrication process to create silicon masters.

The silicon masters were cleaned using the RCA standard-clean-1 (SC-1) process (5:1:1 DI H2O:H2O2:NH4OH) to remove any organic compounds. The masters were then coated with approximately 5 μm of vapor deposited Parylene C (Specialty Coating Systems, Inc., Indianapolis, IN) (Figure 2-8F, Figure 2-9). This release layer facilitates the removal of the PDMS replica from the mold. A list of the process steps to fabricate silicon masters can be found in Appendix A.

Figure 2-9 Image of a silicon mold used to create the (a) bottom and (b) middle layers for the drug delivery device. The silicon masters were coated in Parylene C to facilitate mold release of

the PDMS layer from the master. Once the silicon master was processed, it was mounted on a glass substrate in order to prepare for replicating a PDMS bottom layer. First, a 5’’ x 5’’ (127 mm x 127 21

mm) glass plate was cleaned using isopropyl alcohol. The plate was placed on a hotplate (90 째C). The value of the hotplate cannot exceed 120 째C or it may cause thermal degradation of the Parylene C on the wafer. A few grams of paraffin wax is placed on the center of the glass plate and allowed to melt. When the wax is fully melted, the silicon wafer is placed (patterned side up) on the wax. Firm pressure is applied on unpatterned locations on the wafer in order to ensure the wafer is flush against the glass. Any excess wax that seeps out from under the wafer is removed. The hotplate was turned off and the entire setup was allowed to slowly return to room temperature. The steps to mount the master can be found in Appendix B. Middle and bottom layers of the device were created using soft-lithography techniques. Soft-lithography is a technique used to mold ductile materials with a micromachined mold. One of the most common uses of soft-lithography is to mold PDMS prepolymer using a silicon master. PDMS (Sylgard 184, Dow Corning, Midland, MI) was mixed (10:1 base to curing agent ratio; AR-250 Hybrid Mixer, Thinky Corp., Tokyo, Japan) then poured and spread over the silicon master. The PDMS was degassed in a vacuum oven (Model VO914A, Lindberg/ Blue, Asheville, NC) and cured (90 째C for 1 hour). The molded sheet of PDMS was gently separated from the silicon master. Individual device layers were dissected from the PDMS sheet using a fine-tipped blade. A more detailed fabrication process for the bottom and middle layers can be found in Sections 2.2.3.2.1- The Bottom Layer and 2.2.3.2.2- The Middle Layer, respectively.

2.2.3.1.2 Acrylic Master 22

The top layer was molded using a conventionally machined acrylic master. An acrylic master was used because the dimensions for the top layer did not require the precision of a silicon master.

Furthermore, the size of the top layer changed

frequently, resulting in the need for a rapid and inexpensive method for creating the mold. The acrylic master is created by cutting a square piece with rounded corners (6 mm x 6 mm, 0.236’’ x 0.236’’) from a 0.8 mm (0.031’’) thick sheet of acrylic. The corners were rounded to distribute the stresses which are concentrated in the corners of the reservoir. The pieces were cut using a laser cutter (35 Watt Helix, Epilog Laser, Golden, CO). The laser pattern is defined by a software package (CorelDraw); vector cuts are represented as lines where etching locations are designated with shaded shapes. The squares of acrylic and several glass slides (25.4 mm x 50.8 mm, 1’’ x 2’’) were cleaned using isopropyl alcohol. Five minute epoxy was used to affix the squares on the glass slide 15 mm apart. A glass slide was used as the base of the master in order to ensure a flat bonding surface for the PDMS replicas. The epoxy was allowed to cure at room temperature for 24 hours. The file for the squares and acrylic master fabrication process can be found Appendix C.

2.2.3.2 Layer Fabrication The manually-actuated drug delivery device is comprised of three individually structured layers of PDMS.

Figure 2-10 SolidWorks image of the three layers that comprise the drug delivery device. The entire device is 17 mm in length. Note, suture tabs are not shown.

2.2.3.2.1 The Bottom Layer The bottom layer forms the base of the device outlining the shape of the reservoir, cannula and suture tabs. It also contains mechanical support posts and check valve seat structures. This layer also defines the size of the microchannel within the cannula. The support posts prevent flow restriction if the device were to collapse on itself.

Figure 2-11 SolidWorks image of the bottom layer. Dimensions of the bottom layer are given [mm]. Note, suture tabs are not shown.

The bottom layer is fabricated using a silicon master (Figure 2-12C). The master was created using traditional lithography and etching techniques to fabricate a negative relief of the desired shape (Figure 2-12A, B, C). The fabrication process for the silicon master is discussed in Section 2.2.3.1.1- Silicon Masters. The mask used to create the bottom layer silicon master can be found in Appendix D.

Once the master was fabricated, the bottom layer for the device was replicated. First, PDMS was prepared using a 10:1 base to curing agent ratio (Sylgard 184, Dow Corning, Midland, MI). Approximately 15 grams of PDMS was poured onto the center of the master. The master was tipped to manually spread the PDMS over the entire surface of the wafer, ensuring PDMS coverage on each component (Figure 2-12D). Once all of the components have been covered, the wafer is tipped to allow the excess PDMS to flow off of the wafer. The master is placed in a vacuum oven (<30 mmHg, Model VO914A, Lindberg/ Blue, Asheville, NC) to degas the PDMS. 25

The degassed PDMS can then be cured at room temperature (24 hours) or rapidly cured at 70 ยบC for 30 minutes. Once the PDMS is cured, a razor blade is used to cut along the edge of the master. A circular PDMS sheet containing 20 replicas of the bottom later is carefully lifted from the master mold (Figure 2-12E). The sheet is then transferred to a glass substrate where the individual replicas are cut from the sheet (Figure 2-12F, G, H). The fabrication process steps can be found in Appendix E.

Figure 2-12 Cross-sectional image of the fabrication process for the bottom layer silicon master and individual silicone layer. The cross-section is taken through the line of symmetry (line indicated on Figure 2-13).

Figure 2-13 Red line indicates location of cross-section image for Figure 2-12.

2.2.3.2.2 The Middle Layer The middle layer defines the top cover to the cannula and check valve orifice.

Figure 2-14 SolidWorks image of the middle layer. Dimensions of the bottom layer are given [mm].

Fabricating the silicon master for the middle layer is identical to the bottom layer except the silicon master is etched 250 Îźm deep using DRIE.

The process is 27

described in Section 2.2.3.1.1- Silicon Masters. The mask for fabricating the silicon master is shown in Appendix F.

Fabricating the middle layer component is similar to the bottom layer process described in Section 2.2.3.2.1- The Bottom Layer. However, the check valve orifice must be made in the component prior to cutting each replica from the PDMS sheet (Figure 2-15G). The check valve orifice is made by puncturing the PDMS using a 33-gauge coring needle (O.D. 203 Îźm). Fabrication steps for the middle layer can be found in Appendix E.

Figure 2-15 Cross-sectional image of the fabrication process for the middle layer silicon master and individual silicone layer. The cross-section is taken through the line of symmetry of the middle layer (line is indicated in Figure 2-16).

Figure 2-16 Red line indicates location of cross-section image for Figure 2-15.

2.2.3.2.3 The Top Layer The top layer forms the reservoir. The reservoir interior volume is defined by the shape and size of the acrylic mold. The top layer is prepared after the bottom and middle layers have been assembled. The top and bottom layer assembly is discussed in Section 2.2.3.3- Device Assembly.

Figure 2-17 SolidWorks image of top layer. The interior cavity of the top layer defines the reservoir volume. Dimensions are indicated [mm].

To fabricate the top layer, PDMS is poured over the top layer acrylic mold (Figure 2-18B). The mold and PDMS prepolymer is placed into a vacuum oven to degas the PDMS. The mold is then placed into an oven for 15 minutes at 70 °C. After 15 minutes, check to see if the PDMS has reached a “half-cured” state. To check if the PDMS is “half-cured,” gently touch the surface of the PDMS with a mixing rod. If the PDMS sticks to the rod and deforms slightly when the rod is removed, the PDMS is “half-cured.” The “half-cured” state helps to attach the top layer to the middle layer and creates a stronger bond between the layers. The procedure to create a “half-cured” top layer can be found in Appendix G.

The mold is then aligned over the reservoir cutting pattern (Figure 6-4). A finetipped blade is used to carefully cut a 1 mm border around the edge of the acrylic square (Figure 2-18C). Nest, obtain a pre-assembled bottom/middle layer pair. The bonding and assembly process for the bottom and middle pairs are described in 30

Sections 2.2.3.3.1- Cleaning, 2.2.3.3.2- Oxygen Plasma Bonding, and 2.2.3.3.3Bonding Top Layer to Middle and Bottom Layers.

Using a pair of tweezers,

carefully lift the top layer from the mold (Figure 2-18D). Align the top layer over the middle/bottom layer stack such that the edge of the reservoir interior matches the interior edge of the middle piece. Place the assembled device into a Petri dish and allow the reservoir to finish curing at room temperature for 24 hours.

The

fabrication process and reservoir cutting pattern can be found in Appendix H.

Figure 2-18 Process for making drug delivery device reservoirs. A) Use epoxy to affix acrylic squares onto a glass slide, B) Pour PDMS prepolymer onto acrylic mold and half-cure PDMS, C) Cut reservoirs from molded PDMS piece. D) Remove reservoirs from mold, E) Reservoirs are ready for assembly.

2.2.3.3 Device Assembly After each layer is molded, the three layers must be assembled to form the complete device (Figure 2-19).

The bottom and middle layers are first cleaned using a

hydrochloric acid (HCl) solution. Next, the surface properties of the PDMS bottom

and middle layers are altered using oxygen plasma to promote bonding between the pieces without the need for adhesives.

Figure 2-19 Illustration of how the three layers are fabricated and assembled to form the manuallyactuated drug delivery device.

2.2.3.3.1 Cleaning Each PDMS bottom and middle layer piece is submerged in a 1:10 DI H2O:HCl solution. This cleaning process removes particles or dust that may have accumulated 32

on the pieces after mold release. The piece is rinsed off using DI water and blown dry. The cleaning process can be found in Appendix I.

2.2.3.3.2 Oxygen Plasma Bonding Oxygen plasma was used to modify the surface of the PDMS pieces in order to assist the bonding of the individual layers together. Pairs of bottom and middle layers were placed on a glass slide (one pair per slide) with the desired bonding surface facing up.

The exposed side is modified using oxygen plasma (Figure 2-20).

Pressure, power, and time parameters for oxygen plasma were varied to find the optimal settings which yield the strongest bonds. The most durable bonds were found to form after a pressure of 100 mTorr and power of 100 W were applied for 45 seconds. A more detailed discussion of oxygen plasma bonding can be found in Section 2.2.4.1.1- Oxygen Plasma Bonding Method.

Figure 2-20 Placement of pairs of pieces on glass slide to facilitate placement and alignment of layers after oxygen plasma treatment.

Each pair needed to be assembled quickly because oxygen plasma modified PDMS will revert back to the initial hydrophobic state. A polar liquid, such as ethanol, can be used to slow the reversion (Duffy, et al. 1998). Ethanol also lubricates the pieces and allows for easier alignment. The oxygen plasma treatment process is described

in Appendix J. The layers are assembled under a microscope to ensure the edges of the layers and the check valve opening and valve seat are aligned.

2.2.3.3.3 Bonding Top Layer to Middle and Bottom Layers The top layer of the device is added after the bottom and middle layers have been bonded. Section 2.2.3.2.3- The Top Layer describes the process of bonding the top layer to the bottom/middle layer assembly.

2.2.3.3.4 Reinforcing Layer The reinforcing layer is a thin layer of PDMS that is cured around the assembled device. This layer became necessary because oxygen plasma bonding is not robust enough to withstand the stresses placed on the device during surgical handling. The reinforcing layer is fabricated by placing an assembled device into a crystallization dish with an inclined glass slide (Figure 2-21A). PDMS is poured around the device until the edge of the device is fully covered, ensuring PDMS does not cover the check valve (Figure 2-21B). The crystallization dish is then placed into the oven (70 째C, 1 hour) to cure the PDMS. Excess PDMS is removed from the device to obtain the final shape of the reinforced device (Figure 2-21C).

Figure 2-21 Adding reinforcing layer to drug delivery device. A) Device is placed on an inclined glass slide, B) PDMS prepolymer is poured around the device, covering the edge of the device but not occluding the check valve opening, C) The device is removed from the slide and excess PDMS is cut from the device.

2.2.3.4 Dimensions of Assembled Device A summary of the device dimensions are found in Table 2-1. Given a potential dosage range of between 50-250 nL per dose, the device can hold between 1143-228 doses if the entire volume is depleted.

Table 2-1 Dimensions of Drug Delivery Device

Specification Value Fabrication Material PDMS (Silicone Rubber) External Wall of Reservoir Body (W x L) 7 mm x 7 mm Reservoir Internal Wall of Reservoir Body (W x L x H) 6 mm x 6 mm x 1.58 mm Reservoir Internal Volume 57.15 µL Support Pillars in Reservoir (W x L x H) 0.5 mm x 0.5 mm x 0.1 mm Fabrication Material PDMS (Silicone Rubber) External Wall of Tube (W x L) 1 mm x 10 mm Cannula Internal Wall of Tube (W x L x H) 0.5 mm x 9.5 mm x 0.1 mm Tube Volume 0.475 µL Support Pillars in Tube (W x L x H) 0.4 mm x 0.4 mm x 0.1 mm Valve Orifice Diameter 203 µm Valve 35

Valve Seat (W x L x H)

0.4 mm x 0.4 mm x 0.1 mm

2.2.4 Benchtop Experiments- Methods and Results 2.2.4.1 PDMS Bonding A method for bonding the individual layers together without using adhesives was investigated. The bonding method needed to produce irreversible bonding and be compatible with the PDMS material. Adhesives were not considered as the primary method for bonding because adhesives can seep into the device and clog the microchannel or the check valve.

Oxygen plasma and chemical treatments were evaluated as methods to bond PDMS in both benchtop prototypes and surgical models. Bonding strength was qualitatively measured by observing the fracture resistance of the bond to an applied shear force. PDMS sample coupons were prepared (Figure 2-22A). Prior to oxygen plasma or wet chemical treatment, PDMS coupons (20 mm x 10 mm) were cleaned using in a 0.01% HCl solution. Pairs of coupons were then exposed to oxygen plasma or wet chemical treatment and assembled such that half of each coupon overlapped the other coupon (Figure 2-22B,C). Shear force was applied by pulling on the nonoverlapping sections (tabs) of the coupons (Figure 2-22D).

Figure 2-22 Procedure used to qualitatively determine bond strength after oxygen plasma or wet chemical treatment.

Quantitative measurements of bonding strength were evaluated by bonding two pieces to form an enclosed reservoir (interior volume, 6 mm x 6 mm x 1.59 mm). The enclosed reservoir was fabricated by bonding the top piece of the device (Figure 2-17) to a PDMS coupon. Again, samples were cleaned prior to treatment (Figure 2-23A, B, C). Pressurized water was introduced into the cavity until the bond failed (Figure 2-23D).

Figure 2-23 Testing setup used to quantitatively measure bond strength after oxygen plasma or wet chemical treatment.

2.2.4.1.1 Oxygen Plasma Bonding Method Oxygen plasma treatment of PDMS results in a hydrophilic surface due to the formation of silanol groups (Si-OH).

When two treated surfaces are joined,

irreversible covalent bonds (Si-O-Si) form. The number of silanol groups formed depends on conditions of the plasma treatment (duration, power, and pressure). Polar solutions such as water and ethanol can extend the reactive time of the silanol groups and slows the return of the surface to its original hydrophobic state (McDonald, et al. 2000). Baking the bonded sample can also increase the strength of the bond (McDonald and Whitesides 2002). Oxygen plasma power, pressure, and duration were examined to determine the optimal conditions for maximum bonding 38

strength. Water and ethanol were used to facilitate alignment prior to bonding. Variations in baking time and temperature were also examined.

2.2.4.1.2 Wet Chemical Bonding Method Chemical treatment of PDMS to promote bonding was also evaluated. Samples of PDMS were immersed in 0.012 M HCl. Samples were removed and rinsed with ethanol, blown dry, and assembled. Baking temperature, baking time, and bond compression during baking were examined.

2.2.4.1.3 Results Bonds created following oxygen plasma were found to be more reliable than those created following wet chemical treatment. Optimized oxygen plasma conditions were determined to be 100 W, 100 mTorr, and 45 seconds. Once the surfaces of the layers were treated, the layers were aligned with the aid of a polar liquid (e.g. ethanol or water). The entire assembly was then baked at 100 째C for 45 minutes in order to complete the bonding process (Duffy, et al. 1998). The device was originally assembled using oxygen plasma treatment to bond all three layers. However, the bond strength was insufficient to survive handling during surgical implantation of the device. For example, the surgical procedure required bending the cannula back on itself at 180째 to insert it into the eye. The bonds connecting the two layers that formed the cannula were observed to fail during this procedure. Additionally, leakage from the reservoir was observed. Failure points of the device may have resulted from the hand assembly method to align the layers during bonding. Each layer has a 1 mm border which is used as the bonding surface. 39

However, a slight misalignment will result in a weaker bond if the full 1 mm surface is not utilized. Weaker bonds may also be in part due to the time elapsed between treatment and bonding.

The strongest bonds are formed within 1 minute of

treatment, however, due to the limitations of the oxygen plasma machine, the layers may have been assembled outside of this 1 minute window.

It was observed that half-cured PDMS retained some of the malleable properties of the PDMS prepolymer. It maintained the basic shape but was tackier than the fully cured PDMS. Half-cured PDMS also created a strong irreversible bond when placed on a fully cured piece of PDMS. The half-cured reservoirs bonded more strongly to the bottom and middle layer stack than oxygen plasma treated bonds. Half-cured bottom and middle layers could not be used because the individual replicas could not be separated from the thin PDMS sheets. The half-cured thin PDMS replicas could not be aligned because they did not have sufficient structural integrity to maintain their shape.

The device assembly process was altered to take advantage of half-cured material and PDMS prepolymer to strengthen the bonds between the layers in order to survive surgical manipulation.

The bonding between the bottom and middle layers

continued to use oxygen plasma treatment, a half-cured top layer was added. The assembled device was unable to survive the stresses from surgical handling (Figure 2-24A), therefore, the assembled device was strengthened using a reinforcing layer of PDMS prepolymer, as described in Section 2.2.3.3.4-Reinforcing Layer (Figure 40

2-24B). The reinforcing layer was trimmed to remove excess material and to create suture tabs (Figure 2-24C). The reinforced device was able to survive extensive surgical handling and did not fail during benchtop testing or implantation.

2.2.4.2 Check Valve 2.2.4.2.1 Benchtop Operation The check valve for the device was tested on benchtop to verify its functionality. The device was filled with dyed DI water. The dyed liquid was observed moving through the cannula and out of the check valve. When pressure was removed from the reservoir the droplet of dispensed liquid remained outside of the check valve and did not backflow into the device. Time-elapsed photographs were taken of the check valve operation (Figure 2-25).

Figure 2-25 Time-lapsed photographs of dyed DI water being dispensed from the check valve under manual actuation.

2.2.4.2.2 Characterization 2.2.4.2.2.1 Check Valve Opening and Closing Pressures 2.2.4.2.2.1.1 Methods The check valve can be characterized by determining the cracking pressure and generating a pressure versus flow rate curve over a range of pressures. The check valve is analogous to a diode in the electrical world. A current versus voltage curve can be generated for a diode where current is measured as voltage is applied to the diode. The ideal diode has no current output when zero voltage is applied. When voltage is positive, the current varies linearly with respect to voltage; when the voltage is negative there is no reverse current. Similarly, an ideal check valve can be characterized with a pressure versus flow rate curve, where pressure is applied and the resulting flow rate is measured. Again, in the ideal case, the valve remains closed when no pressure is applied, and opens and allows linear fluid flow with respect to pressure. Under reserve pressure the valve remains closed. 42

Figure 2-26 Typical Diode Current versus Voltage Curve

Figure 2-27 Typical Check Valve Pressure versus Flow Rate Curve.

However, both the diode and check valve do not operate under ideal conditions. The diode conducts voltage after a bias voltage threshold is achieved. Furthermore, a negative voltage will result in leakage current; a large negative voltage (or breakdown voltage) will cause the diode to fail (Figure 2-26). In the case of the non43

ideal check valve, the valve remains closed until the pressure exceeds the cracking pressure of the valve. For reverse pressures, a small amount of leakage may occur prior to the valve sealing closed; a large reverse pressure will cause irreversible damage to and failure of the check valve (Figure 2-27). Operating characteristics of the check valve, such as pressure versus flow rate curve and cracking pressure, were obtained by aligning the bottom and middle layers and clamping the structure in a custom laser-machined testing apparatus and attaching the fixture to a water chamber pressurized by a nitrogen cylinder (Figure 2-28A). Pressurized water is forced through the delivery tube and out of the check valve. A calibrated pipette (50 ÎźL, Clay Adams, Parsippany, NJ) was attached to the output of the check valve (Figure 2-28B). Flow rate is measured by timing fluid passage through a precision calibrated pipette. The pipette was primed by pre-filling it with water.

A small air bubble was introduced at the input of the pipette.

Small

increments of pressurized water were applied to the check valve and the bubble position was monitored. After each pressure increase, the system was held for five minutes at a constant pressure to allow the system to equilibrate. The cracking pressure of the check valve is identified as the lowest pressure required that resulted in visual confirmation of bubble movement over a five minute period. The cracking pressure was recorded. The flow rate was determined by applying pressures larger than the cracking pressure and measuring the elapsed time to move an air bubble along the entire length of the 50 ÎźL pipette.

Figure 2-28- A) Exploded SolidWorks view of the custom-made laser-machined jig to characterize the check valve operation. B) Pressure setup used to open the valve with pressurized water.

2.2.4.2.2.1.2 Results The integrated check valve was characterized to determine the cracking pressure and forward flow rates. Cracking pressure was determined to be 62 kPa (465 mmHg) (Lo, et al. 2006). The cracking pressure is much higher than normal pressures found within the eye. A higher opening pressure than normal intraocular pressures is necessary to prevent the device from accidental dispensing due to normal activities that may put pressure on the device, such as sneezing or rubbing the eyes. In this case, the high cracking pressure may be partially attributed to the flow resistance of microchannel. The microchannel is 500 μm wide; however, the microchannel is narrower at the support posts. The support post is 400 μm x 400μm, leaving only 50 μm on either side of the support post for fluid flow. Another component that adds resistance to the system is the check valve.

The check valve is formed by

positioning a 203 μm diameter hole above a 400 μm x 400 μm square.

The

overlapping area between the two layers is approximately 0.127 mm2. This overlap 45

area may have been weakly bonded together during the oxygen plasma treatment step. The bond may have artificially created an elevated cracking pressure because a higher pressure is needed to break the bond in order to get the check valve to function. Furthermore, variations in the cracking pressure may also be inherent to the PDMS material.

However, these device or material properties can be exploited to modify the valve design to fit a target operation within a specified pressure range if necessary. PDMS stiffness can be changed due to differences in base: curing agent ratio and curing temperature/time. Additionally, the check valve orifice diameter can be increase or decrease; which can be accomplished by using a smaller or larger guage coring needle to create the orifice, respectively. A smaller orifice will have a greater overlap area with the valve seat (shifting the cracking pressure higher), and greater flow resistance. A larger orifice will have the opposite effect.

Flow rate increased when the pressure on the system was increased. The range of actuation pressures was determined by the range of interest for ocular dispensation as well as the limits of the pressure testing system. A maximum flow rate of 321.29 ÎźL/min was obtained at a pressure of 290.61 kPa (2179.78 mmHg) (Figure 2-29).

Figure 2-29 Flow Rate vs. Pressure curve for check valve (mean ± SE, N=4).

2.2.4.2.2.2 Check Valve Closing Time Constant 2.2.4.2.2.2.1 Methods Check valve dosing while varying the applied pressure and the duration of the pressure was also measured.

An electronically-controlled solenoid valve

(LHDA0533115H, The Lee Company, Westbrook, CT) was used to vary the duration of the applied pressure to simulate a patient’s finger. A square wave control signal with a 50% duty cycle and frequencies ranging from 18.5 mHz to 500 mHz was used to control a pressurized water source. In the “on” state the solenoid permits pressurized water to be passed onto the jig. The volume of fluid exiting the valve is measured by noting the distance an air bubble traveled in a calibrated pipette (100 μL) over the “on” and “off” portion of the wave. The closing time constant for 47

the valve was determined by measuring the elapsed time between removing the pressure from the valve and when the accumulated volume exiting the valve reached 63.2% of the final volume.

2.2.4.2.2.2.2 Results Dosed volume was measured for two different applied pressures 250 mmHg (33.33 kPa) and 500 mmHg (66.66 kPa) controlled using a 50% duty cycle square wave control signal in the frequency range 18.5 mHz to 500 mHz (53 to 2 sec periods). Dosed volume and pressure duration were found to be linearly proportional for both applied pressures, resulting in a consistent flow rate independent of the dosing period (Figure 2-30). The steady state flow rates were 1.57 ± 0.2 µL/sec and 0.61 ± 0.2 µL/sec (mean ± SE, n = 4) at 500 mmHg and 250 mmHg, respectively.

Figure 2-30 Check valve control of dosing under 250 mmHg and 500 mmHg of applied pressure. Duration of applied pressure was varied using a solenoid valve controlled using a 50% duty cycle square waves.

Due to the finite closing time of the valve, flow was observed after removal of the pressure source. The time constant associated with valve closing was found to be 10.2 sec for 500 mmHg and 14.2 sec for 250 mmHg (Figure 2-31). Dispensed volume and closing time calculations could not be measured in real-time, therefore these data were extracted from video footage of the air bubble moving through the calibrated pipette.

Dosed volume was calculated using initial and final bubble

positions in the pipette and the applied pressure duration was calculated from the time stamps in the video. The closing time constant was calculated by noting the bubble location starting from when pressure was removed and at specific time intervals until the bubble movement stopped.

The closing time constant was 49

calculated by determining the time at which the accumulated volume reached 63.2% of the final value. The volume dispensed over the duration of closing time is 3.5 ÎźL and 6.3 ÎźL for 250 mmHg and 500 mmHg, respectively. The long closing time constant can significantly increase the dosage amount, especially for very small dosages. Additionally, the valve does not prevent accidental dosing due to transient fluctuations in intraocular pressures (e.g. sneezing, flying).

Therefore,

improvements in response time and overpressure protection will be incorporated in future drug delivery device prototypes.

Figure 2-31 A representative graph depicting the volume dispensed after the applied pressure (250 mmHg and 500 mmHg) is removed from the valve. The dashed lines indicate when the accumulated volume reached 63.2% of the final value, the time at which this point occurred was defined as the closing time constant for the valve.

2.2.4.3 Refillability 2.2.4.3.1 Needle Determination 2.2.4.3.1.1 Methods The device operating lifetime is closely linked to the ability to refill the reservoir and the mechanical integrity of the punctured material. Therefore, a choice of refill needle (e.g. type, gauge, etc) and maximum number of achievable refills must be determined. A commercially available, 30 gauge (305 Îźm in outer diameter, O.D.) needle was used to refill the device. This size was selected as a trade-off between utilizing the needle with the smallest outer diameter to maximum material lifetime and stiffs enough to puncture the device without the needle buckling or bending. The needle must pierce the conjunctiva and reservoir wall in order to replenish the reservoir contents. A small needle size also allows the punctured conjunctiva to self-seal, therefore avoiding the need for sutures.

2.2.4.3.1.2 Results Two types of 30 gauge needles, coring and non-coring, were investigated to determine the most suitable needle profile. The needle must be able to puncture the PDMS reservoir but cause minimal damage to the material after removal. Both types of needles were inserted through PDMS slabs. The needle tracks through the PDMS and at the insertion sites were examined. Scanning electron microscope (SEM) images of 30 gauge coring and non-coring needles were taken to examine the needle tip and needle shaft. The coring needle 51

has a blunt tip with a circular cutting edge. The non-coring needle has a beveled tip which tapers to a point (Figure 2-32A). Both needles were pushed into and withdrawn from a sample piece of PDMS. The resulting needle puncture entrance and needle track were imaged using an optical microscope. A coring needle removed material as it was pushed through the sample. When the needle was removed, a circular hole was formed at the puncture location and a cylindrical shape was cut through the PDMS slab. The material cut from the PDMS sample remains inside the needle and prevents liquid from being dispensed. The non-coring needle displaces material as it moves through the sample and creates a small tear. The material relaxes when the needle is removed and seals the tear (Figure 2-32B, C). A non-coring needle was selected for refilling to maximize device lifetime.

Figure 2-32 Refill needle determination, A) Coring versus non-coring 30 gauge (305 Îźm OD) needle illustration and SEM images, B) Top view of needle track through punctured PDMS slab using each needle, C) Side view of needle track through PDMS slab.

2.2.4.3.2 Maximum Puncture Events and Leakage After Puncture 2.2.4.3.2.1 Methods PDMS membranes (250 μm and 670 μm thick) were evaluated for mechanical integrity by testing for leaks after repeated punctures (or refill events). PDMS sheets were obtained by spreading a thin layer of PDMS (10:1 base to curing agent ratio) on a glass substrate and cured at 70 ˚C for 20 minutes. 0.5’’ x 0.5’’ (12.7 mm x 12.7 mm) square membranes were cut from the sheet; the procedure used to create the membranes can be found in Appendix K. Two membrane thicknesses were tested to determine leakage pressure as a function of material thickness.

The worst-case scenario for refill was investigated and implemented in the leakage pressure study. The leakage pressure of a membrane punctured 8 times in different locations within a circular (5 mm diameter) area was compared to the leakage pressure of a membrane punctured 8 times in the same location using a 30G noncoring needle. To ensure that repeated punctures were through the same point membranes were mounted in a custom laser-machined acrylic jig. The jig contains a small hole to align repeated needle punctures in the same location (Figure 2-33). The method which resulted in a lower leakage pressure was used for the leakage pressure test to show how the number of punctures (8, 12, and 24 punctures) affects leakage pressure.

Figure 2-33 Exploded SolidWorks image of the custom-made laser machined jig used ensure multiple puncture events pierce the membrane in the same location for worst-case scenario testing.

After puncturing, the membrane was transferred to the second jig in which the puncture site was aligned between two reservoirs (Figure 2-34A). The input of the jig was attached to a pressurized water system and the output was connected to a calibrated pipette (50 ÎźL, Clay Adams, Parsippany, NJ) (Figure 2-34B). Pressurized water was applied in increments and water leakage, if any, was monitored by tracking the position of small bubble in the water-filled calibrated pipette. The leakage pressure is determined by the lowest pressure which causes the bubble to move any visible distance over a five minute period. The burst pressure, pressure required to rupture an unpunctured membrane, was also measured.

Figure 2-34 A) Exploded SolidWorks view of the custom-made laser-machined jig to apply pressure to punctured membranes. B) Setup used to provide measure leakage pressure of punctured membranes.

2.2.4.3.2.2 Results Two needle puncture arrangements were examined to determine the spatial arrangement impact on membrane strength. For the case where all punctures were created at the same position on a 250 μm thick membrane, the resulting leakage pressure after 8 punctures was 6.98 ± 0.73 kPa (n = 4) (52.36 ± 5.48 mmHg). The second case involved puncturing a 250 μm membrane punctured 8 times in random locations in a 5 mm x 5 mm square area and resulted in a leakage pressure of 8.14 ± 0.07 kPa (mean ± SE, n = 3) (61.02 ± 0.52 mmHg). This test verified that the needle punctures in exactly the same position lowered the leakage pressure of the membrane, and therefore is the worst-case scenario. This was likely associated with an increase in puncture size as a result of repeated needle insertions.

For the

randomly located puncture case, each puncture location only has one insertion event and thus the needle track size was minimal. The aligned punctures method was used to compare leakage pressure for 8, 12, and 24 punctures.

The maximum pressure a repeatedly punctured membrane can withstand without leaking decreases as the number of punctures increases. The burst pressure for the unpunctured 673 Îźm membrane (525.75 kPa, 3943.5 mmHg) was 5 times larger than the leakage pressure for 8 punctures (106.2 kPa, 796.4 mmHg), while the burst pressure for the unpunctured 250 Îźm membrane (393.5 kPa, 2951.1 mmHg) was 56 times larger than the 8 puncture leakage pressure (6.98 kPa, 52.4 mmHg). This suggests that the additional area in thicker PDMS membranes provided more selfsealing ability than thinner membranes.

For all of the repeated puncture tests, though the leakage pressure for both membranes decreased with increasing number of punctures the thicker membrane was able to withstand higher pressures prior. Also, the leakage pressure for both membranes becomes constant for higher number of punctures (Figure 2-35). This could be attributed to nominal or lack of additional damage to the needle track for each subsequent needle puncture.

Figure 2-35 Leakage pressure for 250 Îźm and 673 Îźm thick membranes punctured 8, 12 and 24 times through the same location with a 30G non-coring needle (n = 4).

2.2.4.3.3 Benchtop Refill and Dispensation 2.2.4.3.3.1 Methods An assembled device was placed on a glass slide and filled using a standard 30 gauge non-corning needle. Dyed DI water was injected into the device to help visualize fluid flow. The device was filled until liquid was seen exiting the check valve. The reservoir was manually-depressed to dispense the contents of the device. The refill and dispensation of the device was repeated three times. 2.2.4.3.3.2 Results Device functionality was verified. Refill and delivery were successfully completed four times without failure. However, it should be noted that benchtop tests benefited from the use of a glass slide to stop the progression of the needle. Also, the device was placed on a solid surface, which provided more support to the device and aided dispensation. When the device is implanted, the needle progression through the 57

device will not be stopped and may penetrate through the entire device. Furthermore, ocular tissue is more compliant than a laboratory benchtop. The eye will move within the ocular orbit and/or the tissue will deform when pressure is applied to the device. This motion may absorb some of the pressure placed on the device. Device modifications may be necessary once the device is tested in vitro and in vivo.

Pressure was applied to the reservoir until the device stopped dispensing any more liquid. However, it was noted that a non-negligible amount of liquid remained in the reservoir. The sidewalls of the reservoir prevent the reservoir from being fully depressed. Also, a cuboid reservoir results in dead volume at the reservoir corners. Future versions of the reservoir shape need to be changed to a circular or oval shape in order to minimize dead volume. A circular or oval reservoir shape would also be beneficial in distributing the stress placed on the device during dispensation as corners are locations for stress concentration and would be more prone to failure.

2.2.5 In Vivo and In Vitro Experiments- Methods and Results 2.2.5.1 Device Placement 2.2.5.1.1 Methods The device placement and surgical procedure to affix the device and introduce the cannula into the eye was determined in vitro using enucleated porcine eyes. Suture tabs were tested to verify the strength and location of the tabs; the device was sutured to the sclera. Surgeons recommended limbal incisions or scleral tunnel insertions to 58

insert the cannula into the anterior chamber of the eye. A limbal incision is a small cut made at the border between the cornea and sclera to access the anterior chamber. A scleral tunnel is a tunnel made 3 mm from the limbus and penetrates the eye wall. The device was first sutured to the sclera, and then the cannula was inserted into the eye via the scleral tunnel. Once the device was secured with the cannula entering the anterior chamber, device dispensation and refill tests were conducted.

The anterior chamber of the eye was used for the in vitro and in vivo studies because the cannula can be visualized through the cornea, as opposed to inserting the cannula into the poster segment of the eye. Future applications that require delivery to the posterior segment can use a similar surgical procedure.

2.2.5.1.2 Results Surgical studies determined that only two sutures, located on the front corners of the device, were needed to secure the device to the sclera (white portion of the eye). Furthermore, it was difficult to insert the cannula through the limbal incision. Once inserted, the insertion route demonstrated two challenges, 1) dispensed liquid seeps out of the incision, thus reducing the amount of time the liquid is in contact with ocular tissues, and 2) the use of sutures to close the incision more tightly around the cannula causes the cornea to wrinkle. A scleral tunnel was more successful in introducing the cannula. During surgical manipulation, a device that was assembled and bonded using only oxygen plasma assisted bonding failed due to layer delamination. 59

A reinforcing layer was introduced to the fabrication process to increase device robustness. Reinforced devices did not fail during implantation. Furthermore, it was determined that reversing the surgical protocol to insert the cannula into the eye via a scleral tunnel and then suturing the device in place places less stress on the cannula.

2.2.5.2 Device Functionality 2.2.5.2.1 In Vitro Delivery 2.2.5.2.1.1 Methods The device was prefilled with dyed DI water. The cannula was inserted through a scleral tunnel and the device was sutured to the sclera of an enucleated porcine eye. Surgical forceps were used to manually depress the reservoir. A surgical microscope with video capture abilities were used to observe dye dispensation into the eye. 2.2.5.2.1.2 Results Dyed DI water can be seen entering the eye (Figure 2-36). The bloom of dispensed liquid can be seen to increase in size as the reservoir is continually depressed.

Figure 2-36 Surgical verification of liquid delivery in vitro using the drug delivery device.

However, as predicted from the benchtop model, depressing the reservoir with a cotton swab did not generate enough force to dispense the liquid. When the reservoir was depressed, the eye and device shifted, preventing the surgeon from putting constant force on the device. The liquid was dispensed by squeezing the device with surgical forceps. While using surgical forceps was acceptable in generating the pressure required for liquid dispensation, this method cannot be used in a practice.

2.2.5.2.2 Device Refill 2.2.5.2.2.1 Methods The device was prefilled with dyed DI water, the cannula inserted into the anterior chamber via a scleral tunnel and the device was sutured to an enucleated porcine eye. The dye was dispensed into the eye by depressing the chamber with surgical forceps. Once the internal volume of the reservoir was significantly depleted, a 30 gauge needle was used to pierce the top of the device reservoir. Dyed DI water was refilled into the device. 2.2.5.2.2.2 Results Increased in internal volume of the device is visually verified during refill (Figure 2-37).

The refilled device was dispensed and refilled several times to verify

successful device functionality and multiple refills.

Figure 2-37 Surgical verification of drug device refill was completed in vitro using a commerciallyavailable, standard 30 gauge non-coring needle.

The needle progressing was visually monitored and controlled.

However, in a

commercially viable device, refill would need to be successful when visual inspection of the device is not possible. A means to prevent the needle from piercing through the entire device is necessary. A stiff backing which cannot be punctured by the needle will need to be incorporated into future designs.

2.2.5.2.3 In Vivo Delivery 2.2.5.2.3.1 Methods The drug delivery device was sterilized one week prior to implantation. Pre-surgical preparations include prefilling the device with a phenylephrine (10% concentration) and Trypan blue mixture. Phenylephrine is a pupil dilating agent; Trypan blue is a dye that stains necrotic tissues and cells but is not taken up by live cells. A male pigmented rabbit was prepared for device implantation. The cannula of the device was introduced into the anterior chamber of the eye via a scleral tunnel and the device was secured to the eye using sutures. Baseline pupil diameter measurements were taken. The chamber was then manually depressed and approximately 25 ÎźL (2.5 mg) of phenylephrine was delivered into the eye (t = 0).

Pupil diameter 62

measurements were taken immediately after delivery (t = 1) and 10 minutes after dispensation (t = 10).

2.2.5.2.3.2 Results The pupil size of the rabbit increased after phenylephrine was introduced into the eye. A summary of the results can be found in Table 2-2. Observation of the dyed phenylephrine provided visual confirmation of delivery into the anterior chamber. Both vertical and horizontal pupil diameter measurements increased following phenylephrine delivery. Table 2-2 Summary of Results from In Vivo Delivery using the Manually-Actuated Drug Delivery Device

Pupil Dimension Baseline Measurement t=0 After Dispensation t = 1 min After Dispensation t = 10 min Total Change

Vertical [mm]

Horizontal [mm]

6.5

6.0

8.0

6.25

8.0

7.0

1.5 mm (23%)

1.0 mm (16%)

2.2.6 Summary A manually-actuated drug delivery device that can be utilized as a method of treatment for chronic ocular diseases has been demonstrated. Device components such as the refillable reservoir and check valve were characterized. The maximum internal pressure the reservoir can withstand, after multiple punctures using a 30 gauge non-coring needle, was determined to initially decrease with additional punctures, but showed no significant decrease after 12 punctures. The check valve diode curve was measured to determine cracking pressure and pressure versus flow 63

rate values. Check valve regulated delivery and closing time constants were also determined. The device was tested in benchtop and ex vivo experiments including device dispensing and refill. In vivo experiments demonstrated successful drug delivery resulting in the corresponding physiological response. This ocular drug delivery system is broadly compatible with existing ophthalmic drugs.

This device also has several modular components, which can simplify device assembly and/or allow the device to be customized to a specific patient dosing requirement or additional applications. The device is made of 3 layers; multiple identical copies of each layer are formed simultaneously, providing interchangeable components.

Additionally, these individual layers allow several devices to be

assembled in parallel. Furthermore, a specific layer can be altered without requiring changes in the other two layers to accommodate the change. For example, the interior cavity of the top layer can be increased, thereby increasing the internal volume of the device, without requiring a redesign of the bottom and middle layers, or changes to the assembly process for the three layers. Changing the internal volume can be used change the number of doses the device can contain and the frequency of refill events.

Finally, the check valve orifice size can be scaled

(increase or decrease in diameter), which will affect the diode curve of the check valve.

2.3 Electrically-Actuated Device with Dual Check Valve Device The electrically-actuated drug delivery device with dual check valve has the same basic components (refillable reservoir, cannula, check valve, and suture tabs) found in the manually-actuated drug delivery device. However, each component has been redesigned to address any challenges observed in the manually-actuated device. Each component is again designed to device constraints, tested to verify functionality, and integrated into one device. The electrically-actuated device with dual check valve also incorporates an electrolysis pump as a means for electronicactuation and a refill port.

The prototype of the electrically-actuated device with dual check valve has been constructed for benchtop testing. The prototype has a medical-grade silicone drug reservoir with integrated refill port, a pumping chamber to house the electrolysis structure and electrolyte, a cannula, and a dual check valve system. The pumping chamber ensures the electrolyte and drug remain separate, therefore the drug cannot be contaminated by the electrolyte, nor oxidize due to electrolysis.

The electrically-actuated device with dual check valve improves upon the manuallyactuated device both in safety and functionality. The manually-actuated device was capable of bolus (e.g. pulse) delivery; the second generation will allow for both bolus and continuous delivery. The electrically-actuated device with dual check valve will be electrically-actuated using an electrolysis structure. Electrolysis passes current 65

through water, which causes water to transform from liquid togas phase.

This

actuation method provides a versatile dosing (bolus and continuous delivery), variable delivery rates, and automatic dosing (Li, et al. 2007, Li, et al. 2008, Meng, et al. 2006). Furthermore, while the manually-actuated single check valve allowed one-way flow, it cannot reliably deliver a constant volume for each manuallyactuated dispensation event.

Nor can the manually-actuated device prevent

accidental dosing from uncontrolled transient pressure spikes (e.g. flying, sneezing, etc). The electrically-actuated device with dual check valve delivery rate can be controlled via electrolysis. Additionally, the check valve contains a pressure limiter which closes the check valve at high pressures.

2.3.1 Device Design 2.3.1.1 The Components 2.3.1.1.1 Check Valve and Cannula A drug delivery system consisting using a Parylene C cannula has been previous demonstrated (Li, et al. 2008).

Drug was pumped directly into the eye by

electrolysis actuation. However, this prototype lacked a flow control valve; drugs and bodily fluids could readily diffuse into and out of the device through the intraocular cannula. Furthermore, the delicate, thin-walled Parylene C cannula was easily damaged during surgical manipulation and implantation.

Its rectangular

profile made it difficult to seal the incision through which it was inserted with sutures alone; leakage paths resulted at the interface between the cannula and

incision site. Therefore, a more robust, circular cannula with an integrated check valve was developed.

A cannula having circular cross-section facilitates wound closure with sutures and prevents leakage around the incision. Ideally, the cannula diameter is < 1 mm; an incision of this size in the eye wall can self-seal even without the use of sutures. Therefore, the valve design should accommodate a circular cannula. Additionally, the valve must be in-plane with respect to the fluid flow. This ensures that that moving mechanical parts of the valve do not come in contact with ocular tissues (Lo, et al. 2009).

This valve orientation also minimizes dead-volume.

To prevent

diffusion of drug from the device into the tissue, the valve must be normally-closed. Finally, the valve must be safe and function reliably under normal intraocular pressure (IOP) conditions (15.5 Âą 2.6 mmHg, 2.1 Âą 0.35 kPa, (mean Âą SD)) (Ritch, et al. 1989), elevated conditions (glaucoma IOP > 22 mmHg, 2.9 kPa), and transient pressures fluctuations (e.g. patient sneezing, eye rubbing, or changes in ambient pressure) (Ritch, et al. 1989, Wilensky 1999).

Many MEMS valves exist and were reviewed recently by Oh and Ahn (Oh and Ahn 2006). To minimize the power requirements for the ocular drug delivery device, only passive mechanical valve designs were considered. These valves allow flow under forward pressure and exhibit diode-like regulation of flow. Examples include valves consisting of flow orifices controlled by pressure-sensitive flaps, membranes, and spherical balls. Lin et al. presented a glaucoma drainage device with Parylene C 67

checks valves (normally-closed and normally-open) valve in series to achieve bandpass regulation. Adhesives were used to secure the valves in a Parylene C tube (Lin, et al. 2009). Lo et al. fabricated a normally-closed silicone valve within a rectangular cannula by stacking patterned layers of silicone rubber (Lo, et al. 2009). However, current valve designs and packaging schemes are not suitable for integration into an advanced ocular drug delivery device, therefore, a new valve and package are necessary.

2.3.1.1.1.1 Design Our valve approach is modular and consists of four plates stacked together to form a normally-closed valve with a pressure limiter feature to provide bandpass fluid regulation (Lo and Meng 2009). The four plates are the valve seat, valve plate, spacer plate, and pressure limiter. Each of these plates can be replaced or exchanged for a different plate design, creating a modular valve design with multiple permeations. The plates are packaged within heat-shrink tubing; resulting in a robust and adhesiveless package. The packaged valve is easily integrated into the drug delivery system (Figure 2-38, Figure 2-39).

Figure 2-38 A MEMS ocular drug delivery device, which is sutured to the eye, contains a refillable drug reservoir, contoured morphology, cannula, and modular valve. The valve comprises four stacked disks (valve seat, valve plate, spacer plate, and pressure limiter. The cannula is inserted into the anterior or posterior segments of the eye for targeted delivery of drugs.

Figure 2-39 Heat-shrink packaged valve integrated into a silicone surgical sham device. Drug reservoir with metal ring indication refill port location, heat-shrink tubing, and valve are indicated. Ruler divisions are 1 mm.

When a pressure greater than the cracking pressure is applied, the valve plate deflects and lifts off of the seat, allowing forward fluid flow. Increased pressure on the valve plate causes it to deflect further. Eventually, at a pressure exceeding the closing pressure, the valve plate seals against pressure limiter to stop flow altogether. Thus, the â&#x20AC;&#x153;bandpassâ&#x20AC;? like behavior cuts off flow to prevent accidental dosing when excessive forward pressures are experienced (Figure 2-40).

Figure 2-40 Valve operation (from left to right): initially normally-closed, valve opens under forward pressure that exceeds cracking pressure, excessive pressures close the valve, and valve remains closed under reverse pressure.

To simplify the packaging processes and to increase the yield, no adhesives were used. Instead, biocompatible heat-shrink tubing was investigated as a packaging method for the valve. Here, the heat-shrink tube also serves as the drug delivery cannula. Heat-shrink tubing has been widely used in the world of electronics for applications such as electrical isolation, environmental protection, repair, and strengthening of joints.

Heat-shrink tubes are available in many thermoplastic

materials, such as polyolefin, fluoropolymer (fluorinated ethylene propylene (FEP), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF)), polyvinyl chloride (PVC), neoprene, and silicone elastomer. The heat-shrink mechanism is achieved by first forming the material into its final shape. Then, ionizing radiation is used to cross-link the material. Once cross-linked, the part is heated to a temperature greater than the melting temperature of the material. The part is then stretched or blown into an expanded configuration and cooled to maintain the expanded state. The part will then shrink when heat, near the melting point, is again applied to the part due to the elastic nature of the cross-linked material (Bradley 1984). Biocompatible heat-shrink tubing (polyolefin) was investigated as a packaging scheme for flexible sensors (Naito, et al. 2008) and glaucoma drainage implants (Pan, et al. 2006).

Due to their conformal nature, circular shape, and

biocompatibility, heat-shrink tubing was selected for packaging the valve for the ocular drug delivery application. 71

The four modular valve components are shown in Figure 2-41 along with the heatshrink tubing. The SU-8 valve seat and silicone valve plate form the normallyclosed portion of the valve. The SU-8 spacer plate defines the distance the valve plate must deflect in order to seal against the SU-8 pressure limiter plate. Therefore, the thickness of the spacer plate, in part, controls the pressure at which the valve closes. The valve seat and pressure limiter provide the structural support for the valve plate.

Figure 2-41 Photo of the valve components (valve seat, valve plate, spacer plate, and pressure limiter), pre-shrink heatâ&#x20AC;&#x201C;shrink tube, and fully assembled valve.

The assembled valve is packaged into a 22G FEP heat-shrink tube (Zeus Industrial Products Inc., Orangeburg, SC) (Figure 2-42). FEP is a well known medical material and is designated a USP class VI biocompatible polymer. FEP is also transparent, with a refractive index of 1.338 (Zeus Industrial Products), thereby allowing visual inspection of the valve after packaging. FEP is resistant to most chemicals and solvents and can withstand temperatures in excess of 260 ÂşC, making it suitable for a wide range of applications. 72

Figure 2-42 a) Side view and b) top view of the packaged valve in a FEP heat-shrink tube. The valve was placed inside the tube with a custom jig. The entire fixture was heated to 215 ºC at 1.5 ºC/min and cooled at the same rate to room temperature.

Upon heating, the heat-shrink tube contracts around the valve forming a robust package that securely holds the valve assembly in place without any adhesives. The previous Parylene C cannula was prone to clogging or damage during surgical implantation (Figure 2-43), therefore a more robust cannula design was necessary. The heat-shrink tube wall thickness (approximately 200 μm) is greater than that of the Parylene C cannula (thickness 7.5 μm), resulting in a more mechanically robust structure. As mentioned previously, the circular cannula facilitates sealing of the incision, thereby minimizing leakage at the cannula and tissue interface.

Figure 2-43 a) Parylene C cannula integrated with a drug delivery pump, b) clogging of Parylene C cannula after ex vivo testing.

2.3.1.1.1.2 Theory The valve diameter was selected to meet the surgical requirements; a maximum incision length of 1 mm was permitted. Therefore, valve components were limited to 900 μm in diameter, leaving 100 μm for packaging. The dimensions and geometry of the individual valve components were determined using theoretical equations and finite element modeling.

The analytical solution for large-deflection of a flexible plate of uniform thickness guided selection of the thicknesses of the spacer and valve plates (Equation 2-1, Equation 2-2). The maximum deflection (wmax) of a uniform and homogenous place was calculated from the plate thickness (t), applied pressure (p), plate radius (a), and flexural rigidity (D). Flexural rigidity is a function of Young’s modulus (E), plate thickness (t), and Poisson’s ratio (ν) (Ugural 1999). 74

Equation 2-1 Large deflection in a homogenous, thin film plate

pa 4 w 2 max wmax (1 + 0.486 2 ) = 64D t

Equation 2-2 Flexural rigidity equation to determine deflection in thin film plate

Et 3 D= 12(1 −ν 2 )

The outer edge (150 μm wide band) of the valve plate was reserved for clamping by the valve seat and pressure limiter, leaving a 600 μm diameter area for the active deflecting area of the plate. In the analysis, applied pressure was varied between 01000 mmHg (0-133.3 kPa) for valve thicknesses between 0-150 μm. The resulting calculated wmax was assigned as the maximum thickness of the spacer plate. It should be noted that wmax is the deflection at the center of the plate; sealing against the pressure limiter requires greater deflection. The final values were chosen based on estimated pressure operating ranges and ease of handling. The values used in the large-deflection equations are shown in Table 2-3.

Table 2-3 Summary of values used in theoretical calculations of large deformations in uniform thin plates.

Variable Thickness (t) Applied Pressure (p) Plate Radius (a) Young’s Modulus (E) Poisson’s Ratio (ν)

Value 0-150 μm 0-1000 mmHg, 0-133.3 kPa 300 μm 2 MPa 0.48 75

2.3.1.1.1.3 Finite-Element Modeling SolidWorks models of the valve components were created for FEM analyses. Stress and deformation FEM analyses determined the stress distribution and valve behavior for forward pressure values ranging from 0-1000 mmHg (0-133.3 kPa) and the reverse pressure value of -500 mmHg (0-66.7 kPa).

FEM results provided

convenient visualization of valve plate movements and its interaction with the pressure limiter.

Three different valve plate designs (hole, straight arm, and s-shape arm) were investigated (Figure 2-44).

Each design possessed a different effective fluidic

resistance and thus differing bandpass flow regulating characteristics (e.g. opening and closing pressure).

FEM estimations and theoretical analyses guided the

assignment of valve geometries such that the operational pressure range would be limited at the lower bound by normal intraocular pressure (IOP), <35 mmHg (4.7 kPa), and an upper bound that was arbitrarily chosen to be at least 2 orders of magnitude greater than normal IOP values (e.g. 2000 mmHg, 266.6 kPa). However, the operating pressure ranges of the valve are easily customized by altering the dimensions of the valve plate and spacer plate.

The dimensions of the valve

components are presented in Table 2-4.

Figure 2-44 Three different valve plate designs a) hole, b) straight arm, and c) s-shape arm; and the corresponding fabricated valve plates d) hole (through holes are indicated by the arrows), e) straight arm, and f) s-shaped arm.

Table 2-4 Dimensions of valve components, including the three valve designs (hole, straight arm, sshape arm). All components are 900 Îźm in diameter.

2.3.1.1.1.4 Valve Fabrication 2.3.1.1.1.4.1 SU-8 Valve Seat and Pressure Limiter

The SU-8 valve seat and pressure limiter shared identical designs. This choice simplified fabrication and ensured interchangeability of the two parts. A two-layer SU-8 process was used (Figure 2-45). First, a soda-lime wafer (Mark Optics, Santa Ana, CA) was dehydrated for 20 minutes at 120 ºC. Then the wafer was treated with Omnicoat (MicroChem, Newton, MA) to facilitate release of the SU-8 components. Three layers of Omnicoat were spun onto the wafer (3000 rpm, 30 sec) with a bake step (1 min at 200 ºC) performed after each coat (Figure 2-45a). Multiple Omnicoat layers reduced the time and temperature required for the release step. SU-8 2100 (MicroChem, Newton, MA) was prespun onto the wafer (30 sec, 500 rpm) to provide an even coating. Then, 160 μm SU-8 was applied (30 sec, 1750 rpm) to form the first layer of the component (Figure 2-45b). This layer was softbaked on a hotplate at 95 ºC for 2 hours (3 ºC/min) and slowly cooled to room temperature. The layer was then patterned (390 mJ/cm2); the energy dosage was determined by using the suggested energy level for 160 μm (260 mJ/cm2) and adjusting with a 1.5 multiplier for using a glass substrate instead of silicon (Figure 2-45c). The mask used to pattern the first layer can be found in Appendix M. Dicing saw tape was placed behind the wafer prior to exposure to prevent unwanted exposure from the reflected UV from the aligner chuck. A post-exposure bake (12 min, 95 ºC) was completed, again ramping from room temperature to 95 ºC at 3 ºC/min and slowly cooled back to room temperature. 40 μm of SU-8 2050 (MicroChem, Newton, MA) was spin coated (30 sec, 4000 rpm) to form the features in the valve seat and pressure limiter (Figure 2-45d). The wafer was then baked for 3 hours at 95 ºC (with ramp up and 78

cool down).

The 40 ฮผm was patterned (192 mJ/cm2; 160 mJ/cm2 times a 1.2

multiplier for a SU-8 substrate), and post exposure baked for 14 minutes at 95 ยบC Figure 2-45e). The mask used to pattern the second layer of SU-8 can be found in Appendix N. The components were developed using SU-8 developer (MicroChem, Newton, MA) (Figure 2-45f).

To remove the valve seats and pressure limiters from the wafer, the wafer was immersed in Remover PG (MicroChem, Newton, MA) (Figure 2-45g).

The

components were rinsed in isopropyl alcohol (IPA) and DI H2O and then hardbaked at 215 ยบC for 1 hour. This final step annealed the SU-8 components to improve thermal resistance for the subsequent heat-shrink packaging process. This step was performed under vacuum to prevent oxidation of the SU-8 and reduce the residual stress in the thick film structure (Daniel, et al. 2001). The hardbake step was later removed to simplify the fabrication process; the entire assembled valve was hardbaked during the heat-shrink tubing process (heat-shrink packaging occurred under vacuum at 215 ยบC).

The complete fabrication process can be found in

Appendix O.

Figure 2-45 Fabrication process for the valve seat and pressure limiter plates. Fabrication steps are cross-section views at the A-A’ line.

2.3.1.1.1.4.2 SU-8 Spacer Plate The spacer plate was fabricated on a dehydrated wafer (20 min, 120 ºC) coated with 3 layers of Omnicoat (as described in the fabrication of the valve seat and pressure limiter) (Figure 2-46a). The 40 μm thick spacer plate was spin coated (SU-8 2050, 30 sec, 4000 rpm) (Figure 2-46b). The layer was softbaked at 95 ºC for 1 hour, ramping at 3 ºC/min from room temperature to 95 ºC. Dicing saw tape was applied to the backside of the wafer prior to exposure (240 mJ/cm2; 160 mJ/cm2 times a 1.5 multiplier for a glass substrate) (Figure 2-46c). The mask used to pattern the spacer plate can be found in Appendix P. The wafer is post-exposure baked for 6 minutes at 95 ºC (ramping from 3 ºC/min from room temperature to 95 ºC, and slowly cooled back to room temperature). The wafer was immersed in SU-8 developer (Figure 2-46d). The spacer plates were then released from the substrate using Remover PG and rinsed using IPA and DI H2O Figure 2-46e). A complete fabrication recipe for the spacer plate can be found in Appendix Q.

Figure 2-46 Fabrication process for the SU-8 spacer plate. Fabrication steps are cross-section views at the A-A’ line.

2.3.1.1.1.4.3 Silicone Valve Plate The valve plate was fabricated by casting medical grade silicone pre-polymer (MDX4-4210, Dow Corning, Midland, MI) on a SU-8 master mold. The simplest design for the valve plate mold is a single layer of SU-8 which defines the valve plate thickness, valve plate diameter, and the through holes of the valve plate.

2.3.1.1.1.4.3.1 Simple Valve Plate: No Bossed or Overhang Features The SU-8 master was created on a soda lime wafer using SU-8 2050. First the wafer was treated with A-174 (a silane adhesion promoter) to enhance Parylene C adhesion to the soda lime wafer. A 4 μm layer of Parylene C (Specialty Coating Systems, Inc., Indianapolis, IN) was vapor deposited onto the wafer to prevent the SU-8 from delaminating from the wafer due to mismatch of the thermal coefficients of expansion between soda lime and SU-8 (Li, et al. 2008). A 75 μm layer of SU-8 2050 was spin coated (30 sec, 2000 rpm) and softbaked for 90 minutes at 95 ºC (Figure 2-47a). This layer of SU-8 defined the valve plate thickness. The SU-8 layer was patterned (308 mJ/cm2; 208 mJ/cm2 dose times a 1.5 multiplier for the glass substrate), post-exposure baked at 95 ºC for 7 minutes, and developed using 81

SU-8 developer (Figure 2-47b,c). The mask used to pattern the valve plate can be found in Appendix R. MDX4-4210 (10:1 base to curing agent ratio), was poured onto the mold and degassed under vacuum.

Excess silicone was removed by

scraping the mold with a metal squeegee (Figure 2-47d) (Kee Suk, et al. 2004). The silicone is cured at room temperature for over 24 hours or, for accelerated curing, at 90 ÂşC for 1 hour. Silicone is less prone to shrinkage if cured slowly at room temperature. Valve plates where released from the mold; any excess silicone was manually removed using a fine-tipped blade (Figure 2-47e). The fabrication process for creating the SU-8 mold and casting the silicone is found in Appendix S.

Figure 2-47 Fabrication process for the valve plate using an SU-8 master mold. Fabrication steps are cross-section views at the A-Aâ&#x20AC;&#x2122; line. Straight arm valve is shown; hole and s-shaped arm valves are fabricated in an identical manner.

2.3.1.1.1.4.3.2 Valve Plate with Bossed Feature and Valve Plate with Bossed and Overhang Features The valve plate can designed to include additional features, which affect valve function and performance. Two optional features include a bossed structure or an 82

overhang (Figure 2-48). The bossed structure causes the valve plate to press more tightly against the valve seat, therefore increasing the cracking pressure of the valve. The overhang structure is a proposed mechanism for locking the valve plate in place if, during experimental testing, it was determined that the valve plate shifts during pressure application. Complete process to fabricate the SU-8 mold for a valve plate with just the bossed feature or both the bossed and overhand features can be found in Appendix U and Appendix W, respectively.

Figure 2-48 Illustration of the additional features (bossed and/or overhang) which can be added to the simple valve plate designs.

2.3.1.1.1.5 Valve Heat Shrink Packaging Valves were assembled by stacking individual components. First, the components were gathered onto a silicone sheet under a stereo microscope. Silicone provided a tacky surface to hold the stack steady while making alignment adjustments.

First, the valve seat was placed face up (sealing rings up) on the silicone working space (Figure 2-49a). Next, the valve plate was stacked on top (Figure 2-49b). The valve plate must be aligned such that none of the through holes are placed over the valve seat opening. Misalignment may compromise the normally-closed function of 83

the valve, or prevent the valve from closing at elevated pressures. The spacer plate was added on top of the valve plate, again, ensuring that the spacer plate was aligned and not covering the valve plate through holes (Figure 2-49c). Finally, the bottom side of the pressure limiter, the side with the sealing rings, was identified and placed face down on top of the spacer plate (Figure 2-49d).

Figure 2-49 Top and side views of valve assembly. a) valve seat, b) valve plate added to valve seat, c) spacer plate placed on valve plate, d) pressure limiter added to assembled valve.

The assembled valve was then packaged with 1.3:1 shrink ratio FEP heat-shrink tubing with the aid of a custom Teflon jig containing stainless steel centering pins (813 Îźm diameter) (Figure 2-50a,b). A 22G (inner diameter prior to shrinkage: 914 Îźm, maximum wall thickness: 254 Îźm) heat-shrink tube was placed around the centering pin on the jig base. The heat-shrink tube must be shorter than the centering pin.

Next, the assembled valve (valve seat, valve plate, spacer plate, pressure

limiter) was carefully placed on the centering pin (Figure 2-51a). The jig top, which has a matching and adjustable stainless steel centering pin, was aligned and secured to the jig base using four 10-32 machine screws. The distance between the jig base 84

and top was set using hex nuts positioned along the screws. The two centering pins were aligned and the top pin was slowly lowered until the valve stack was securely clamped. The FEP tubing was carefully slipped around the valve (Figure 2-50b, Figure 2-51b). The entire jig was then placed in an vacuum oven and heated to 215 ยบC at a rate of 1.5 ยบC/min; held at 215 ยบC for at least 30 minutes, and then cooled to room temperature at the same rate (Figure 2-51c). The baking and cooling steps were ramped to limit the thermally induced stress on SU-8 which may lead to cracking. The jig was removed from the oven and disassembled. Then the packaged valve was slipped off the centering pins (Figure 2-51d).

A complete SOP for

assembling and packaging the valve can be found in Appendix X.

Figure 2-50 a) Heat-shrink jig setup. Teflon base and top each contains a centering pin. The top and base are aligned with machine screws. Nuts set the top and base distance. b) Close up view of an assembled valve with pre-shrink heat-shrink tube surrounding the valve.

Figure 2-51 Process steps to package assembled valve. a) FEP heat-shrink tube is placed around bottom centering pin, assembled valve is placed on centering pin, b) jig top is added, valve is clamped between top and bottom centering pins, FEP tube is lifted around valve, c) jig and valve assembly is placed in vacuum oven, and d) packaged valve is removed from jig.

2.3.1.1.1.6 Benchtop Experiments- Methods and Results 2.3.1.1.1.6.1 Valve Plate Deflection 2.3.1.1.1.6.1.1 Methods The deflection for each valve plate design (hole, straight arm, s-shaped arm) under forward pressure was measured and compared to theoretical values for large deflection of a uniform plate (Equation 2-1, Equation 2-2). Each plate was clamped at the periphery in a custom-made jig which allowed pressurized air to be applied to the backside (Figure 2-52).

Plate deflection was measured using a compound

microscope with 1 Îźm resolution. The microscope was focused on the center of the valve plate under zero applied pressure. Pressurized nitrogen gas (0-500 mmHg, 066.7 kPa) was applied to deflect valve plate. The microscope was refocused on the center of the deflected plate and deflection was calculated from the change in the microscope fine focus knob position.

Figure 2-52 Valve plate deflection setup.

2.3.1.1.1.6.1.2 Results The experimentally obtained valve plate deflection for each valve plate design was compared to theoretical values (Figure 2-53) and found to be in agreement. While the theoretical model did not completely predict the behavior, it was still a useful design tool.

Deviations from the measured data could be attributed to the

geometrical differences from the theoretical thin plate geometry. The plate thickness used in the equation was 75 μm, whereas the fabricated valve plates were slightly thicker at 84 ± 3.7 μm, 87.8 ± 5.3 μm, and 82.2 ± 5.4 μm (mean ± SE, n = 4) for the hole, straight arm, and s-shaped arm valve plates, respectively. A thicker plate generally leads to less deflection. However, changing the geometry from a flat plate to a selectively perforated plate increased achievable vertical deflection due to increased flexibility. Thus, the straight-arm valve plate deflected more than the hole design even though the straight-arm plates were slightly thicker.

The clearest

demonstration of the impact of tether compliance on achievable deflection was the sshaped arm valves. The s-shaped tethers bend allowing the plate to twist upward and 87

away from the valve seat as pressure is applied, providing additional deflection (Wang, et al. 1999). Therefore, the s-shaped arm valve plate achieved the greatest deflection for a given applied pressure.

Figure 2-53 Comparison of measured valve plate deflection to the theoretical values for a flat plate.

2.3.1.1.1.6.2 Heat-Shrink Packaging Characterization 2.3.1.1.1.6.2.1 Methods The heat-shrink packaging method was evaluated to determine the dimensional changes during the thermal shrinking process, the robustness of the package, and the fluidic integrity (Figure 2-54). Two different gauges (22 AWG and 18 AWG, preshrunk O.D. 1.29 mm and 1.88 mm, respectively) of FEP heat-shrink were characterized (Zeus Inc., Orangeburg, SC). The outer diameters of pre-shrink and 88

post-shrunk tubing were compared and the percent change in outer diameter was calculated. The fluidic integrity of each tube was quantified by packaging a solid 200 μm thick SU-8 disk. A 900 μm diameter disk was used in the 22 AWG tube; the solid disk possesses the same diameter as the individual valve components. The 18 AWG tube was packaged with a 1.5 mm diameter disk for comparison. The solid disks were packaged under the same conditions as the valve (room temperature to 215 ºC at ≤ 1.5 ºC/ min and cooled from 215 ºC to room temperature at ≤ 1.5 ºC/min).

Figure 2-54 Pre and post heat-shrink tubing.

Solid disk packaged in heat-shrink tubing to test robustness of the adhesiveless packaging method.

Both pressurized water and nitrogen gas (0-2000 mmHg, 0-266.6 kPa) were applied through the heat-shrink tube against one side of the solid disk. A 100 μL calibrated pipette (Clay Adams, Parsippany, NJ, USA) was placed at the outlet to measure leakage of water between the disk and heat-shrink tubing. For pressurized N2, the tubing outlet was immersed in water to visualize any bubbles due to leakage.

2.3.1.1.1.6.2.2 Results The final post-shrink diameter for the 22 AWG cannula used to package the valve was approximately 1 mm. The outer diameter of the heat-shrink tube decreased 19.4-25% post-shrinkage. In the valve region, the diameter was slightly greater than 1 mm. This slight increase in diameter does not compromise the incision site which must be sealed around the cannula alone and not the valved portion.

A segment of heat-shrink tube was packaged with a solid SU-8 disk to determine the robustness of the packaging method and the quality of the seal around object. For both the 18 AWG and 22 AWG tubes, the solid disks remained in position under applied pressure and the entire system was leak-tight up to 2000 mmHg (266.6 kPa) of pressurized water. This value is the pressure limit of our testing apparatus and almost 2 orders of magnitude greater than normal IOP values. The packaged system was also able to withstand up to 2000 mmHg (266.6 kPa) of pressurized nitrogen gas as verified by the absence of bubbles while submerged under water. The maximum pressure for microfluidic interconnects using heat-shrink tubing also reported leakfree connections up to 200 kPa (Pan, et al. 2006). These results are comparable to devices which are secured using adhesives (Lee, et al. 2004, Puntambekar and Ahn 2002, Tsai and Lin 2001). A summary of the results is presented in Table 2-5. This characterization demonstrates that this packaging technique is extremely robust and thus suitable for a wide variety of applications. A diverse selection of materials and gauges of heat-shrink tube are commercially available and can be selected to match specific packaging needs. 90

Table 2-5 Summary of heat-shrink tube characterization results for two tube gauge sizes (22 AWG and 18 AWG)

FEP Heat-Shrink Characterization Valve O.D. [mm] Initial tube O.D. [mm] (n=5, mean ± SE) Post-shrink O.D. Tube + Valve [mm] (n=5, mean ± SE) Post-shrink O.D. Tube Only [mm] (n=21, mean ± SE) % change in O.D. Leakage Pressure [mmHg, kPa]

22 AWG

18 AWG

0.9

1.5

1.29 ± 0.014

1.88 ± 0.006

1.23 ± 0.002

1.84 ± 0.004

1.04 ± 0.006

1.41 ± 0.005

19.40%

25%

>2000, 266.6

2.3.1.1.1.6.3 Packaged Valve Characterization 2.3.1.1.1.6.3.1 Finite-Element Analyses Results Finite-element analyses of displacement and stress were conducted on an assembled hole valve (Table 2-6). A linear FEM model with small-displacement conditions was used to provide a qualitative understanding of valve behavior. As the applied pressure increased, displacement and stress values also increased. The valve plate deflected until it was constrained by the pressure limiter and eventually sealed. However, the center of the valve plate continued to deflect with increasing pressure, albeit in smaller increments. Under reverse pressure application, the valve plate deflected <7 μm and maintained an effective seal against the valve seat.

The stress analysis provided guidance on the selection of suitable materials on the basis of mechanical robustness. At the maximum forward applied pressure (1000 91

mmHg, 133.3 kPa), stress accumulated in the bottom of the valve seat and valve plate. The maximum stress was experienced by the valve plate (0.99 MPa) and was concentrated along the edge in contact with the valve seat. The observed stress was <20% of MDX4-4210 tensile strength (5 MPa) and significantly less than the tensile strength of SU-8 (60 MPa).

Reverse pressure (500 mmHg, 66.7 kPa) analysis

verified the induced stresses (0.46 MPa) were at least an order of magnitude less than the tensile stresses of MDX4-4210 or SU-8.

Table 2-6 Summary of the FEM results for displacement and stress on an assembled valve.

2.3.1.1.1.6.3.2 Benchtop Operation The valve operating range was determined by visually observing valve operation and measuring flow rate at specific pressure set points. Pressurized Rhodamine B was applied to the cannula inlet and enhanced visualization of fluid flow through the 92

valve. Rhodamine B was observed to exit only at the pressure limiter through hole. No leakage at the interface between the assembled valve and heat-shrink tube was observed (Figure 2-55). This demonstrates robustness of this packaging method for stacked components fabricated from different polymers.

Figure 2-55 Visualization of flow rate through a packaged valve using Rhodamine B.

2.3.1.1.1.6.3.3 Packaged Valve Opening and Closing Pressures 2.3.1.1.1.6.3.3.1

Methods

The bandpass flow regulation behavior of a packaged valve (hole valve plate) was determined.

Pressurized water (0-1000 mmHg, 0-133.3 kPa) was applied in

incremental steps to the valve inlet. The flow rate from the packaged valve was measured using a 100 ÎźL calibrated pipette connected to the outlet (Figure 2-56). The pipette was prefilled with double distilled water and a bubble was introduced between the valve outlet and pipette inlet. The system was held at each test pressure 93

set point for 3 minutes to allow the system to equilibrate. The cracking pressure and flow rates for different pressures were measured. Reverse pressure (0-500 mmHg, 066.7 kPa) was also investigated. Several flow profiles (flow rate versus pressure) for a hydrated valve (valve that was kept in contact with water at all times) were obtained to verify repeatability of valve operation. The hydrated valve data was also compared to a dry valve (valve where water was allowed to evaporate between experiments). The testing process procedure can be found in Appendix Y.

Figure 2-56 Test setup to determine valve operating characteristics.

2.3.1.1.1.6.3.3.2

Results

Consistent flow rate profiles (pressure versus flow rate) were repeatedly obtained in sequential experiments when the valve remained hydrated between runs.

All

experimental trials were performed within a 24 hour period. The valve cracking pressure was approximately 25-50 mmHg (3.3-6.7 kPa) and the maximum flow rate (3.18 ± 0.18 µL/sec, mean ± SE, n=4) occurred near 500 mmHg (66.7 kPa) (Figure 2-57). The valve closed between 1750 and 2000 mmHg (233.3 and 266.6 kPa) and remained leak-free under 500 mmHg (66.7 kPa) of reverse pressure, which is at least an order of magnitude greater than normal IOP values.

The averaged flow rate profile (mean Âą SE, n = 4) was compared to that of a dried valve. For dried valves, the cracking pressure was much higher (200-300 mmHg, 26.7-40 kPa). The increase might be attributed to stiction between the valve plate and seat. Additionally, the dried valve had a smaller closing pressure (1000-1250 mmHg, 133.3-166.7 kPa). Hydration causes the silicone to swell, increasing the valve plate thickness and altering the deflection behavior. An implanted valve will remain hydrated from contact with the aqueous or vitreous humors, therefore, the hydrated flow profile is more representative of long-term valve behavior. However, this also suggests that valves may need to be preconditioned prior to implantation.

Figure 2-57 Flow profiles from 4 runs on same valve, valve was kept hydrated in double distilled water between runs to prevent valve from drying out. The hole valve plate was used in this packaged valve.

2.3.1.1.1.6.3.4 Packaged Check Valve Closing Time Constant 2.3.1.1.1.6.3.4.1

Methods

The closing time constant for the valve was determined by applying pressurized water (250, 500, and 750 mmHg, 33.3, 66.6, and 100 kPa respectively) to the valve, shutting off the pressure with a pneumatic solenoid valve, and measuring the accumulated volume of water exiting the valve after pressure shut-off. A calibrated 100 ÎźL pipette (Clay Adams, Parsippany, NJ) was used to measure the accumulated volume. A circuit controlled the pneumatic solenoid valve and a light-emitting diode was used to indicate the valve state (open or closed). Closing time was defined as the duration between the elapsed time from pressure shut-off to when 63.2% of the total accumulated volume had exited the valve.

2.3.1.1.1.6.3.4.2

Results

The valve has a finite response time when the applied pressure is removed. The closing time constants were determined for three different applied pressures (250, 500 and 750 mmHg, 33.3, 66.7, and 100 kPa, respectively) (Figure 2-58). Recall that the flow rate is maximal near 500 mmHg (66.7 kPa).

An electronically

controlled pneumatic valve, with a response time of 3 ms, was used to provide a near instantaneous application and shut-off of pressure. Dispensed volume data was extracted from video footage of the flow tracked by a bubble moving in a 100 ÎźL pipette after pressure removal. The bubble was observed for 5 minutes after the pressure was removed from the valve to ensure the valve was completely closed. Accumulated volume experiments for each pressure were repeated four times. The data are summarized in Table 2-7. 96

Figure 2-58 Accumulated volume measurements to determine closing time constant. Closing time constants were calculated by determining the amount of time for 63.2% of the total accumulated volume to exit the valve. Table 2-7 Summary of closing time constants for the packaged valve.

Pressure [mmHg] ([kPa])

Accumulated Volume [μL] (mean ± SE, n = 4)

63.2% Volume [μL]

Closing Time Constant [sec]

250 (33.3)

9.60 ± 0.079

5.98

7.6

500 (66.7)

19.43 ± 0.378

12.11

7.85

750 (100)

30.13 ± 0.401

18.77

8.05

Closing time constants were very consistent with only a slight increase in response time at higher pressures. As pressure increases, the valve plate deflects further from the valve seat and has a greater distance to travel when returning to the initial position.

One would expect the highest accumulated volume to correspond to the highest flow rate (500 mmHg, 66.7 kPa). However, 750 mmHg (100 kPa) resulted in the largest accumulated volume (Figure 2-58) and is attributed to the difference between transient and steady state flow rates in the closing time and flow rate profile experiments, respectively.

The total accumulated dosage after the pressure is removed from the valve depends on the applied pressure and the amount of time the valve was pressurized (i.e. if the flow rate has reached steady state). However, the accumulated volume can affect the final dosage, especially for small targeted values. Therefore, shorter closing times are desirable; designs to shorten the closing time can be investigated for high precision applications.

The addition of an electrolysis pump to serve as the driving force should further decrease the error. The electrolysis structure is made of platinum, which catalyzes the recombination of oxygen and hydrogen gases back into water. Once the current to drive the electrolysis pump has been terminated, the internal volume of the pump chamber will decrease. The decreased volume will pull a vacuum in the drug chamber, thus forcing the packaged valve to close faster.

2.3.1.1.2 Electrolysis Pump and Pump Chamber 2.3.1.1.2.1 Theory Electrolysis pumping was selected as the driving force for expelling drugs from the device into the body. Electrolysis has many advantages over other pumping schemes 98

because of its low heat generation, low power consumption, simple construction, and ability to generate large displacements. Electrolysis is an electrochemical reaction which breaks water into hydrogen and oxygen gas when a current is passed through a metal conductor such as gold or platinum. The electrolysis reaction can be described in the following manner:

Equation 2-3 Electrochemical reaction during electrolysis of water

cathode : 2H2O(l) ↔ O2(g) + 4H+(aq) + 4e− anode : 4H+(aq) + 4e− ↔ 2H2(g) net : 2H2O(l) ↔ O2(g) + 2H2(g)

The efficiency of the electrolysis structure is dependent on many factors including, electrode design (e.g. spacing, width, thickness, material, and surface area), electrolysis solution, external conditions (e.g. temperature and pressure), and the electrical parameters (e.g. current amperage). 2.3.1.1.2.2 Design The electrolysis structure is two interdigitated platinum electrodes fabricated on a flexible Parylene C substrate. The overall footprint of the interdigitated section is circular in order to fit within a rounded reservoir. The electrolysis structure is patterned onto a Parylene C substrate. This allows the electrolysis structure to be placed onto a non-planer surface.

The pump chamber is fabricated using Parylene C in a bellows structure. This structure can expand and contract to accommodate gas generation and recombination.

The Parylene C bellows is flexible, and therefore, does not

significantly impeded pumping efficiency. The bellows structure is attached to the Parylene C electrolysis structure to create an enclosed pump system.

2.3.1.1.3 Refillable Reservoir 2.3.1.1.3.1 Design In the manually-actuate drug delivery device, the refillable reservoir was fabricated by molding PDMS around a Plexiglas rectangular cuboid. The reservoir shape was unsuitable for long term implantation due to several reasons, 1) the external shape had sharp corners and edges, which can aggravate biological tissue and could lead to conjunctival thinning, and 2) the walls of the reservoir prevented the reservoir from being fully depressed, thus the corners of the interior space had the potential of accumulating dead volume; preventing all of the drug from being dispensed and can lead to contamination of newly refilled drug, and 3) the corners and edges of the reservoir were areas of stress concentration during reservoir depressing; these areas have a greater potential of failure.

A new design which provided a more suitable biologically compatible morphology, while removing areas of stress concentration and dead volume investigated. A domed shape reservoir was chosen as it satisfied the above criteria. 2.3.1.1.3.2 Fabrication 2.3.1.1.3.2.1 Silicone Reservoir The silicone reservoir was fabrication technique was designed and optimized during the construction of the hollow surgical sham (Section 2.4.2.1.3.1.1- Reservoir). The same technique was utilized for fabricating the reservoir for the electrically-actuated 100

device with dual check valve using reservoir molds designed for this device (Figure 2-59).

In summary, a silicone reservoir can be fabricated using a clam-shell custom-made Plexiglas mold. The bottom mold, a convex double-dome shape which defines the reservoir interior, was fabricated using laser ablation of a gradated double-oval pattern. The internal volume of the reservoir can be calculated by determining the volume of the convex portion of the mold. The top mold, which is a concave double-dome, creates the exterior surface of the reservoir.

The reservoir was fabricated by filling the bottom mold with MDX4-4210, a medical grade silicone. The mold was placed under vacuum to remove any residual air in the silicone prepolymer. Two metal shafts (1.27 mm O.D.) were placed on the edge of the mold to create a separation between the top and bottom molds. This separation dictated reservoir wall thickness. Finally, the top mold was carefully placed and aligned to the bottom mold. The silicone was cured and the reservoir was released from the mold. The excess silicone was then removed from the reservoir.

The base of the reservoir is also fabricated using a Plexiglas mold. The base mold was filled with MDX4-4210 and placed under vacuum. A silicone tube and PEEK baseplate was carefully placed in the mold and cured

101

Figure 2-59 Top and side views of the molds used for fabrication the second generation drug delivery device reservoir.

The silicone reservoir was proposed as a rapid method of fabricating and prototyping reservoirs. Molds for silicone reservoirs could be easily made and altered to fit any design change. However, due to the compliant nature of silicone, which can affect the dispensation characteristics, the reservoir must be eventually fabricated using a stiffer material (e.g. injection molded medical grade polypropylene).

2.3.1.1.4 Cannula The cannula for the electrically-actuated device with dual check valve is mainly the heat-shrink package around the dual function valve.

The heat-shrink package 102

(biocompatible FEP) and circular cross-section makes the package well-suited for implantation. To connect the packaged valve to the reservoir, a silicone tube is cured into the reservoir base. The silicone tube is positioned using an indentation in the reservoir base mold. The same silicone tubing (O.D. 0.085â&#x20AC;&#x2122;â&#x20AC;&#x2122;, 2.159 mm) (REF 60411-44, HelixMark, The Netherlands) was used in the testing of both the packaged solid disk and packaged valve. The interface between the silicone tubing and heatshrink tube was leak-tight up to 17 psi without the aid of any adhesives or mechanical cinching. This seal is adequate for normal valve operation, but can be further strengthened by applying silicone prepolymer at the heat-shrink tube and silicone tube junction prior to implantation.

The use of a silicone tube as a connection between the reservoir and packaged valve provides several valuable features. First, not applying silicone prepolymer to the heat-shrink tube/ silicone tube junction adds increased modularity of the electricallyactuated device with dual check valve as packaged valves can be easily exchanged with no damage to either the assembled reservoir or packaged valve. Additionally, during implantation, the cannula length can be adjusted to fit patient needs removing the packaged valve, cutting excess silicone tubing, and then replacing the valve. This would not be possible if the tube was a single piece.

The heat-shrink tube is very stiff. If a more flexible cannula is desired, the length of the heat-shrink can be shortened such that heat-shrink tubing is only slightly longer than the height of the stacked valve. In this mode, the cannula is made entirely of the 103

flexible silicone tubing and the packaged valve can be inserted into the end of the silicone tube, whereby the packaged valve is entirely contained within the silicone tube.

2.3.1.1.5 Baseplate A baseplate to prevent the refill needle from penetrating through the entire device is added to the reservoir base. The baseplate is made of PEEK (polyetheretherketone), which is a commercially available, bio-compatible material. A Plexiglas stencil is used to trace the desired baseplate shape onto a 0.01â&#x20AC;&#x2122;â&#x20AC;&#x2122; thick PEEK sheet; the shape is then cut from the sheet. The PEEK baseplate is added to the silicone prepolyer in the reservoir base mold; upon curing, the PEEK sheet is fully encased by the silicone.

2.3.1.1.6 Suture Tabs Two suture tabs are added to the reservoir to provide locations through which sutures can be threaded to secure the device to the eye. Suture tabs are torus-shaped; a predefined center hole allows sutures to be passed through the suture tab without the suture needle tearing the silicone material.

A tear may propagate through the

material causing the suture tab to fail, or even cause a leakage path to form through the reservoir.

2.3.1.1.7 Refill Port 2.3.1.1.7.1 Port Material The material used to fabricate the refillable portion of the reservoir is being investigated. The current material, MDX4-4210, is being used to model the device because it is easily obtained and can be used to rapidly create prototypes. 104

Additionally, MDX4-4210 is a USP Class IV biocompatible material; however, silicone has been reported to absorb liquids and solvents. The requirements of the material include: self-sealing behavior after needle puncture, be able to withstand the operating pressures of the device, no leakage through puncture site under normal operating pressures, USP Class IV biocompatibility, moldable, and compatible with the fabrication steps being used to create the other components of the device.

2.3.1.1.7.2 Refill Port Placement The refill port is placed in the smaller of the two circular domes, which make up the reservoir body. The electrolysis bellows occupies the larger of the two domes, therefore, this placement separates the refill area from the main reservoir body and prevents the refill needle from compromising the integrity of the pump chamber during refill.

A stainless steel ring is embedded into the reservoir body to help surgeons locate the refill portion of the device. The stainless steel ring is clearly visible as a dark shadow when the eye is transilluminated (Figure 2-77). The refill needle pierces the center of the ring in order to access the device interior.

2.3.1.2 Assembled Device The device is assembled on benchtop. All of the components are pre-fabricated to expedite device assembly.

The following components are necessary for device 105

assembly: silicone reservoir base layer (with embedded PEEK baseplate and silicone cannula), silicone spacer layer, silicone reservoir dome (with embedded stainless steel refill ring), and electrolysis pump with Parylene C bellows.

First, the suture tabs in the reservoir base are cored using a 19G needle (O.D. 1.067 mm). 20G (O.D. 0.902 mm) needle shafts are then threaded through the suture holes to prevent the sutures holes from clogging during assembly. The spacer layer is then affixed to the reservoir base using MDX4-4210 prepolymer; both pieces are placed in an oven for 5 minutes at 80 ยบC to cure.

Next, the electrolysis pump and bellows component is attached to the reservoir base using MDX4-4210 prepolyer. Special care is needed to ensure the MDX4-4210 does not reflow over the electrodes prior to curing. Again, the assembly is cured at 80 ยบC for 5 minutes. DI H2O soaked Techwipes are placed around the device during curing to increase the local humidity. This mitigates the evaporation of electrolyte from the pump chamber.

Two different types of spacer layers can be added to the device. The spacer layers increase the reservoir height by raising the reservoir dome. The increased height may be necessary to accommodate the bellows expansion during pumping. The spacer layers are 1 mm thick by 1 mm tall silicone pieces that are shaped like the device footprint. The first spacer layer has a section missing to facilitate fabrication by allowing the wires from the electrolysis pump to be fed through the spacer layer. 106

Prior to the addition of this layer, the device assembly was challenging because the wires tended to prop up the reservoir dome on one side; sealing the gap between the reservoir base and dome was very difficult.

This layer, in addition to adding

reservoir height, makes it easier to secure the reservoir dome to the rest of the device, because the wires are now recessed. The second spacer layerâ&#x20AC;&#x2122;s sole purpose is to add reservoir height and is optional.

Next, the reservoir dome is secured using MDX4-4210 and cured in place. The fully assembled device is filled with water to identify any leaks in the reservoir body. The dual check valve is then plugged into the end of the silicone cannula and the 20G needle shafts are removed from the suture tabs (Figure 2-60).

107

Figure 2-60 Fully integrated electronically-actuated drug delivery device. Device includes a refillable reservoir, electrolysis pump, separate refill area, refill ring, PEEK baseplate, silicone cannula, heat-shrink packaged dual check valve, and suture tabs.

2.3.2 Summary An electrically-actuated drug delivery device which uses electrolysis actuation and has a dual-regulation check valve has been fabricated and demonstrated. A modular dual-regulation check valve, which provides bandpass regulation of flow between two pressure ranges, was verified on benchtop and within an integrated system. Three variations of the valve plate were investigated to determine the best design for the ocular drug delivery device application. Theoretical equations and FEM analysis guided valve design. Check valve cracking pressure, closing pressure and closing time constants were empirically determined.

108

This device contains multiple modular components, which can be used to customize this device to each patient, or used to create a drug delivery mechanism for applications other than ocular drug delivery.

The dual regulation valve consists of 4 plates, all of which can be fabricated in parallel with multiple identical copies made during each process run. Addtionally, the valve seat and pressure limiter are the same part, thereby simplifying the process fabrication process as a process for the pressure limiter is not necessary. Interchangeable parts, like the manually-actuated device, allows multiple valves to be assembled in parallel.

Furthermore, adjustments to the valve plate (using the hole, straight-arm, or s-shaped arm design) and the spacer plate can affect the valve performance. The each valve plate has varying flow resistance and deflection characteristics, thereby changing the band width of the bandpass flow regulations, cracking pressure, and closing pressure. Scaling the spacer plate thickness, making it thinner or thicker, will also affect the bandwidth. A thinner spacer plate will decrease the bandwidth, while a thicker spacer plate will increase the bandwidth.

Finally, the entire packaged valve is a modular component which and be easily removed or replaced in the assembled device. Valve replacement may be necessary to change a faulty valve, or to replace with a valve which is better tuned to a specific application. Additionally, hanging the cannula length may be necessary depending 109

on the reservoir placement and delivery location. However, the preferred valve placement is at the cannula tip. Valve placement at the cannula tip ensures the dosed volume exits the cannula. If the valve were placed at the cannula/ reservoir junction, the delivery mechanism of the dosed liquid would be significantly different than the current mechanism as the volume would need to diffuse out of the cannula interior. The silicone cannula can be shortened by removing the valve, cutting the cannula, and then re-inserting the valve.

2.4 Surgical Shams 2.4.1 Solid Surgical Shams A solid surgical sham was designed to provide surgeons a model in which to optimize the surgical procedure.

The solid shams can also be used in chronic

implantation studies to determine the biological response to a shape which is similar to the final design morphology.

2.4.1.1 Design Surgical models, or surgical shams, were designed to model the final device shape and size.

Design parameters dictated several design requirements: 1) an oval

reservoir shape, 2) a maximum thickness of 2mm and, 3) an interior volume of at least 200 ÎźL. The cannula could be placed along the major or minor axis centerline of the oval shape (Figure 2-63). The targeted sham internal volume dictated the overall sham dimensions. To calculate the dimensions for the sham, the equation to calculate the volume of an ellipsoid (Equation 2-4) was modified to calculate all 110

possible values for the major and minor axes, as well as device thickness (Equation 2-5).

Equation 2-4- Volume of an Ellipsoid

4 abc VolumeEllipsoid = π 3 222 a = height of ellipsoid b = legnth of ellipsoid c = width of ellipsoid Equation 2-5- Volume of a Dome

1 Volumedome = παβχ 6 α = height of dome

β = major axis of dome χ = minor axis of dome Here, the minor axis is defined as the axis through which the silicone tube intersects where the major axis the perpendicular to the silicone tube (Figure 2-61).

Figure 2-61 Definition of major and minor axes on surgical sham devices.

Table 2-8 lists the shams which were fabricated using custom-made laser-ablated acrylic molds. Laser files for the molds can be found Appendix BB. 111

Table 2-8 Dimensions of Fabricated Version 1 Surgical Shams.

Depth [mm] 0.75 0.75 0.875 0.875 0.875 0.875 0.875 0.875 0.875 0.875 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2

Width [mm] 16 31.9 16 15 14 13.6 27.3 29.1 31.2 32.1 16 15 14 13 12 23.9 25.5 27.3 29.4 31.9 14 12 10 8 13.7 15.9 19.1 23.9

Length [mm] 31.9 16 27.3 29.1 31.2 32.1 16 15 14 13.6 23.9 25.5 27.3 29.4 31.9 16 15 14 13 12 13.7 15.9 19.1 23.9 14 12 10 8

Volume [ÎźL] 200.43 200.43 200.12 199.98 200.12 200.01 200.12 199.98 200.12 200.01 200.22 200.28 200.12 200.12 200.43 200.22 200.28 200.12 200.12 200.43 200.85 199.81 200.01 200.22 200.85 199.81 200.01 200.22

The molds created solid surgical shams with suture tabs, a stainless steel ring, and a silicone cannula. The embedded stainless steel ring is used to model the designated refill location. The dimensions of the silicone body, cannula, and suture tabs (one set located on the reservoir of the sham, and two sets along the silicone tube) are given (Figure 2-62). Two size options for the stainless steel rings, 1) 2.51 mm outer diameter (O.D.), 1.6 mm inner diameter (I.D.), 0.46 mm thick and 2) 5.31 mm O.D., 112

2.92 mm ID, 0.46mm thick were presented to the surgical staff. The 5.31 mm O.D. ring was preferable to provide the maximum target area. Surgeons chose two final sizes to implant into Dutch Belted male pigmented rabbits for chronic tests. After initial testing, the sutures surrounding the cannula were removed because they impeded the insertion of the cannula into the anterior chamber of the eye. The shams were continually modified to accommodate surgical considerations. The full solid sham design progression can be found in Section 2.4.1.1.1-Solid Sham Timeline.

Figure 2-62 First version of the implanted solid surgical shams and the dimensions.

2.4.1.1.1 Solid Sham Timeline A list of the progression of the solid shams, as well as a summary of the design, can be found in Table 2-9.

Table 2-9 Solid sham timeline and description of solid sham characteristics.

Sham Mold File Location Solid/ Hollow

v1_large Figure 2-62A Solid

Material

PDMS

Solid Sham Timeline v1_small v2_large v2_small v3_1 Figure Appendix Appendix Appendix 2-62B CC CC DD Solid Solid Solid Solid PDMS or PDMS or PDMS or PDMS MDX4MDX4MDX44210 4210 4210 113

Footprint Shape Major Axis Length [mm] Minor Axis Length [mm] Thickness [mm] Volume [ÂľL] Internal Volume [ÂľL] Suture Tab location Refill Ring ID [mm] Refill Ring OD [mm] Baseplate Size

Oval

29.4

15.9

29.4

15.9

16.9

1.00

2.00

1.00

2.00

200.12

199.81

200.12

199.81

230.07

N/A

Cannula Cannula and and Reservoir Reservoir Reservoir Reservoir

Reservoir

2.92

5.31

N/A

2.4.1.2 In Vivo Experiments 2.4.1.2.1 Implantation 2.4.1.2.1.1 Methods Two surgical shams, v1_large (1 mm x 13mm x 29.4mm) and v1_small (2mm x 12mm x 15.9mm) (Figure 2-63), were tested in vivo. The larger stainless steel ring (5.31 mm OD, 2.92 mm ID, 0.46mm thick) was used in these shams. The solid reservoir was sutured under the conjunctiva and the silicone cannula was introduced into the anterior chamber of the eye via a scleral tunnel.

114

Figure 2-63 Implanted surgical shams, A) 2 mm x 12 mm x 15.9 mm and B) 1 mm x 13 mm x 29.4 mm

It was determined that the suture tabs surrounding the silicone tube were unnecessary however, the larger sham required more suture tabs along the reservoir to anchor the reservoir in place. A second set of surgical shams (v2_large and v2_small) were fabricated to facilitate surgical implantation (Figure 2-64). The file used to fabricate the molds using a laser-cutter can be found in Appendix CC.

Figure 2-64 Mold used to fabricate version 2 of the surgical shams. Dimensions are the same as version 1 with additional sutures on the 1mm thick sham (v2_large) and the sutures removed from the silicone cannula from both shams.

2.4.1.2.1.2 Results

115

Chronic in vivo data of v2_large demonstrated that the footprint size was not well tolerated in the limited space available within the eye wall. The device was difficult to insert, and was found to cause conjuctival thinning over the device. v2_small had better results and was tolerated by the ocular tissue in acute in vivo studies.

A slightly larger sham, v3_1 was created to test a device that would have the same overall shape as a sham with a 200 ÎźL interior. The major and minor axes were increased by 1 mm to mimic a hollow sham whose interior is a similar shape to v2_small with a 0.5 mm thick wall. This sham was also tested in acute in vivo studies and demonstrated minimal adverse affects.

2.4.1.2.2 Refill Ring 2.4.1.2.2.1 Results The stainless steel ring embedded within the solid surgical sham was visible through the conjunctiva (Figure 2-65). The surgeon was able to insert a commerciallyavailable 30 gauge non-coring needle (O.D. 305 Îźm) through the conjunctiva and through the center of the stainless steel ring (I.D. 2.92 mm) indicating that targeted refill is possible. However, a needle stop is still needed to indicate when the needle has reached the base of the device. Also, a means for visualizing the stainless steel ring may be necessary if fibrous tissue formation or complications from surgery prevent the ring from being visible.

116

Figure 2-65 Implanted solid surgical sham with stainless steel ring visible through the conjunctiva. The surgeon was able to simulate refill by targeting the center of the stainless steel ring using a commercially available 30 gauge needle. The stainless steel ring is outlined in this image to help indicate its location.

2.4.2 Hollow Surgical Shams The hollow surgical sham contained suture tabs, a stainless steel ring, a polyetheretherketone (PEEK) (0.254 mm thick) baseplate, and a silicone tube. The stainless steel ring, as with the solid shams, helps surgeons identify the refill location. The refill location is where the surgeon can puncture the device and replenish the device interior. This location will be designed using materials that can withstand multiple punctures without leakage. The PEEK baseplate, which serves as a needle stop, prevents the needle from puncturing through the device. The silicone tube is the cannula that allows the liquid held in the device interior to enter the anterior chamber. Hollow surgical shams were made so that surgeons could practice

117

refilling a device with a designated refill port and baseplate to prevent the needle from piercing through the entire device (Figure 2-66).

Figure 2-66 Illustration of the hollow surgical sham. A refill needle access the sham interior by piercing the refill port location (designated by a refill ring). A PEEK baseplate prevents the needle from piecing through the entire device.

2.4.2.1 Design 2.4.2.1.1 Needle Stop In vivo testing of the solid sham demonstrated a need for a mechanism to determine how far the needle has penetrated into the device. Two main failure modes, both which fail to refill the device, can occur if needle depth is not controlled. If the needle insertion is too shallow, part of the needle opening may not be fully inserted into the device. When the refill syringe is depressed, the refill drug will flow out of the needle tip and onto the eye surface instead of into the device. However, if the needle is inserted too far during refill, the needle may puncture through the entire device, where the needle tip will enter the eye interior. Upon refilling, the drug will be injected directly into the eye. Additionally, this failure mode will cause further

118

damage to eye tissues, similar to the side effects of direct ocular injection treatments. Therefore, a method to guide needle penetration depth is necessary.

2.4.2.1.1.1.1 Needle Ring Guide The needle ring guide idea was previous mentioned in Section 2.2.2.1-Refillable Reservoir and Refill Guides. A needle ring guide is an indication on the needle shaft which shows the surgeon how far to insert the needle. A silicone ring, placed on the needle shaft, can be used to mark the desired needle depth. When the device is implanted, but prior to covering the device with the conjunctiva, the surgeon can insert a needle into the device and adjust the location of the silicone ring to mark how far the needle must be inserted to safely reach the device interior (Figure 2-67). During refill, the surgeon only inserts the needle until the silicone ring touches the eye surface.

119

Figure 2-67 Illustration of the application of a refill ring on the refill needle.

However, it was determined that this method of regulating needle depth does not account for conjunctival thickness, or changes that may occur to the ocular tissue during the lifetime of the device (e.g. fibrous tissue formation). Therefore, a second method for controlling needle depth must be developed. 2.4.2.1.1.1.2 Rigid Device Baseplate A rigid baseplate was proposed as a method for preventing the needle from puncturing through the entire device. The device thickness measures 2 mm in thickness and the opening of a beveled needle was measured to be 1.2 mm long from needle tip to the opening termination. Therefore, if the needle is inserted until the needle tip touches the baseplate, then the entire needle opening is contained with the device. 120

PEEK (polyetheretherketone) was chosen as the baseplate material because it is a USP Class VI biocompatible material. Furthermore, thin PEEK sheets (0.01â&#x20AC;&#x2122;â&#x20AC;&#x2122;) are commercially available; therefore the PEEK baseplate can be added to the device base without increasing the overall device thickness (Figure 2-68).

Figure 2-68 Image of the PEEK baseplate to limit refill needle insertion depth.

2.4.2.1.2 Hollow Sham Timeline Several versions of hollow surgical shams were designed and fabricated to accommodate surgical needs and requests. Each sham was created using custommade laser-machined acrylic molds.

A complete timeline of the hollow sham

devices can be found in Table 2-10.

v3_2 is a hollow counterpart to the v3_1 solid sham. However, this hollow sham did not contain a rigid baseplate because it was a benchtop demonstration prototype. 121

v3_3 was fabricated using medical grade silicone (MDX4-4201) and included a baseplate. The baseplate was made using a hole-punch, and was placed directly beneath the refill ring. However, it was determined that if the refill needle was inserted at an angle (as opposed to perfectly perpendicular) to the device surface, it was possible for the needle tip to miss the PEEK baseplate. Therefore, v4_1 was fabricated with a larger PEEK baseplate that would cover the majority of the device footprint.

v5_1 and v6_1 were created to be better suited for chronic in vivo testing with rabbit eyes.

They are approximately 40% smaller than the v3 devices.

The major

difference between v5_1 and v6_1 was the introduction of a PEEK baseplate that is the same shape and size as the device footprint. Additionally, a smaller refill ring was necessary in order to fit the smaller device.

v7_1 is the initial design for the shape of the modular device which integrates all of the major device components: refill reservoir, refill ring, PEEK baseplate, suture tabs, electrolysis pump, electrolysis bellows, and dual regulation check valve. The reservoir body is different from the previous shams as it is two overlapping dome shapes as opposed to a single dome (Figure 2-69). This layout separates the main reservoir from the refill port; preventing the refill needle from accidentally puncturing the pump bellows during refill.

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Figure 2-69 Top and side view of the initial reservoir design for the integrated drug delivery device. The reservoir body is separated from the refill port to prevent the pump chamber and Parylene C bellows from accidentally being punctured by the refill needle.

In the final integrated device, the cannula diameter was increased to accommodate the dual check valve. Additionally, the cannula was moved away from the refill port to prevent refill liquid from exiting the cannula as opposed to refilling the reservoir. The final integrated device is discussed in Section 2.3.1.2- Assembled Device. .

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Table 2-10 Timeline for hollow surgical sham, including major device characteristics.

Sham Mold Diagram Solid/ Hollow Material Footprint Shape Major Axis Length [mm] Minor Axis Length [mm] Thickness [mm] Volume [ÂľL] Internal Volume [ÂľL] Suture Tab location Refill Ring ID [mm] Refill Ring OD [mm] Baseplate Size [mm]

Hollow Sham Timeline v4_1 v5_1 v6_1 Appendix Appendix Appendix FF EE FF Hollow Hollow Hollow PDMS or MDX4MDX4MDX4-4210 4210 4210

v3_2 Appendix EE Hollow PDMS or MDX44210

v3_3 Appendix EE Hollow PDMS or MDX44210

Oval

Overlapping Offset Circles

16.9

9.845

7.7

1.89 217.88

1.65 65.49

10.285 and 6.655 2 413.43

126.08

42.94

213.12

Reservoir

2.92

1.98

Bump

5.31

4.76

Bump

N/A

Circle D: 6.53

Circle D:11.66

Circle D: 6.53

Oval 9.845 x 7.7

Overlapping Offset Circles D: 8.5 & 5.5

Appendix GG Hollow MDX4-4210

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2.4.2.1.3 Fabrication The steps to fabricate all of the hollow sham designs were similar. The reservoir is made by molding PDMS between a convex and concave dome molds, while the base is fabricated by molding the PDMS into the desired footprint shape and incorporating a silicone tube (Figure 2-70).

Figure 2-70 Illustration of acrylic molds used to fabricate the hollow surgical sham.

The reservoir dome and the device base were made separately and assembled. The pieces can be made in parallel; however, for clarity each fabrication process is described separately. A list of the fabrication process steps for oval shaped hollow shams can be found in Appendix HH. 2.4.2.1.3.1.1 Reservoir To make the dome portion, PDMS prepolymer was poured into the concave half of the dome mold (Figure 2-71B). A stainless steel washer (ID 2.92mm, OD 5.31mm) 125

was placed into the concave dome mold (Figure 2-71C).

The mold was then

transferred to a vacuum oven to degas the PDMS prepolymer. The convex half of the dome mold was then aligned and pressed onto the concave mold (Figure 2-71D). Two glass microscope coverslips were used to separate the two halves of the mold. The mold was then placed into an oven for 30 minutes at 70 째C to rapidly cure the PDMS. Once cured, the dome piece was removed from the mold and excess PDMS was cut from the dome (Figure 2-71E). 2.4.2.1.3.1.2 Base The device base was made by pouring PDMS prepolymer into the base mold (Figure 2-71B). The mold was placed into a vacuum oven to degas the PDMS. Once degassed, the PEEK baseplate was carefully placed into the base mold, ensuring bubbles were not introduced into the PDMS (Figure 2-71C). The baseplate was made by cutting the desired baseplate size from a polyetheretherketone (PEEK) sheet (0.254 mm thick). A one inch length of silicone tubing (0.305 mm ID, 0.61 mm OD), threaded with a stripped piece of 30 gauge wire (0.254 mm diameter), is inserted into the indentation on the base mold which indicates the tube location. The wire prevents the tube from being clogged by the PDMS prepolymer. The mold was placed in an oven at 70 째C for 30 minutes for rapid curing. The cured base piece was removed lifted from the base mold; extra PDMS was carefully cut from the base piece and the wire is removed from the tube (Figure 2-71E).

2.4.2.1.3.1.3 Device Assembly 126

Once both pieces of the hollow sham were ready the two pieces were carefully aligned (Figure 2-71F). A thin line of PDMS prepolymer was applied along the edge of the two pieces, bonding them together (Figure 2-71F). The bonded device was then placed in an oven (70 째C) for 10 minutes to completely cure the PDMS.

Figure 2-71 Fabrication steps for making the hollow surgical sham.

2.4.2.1.3.1.4 Benchtop Verification The hollow sham was filled on the benchtop by piercing the device through the middle of the stainless steel ring using a 30 gauge non-coring needle (Figure 2-72). The needle was pushed into the device until the needle tip progression through the

127

device was prevented by the PEEK baseplate. Dye liquid is injected into the device until excess liquid exits the cannula.

Figure 2-72- Hollow surgical sham being filled on benchtop.

The contents within the sham were dispensed by manually depressing the reservoir (Figure 2-73). The sham was refilled and dispensed multiple times.

Figure 2-73 Benchtop demonstration of manual dispensation of dyed liquid from within a hollow sham device.

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2.4.2.2 Acute and Chronic In Vivo Refill and Dispensation 2.4.2.2.1 Methods 2.4.2.2.1.1 Acute In Vivo Dispensation The hollow sham will be implanted into rabbits to demonstrate device functionality in an acute in vivo study. The device is placed in the superior temporal quadrant of the eye, with the cannula entering the anterior chamber of the eye. The device fully enclosed with the eye wall by covering the device with the conjunctiva.

This

minimizes the possibility of infection entering the eye interior (Figure 2-74).

Figure 2-74 Illustration of the hollow sham placement in the eye.

Prior to implantation of the device, hollow shams were sterilized. The sterilized sham was filled on benchtop with saline solution and manually-depressed to verify device functionality before implantation.

The device was then refilled with a 129

mixture containing phenylephrine (10% concentration) and Trypan blue dye. The silicone tube was pinched closed by tying a suture around the base of the tube; the tube was closed off to prevent accidental dispensation of phenylephrine during implantation.

The device was implanted beneath the conjunctiva and secured with suture tabs. A 3 mm wide scleral tunnel was created 2 mm posterior to the limbus. The cannula of the device was cut so that the tip of the cannula extended approximately 2 mm into the anterior chamber. The tip was cut at an angle; this created a beveled tip on the cannula which aided insertion of the cannula through the scleral tunnel. The closing suture around the cannula was removed and device functionality was verified prior to suturing the conjunctiva over the device (Figure 2-75).

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Figure 2-75 Images of hollow sham device implantation for acute and chronic in vivo studies

The baseline pupil diameters were measured prior to releasing the suture closing the cannula. The suture around the cannula was cut and the device was manually depressed using blunt forceps. The pupil dilation was measured after dispensation and again after the conjunctiva was replaced over the device and sutured in place. The surgical protocol is listed in Appendix II. 2.4.2.2.1.2 Chronic In Vivo Study The chronic study of the device was conducted to verify device functionality over a 6 month period. The device was implanted using the same protocol listed in the acute

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study. After the initial verification of dispensation of the implanted device, the device was refilled once a month with Trypan blue (Figure 2-76).

Each month, the surgeons determined if any biofouling prevented them from identifying the refill location, as well as if the tube was occluded and prevented successful delivery of the dye into the eye. Biocompatibility was also monitored using color photography and fluorescein angiography. At the end of the study, the endothelial cell density was counted, and any damage to ocular tissue was noted.

2.4.2.2.2 Results 2.4.2.2.2.1 Acute In Vivo Results Two Parylene C coated devices were implanted in the right eye of Dutch-belted pigmented rabbits, the left eye acted as the control. The baseline horizontal and vertical pupillary diameters were measured immediately prior to the release of the suture closing the cannula. The phenylephrine was delivered by supporting the base of the device with blunt forceps and depressing the reservoir using a Q-tip; this event was marked as t= 0.

At t=1 min 29 sec and t=9 min 58 sec, pupil diameter 132

measurement was taken. A summary of the pupil diameter values can be found in Table 2-11. Table 2-11 Summary of Results from In Vivo Delivery using Hollow Surgical Sham

Pupil Diameter Baseline t = 0 minutes After Dispensation t = 1 min 29 sec After Dispensation t = 9 min 58 sec Total Change

Vertical

Horizontal

4.5 mm

7 mm

7.5

3 mm (66% change)

It was also shown that the stainless steel ring of an implanted device can be made more visible by transilluminating the device. A light is placed along the exterior of the eye.

The stainless steel ring is seen as a darker shape compared to the

illuminated eye tissue (Figure 2-77). This minimally invasive and real-time method of identifying the stainless steel ring will aid medical personnel when refilling the device.

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Figure 2-77 Transilluminated eye with implanted hollow sham device. The device and stainless steel ring outlines are clearly visible through the eye tissue (i.e. conjunctiva) covering the device.

2.4.2.2.2.2 Chronic In Vivo Results Surgical procedures were deemed by the surgeons to be minimally invasive and well tolerated.

The time to implant a surgical sham from the first incision in the

conjunctiva to suturing the conjunctiva over the device was approximately 60 minutes.

All of the implanted devices were fabricated using USP Class VI,

biocompatible materials and did not show any biofouling to affect device functionality during 6-month follow-up period. Additionally, no leakage around the insertion site or filtering bleb formation over any of the implants was observed.

Devices were refilled up to 6 times at 4- to 6-week intervals during a period of 4 to 6 months. Transconjunctival refilling was performed in less than 1 minute by a single surgeon without any complications (Figure 2-78). 134

Figure 2-78 Images of in vivo device refilling and dispensing. First, the refill site is checked for any damage, infection, or scarring from previous refills. Next, the eye is transilluminated to help identify the refill ring location (the refill ring appears as a darker shadow). The refill needle (30G non-coring) is inserted through the center of the refill ring until the needle progressing is stopped by the device baseplate. Trypan blue dye is injected into the device; dye can be seen spreading through the device as a dark plume. The dye exits the cannula and into the anterior chamber. Finally, the puncture site is inspected for damage or leakage.

Anterior chamber depth and intraocular pressure were measured after surgical implantation and monthly refilling; values were normal in all implanted eyes compared to the contralateral control eyes. Surgeons reported no retinal or optical disc damage on indirect ophthalmoscopy examination or fluorescein angiogram. Examinations slit-lamps, anterior color photography, or fluorescein angiograms did not show any cornea, iris or lens damage. Finally, the surgeon reported observing no infection of the ocular tissue surrounding the device, all of the devices remained in 135

place (i.e. did not extrude), and the cannula was not occluded throughout the entire duration of the study.

At the conclusion of the chronic study, ocular tissue was prepared to determine any tissue damage from the implant or refill events. Light microscopic examination showed endothelial cell loss close to the cannula insertion site. The difference in the final corneal thickness mean between the implanted (0.42 ± 0.02 mm) and control (0.41 ± 0.02 mm) eyes was not statistically significant; the mean peripheral corneal thickness in implanted eyes was 0.49 ± 0.03 mm vs. 0.51 ± 0.02 mm in control. Additionally, no evidence of corneal edema was seen and epithelial integrity was uniform. However, scanning electron microscope images of the endothelial side of the cornea showed changes in density, size, structure and morphology of endothelial cells in all quadrants of the cornea after 6 months.

A summary of the mean endothelial cell density in the implanted and control eyes are found in Table 2-12. However, it was found that the endothelial cell changes improved significantly in one rabbit in which refill and dispensation of Trypan blue solution was ceased at 4 months after surgery. Table 2-12 Summary of endothelial cell density at the conclusion of the 6 month study for eyes that were implanted and refilled 6 times during the course of the study and an implant were the refills were terminated 2 months prior to the end of the study at month 4.

Superior Temporal Quadrant Cornea (6 months, 6 refills) Central Cornea (6 months, 6 refills)

Implanted Eye

Control Eye

1348 ± 231 cells/mm2

4511 ± 177 cells/mm2

2603 ± 214 cells/mm2

4305 ± 202 cells/mm2 136

Superior Temporal Quadrant Cornea (6 months, 4 refills, refill ceased at 4 months) Central Cornea (6 months, 4 refills, refill discontinued at 4 months)

4161 ± 278 cells/mm2

4806 ± 159 cells/mm2

4326 ± 244 cells/ mm2

4551± 126 cells/mm2

A device was implanted for 3 weeks and removed prior to any refill or dispensation to determine if surgical implantation caused any damage.

SEM images of the

endothelial cells appear to be similar to the control and endothelial cells of the device with fewer refills.

Corneal endothelial cell damage in the implants is similar to those found in commercially available glaucoma drainage device implantation such as the Ahmed glaucoma valve (Kim, et al. 2008, Lim 2003). However, endothelial cell loss can be minimized by restricting the movement of the cannula relative to the cornea. The most common causes of damage due to macroscopic contact of cannula with the cornea is non-ideal positioning of a long tube or anterior chamber shallowing (Lim 2003). These results suggest a careful placement of a shorter bevel-tipped cannula with a rounded edge may decrease endothelial damage. The difference in endothelial cellular damage between the implants that were refilled and dispensed Trypan blue for the full period of the 6 month study versus the implant that was not refilled for the last 2 months of the study may be attributed to toxicity of Trypan blue (van Dooren, et al. 2004).

137

2.4.3 Summary Surgical shams to optimize the device shape, component functionality, and component placement were created. Acute ex vivo studies using the shams allowed surgeons to create and refine a surgical protocol for implanting and refilling the electronically-actuated device.

Chronic, 6 month, in vivo studies demonstrated

device biocompatibility and tolerance to monthly refills. No biofouling of the device or cannula was observed. Some endothelial cell damage was found, but may be attributed to the toxicity of Trypan blue, the dying agent used to verify device delivery.

Similar to the manually-actuated drug delivery device, the shams are fabricated using interchangeable layers. Replacement of layers is also possible, where the dome layer can be change to increase or decrease the interior volume. As demonstrated in the sham timeline, the dimensions of the refill ring and PEEK baseplate were easily changed and incorporated into the dome or base layers. Additionally, the location of the refill port can be moved without affecting the base layer or cannula location.

2.4.4 Additional Applications The applications of MEMS based, refillable drug delivery system can be extended to any application where precise delivery in a difficult to access, localized area is necessary. Two additional drug delivery device applications, which are in the initial phase of development and are currently being investigated, are presented.

138

2.4.4.1 Rat Retinitis Pigmentosa Drug Delivery Device A prototype device which is capable to delivering medications which treat retinitis pigmentosa (RI) into a rat animal model has been proposed. Retinitis pigmentosa is a degenerative disease that destroys photoreceptors, leading to irreversible damage of ocular tissues. The final device will contain a refillable reservoir, electrolysis pump, cannula, flow control valves, and suture tabs.

2.4.4.1.1 Design and Fabrication The initial device is based on the hollow surgical models described in Section 2.4.2Hollow Surgical Shams. Similar to the hollow shams, the Rat RI device is fabricated using medical grade silicone (MDX4-4210), and constructed be assembling a molded dome on a base with an embedded cannula.

The cannula from the hollow shams (silicone tube, O.D. 0.024’’, 0.609 mm) is much too large for a rat eye; which is typically 4 mm in diameter. Therefore, a smaller cannula is incorporated into the device. Polytetrafluoroethylene (PTFE) cannula, 38 or 34 AWG in size (Zeus Inc., Orangeburg, SC, I.D.: 0.102 mm or 0.152 mm, wall thickness: 0.051 mm or 0.076 mm, respectively), were used.

Additionally, the device cannot be sutured into the eye wall (as was proposed for the large mammal ocular drug delivery device). Instead, the device is secured to the rat skull using suture tabs and 0-80 thread 1/8’’ hex screw bone screws (92196A052,

139

McMasterCarr, Santa Fe Springs, CA) (Figure 2-79). The flexible cannula is then threaded down to the eye for insertion.

Figure 2-79 Assembled device with bone screws used to secure device to rat skull.

Initial molds for the rat RI device were fabricated based on the dimensions of a rat skull (Figure 2-80). The skull is approximately 2 cm in width and 4 cm in length.

Figure 2-80 Image of proposed device superimposed on a image of a rat skull.

However, surgeons asked for a 25% reduction in size in order ensure the device could be easily implanted. The molds for the smaller device are shown in Figure 2-81. The device made from these molds has an internal volume of 56.2 ÎźL 140

Figure 2-81 Laser file to create molds for the rat retinitis pigmentosa drug delivery device.

The purpose of the reservoir convex and concave molds and the device base mold are identical to the hollow sham molds. The curing stand piece was created to prevent the suture tabs from becoming occluded during device assembly. The curing piece was marked with dots located at the centers of each suture tab. Holes 1.27 mm in diameter will drilled partially through the Plexiglas mold at each of the dots. A 18 G needle shaft (O.D. 1.27 mm) was placed into each hole to create the stand (Figure 2-82a). Once the device base was fabricated, it was placed onto the stand such that 141

each needle shaft penetrated the corresponding suture tab. The reservoir dome was then aligned and affixed onto the base (Figure 2-82b). Once cured, the entire device was removed form the stand.

Figure 2-82 Image of a) curing stand to prevent suture tabs from becoming sealed during assembly, b) device assembly on curing stand.

The PEEK cutout guide was used to trace a PEEK baseplate that was the same size and shape as the oval portion of the device baseplate.

2.4.4.1.2 In Vivo Testing 2.4.4.1.2.1.1 Methods The device was tested in vivo on mature adult rats. The rat skull was exposed by making a small incision in the scalp.

The device was placed on the skull to

determine the location for 3 securing bone screws. Three holes were drilled into the skull using a #56 drill bit and hand-held drill pen. The device was then secured to the skull by placing the bone screws through the suture holes and pre-drilled holes in the skull.

142

A small scleral tunnel was made in the rat eye between the cornea and retina using a 28G needle. The lens in a rat eye is particularly large compared to the rat eye; additionally, the space between the cornea and retina is very small. Therefore, the surgeon must take particular care when making the scleral tunnel to not touch the lens, nor cause retinal detachment.

The cannula was then inserted into the scleral tunnel. Small sutures were used to close the tunnel around the cannula. 2.4.4.1.2.1.2 Results The initial surgery determined the device was both easy to 1) secured to the skull and, 2) insert the cannula into the eye. However, the bending radius of the cannula limited cannula motion. The bending radius prevented the cannula from following the natural curve of the animal head from the skull to the eye. Kinks in the cannula significantly altered flow resistance. Therefore, it was proposed that the cannula be made of silicone and terminates with a small length of the PTFE tube. Only the PTFE portion of the cannula will enter the eye. Additionally, suture tabs will be placed at the along the silicone tube and silicone/ PTFE junction to help secure the cannula to the animal as well as to the eye, respectively.

2.4.4.2 Cancer Treatment Device A device which is capable of delivery pharmacological solutions to cancerous growths in a mouse animal model was proposed. Two different devices and delivery modes were investigated to determine if continuous delivery to a tumor can 143

significantly slow the growth of the tumor. Both devices have a refillable reservoir, flexible silicone cannula, and PEEK baseplate. However, one set of devices relies on diffusion for drug dosing, which the other will contain an electrolysis pump.

Two cancerous growths were cultivated in on the hindquarters of a mouse animal model (one per side). An incision was made in the skin covering the back of the animal. The device was secured to the subcutaneous muscle. The cannula tip was directed to one of the tumors. The size of the treated tumor was compared to the untreated tumor to determine the effectiveness of the rat cancer drug delivery device.

2.4.4.2.1 Design and Fabrication 2.4.4.2.1.1 Diffusion Device The hollow sham molds from the ocular drug delivery device was used as the initial prototype for the diffusion driven mouse cancer delivery device. Both v4_1 and v6_1 were used to determine if one size was better suited for the animal model. The diffusion device was not optimized for this study; however, shams v4_1 and v6_1 were determined to be suitable for this application. Fabrication steps for the v4_1 and v6_1 sham devices can be found in Section 2.4.2.1.3- Fabrication.

2.4.4.2.1.2 Electrolysis Delivery Device The electrolysis delivery device dimensions were driven by the needs of the electrolysis pump and Parylene C bellows. The device body diameter was larger than the pump footprint and the height of the devices needed to accommodate a fully expanded bellows. 144

Component

Dimensions dia = 18 mm Dome h = 3.5 mm length = 63.5 mm, 2.5'' Cannula I.D. = 0.305 mm, 0.012'' O.D. = 0.610 mm, 0.024'' dia1 = 3.5 mm Unactuated Bellows dia2 = 4.5 mm h = 1.6 mm dia1 =13 mm Pump Substrate dia2 = 6 mm (PEEK) t = 0.26 mm Total Drug Reservoir Space

Volume [ÂľL], Est 674.68 4.63

81.68

36.35 561.29

A refill ring was not included in this device because it would not be visible through the skin of the animal. Therefore, a raised bump was placed on the reservoir. This bump can be felt through the skin to help indentify the refill location. A refill bump also increases the amount of material at the refill location. As shown in Figure 2-35, a thicker refill port increases the leakage pressure valve and increases the number of times the device can be refilled. Additionally, the bump was located off-center to prevent the refill needle from puncturing the Parylene C bellows and compromising the pump chamber. The pump chamber was also placed off-center so that the edge of the bellows was clear of the refill bump.

The device body was fabricated in a manner similar to the hollow surgical shams; the molds used to fabricate the pieces of the device body can be found in Figure 2-83. In summary, the reservoir top and base molds were filled with medical grade silicone, placed under vacuum, and cured. However, an additional spacer piece was also 145

made for this device to add additional height to the device interior in order to accommodate the Parylene C bellows. The spacer piece also had an opening, which served as a pass-through for the electrical connections to the electrolysis electrodes.

146

Figure 2-83 Laser file to create molds for mouse cancer drug delivery device.

147

Device assembly begins by fabricating all of the individual pieces for the device body: (reservoir dome, reservoir base, spacer layer), and the packaged actuator (Figure 2-84).

Figure 2-84 Image of the components to fabricate the rat cancer drug delivery device (device body and electrolysis actuator).

The device was assembled by first securing the electrolysis actuator to the reservoir base using a small drop of silicone prepolymer. The silicone was cured in an oven for 5 minutes at 70 ยบC. DI H2O soaked paper towels were placed near the device in the oven to increase the humidity around the device in order to mitigate any diffusion of the water contained within the actuator.

Next, the spacer piece was aligned to the reservoir base. The spacer plate follows the outline of the base. The wires from the electrolysis actuator were aligned to the opening in the spacer piece. The spacer piece was secured with silicone prepolymer and cured in the oven.

148

The holes in the suture tabs were created using a 16G coring syringe needle (O.D. 1.651 mm). 16G needle shafts where then inserted into the holes to prevent the holes from becoming clogged during the final assembly stages.

The reservoir dome was then affixed to the spacer piece using silicone prepolymer. The orientation of the dome was adjusted to place the refill bump over a portion of the reservoir interior not occupied by the electrolysis actuator.

The device was then filled by piercing the refill bump with a 30G needle (O.D. 305 Îźm) non-coring needle to verify the absence of leaks in the reservoir assembly. The metal shafts were removed from the suture holes and the device was refilled again to ensure no leaks were present at the suture locations. The wires were covered using electrical heat-shrink tubing to prevent the animal from chewing through to the metal core of the wires (Figure 2-85).

Figure 2-85 Fully assembled rat cancer drug delivery device with electrolysis actuator. Heat-shrink wrapping on wires not shown.

149

2.4.4.2.2 In Vivo Testing 2.4.4.2.2.1 Methods The device was tested in mice animal models. Cancerous tissue was grown on the hindquarters of the animal (one per side) starting at Day 0 until Day 3. One growth will be treated with drug from the device, while the contralateral growth will serve as the control.

An incision was made through the skin on the back of the animal. The device was sutured to the back of the animal with the cannula tip placed in close proximity to one of the cancerous growths. The devices were then filled with either siRNA drug, gold particles, siRNA and gold nanoparticles, or phosphate buffer solution. The cancer growths were monitored for 19 days following implantation.

The electrolysis pump device was refilled once and was pumped every day for approximately 30 minutes (0.78 mA) to deliver a total of 50 ÎźL per dosing period. The diffusion pumps were not refilled. 2.4.4.2.2.2 Results After 19 days, preliminary data shows only the active pumping device demonstrated any significant difference between the treated cancer growth and the control growth. The treated growth was approximately 30% smaller in volume than the untreated growth.

150

One potential reason the diffusion pumps were not as successful may be attributed to the slow administration of drug. However, one possible failure mode is an air gap anywhere in the fluid path between the liquid filled reservoir and the cannula tip. This air gap would prevent diffusion of the drug into the body.

Further tests are planned for an optimized drug delivery device with an electrolysis actuator. The optimized device will be smaller to have a better fit with the animal model and have wireless power actuation. Additionally, the device will be fabricated with two cannulae in order to allow treatment of either two cancer growths, or to provide two points of treatment on the same growth.

151

3 Microfluidic Interconnects 3.1 Introduction Microfluidics, and in particular micro total analysis systems (ÎźTAS) and lab-on-achip (LOC), have many features advantageous for advanced chemical and biological analyses.

The improved performance achieved in part through system

miniaturization, laminar flow, high throughput, reduced sample consumption, and shorter analysis time has enabled new diagnostic tools and resulted in the application of these technologies to areas such as chemical synthesis, genetic analysis, drug screening, and even single cell/molecule analysis (Ho and Tai 1998, Whitesides 2006). To realize the full potential of microfluidics, a suitable packaging technology to reliably couple micromachined microchannels to the macro-world is required. The micro-to-macro fluidic interfaces, or interconnects, are usually a custom designed solution and manually assembled one at a time. The assembly process is time consuming and can require precision alignment or complicated fabrication steps. The lack of a batch fabricated approach to interconnects greatly complicates the packaging of the microfluidic system and is an obstacle to the widespread commercialization of microfluidic systems. A modular design which can be easily fabricated, incorporated and customized for each system would help address the issues facing MEMS packaging.

Many interconnects have out-of-plane interfaces in which the tubing and interconnect are connected perpendicularly with respect to the substrate surface 152

(Christensen, et al. 2005, Galambos, et al. 2001, Lee, et al. 2004, Li and Chen 2003, Matsumoto, et al. 2003, Meng, et al. 2001, Pattekar and Kothare 2003, Puntambekar and Ahn 2002, Yang and Maeda 2003). Out-of-plane interconnects can obstruct optical viewing of the microfluidic system and interfere with operation of microscope objectives. To accommodate microscope operation, interconnects are placed further apart which increases dead volume and overall system size. Robust mechanical connections in an out-of-plane approach are difficult to achieve due to limited contact area between the device and tubing. Adhesives can reinforce the connection (Li and Chen 2003, Meng, et al. 2001, Pattekar and Kothare 2003), but are difficult to control; device yield is reduced when the adhesive bleeds beyond the application area and clogs the microfluidic system. When a removable connection or modular approach is desired as opposed to a permanent connection, adhesives cannot be used. Most existing interconnects cannot be removed from the system without leaving a permanent fluidic breach in the system (Baldock, et al. 2004, Chiou and Lee 2004, Christensen, et al. 2005, Lee, et al. 2004, Li and Chen 2003, Meng, et al. 2001, Pattekar and Kothare 2003, Puntambekar and Ahn 2002). A summary of the advantages and limitations of connector orientation and attachment methods is presented in Table 3-1. An alternative approach to forming connections that are robust but do not require additional complex fabrication steps, precision alignment, or adhesives is presented.

153

Table 3-1 Comparison of Connector Design Options

Category Orientation Vertical

References

(Anderson et al., 2000; Bhagat et al., 2007; Christensen et al., 2005; Li and Chen, 2003; Meng et al., 2001; Murphy et al., 2007; Pattekar and Kothare, 2003; Yang and Maeda, 2003; Yao et al., 2000), Upchurch Scientific Horizontal (Baldock et al., 2004; Chiou and Lee, 2004; Dahlin et al., 2005; Lo and Meng, 2008) Attachment Method Adhesives (Lee et al., 2004; Li and Chen, 2003; Meng et al., 2001; Murphy et al., 2007; Pattekar and Kothare, 2003)

Thermal

Compression

Other

(Meng et al., 2001; Murphy et al., 2007; Pattekar and Kothare, 2003; Puntambekar and Ahn, 2002) (Anderson et al., 2000; Christensen et al., 2005; Dahlin et al., 2005; Lee et al., 2004; Liu et al., 2003; Yao et al., 2000) (Baldock et al., 2004; Chiou and Lee, 2004; Yang and Maeda, 2003)

Pros

Cons

• Possibility of large surface area available for fluidic connections

• Mechanically unstable • Increased dead volume • Can obstruct microscope observations • Increased lateral dimensions

• Mechanically robust • Less dead volume

• Increased device thickness to accommodate interconnect/ tubing

• Simple • Commercially-available materials • Increased mechanical strength and maximum pressure range • Simple • Water-tight seal

• May clog device • Crack formation within adhesive, leads to leaking and decreased operating pressure range

• Rapid connection • Tube can be replaced

• System operating pressure a function of surface area contact between tube and connector • Removing tube may cause leakage N/A

N/A

• May not be thermally compatible with other device materials

154

Reusable

(Anderson et al., 2000; Christensen et al., 2005; Dahlin et al., 2005; Lee et al., 2004; Liu et al., 2003; Lo and Meng, 2008; Yao et al., 2000)

â&#x20AC;˘ Can replace damaged or contaminated connections

â&#x20AC;˘ Removing tubing may expose microfluidic interior

155

A novel interconnect is investigated to address the current challenges in microfluidics packaging. The interconnect design follows the plug-in format (pinand-socket) found in microelectronics. In this case, the “pin” is a commerciallyavailable, small diameter needle while the “socket” corresponds to an integrated PDMS septum contained within a SU-8 housing located at the inlet and/or outlet of a microfluidic system (Figure 3-1). The SU-8 housing also serves to designate the needle insertion area and forms the microchannel between the inlet and outlet. The microfluidic system can be accessed by piercing a needle through the septum. By using a non-coring syringe needle, fluidic connections may be repeatedly established via septa; once the needle is removed, the PDMS septum reseals preserving the integrity of the microfluidic system and any contained fluids (Lo, et al. 2006).

Figure 3-1 Microfluidic system with integrated circular interconnects. 33 gauge non-coring needles were inserted into the input and output septa. Rhodamine was introduced into the system to demonstrate system functionality. PDMS septum is outlined to indicate its location.

The in-plane layout of the interconnect, in which the interconnect is oriented in the same plane as the substrate, enables robust microfluidic connections by increasing the contact area between the macro-world needle and the microchannels in the chip. Connections are established on-demand and without the need for adhesives, precision alignment, thru-wafer drilling/etching, or other complex post-processing 156

and assembly steps. Furthermore, the interconnect does not impede microscope observation of the system. This microfluidic interconnect approach incorporates packaging in the design and layout of the microfluidic system and can be batch fabricated.

These interconnects are easily adapted to other microfluidic system

designs by simply adding a single mask to an existing fabrication process to create SU-8 anchors for the septa. Additionally, the interconnect design is applicable to both bulk and surface micromachined microfluidic devices. The single interconnect design can be extended into an arrayed interconnect design where multiple needles simultaneously pierce an array of septa. Both the single and arrayed interconnects are presented.

3.2 Single Interconnect 3.2.1 Interconnect Design The pin-and-socket interconnect consists of a PDMS septum housed in a SU-8 anchor and a non-coring needle that punctures the septum to establish the macromicro interface. The PDMS septum size and shape is defined by the layout of the SU-8 anchor. Anchor thickness is determined by the outer diameter of the needle and practical limits of fabricating thick film SU-8 structures (including film uniformity and process time). In this work, the SU-8 structure height was selected to be 100-200 μm greater than the outer diameter of the needle. For a 33 gauge needle (OD 203 μm) the SU-8 layer was 300 μm thick, for a 30 gauge needle (OD 305 μm) the SU-8 layer was 500 μm thick.

157

3.2.1.1 Proof-of-Concept The idea of a horizontal, or in-plane, interconnect was rapidly prototyped using a simple setup to demonstrate proof-of-concept.

Two chambers connected by a

channel were cut into the center of a 500 Îźm PDMS membrane using a fine tipped blade. The membrane was then sandwiched between two glass slides to create an enclosed system (Figure 3-2).

Figure 3-2 Exploded view of the setup used to demonstrate horizontal interconnect proof-of-concept.

Binder clips were used to apply constant pressure on the membrane. Needles were inserted from the edge of the membrane to access the chambers. Dyed DI water was injected into one chamber using a syringe. The liquid was observed to flow from one chamber to the other via the channel exit the system through the second needle (Figure 3-3).

158

Figure 3-3 Images showing fluid progression in proof-of-concept setup.

3.2.1.2 SU-8 Anchors The SU-8 anchors mechanically interlock with the PDMS septum preventing septum damage or shifting during needle insertion and removal. Three anchor shapes (square, circular, and barbed) were fabricated and examined (Figure 3-4). The length of the septum also determines the contact length between the needle and PDMS. Thus, there exists a design trade-off between interconnect strength and footprint.

159

Figure 3-4 A) Image of an assembled circle septum interconnect. B) Top view of three different septum connector shapes (circle, barbed, and square) that were designed and integrated into the test microfluidic system. Needle, PDMS septum, SU-8 housing, and microchannel in the designs are indicated. C) Side view of the needle piercing the PDMS septum. Image is not drawn to scale.

The SU-8 anchor was fabricated on a glass slide substrate. For devices in which electrical traces were required, Parylene C was deposited between the glass substrate and the SU-8 to provide electrical isolation, but was also found to alleviate the thermal stress-induced delamination of the SU-8 (Despont, et al. 1997).

SU-8

delamination was observed in 100% of the setups without the Parylene C layer. The difference in the coefficient of thermal expansion of the glass slide (8.9x10-6 /째C) compared to SU-8 (5.2 x 10-5 /째C) can result in delamination of SU-8 structures during processing. Parylene C has a high percent elongation (200%), which allows

160

the Parylene C to absorb the stresses due to the thermal mismatch between the glass and SU-8.

3.2.1.3 Septum The SU-8 layer includes the microchannel which is terminated on either end by a region reserved for the PDMS septum (Sylgard 184, Dow Corning, Midland, MI). A PDMS septum is located at both the input and output and allows rapid access to the sealed microchannel (Figure 3-1, Figure 3-4). Mechanical interlocking structures patterned in the SU-8 layer secure the PDMS septa to the substrate during both needle insertion and removal.

3.2.1.4 Interconnect Integration Interconnects were fabricated at the inlet and outlet of a single SU-8 microchannel. The interconnect was also integrated into a simple microfluidic system that contained a microchannel, microchambers, electrolysis pump, and resistive sensors without the need for any additional masks (Figure 3-5).

Figure 3-5 Integrated interconnect with microfluidic system. System contains SU-8 layer which defines the septum housing, microchambers, and microchannel. Electrolysis structure and flow sensors are fabricated with a Ti/Pt metal layer. PDMS septum and glass cover plate are not present.

161

3.2.2 System Fabrication 3.2.2.1 Test Interconnect Microfluidic systems each containing one channel and integrated interconnects at both the inlet and outlet were batch-fabricated using conventional micromachining techniques.

Test chips with only the SU-8 anchor and PDMS septum were

fabricated without metal components for the interconnect test devices. First, the substrate, either a 76 mm (3 inch) soda lime wafer (Silicon Quest International, Santa Clara, CA) or soda lime slide (75 mm x 50 mm, Corning Glass Works, Corning, NY), cleaned and coated with Parylene C (Specialty Coating Systems, Inc., Indianapolis, IN). The Parylene C was vapor deposited (2 μm thick) to help prevent the SU-8 from delaminating from the glass surface (Figure 3-6B). Next, a 300 μm layer of SU-8 2100 (MicroChem Corp., Newton, MA) was obtained by using a two-step spin coating process to provide better thickness uniformity across the substrate. The first coat was spun at 1.5 krpm (approximately 200 μm thick) followed by a second planarization coating spun at 3 krpm (for an additional 100 μm) (Figure 3-6C). After each spin coat, the applied SU-8 layer is left at room temperature for 3 hours to improve planarization. Then, the layers were each softbaked at 90 °C; the first layer softbaked for 90 minutes and the second for 3 hours. Baking steps were all performed on a programmable hotplate (Dataplate Series 730, Barnstead International, Debuque, IA) set to ramp at 3 °C/min. The lower softbake temperature was selected to avoid thermal degradation of the underlying Parylene C. Substrates were allowed to slowly cool to room temperature 162

after each bake step to avoid thermal stress cracks in the SU-8. The SU-8 was patterned (600 mJ/cm2), post-exposure baked for 30 minutes at 90 °C, and then developed using SU-8 developer (MicroChem Corp., Newton, MA) (Figure 3-6D). A final hardbake step was performed at 90 °C for 30 minutes. A list of the fabrication steps for the interconnect test structure can be found Appendix JJ.

The dehydration step (90 °C for 30 minutes) prior to SU-8 coating is lower than the normal 120 °C in order to prevent the thermal degradation of the Parylene C. Parylene C is rated to survive for over 10 years at 100 °C in an air environment. However, Parylene C will thermally degrade in air at 125 °C (Systems). It has been observed that some hotplates overshoot the temperature while ramping to the desired set temperature. Therefore, a lower temperature is chosen to ensure that the Parylene C is not exposed to excessive heat.

163

Figure 3-6 Cross-sectional fabrication steps for the test interconnect. Cross-section is taken through the microchamber.

3.2.2.2 Integrated System A similar process as the one described in Section 3.2.2.1 was used to fabricate an interconnect system that included electrolysis and resistive thermal sensors. After substrate was cleaned and prior to Parylene C deposition, the substrate was spin coated with AZ 4400 photoresist (AZ Electronic Materials, Branchburg, NJ) (4 krpm, 40 s, 4 μm) (Figure 3-7A). After exposure, a liftoff mask was produced. Ti/Pt (200 Å/2000 Å) (International Advanced Materials, Spring Valley, NY) was e-beam evaporated and defined using standard liftoff processes by removing the photoresist layer in acetone, isopropyl alcohol, and deionized water (Figure 3-7B). The resistive thermal sensors and electrolysis structures were formed during these steps. Parylene C (Specialty Coating Systems, Inc., Indianapolis, IN) was vapor deposited (2 μm) to 164

electrically isolate the metal traces and to prevent the SU-8 from delaminating from the glass (Figure 3-7C). Photoresist, AZ 4400, was spin coated (4 Îźm, 4 krpm, 40 s), patterned, and used as an etch mask for oxygen plasma removal of Parylene C by reactive ion etching to reveal the contact pads (Figure 3-7D). The process to spin coat and develop the SU-8 is the same as for the test interconnect structure (Figure 3-7E). The entire processes to fabricate the integrated system can be found in Appendix KK. Finally, the septum is filled with PDMS and the microsystem is capped; the steps are described in Section 3.2.2.3.

165

Figure 3-7 Simplified fabrication process for the microfluidic chip with integrated interconnect. Cross section views are through the PDMS septum and microchamber with interdigitated electrodes for an electrolysis pump.

The masks used to fabricate both the 300 m and 500 m channel interconnect can be found in Appendix MM. Only the SU-8 mask was needed to fabricate the test interconnect system discussed in Section 3.2.2.1.

3.2.2.3 Septum Formation The septa on either end of the microchannel were formed after completing the SU-8 fabrication process the SU-8 anchors were filled with PDMS (Figure 3-7G). First, the regions adjacent to the septum (microchambers and microchannel) were filled 166

with deionized water. Water serves as a convenient mask that prevents PDMS prepolymer from flowing into water-masked areas. PDMS is oil-based and is thus immiscible in water, allowing water to serve as a mold for casting PDMS (Chao, et al. 2007). PDMS also has a low surface energy and its hydrophobic property further enhances the water masking technique. A similar water masking technique has been previously demonstrated (Li, et al. 2007, Li, et al. 2008). PDMS was mixed in a 10:1 elastomer-to-curing agent ratio (AR-250 Hybrid Mixer, Thinky Corp., Tokyo, Japan) and then precisely introduced into the septum area through a 20 gauge needle and syringe. PDMS prepolymer was degassed in a vacuum chamber to remove trapped bubbles and then partially-cured (65 °C for 20 minutes) in order to facilitate the final adhesion of the capping layer. To complete the microfluidic system, the top of the microchannel was formed by capping the SU-8 microchannel and PDMS septum with a soda lime glass slide (75 mm x 50 mm x 1 mm, Corning Glass Works, Corning, NY) (Figure 3-7H). First, the glass slide was diced to obtain 10 mm x 50 mm pieces to match the die size. To join the substrate and cover, PDMS was used as an adhesive sealant. A thin, partiallycured PDMS membrane (~300-400 μm thick, 65 °C for 20 minutes) was placed on top of the SU-8 layer to prevent excess PDMS from entering the microchannel below.

PDMS prepolymer was spread on top of the partially-cured PDMS

membrane as an adhesive layer and the glass cover was placed on top of the microchannel assembly. This prepolymer layer further planarizes any remaining thickness non-uniformity in the SU-8 layer. The entire structure was left at room 167

temperature for 24 hours to allow the PDMS to cure completely or rapidly cured at 70 째C for 1 hour. Finally, a 33 gauge stainless steel non-coring syringe needle (Hamilton Company, Reno, NV) was manually inserted into the interconnect (Figure 3-8).

Figure 3-8 Edge view of the needle insertion location. The 33 gauge non-coring needle pierces the PDMS septum through the edge of the system, creating an in-plane connection.

3.2.3 Experimental Methods and Results To optimize the performance of this new microfluidic interconnect method, needle tip types were assessed and compared. The interconnect performance was evaluated using a needle with the most suitable tip type. The robustness and reusability of the needle-septum connection was evaluated by measuring the pull-out forces associated with needle removal. Leakage was examined in both short and long term studies under pressurized operation.

3.2.3.1 Coring vs. Non-coring Needle Tip Type 3.2.3.1.1 Methods 168

Access to a microchannel was gained by piercing a needle through the PDMS septum such that the lumen of the needle established a continuous fluidic path to the microchannel. Stainless steel coring and non-coring needles (Hamilton Company, Reno, NV) (30 gauge) were examined to determine the needle tip type that could maximize the lifetime of the interconnect (Lo, et al. 2006). Needle puncture marks of both coring and non-corning needles through PDMS membranes were compared.

3.2.3.1.2 Results The results of this study were similar to the conclusions presented in Section 2.2.4.3.1.2. The non-corning needle was determined to be best suited to access the microchamber via the septum.

3.2.3.2 Pull-out Force and Reusability 3.2.3.2.1 Theory A needle inserted through a PDMS septum can be modeled as a stiff fiber embedded in a soft matrix. Total pull-out force, the force required to completely remove the needle from the PDMS septum, can be used as a measure of the interface strength between the needle and the septum.

Debonding in this model system can be

achieved by the application of tensile force, torque, or a compressive force, however, only the tension-induced debonding is considered here.

Pull-out forces for

fiber/matrix joints subjected to tension have been explained by Gent and Liu using a modified theory based on the Griffith fracture energy criterion for debonding that also accounts for the work associated with frictional sliding at the debonded interface 169

(Gent and Liu 1991).

The strength of adhesion is associated with the energy

criterion for fracture and can be expressed as:

Equation 3-1 Adhesion Force

F0 2 = 4π ArEm Ga where F0 is the adhesion force, A is the cross-sectional area of the matrix, r is the fiber radius, Em is the Young’s modulus of the matrix material, and Ga is the adhesive fracture energy. The frictional pull-out force, Ff, is expressed as:

Equation 3-2 Frictional Pull-Out Force

F f = 2π r μ pX

where r is the radius of the fiber, µ is the coefficient of friction, p is the compressive stress, and X is the contact length between the fiber and the matrix. This result assumes that the coefficient of friction is constant. If there is a 2% or greater pressure at the fiber tip compared to the Young’s modulus of the matrix, then the product of the coefficient of friction and compressive stress can be represented by a constant value, k = μ p .

Under this condition, the coefficient of friction is

independent of pressure and the theoretical pull-out force due to friction can be simplified (Equation 3-3).

Equation 3-3 Frictional Pull-Out Force Independent of Pressure

F f = 2π rkX

The total pull-out force, F, is a combination of the frictional and adhesion forces (Equation 3-4). 170

Equation 3-4 Total Pull-Out Force

F = F f + F0 = 2Ď&#x20AC; rkX + F0

The equation shows a linear relationship between the pull-out force and the fiber/matrix contact length. The strength of adhesion Ga is found from Equation 3-1 by extrapolating the pull-out force F to the case where X = 0 to obtain the intercept

F0.

3.2.3.2.2 Methods The reusability of the interconnects was assessed by determining the pull-out forces required to remove the needle after multiple insertions into the same septum. For these experiments, a 33 gauge non-coring needle was used and the three septum shapes were each evaluated. The microfluidic system was mounted such that the microchannel was oriented perpendicular to the ground by using a custom laser machined test setup (Mini/Helix 800, Epilog, Golden, CO) (Figure 3-9). The needle was inserted through a hole in the base of the test fixture and then through the PDMS septum to gain access to the microchannel. Pull-out forces were applied to the needle by gradually increasing the brass weights contained in a bag attached to the needle. The bag was preloaded with a 50 g brass weight. Weights were then added incrementally with a 10 minute pause between weight additions to allow the system to equilibrate. The smallest weight used was 1 g which corresponds to a force resolution of 9.8 mN. The total weight attached to the needle was recorded after the needle was pulled out of the septum. The resulting pull-out force was calculated from the final pull-out weight and recorded.

The same interconnect was used

repeatedly in up to 8 trials following the same procedure described above. 171

Figure 3-9 Pull-out test setup. Connector is held perpendicular to the ground by placing the microfluidic device in the Plexiglas test fixture. Weights are added to a container attached to the luer lock portion of the needle. Pull-out force is determined by multiplying gravity by the combined mass of the weights, needle, and container. Image is not drawn to scale.

3.2.3.2.3 Results The pull-out forces for each septum shape were obtained and compared to theoretical values (Figure 3-10). The theoretical maximum (1.19 N) and minimum (0.86 N) pull-out force for the interconnects were obtained from Equation 3-4 using the values in Table 3-2.

The theory can only be applied to the first pull-out event and

corresponding pull-out force; the equation does not account for damage or effects of

172

multiple pull-outs and therefore is not used for comparison in subsequent pull-out events. Table 3-2 Values used for theoretical pull-out force calculation.

Variable Em Ga r μp A

Value 360 kPa - 870 kPa 180 J/m2 - 240 J/m2 101.5 μm 0.1 kPa 2.1 mm2

The wide range in theoretical values is attributed to the variation published values for the Young’s modulus of PDMS (Armani, et al. 1999, Gent and Liu 1991); differences in material properties may arise due to varying processing conditions (e.g. temperature and time for PDMS curing).

Figure 3-10 Pull-out force of the interconnects are compared to the calculated theoretical values.

As predicted in the simple fiber/matrix model, pull-out force increased with interconnect contact length and contact area. It is important to note that Gent and Liu modeled pull-out of stainless steel fibers from PDMS that were embedded into the material before curing (Gent and Liu 1991). The model may not adequately account for the increase in compressive force experienced by the needle due to the 173

displaced material or the irregular path the needle may take. The first pull-out force value for the square, circular, and barbed interconnects may vary from the model because of the inability to precisely determine the contact length and area. The flexible, small diameter needle was manually inserted and the angle and exact location of needle insertion varied between interconnects. It is possible that some needles may have been inserted near or at the glass or SU-8 interfaces. Thus, an incomplete PDMS-to-needle seal would result in which the PDMS would compress the needle against the hard surface instead of completely surrounding it. Furthermore, the needle tears the PDMS as it is pushed through the PDMS matrix, again resulting in uneven compression over the contact area between the needle and PDMS.

The pull-out force for the first removal with respect to contact length (Figure 3-11) and contact area (Figure 3-12) for the circle, square, and barbed interconnect was compared to other pull-out values for published connectors (Table 3-3) (Chiou and Lee 2004, Li and Chen 2003, Yao, et al. 2000). Deviations from the linear behavior predicted by Equation 3-4 may be attributed to the differences in operating principle between each interconnect system and the fiber/matrix materials used.

174

Figure 3-11 Comparison of the interconnect (circular, square, and barbed) and that of other published connectors of the first pull-out force with respect to contact length.

Figure 3-12 Comparison of the interconnect (circular, square, and barbed) and that of other published connectors of the first pull-out force with respect to contact area.

The pull-out force for the different connectors does show a linear relationship between force and length (Figure 3-11), as predicted in the theoretical equation (Equation 3-4).

Also, force increases as contact area increases, as expected. 175

Variations in pull-out force may also be attributed to different setups and fabrication processes. The interconnect designed by Chiou and Lee used a fused silica capillary that was placed in PDMS prepolymer and cured in place (Chiou and Lee 2004). This connector benefited from a perfect match between the PDMS and the capillary, which may have resulted in elevated pull-out force values. The Li and Chen as well as the Yao et al. connectors had a predefined cylinder, which was smaller than their fiber, in the matrix material (Li and Chen 2003). The fiber was inserted into the cylindrical hole, where the matrix material compressed along the entire contact area between the fiber and the matrix.

Furthermore, the Yao et al. matrix was

encompassed in a silicon structure, providing further compression force on the fiber as the matrix was in a limited area (Yao, et al. 2000).

Table 3-3 Summary of Connector Parameters for Published Connectors

(Chiou and Lee 2004, Li and Chen 2003, Yao, et al. 2000) Contact Contact Diameter Fiber Length Area Connector [mm] Material [mm] [mm2]

Matrix Material

Circle 1

0.203

7.010

4.471

Stainless Steel

Sylgard 184

Circle 2

0.203

9.400

5.995

Stainless Steel

Sylgard 184

Square 1

0.203

7.240

4.617

Stainless Steel

Sylgard 184

Square 2

0.203

10.540

6.722

Stainless Steel

Sylgard 184

Barbed 1

0.203

8.030

5.121

Stainless Steel

Sylgard 184

Barbed 2

0.203

8.960

5.714

Stainless Steel

Sylgard 184

176

Chiou 1

0.361

14.990

17.000

Fused Silica

Sylgard 184

Chiou 2

0.361

9.960

11.296

Fused Silica

Sylgard 184

Chiou 3

0.361

6.260

7.100

Fused Silica

Sylgard 184 MRTV1 American Safety Technologies, Inc. MRTV1 American Safety Technologies, Inc.

Yao 1

0.500

0.250

0.393

Glass

Yao 2

0.400

0.250

0.314

Glass

Li 1

1.020

3.000

9.613

Teflon (PTFE)

Sylgard 184

Li 2

0.840

3.000

7.917

Glass

Sylgard 184

The pull-out force data for multiple trials (up to 8 pull-outs) were compared to the performance of other published microfluidic interconnects (Figure 3-13) (Chiou and Lee 2004, Li and Chen 2003, Yao, et al. 2000). The measured pull-out force was consistent over 8 pull-outs though, in some cases, exhibited a slight decrease after the first pull-out. Again, pull-out force was dependent on the contact area between the interconnect fiber and matrix. The pull-out force was normalized with respect to contact area in order to better compare the pull-out force of the existing interconnects (Figure 3-14). Most of the normalized pull-out forces fell within the range of 0.1 to 0.5 N/mm2. 177

Figure 3-14 Comparison of normalized pull-out force with respect to contact area.

Each of the mechanical anchoring schemes for the interconnects (square, circular, barbed) prevented the septum from dislodging from the SU-8 housing. Though all of 178

the interconnect shapes survived multiple uses, the circular shaped anchor may be the most desirable structure for two reasons. First, the circular shape does not contain as many corners that may allow for stress concentration in the SU-8 layer. Secondly, the smooth, circular septa did not contain sharp corners and were easier to fill with PDMS. In the square and barbed septum cavities, the PDMS prepolymer required manual spreading to ensure complete filling of the cavity corners.

Device robustness can be increased by increasing the contact area between the septum and needle.

Therefore, a trade-off between available space and device

integrity can be made to tailor the single interconnect to each microfluidic application.

3.2.3.3 Maximum Operating Pressure 3.2.3.3.1 Methods The operating range of each of the three interconnect designs was determined for both pressurized dyed water and nitrogen gas. Dyed water was used to help visualize fluid flow through the device. Non-coring needles were inserted through the input and output septa.

Dyed water was introduced from the input, through the

microchannel, and to the output needle to ensure a continuous fluidic pathway between the input and output. The output needle was blocked (P-656 luer lock assembly and P-770 plug, Upchurch Scientific, Oak Harbor, WA) and the input needle was attached to a custom pressure testing system (Figure 3-15).

179

Figure 3-15 Test setup for leakage pressure test and prolonged pressure test using pressurized water. Output needle is blocked using an Upchurch plug.

For both pressurized water and pressurized nitrogen gas tests, the applied pressure was slowly increased with a 10 minute pause between pressure increments to allow the system to equilibrate. In the case of pressurized water, leakage was determined when using visual confirmation of device failure. When using pressurized nitrogen gas, the assembly was submerged in deionized water and the escape of nitrogen bubbles was used to determine the point of leakage failure (Figure 3-16). The pressure at which the interconnect started to leak and the location of the leakage were recorded.

180

Figure 3-16 Test setup for leakage pressure test using pressurized N2. Leakage is visualized by N2 bubbles escaping from the submerged the microfluidic chip.

3.2.3.3.2 Results The leakage test identified the maximum operating pressure as well as the failure mode in each case (Table 3-4). The maximum operating pressure was 51 kPa for water operation (barbed interconnect) and 60.4 kPa for N2 operation (circle interconnect). Table 3-4 Summary of Leakage Pressure Results

Port Type

Test Medium

Leakage Pressure [kPa]

Circle

Water

36.27

Square

Water

20.82

Barbed

Water

51.37

Needle insertion at output

Circle

60.4

Between glass and Parylene C interface

Leakage Location Between glass and Parylene C interface Between glass and Parylene C interface

181

Square

25.72

Needle insertion at output

Barbed

15.72

Between glass and Parylene C interface

Two failure modes were observed: (1) the needle insertion point and (2) at the glassParylene C interface. The first failure mode suggests the presence of a leakage path along the needle insertion path or a compromise of the seal between the needle and the PDMS septum (Figure 3-17). The second failure mode is the result of poor adhesion between the glass and Parylene C. The failure modes are further discussed in Section 3.2.3.5.

Figure 3-17 Interconnect failure at the PDMS septum and stainless steel needle interface. A) Water surrounds the needle shaft as PDMS is debonded from the needle and B) seeps from the needle insertion point.

3.2.3.4 Prolonged Pressure Operation 3.2.3.4.1 Methods Long term operation of the interconnects under pressurized water was also evaluated. The same custom pressure testing system was used (Figure 3-15). An interconnect was pressurized at 36 kPa and monitored over a 24 hour period. This pressure value is the average of the maximum operating pressures using pressurized water. 182

3.2.3.4.2 Results The prolonged pressure test demonstrated that the connector can maintain pressurized water at a pressure of 36.2 kPa for over 24 hours. No measurable leakage was observed over this period of time. These interconnects can therefore be used in devices that have applications with long operation times.

3.2.3.5 Failure Modes 3.2.3.5.1 Delamination Needle insertion angle through the input and output septa was observed to be a critical factor in interconnect failure. When the needle was inserted at a downward angle relative to the glass substrate, the tip of the needle would penetrate into the Parylene C layer and could potentially become lodged at the glass/Parylene C interface. If the needle tip did not become embedded under the Parylene C, the Parylene C layer is still damaged when the tip penetrated the layer, resulting in a possible leakage exit path. When a test medium, such as dyed deionized water, was introduced through the needle, failure due to delamination was observed when the fluids seeped under the interconnect structure (Figure 3-18). Subsequent fabrication runs were modified to include an adhesion promotion step with silane-based A-174 prior to Parylene C deposition to prevent Parylene C delamination from the glass substrate. In these interconnects, if the needle was inserted at an angle, the needle tip would scratch the Parylene C but the film would not readily delaminate from the glass surface.

183

Figure 3-18 Interconnect failure due to Parylene C delamination. Dyed water can be seen spreading between the Parylene C and substrate layers.

3.2.3.5.2 Needle Misalignment Misalignment of the needle may occur as the needle penetrates the PDMS septum at an angle parallel to the plane of the substrate. In this case, the needle trajectory would cause the needle tip to collide with the surrounding SU-8 housing and thus block the lumen of the needle.

The needle could be removed and reinserted;

however, it was demonstrated that repeated insertions were associated with decreasing needle pull-out forces. Thus, careful alignment of the needle to the microchamber is necessary to avoid degradation of interconnect strength related to multiple misaligned needle insertions.

Another failure mode occurred when the needle was inserted at an upward angle relative to the glass substrate. The needle could become lodged in the PDMS/glass interface where its circumference was not completely sealed by PDMS. When the needle was inserted immediately adjacent to the glass cap, the needle was not

184

surrounded by PDMS. The small gaps between the needle shaft and the displaced PDMS form low resistance leakage paths (Figure 3-17). A future refinement to this interconnect would be to include a needle insertion guide, either external or integrated, to prevent failure modes resulting from the needle penetrating through the PDMS septum boundaries and into interfaces. The needle guide would direct the needle to the center of the PDMS septum and prevent the needle from being inserted at an angle. For high density microfluidic connections, multiple interconnects can be positioned in a linear array at the edges of a microfluidic chip. This interconnect format would be analogous to ribbon cables and sockets on jumper pins commonly found in the microelectronics industry.

3.2.4 Summary Practical in-plane integrated interconnects that can be batch fabricated with microfluidics have been demonstrated. Needle pull-out force was modeled as debonding in which both frictional and adhesion forces were accounted for. In this model, pull-out force scales with needle/septum contact length and this trend was confirmed in experiments and by comparisons with other published interconnects. The reusability of the interconnects was demonstrated in multiple pull-out trials in which the pull-out force remained constant over 8 trials. In experiments which the interconnects were subjected to incrementally increasing gas or water pressure, the Parylene C-to-glass interface adhesion was found to be critical in preventing leakage. Also needle insertion angle and alignment affected the robustness of this

185

interconnect scheme. No leakage was observed under prolonged exposure to pressurized water.

As demonstrated with theoretical equations, empirical data, and comparison with existing connection schemes, device robustness is proportional to contact area between the septum and needle. The single interconnect design can be scaled to increase or decrease the contact area as needed to fit specific operating pressure criteria.

3.3 Multiple Interconnects The first version, or single interconnect version, of the horizontal interconnect, like many published interconnects, allows only one connection to be made at a time. The second version of the interconnect design will allow many connections to be made simultaneously (arrayed interconnect version); decreasing the footprint of each connector will result in a higher density of connectors within the same space.

3.3.1 Design The arrayed interconnect uses the pin-in-socket approach, similar to that of the single interconnect (Lo and Meng 2008). The high-density design allows multiple needles to simultaneously access corresponding microfluidic channels via their integrated septa. The septa were fabricated by filling an SU-8 septa housing with PDMS prepolymer than allowing it to cure. An array of commercially available non-coring needles was inserted into the device by piercing the septa to establish a fluidic connection. 186

3.3.1.1 Septa Design PDMS was chosen as the septa material due to its compliant and resealing properties. In particular, PDMS septa will seal around the non-coring syringe needles following insertion and removal to avoid formation of any leakage paths. Several versions of the arrayed interconnect were fabricated to demonstrate the versatility of the technique. Differing septa shapes (oval, oval overlap, rectangular) were fabricated on soda lime substrates; the septa shape determined the septa spacing (2.54 mm or 1 mm center-to-center spacing).

Additional features such as 1) merged septa for

higher-density interconnects, 2) sideports to incorporate a second input stream in a single channel, 3) needle guides to align the needle to the septum centers, and 4) SU8 or Parylene C microchannels (Figure 3-19). Electrolysis pumps (interdigitated electrodes) were also integrated into microchannels.

Modular interconnects are

possible (many different combination of the arrayed interconnect) simply by choosing between different septa shapes, septa spacing, merged septa, sideports, needle guides, microchannel material, and metal structures.

Additionally, the

arrayed interconnect can turn existing microfuildic systems into modular components by provide simply and standard connections which allow entire systems to be connected in series or in parallel.

187

Figure 3-19 Schematic indicating key features of our interconnect technology. Here, interconnects with surface micromachined Parylene C channels are shown. Needle guides to help align the needle arrays to the septa. Additional features which can be added to the arrayed interconnect include sideports and interdigitated electrodes for electrolysis or electrochemical sensing.

3.3.1.1.1 Septa Shape Oval, overlapped, and rectangular septa housing shapes were chosen for their ability to retain PDMS without additional anchoring features (Figure 3-20). We previously presented the relationship between septa design and pull-out force(Lo and Meng 2008). The theoretical equations predicted and experimental results verified that pull-out force varies linearly with the contact surface area between the septa and needle. Septa shape did not affect the pull-out force, however, design choices which included a septa locking feature (e.g. a shape which prevented the PDMS septa from being dislodged from the septa housing during needle insertion/ removal) were preferred. Therefore, designs which maximized contact length while minimizing septa width (e.g. footprint) were selected. 188

The square septum of the single interconnect have sharp corners. These locations were found to increase stress concentration in the SU-8 anchor during insertion and was a potential failure locations. Removing corners results in a more robust SU-8 layer. Oval septa also are easier to fabricate compared with structures that contain sharp corners. When PDMS was dropped into the circular structure, the PDMS completely filled the circular structure without any additional manual manipulation. PDMS filling of the square and barbed septa required the use of a sharp tool to help encourage the PDMS to completely fill the septum corners.

This manual

manipulation could introduce bubbles into PDMS prepolymer and was a time consuming process. The corners in the rectangular setpa were rounded to minimize stress concentration. Furthermore, the overlapping septa allowed multiple septum to be filled simultaneously, simplifying the packaging process.

3.3.1.1.2 Septa Spacing The oval septa design has 2.54 mm center-to-center spacing between adjacent septa. Each septum is a distinct unit and therefore must be filled individually. Overlapped and rectangular septa feature denser interconnect packing (1 mm spacing) and simultaneous filling of multiple septa as they are fluidically connected.

The

thickness of the SU-8 septa housing was determined by the practical fabrication limits for thick planar SU-8 layers (time and process complexity) and the needle outer diameter. For 33G needles (203 Îźm OD), a 300 Îźm layer of SU-8 was used.

189

Figure 3-20 Septa configurations used in the arrayed interconnect designs.

Septa spacing, and consequently, the density of the connections were determined by the dimensions of the microfluidic microchannels and integrated components, as well as the septum shape. Two septa spacing arrangements were considered. A 2.54 mm center-to-center spacing design utilized individual oval septa. This spacing was chosen to emulate the standard spacing found in electrical pin packages. Denser interconnects with 1 mm center-to-center spacing were fabricated using overlapping oval septa and connected rectangular septa.

Sideports, as well as converging

microchannel designs, that allow multiple fluids to be introduced into a single input or channel, respectively, were also investigated.

3.3.1.2 Needle Guides The angle of needle insertion is important for proper alignment and to prevent interconnect failure. Needle misalignment may cause the needle to veer off-center during insertion and become lodged against the SU-8 anchor walls. Misalignment in our previous interconnects resulted in blockage of the needle lumen and fluid path (Lo and Meng 2008).

Thus, this improved interconnect incorporates needle

190

alignment structures in the SU-8 housing, which direct the needle through the center of the septum.

A needle guide, which guides the trajectory of the needle, is included in the arrayed interconnect design. The needle guide is incorporated into the SU-8 anchor and starts as a large opening that tapers to a smaller opening (Figure 3-21). A needle inserted through the needle guide will be aligned to pierce the center of the septum.

Figure 3-21 Illustration of the needle guides designed to align the trajectory of the needle for the arrayed interconnect design.

3.3.1.3 Side Ports Side access ports to the microchamber are placed in the arrayed interconnect to increase the number of possible applications. A second input can be fed through the side port to mix two inputs. The side port can be placed in-line with the existing interconnect inputs so that the connections can be made in parallel for both the nonoverlapping and overlapping septa (Figure 3-22A, B). Parallel sideports have several 191

advantages. Needles used to access the main interconnect ports as well as the sideports can be inserted simultaneously. Furthermore, because the sideports are adjacent to the main interconnect septa the SU-8 piece can be an single rectangular structure that contains all of the ports and septa.

Figure 3-22 Parallel sideport structures integrated into arrayed interconnect designs that have A) individual septum, and B) combined septa.

This work demonstrates the functionality of parallel sideports, however, a second design that places the side-port perpendicular could be fabricated to extend the sideport functionality. Perpendicular sideport applications include interrogation of

192

the liquid using sensing elements and introduction/ removal of samples along different points in the flow path (Figure 3-23).

To interrogate the fluid within the microsystem, a needle can be used to pierce the septum into the microchamber, a sensor (e.g. fiber optic cable treated with a fluorescent agent to detect the presence of a molecule) can be fed through the needle shaft. The needle can then be removed leaving the sensor behind; the PDMS will seal around the sensor to prevent leakage. While this design may be less robust and require additional time to connect the sideports compared to its parallel design counterpart,

perpendicular

access

provides

additional

sensing

application

possibilities.

To provide spatial control of sample introduction, several perpendicular sideports can be placed along a microchannel. Different fluids can be fed through, or removed from these locations.

193

Figure 3-23 Illustration of the perpendicular sideports in the arrayed interconnect design.

3.3.1.4 Microchannels The microchannels in the arrayed interconnect design were fabricated using SU-8 or Parylene C.

3.3.1.4.1 SU-8 Microchannels Arrayed interconnects with SU-9 microchannels were fabricated because the SU-8 microchannel was previously tested and optimized in the single interconnect design. The fabrication process for the SU-8 microchannel is simpler and requires fewer steps than microchannels using another material for the microchannel (e.g. Parylene C) because the microchannel, septum, and microchambers can be formed simultaneously. Because the SU-8 components are fabricated together, the channel height is by septa requirements on the thickness of the SU-8 layer. Furthermore, the 194

width of the microchannel was also limited based on the manufacturer’s recommended

aspect

ratio

for

SU-8

structures

(10:1

height

width

ratio(MicroChem)). Therefore, for a 300 μm thick SU-8 layer, a minimum channel width of 30 μm was used.

3.3.1.4.2 Parylene C Microchannels For applications requiring smaller channel dimensions, Parylene C microchannels can be fabricated.

The channel dimensions and Parylene C thickness must be

carefully selected to prevent the channel from collapsing when the sacrificial photoresist within the channel is removed(Yao, et al. 2002). The critical width for microchannels is obtained from the critical length (lcrit) for preventing the collapse and stiction of cantilevers. It is governed by the Young’s modulus of the channel material (E), the material thickness (t), gravity (g), the surface tension between an air-liquid interface (γla), and the contact angle of the material (θc)(Tas, et al. 1996):

Equation 3-5 Critical width to prevent stiction in cantilevers

lcrit

⎛ 3Et 3 g 2 ⎞ =⎜ ⎟ 16 cos γ θ la c ⎠ ⎝

Yao et al. determined a maximum distance of 150 μm between supporting structures in a 4.5 μm thick Parylene C beam. In a channel, the channel walls serve as the supporting structure, therefore, a channel width of 100 μm was chosen, eliminating the need for support posts within the channel(Yao, et al. 2002).

195

The fabrication process for the Parylene C microchannel interconnects is described in Section 3.3.1.7.2. Briefly, to fabricate the microchannel, a 2μm thick layer of Parylene C is vapor deposited. A 4μm layer of photoresist is patterned to the shape of the microchannel interior. Support posts at the microchannel opening are defined. A 4μm layer of Parylene C is vapor deposited. A 4μm layer negates the need for support posts within the microchannel because the layer has enough structural integrity to prevent stiction (Yao, et al. 2002). Another layer of photoresist is spun and patterned to define the microchannel opening. The 4 μm of Parylene C covering the microchannel opening is etched using reactive ion etching (RIE). Finally, the sacrificial photoresist is removed.

3.3.1.4.3 Converging Microchannels Converging microchannel designs were included to demonstrate another interconnect application. Parallel connections can be made and multiple streams of liquid are joined within the microchannel. Both the rectangular and oval septum designs with converging microchannels will be fabricated (Figure 3-24).

196

Figure 3-24 Converging microchannel designs of A) 4 rectangular, B) 8 rectangular, and C) 4 oval overlapping septum designs.

3.3.1.5 Metal Structures 3.3.1.5.1 Electrolysis The electrolysis structure designed in the arrayed interconnect is similar to the single interconnect.

Due to size constraints, only the interconnect designs with oval

microchambers will contain electrolysis structures.

This structure also has

interdigitated leads, but is shaped to fit within the microchannel border.

The

electrolysis structure found within the Parylene C microchannel interconnects is smaller in order to fit both the microchannel opening and the electrolysis structure within the microchamber. The electrolysis structure cannot function if it is covered by the Parylene C used to create the microchannel. Furthermore, the electrolysis structure cannot be placed within the microchannel because 1) the bubbles generated by the electrolysis structure may block microchannel and 2) the pump is not located in a position to pump the liquid from the microchamber.

197

3.3.1.6 Arrayed Interconnect Permeations Microfluidic devices with integrated arrayed interconnects with different septa shapes (oval, oval overlap, or rectangular), number of septa (4 or 8), septa spacing (2.54 mm or 1 mm), microchannel material (SU-8 or Parylene), and optional sideports were designed and fabricated. Some devices also incorporated converging channels and metal structures to demonstrate the versatility of this interconnect technique. A representative arrayed interconnect with Parylene C microchannels, oval overlap septa with 8 inputs and outputs, sideports, and needle guides is shown in Figure 3-20.

Figure 3-25 Fabricated arrayed interconnect with Parylene C microchannels and sideports. Salient features of the arrayed microfluidic system with integrated interconnects are highlighted. External access via needles is not shown in these photographs.

Table 3-5 summarizes the interconnect combinations which were fabricated. Images of these interconnects can be found in Table 3-6 (SU-8 microchannel, no metal), Table 3-7 (SU-8 microchannel with metal), Table 3-8 (Parylene C microchannel, no metal), and Table 3-9 (Parylene C microchannel with metal). Table 3-5 Summary of fabricated arrayed interconnect combinations.

198

Channel Type SU-8 SU-8 SU-8 SU-8 SU-8 SU-8 SU-8 SU-8 SU-8 SU-8 SU-8 SU-8 SU-8 SU-8 SU-8 Parylene C Parylene C Parylene C Parylene C Parylene C Parylene C Parylene C

# Septa 4 4 4 4 4 4 4 4 4 8 8 8 8 8 8 4 4 4 4 8 8 8

Septa Type Oval Oval Oval Oval Oval Overlap Oval Overlap Oval Overlap Rectangular Rectangular Oval Oval Oval Overlap Oval Overlap Rectangular Rectangular Oval Oval Oval Overlap Oval Overlap Oval Oval Overlap Oval Overlap

Converging Channels Sideports N N N Y N N N Y N Y N N Y N Y N N N N N N N N Y N N Y N N N N N N Y N Y N N N N N Y N N

Metal N N Y Y N N N N N N Y N N N N Y Y N N Y N N

3.3.1.7 Fabrication The fabrication processes for both the SU-8 and Parylene C microchannel interconnects is discussed below. The SU-8 interconnect has a simpler fabrication process than the Parylene C interconnects. The mask files for SU-8 microchannel interconnects, SU-8 microchannel interconnects with metal structures, Parylene C microchannel interconnects, and Parylene C interconnects with metal structures can be found in Appendix OO, Appendix PP, Appendix QQ, and Appendix RR, respectively.

199

The fabrication of the SU-8 microchannel is similar to the fabrication of the single interconnect device. The fabrication steps for the arrayed interconnect structures which contain either the SU-8 microchannel or the Parylene C microchannel are presented below.

3.3.1.7.1.1 Arrayed Interconnect, SU-8 Microchannel without Metal To fabricate the arrayed interconnect designs that have a SU-8 microchannel and no metal features, first obtain a 3 inch (76 mm) soda lime substrate (Silicon Quest International, Santa Clara, CA) (Figure 3-26A). Treat the wafer with A-174, a Parylene C adhesion promoter. Next, vapor deposit 2 μm of Parylene C (Specialty Coating Systems, Inc., Indianapolis, IN) on one side of the wafer (Figure 3-26B). The Parylene C layer provides mechanical support to prevent the SU-8 from delaminating from the glass surface. The SU-8 layer (300 μm) is fabricated using a two-step spin-coating method using SU-8 2100 (MicroChem Corp., Newton, MA) (Figure 3-26C). The first coat results in a 200 μm (1.5 krpm, 30 sec). The layer is then left at room temperature for 3 hours to improve planarization. The first layer is then softbaked at 90 °C (ramped at 3 °C/ min from room temperature to 90 °C) for 90 minutes. The layer was then allowed to slowly cool to room temperature in order to prevent the formation of thermal stress cracks in the SU-8. Next, the planarization layer of SU-8 was applied (100 μm, 3krpm, 30 sec). Again, the layer was left at room temperature and then softbake for 3 hours using the same softbake and ramping scheme was used for the first layer. The SU-8 was then patterned (600 mJ/cm2) and post-exposure baked at 90 °C (3°C/ min ramp) for 30 minutes. The SU-8 layer was 200

developed using SU-8 Developer (MicroChem Corp., Newton, MA); developing requires approximately 30 minutes (Figure 3-26D). The structure is then hardbaked for 30 minutes at 90 째C (3 째C/ min ramp) and allowed to slowly cooled to room temperature. The wafer is then diced to separate the various structures. The septa are filled and the setup is capped with a glass slide, these procedures were previously described in Section 3.2.2.3 (Figure 3-26E, F). The masks used to fabricate these structures are presented in Appendix OO. A detailed fabrication process for the arrayed interconnect structures with SU-8 microchannels can be found in Appendix SS.

Images of the fabricated arrayed interconnects with SU-8 microchannels without metal structures can be found in Table 3-6.

Figure 3-26 Fabrication steps for the SU-8 wafer that contains interconnect designs that do not require metal structures. The cross-section is taken horizontally along the microchannel. The SU-8 is

201

lighter in color at step D because after SU-8 patterning, no SU-8 exists along the cross-section line. However, the lighter SU-8 represents the SU-8 material remaining surrounding the needle guide and microchannel in order to better visualize the process flow after step D. This process flow is used for designs shown in Figure 6-37A.

202

Table 3-6 Summary of the SU-8 microchannel arrayed interconnects which were fabricated. These interconnects do not have any metal structures.

Channel Type, # Septa, Septa Type

SU-8, 4, Oval

Converging Channels

Sideports

Metal

Image

10 mm

SU-8 4 Oval

SU-8 4 Oval Overlap

203

Table 3-6 Summary of the SU-8 microchannel arrayed interconnects which were fabricated. These interconnects do not have any metal structures. (cont)

Channel Type, # Septa, Septa Type

Converging Channels

Sideports

Metal

SU-8 4 Oval Overlap

SU-8 4 Rectangular

SU-8 8 Oval

Image

10 mm

204

Table 3-6 Summary of the SU-8 microchannel arrayed interconnects which were fabricated. These interconnects do not have any metal structures. (cont)

Channel Type, # Septa, Septa Type

Converging Channels

Sideports

Metal

SU-8 8 Oval Overlap

SU-8 8 Rectangular

Image

10 mm

205

3.3.1.7.1.2 Arrayed Interconnect, SU-8 Microchannel with Metal The fabrication for the arrayed interconnects which have SU-8 microchannels and metal structures are similar to the process described in Section 3.3.1.7.1.1. The additional steps for these structures are as follows.

Prior to the Parylene C

deposition, the wafer is spin-coated with AZ 4400 photoresist (AZ Electronic Materials, Branchburg, NJ) (4 krpm, 40 s, 4 μm) (Figure 3-27B). The photoresist is patterned and developed to create a lift-off layer for the metal (Figure 3-27C). Ti/Pt (200 Å/2000 Å) (International Advanced Materials, Spring Valley, NY) is evaporated onto the wafer surface using an electron-beam metal deposition system (Figure 3-27D). The underlying photoresist is dissolved using acetone and lifts-off portions of the metal layer (Figure 3-27E). The wafer is cleaned using oxygen plasma (100W, 100mT, 5 minutes) to remove any remaining photoresist residue. The wafer is treated with A-174, a Parylene C adhesion promoter and then coated with 2 μm of Parylene C (Specialty Coating Systems, Inc., Indianapolis, IN) to provide mechanical support of the SU-8 and to electrically isolate the metal structures (Figure 3-27F). The wafer is spin-coated with AZ 4400 photoresist (4 μm, 4 krpm, 30 sec) (Figure 3-27G). The photoresist is patterned and developed to create a Parylene C etch mask. The Parylene C coating the electrode pads and electrolysis structures is removed using oxygen plasma (Figure 3-27H). The photoresist is stripped from the wafer using acetone, isopropyl alcohol, and DI water (Figure 3-27I). The steps to fabricate the SU-8 layer, dice the wafer, form the septum, and cap the microsystem are the same as those in Section 3.3.1.7.1.1 (Figure 3-27J-M).

The masks used for this fabrication process can be found in Appendix PP. A complete fabrication process for these structures can be found in Appendix TT.

Images of the fabricated arrayed interconnects with SU-8 microchannels and metal structures can be found in Table 3-7.

Figure 3-27 Fabrication steps for the SU-8 wafer that contains interconnect designs that do not require metal structures. The cross-section is taken horizontally along the microchannel. The SU-8 is lighter in color at step K because after SU-8 patterning, no SU-8 exists along the cross-section line. However, the lighter SU-8 represents the SU-8 material remaining surrounding the needle guide and microchannel in order to better visualize the process flow after step D. This process flow is used for designs shown in Figure 6-37B.

Table 3-7 Summary the SU-8 microchannel arrayed interconnects with metal, which were fabricated.

Channel Type, # Septa, Septa Type

SU-8 4 Oval

Converging Sideports Channels

Metal

Image

10 mm

SU-8 4 Oval

209

Table 3-7 Summary the SU-8 microchannel arrayed interconnects with metal, which were fabricated. (cont).

Channel Type, # Septa, Septa Type

SU-8 8 Oval

Converging Sideports Channels

Metal

Image

10 mm

210

3.3.1.7.2 Parylene C Microchannel The fabrication of the arrayed interconnect structures that contain a Parylene C microchannel is more complicated process than its SU-8 microchannel counterpart because two layers of Parylene C are required to create the microchannel. The fabrication steps for the Parylene C interconnect designs are described below.

3.3.1.7.2.1 Arrayed Interconnect, Parylene C Microchannel without Metal The arrayed interconnect which has a Parylene C microchannel is fabricated on a 3 inch (76 mm) soda lime wafer

(Silicon Quest International, Santa Clara, CA)

(Figure 3-28A). The wafer is treated with a Parylene C adhesion promoter, A-174. Next, 2 μm of Parylene C (Specialty Coating Systems, Inc., Indianapolis, IN) is vapor deposited on one side of the wafer (Figure 3-28B). Photoresist, AZ 4400 was spin-coated (4 μm, 4krpm, 40 sec) and patterned to define the interior shape of the Parylene C microchannel (Figure 3-28C,D). A second layer of Parylene C (4 μm) is vapor deposited over the photoresist and initial Parylene C layer (Figure 3-28E). The two layers of Parylene C are then annealed together under vacuum at 160 °C (Figure 3-28F). Parylene C will thermally degrade at temperatures above 100 °C in air, however, it can withstand higher temperatures under vacuum (Systems).

Next, a layer of photoresist, AZ 4903 (AZ Electronic Materials, Branchburg, NJ) is spin-coated (6 μm, 4 krpm, 40 s) (Figure 3-28G). The photoresist is patterned in order to create a Parylene C etch mask (Figure 3-28H). The Parylene C coating the 211

channel opening is etched using oxygen plasma (Figure 3-28I). The photoresist is then stripped using an acetone, isopropyl alcohol, and DI water rinse (Figure 3-28J).

The SU-8 layer is applied, exposed, and developed using the two-step process described in Section 3.2.2.1 (Figure 3-28K,L). The individual arrayed interconnect structures are diced apart using a dicing saw.

The structures are placed in an

isopropyl alcohol bath (at room temperature) for 3 days to remove the sacrificial photoresist inside the channel (Figure 3-28M). The septa are filled and the entire structure is capped using the process described in Section 3.2.2.3 (Figure 3-28N,O). The masks used to fabricate the arrayed interconnect, Parylene C microchannel setups can be found in Appendix QQ. A detailed fabrication process is presented in Appendix UU.

Images of the fabricated arrayed interconnects with Parylene C microchannels without metal structures can be found in Table 3-8.

212

Figure 3-28 Process flow for Parylene C microchannel arrayed interconnect designs. The crosssection line is taken along the microchannel. Translucent SU-8 represents SU-8 which surrounds a component but not within the cross-sectional line. The translucent SU-8 is included to aid in illustrating the fabrication process. This fabrication process is used for designs shown in Figure 6-38A.

213

Table 3-8 Summary of the Parylene C microchannel arrayed interconnects which were fabricated. These interconnects do not have any metal structures.

Channel Type, # Septa, Septa Type

Converging Sideports Channels

Metal

Parylene C 4 Oval Overlap

Parylene C 8 Oval Overlap

Image

N 10 mm

214

3.3.1.7.2.2 Arrayed Interconnect, Parylene C with Metal The fabrication process for the arrayed interconnect with Parylene C microchannels and integrated metal components is the most complex of all of the setups. Additional steps are needed to create the metal components and etch the Parylene C covering the metal.

The fabrication starts with a soda lime substrate (76 mm or 3 inch wafer, Silicon Quest International, Santa Clara, CA) (Figure 3-30A).

2 μm of Parylene C

(Specialty Coating Systems, Inc., Indianapolis, IN) is vapor deposited on one side of the wafer (Figure 3-30B).

Photoresist, AZ 4400 (AZ Electronic Materials,

Branchburg, NJ), is spin coated (4 krpm, 40 s, 4 μm) on the Parylene C layer (Figure 3-30C). The photoresist is exposed and patterned to form a Parylene C etch mask (Figure 3-30D). The Parylene C is etched using oxygen plasma in order to access the substrate and deposit the metal electrodes (Figure 3-30E). The electrodes must be formed on the substrate in order to create robust connections that can withstand electrical connections. The photoresist is then stripped from the surface using an acetone, isopropyl alcohol, DI water rinse (Figure 3-30F).

Another photoresist layer, AZ 4400, is spin-coated (4 μm, 4 krpm, 40 s), exposed, and developed to create the metal lift-off layer (Figure 3-30G). Ti/Pt (200 Å/3000 Å) (International Advanced Materials, Spring Valley, NY) is evaporated using an electron-beam deposition system (Figure 3-30H). The photoresist lift-off layer is 215

then removed using acetone to remove the unnecessary metal (Figure 3-30I). Any acetone or photoresist residue is cleaned using oxygen plasma. Current (0.3 mA) is applied to the electrolysis structures to verify functionality (e.g. determine if the electrodes are shorted, determine if electrodes will delaminate, visually verify bubble formation).

AZ 4400 is spin coated (4 μm, 4 krpm, 40 s) and pattern to define the interior of Parylene C microchannel (Figure 3-30J-K). The second layer of Parylene C (4 μm) is vapor deposited (Figure 3-30L). The two layers of Parylene C are annealed together under vacuum at 160 °C (Figure 3-30M).

AZ 4903 photoresist (AZ Electronic Materials, Branchburg, NJ) is spin-coated (6

μm, 4 krpm, 40 s), exposed and patterned in order to create a Parylene C etch mask (Figure 3-30M,N).

The Parylene C coating the channel opening, electrolysis

structure, and electrode pads is etched using oxygen plasma (Figure 3-30O). The photoresist is then stripped using an acetone, isopropyl alcohol, and DI water rinse (Figure 3-30P). Again, electrolysis functionality is verified to determine if any Parylene C coating remains on the metal structures.

Again, the SU-8 layer is applied, exposed, and developed using the two-step process previous described in Section 3.2.2.1 (Figure 3-30Q,R).

All of the electrolysis

structures are tested for a final time prior to packaging to verify their functionality (Figure 3-29). 216

Figure 3-29 Time-lapsed images of the working electrolysis structures prior to packaging. 0.3 mA of current was applied to the electrodes. Bubble formation was visually confirmed.

The arrayed interconnect structures are diced apart using a dicing saw and then placed in an isopropyl alcohol bath (at room temperature) for 21 days to remove the sacrificial photoresist inside the channel (Figure 3-30S). The septa are filled and the entire structure is capped using the process described in Section 3.2.2.3 (Figure 3-30T,U).

The masks used to fabricate the arrayed interconnect, Parylene C

microchannel setups can be found in Appendix RR. A detailed list of the steps needed to fabricate arrayed interconnects with Parylene C microchannels and metal components can be found in Appendix VV. 217

Images of the fabricated arrayed interconnects with Parylene C microchannel and metal structures can be found in Table 3-9.

218

Figure 3-30 Process flow for Parylene C microchannel arrayed interconnect designs. The crosssection line is taken along the microchannel. Translucent SU-8 represents SU-8 which surrounds a component but not within the cross-sectional line. The translucent SU-8 is included to aid in illustrating the fabrication process. This fabrication process is used for designs shown in Figure 6-38B.

219

Table 3-9 Summary of the Parylene C microchannel arrayed interconnects with metal structures, which were fabricated.

Channel Type, # Septa, Septa Type

Parylene C 4 Oval

Converging Sideports Channels

Metal

Image

10 mm

Parylene C 4 Oval

220

Table 3-9 Summary of the Parylene C microchannel arrayed interconnects with metal structures, which were fabricated. (cont)

Channel Type, # Septa, Septa Type

Parylene C 8 Oval

Converging Sideports Channels

Metal

Image

10 mm

221

A first layer of Parylene C is deposited prior to the metal deposition layer because it simplifies the Parylene C etching step. If the metal was deposited prior to the first Parylene C coating, the Parylene C etching used to expose the microchannel opening, electrolysis opening, and electrode openings would be through different thicknesses of Parylene C. The microchannel opening would be covered with 4Îźm of Parylene C while the electrolysis and electrode covered with 6Îźm. Controlling the etch to expose all of the metal without damaging the microchannel would be difficult, therefore the deposition of the metal layer is moved in the fabrication process. However, the electrodes must be in contact with the substrate so that the electrical probes will not damage the electrodes. If the electrodes were placed on Parylene C, the probes would be able to scratch or punch through the metal layer because the underlying Parylene C layer is soft. Isopropyl alcohol is used to remove the sacrificial photoresist within the microchannel because acetone has been observed to cause SU-8 delamination of initial test structures. Additionally, acetone has been previously demonstrated to be an effective method of removing SU-8 residue but causes delamination of SU-8 when the acetone rinse is not carefully controlled (Agarwal, et al. 2005). Removing the sacrificial photoresist from within the microchannel requires several days of soaking in isopropyl alcohol; it is important to ensure that the isopropyl alcohol bath does not completely evaporate and leave isopropyl alcohol residue within the

222

microchannel.

The residue may block the microchannel and prevent it from

functioning.

3.3.1.8 Needle Array The needles were housed in channels (0.0135’’, 342.9 μm) spaced 2.54 mm or 1 mm apart, center-to-center. Two different types of needle arrays were fabricated: shared input (Figure 3-31a-c) and separated inputs (Figure 3-31d-e).

Figure 3-31 Needle arrays which provide shared or separate input capabilities to needles and thus microchannels. a) 4 shared 4 needles, 1 mm spacing, b) 4 shared needles, 2.54 mm spacing, c) 8 shared needles, 1 mm spacing, d) 4 separate needles, 1 mm spacing, and e) 8 separate needles, 2.54 mm spacing. The scale bar represents 10 mm.

3.3.1.8.1 Shared Input Needle Arrays The shared input needle array was fabricated by drilling channels (0.0135’’ O.D., 80G drill bit) partially through a Plexiglas block. A larger diameter channel (0.04’’ O.D., 60G drill bit) was drilled through the side of the block that intersected all of 223

the smaller channels. A 10-32 threaded hole allowed connection of a liquid or gas source to the needle array with conventional fittings. Commercially available 33G non-coring needles (21033A Point Style 2, Hamilton Company, Reno, NV) were carefully placed in each of the 80G holes and affixed using epoxy.

In this

configuration, pressurized media was applied to all of the needles simultaneously; however, needle arrays with separate access to each needle were also fabricated.

3.3.1.8.2 Separate Input Needle Array A custom-made Plexiglas mold was used to fabricate a needle array with individual needle access. Individual needles will be encased in liquid plastic casting resin with the distance between needles (2.54 mm or 0.1’’ center to center and 1mm or 0.04’’ center to center) the same distance as between the non-overlapping and overlapping interconnects (center to center), respectively. Silicone tubes were attached to each needle, providing separate input into each needle.

The needle array is made by using a custom-made jig to align the needles and provide the mold for the surrounding plastic resin (Figure 3-32).

The jig is

comprised of four levels. The bottom level serves as the base for the plastic resin mold and has an etched outline of the holes cut from the middle two layers. The two middle layers align the needles. The middle layers have a rectangular hole cut from the jig to allow the plastic resin to coat around the needles. Each middle piece has grooves cut into a surface to designate the needle locations. The needle extends from one edge of the piece to 18.6 mm (0.732 inches) into the piece. The length of the 224

groove and placement of the holes results in the beveled end of the needle extending 10 mm (0.394 inches) from the resin block on one side, and a 5 mm (0.197 inches) long needle base extending from the other side of the resin block. The needles are aligned by sliding the needle along the groove until its progress is stopped when it reaches the end of the groove. A thinner rectangular hole is cut from the layer to prevent the plastic resin from wicking along the needle/groove interface and clogging the end. The top layer to the jig contains an outline of the holes found in the middle layers as well as two holes. Once the four jig layers and needles are assembled, liquid plastic resin is poured into one hole with the other hole serving as an outlet for the displaced air. The entire jig is held together using four standard 1032 screws located at the corners of the jig. When the resin is cured, the jig can be disassembled to remove the molded needle array. The jig can then be reused to make more needle arrays.

225

Figure 3-32 Custom-made laser machined molds for creating an array of needles (4 or 8). All layers are made of acrylic and are color coded to illustrate assembly.

3.3.1.9 Experimental Methods and Results 3.3.1.9.1 FEM Analysis of Stress Distribution 226

3.3.1.9.1.1 Methods Finite element analysis and modeling estimated the stress on the septa as the needles were inserted. The oval overlap septa were chosen as the model because this septa design was the simplest design to fabricate and implement, and therefore, the most likely candidate for future use.

Additionally, the septa were combined in one

complete piece; any stress, induced during insertion, which may affect neighboring septa/needle pairs, will be visible in this design. The stress distribution in the PDMS septa set a practical limit to the achievable needle density by dictating the minimum spacing between the needle path and SU-8 housing. A suggested design rule is a minimum distance between the needle shaft and the SU-8 housing equaling twice the length required to dissipate 36.8% of the maximum stress value.

The stress distribution within the septa was modeled at three needle insertion points: 1) as needles touched the surface of the septa, 2) after the needles pierced the septa and are partially inserted, and 3) after needles were fully inserted. In the model, the surface area of the septa which would normally be in contact with the septa housing (e.g. SU-8 anchor, device substrate, and device cap) was fixed to represent the packaging. The bonding strength between the PDMS and SU-8 or Parylene C coated substrate does not preclude the PDMS from delaminating from either surface, however, debonding between the PDMS and SU-8 or substrate boundaries is a dynamic interaction which is difficult to approximate in the model. The septa faces not in contact with the SU-8 housing, substrate, or packing (e.g. faces through which the needle can enter or exit) were not constrained. The insertion force at the needle 227

tip and friction force along the needle shaft were applied using force data obtained experimentally with a Bose 3100 ElectroForce mechanical fatigue test instrument. The modeling results were also compared to real-time photoelastic stress images.

3.3.1.9.1.2 Results Finite element modeling of both a single septum and multiple septa designs showed the stress concentration remained localized around the needle. A radial stress pattern was observed at the needle tip pre-puncture, and was asymmetric during insertion due to the beveled tip of the needle.

Post insertion, the stress was uniformly

distributed along the needle shaft and did not appear to affect neighboring septa (Figure 3-34). The maximum stress was observed at the needle/septa interface; stress decayed exponentially with respect to distance from the needle. The distance over which the stress decayed to 1.35 x 105 N/mm2 (36.8% of the maximum stress, 3.63 x 105 N/mm2) was approximately 60 Îźm. Measurements were taken at the center of the septa Figure 3-33.

Figure 3-33 Centerline of FEM analysis of needle insertion induced stress in arrayed interconnect. 228

The FEM results showed the stress distribution for ideal conditions where: 1) the needles are all aligned within the septa, 2) the needles do not deviate from a straight path, 3) the needles maintain a uniform distance from one another, 4) all of the needles are the same length, 5) all of the needle tips (e.g. the bevels) are orientated in the same direction, and 6) the needle insertion force is only directed parallel to the needle shaft. The resultant stress distribution identified the minimum dimensions necessary for the interconnect design to prevent unwanted stress interference on the SU-8 septa housing or adjacent septum/needle pairs (120 Îźm).

Figure 3-34 FEM images of stress distribution within septa during needle insertion, a) pre-puncture, b) partial puncture, and c) complete insertion.

The arrayed septa and needle design allows for multiple simultaneous macro-tomicro connections to be established in a microfluidic device. PDMS is an excellent choice as a septa material. The compliant nature of PDMS is beneficial for three reasons, 1) it allows the septa to deform around the needle, providing a reliable and robust seal for multiple use; 2) the displaced septa material during insertion returns to the original state after the needle are removed, sealing access to the device interior; and 3) allows a high density of needles to be inserted simultaneously without insertion stresses interfering with neighboring needles. 229

FEM results showed needle insertion induced stress within the septa dissipates exponentially with respect to distance from the needle shaft. The stress decayed to 36.8% of the maximum value within 60 μm. To prevent the stress from extending to the SU-8 anchor, a minimum distance between the needle shaft and SU-8 housing of 120 μm is recommended. The rectangular septa design, the one having the smallest spacing between the needle and SU-8 anchor, had a septum width of 500 μm. Insertion of a 33G needle with an outer diameter of 203 μm left approximately 150

μm of PDMS between the needle and SU-8 anchor components. Denser rectangular septa are possible, however, additional space may be prudent to account for any deviations in the needle path (i.e. needle misalignment) from the septa center.

3.3.1.9.2 Photoelastic Stress 3.3.1.9.2.1 Methods PDMS is a photoelastic material; stresses in the PDMS during needle array insertion and removal can be visualized using polarized light. The principle stresses (σx, σy) can be visually observed as a phase difference (Δ) that is dependant on the wavelength (λ), the material stress-optical coefficient (C), and material thickness (h)(Timoshenko and Goodier 1970). Equation 3-6 Phase difference due to stress

Δ=

2πh

C (σ x − σ y )

230

PDMS slabs were pierced using a single needle and needle array to visualize stresses in the material.

The sample was placed between two polarizing plates and

illuminated with a broadband light source positioned below the stack. The polarizing plates were rotated to an orientation which provided the largest contrast in stressed versus non-stressed areas (Figure 3-35). Low stress areas appear as a white haze where higher stress areas exhibit a rainbow effect. Photoelastic images were taken during initial needle puncture and partial needle insertion into the PDMS sample to compare with FEM results.

Figure 3-35 Experimental setup to visualize photoelastic stress.

3.3.1.9.2.2 Results In order to observe the photoelastic stress, larger needles (single needle: 18G, needle array: 27G) were necessary to enhance the visible stress during needle insertion. Photoelastic stress using 33G needles was not visible with the current imaging setup. 231

From the FEM analysis, the visible stress within the PDMS would extend approximately 100 Îźm from the needle; the recording camera could not resolve this distance, therefore, larger diameter needles were necessary.

Stress concentrations were visible along the needle shaft and as a plume at the needle tip during insertion. Photoelastic visualization of insertion of a 2.54 mm spaced needle array demonstrated that the stress distribution from one needle shaft did not overlap with that of a neighboring needle.

This suggests stresses from each

needle/septum pair do not affect the stress of the neighboring pairs. These results are similar to the FEM prediction for stress distribution (Figure 3-36); however, a direct comparison cannot be made due to the difference in needle size and variation in needle orientation in hand made needle arrays.

Figure 3-36 Photoelasic stress in PDMS from needle insertion for a single (18G) and needle array (four 27G). Yellow arrows indicate areas of stress.

232

3.3.1.9.3 Insertion Test 3.3.1.9.3.1 Theory The force required to pierce a PDMS sample can be modeled using equations which calculate the force required for a needle to puncture a piece of tissue. The total insertion force can be seen as a combination of forces that occur before (stiffness force) and after (frictional force and cutting force) the needle punctures the material (Equation 3-7) (Simone and Okamura 2002).

Equation 3-7 Insertion Force of a Needle into a Membrane

Axial Insertion Force = Stiffness Force + Frictional Force + Cutting Force

Stiffness force, or the force the material exerts on the material as the material deforms, is present after the needle touches the material and prior to the needle tip entering the material. The stiffness force disappears when the needle punctures the material (Equation 3-8, Figure 3-37). Note, z2 is less than z3 because the membrane relaxes after it has been pierced. The stiffness force can be modeled as a non-linear spring, however, it has been shown that a second-order polynomial may provide a better fit to the data and a lower root mean square (rms) value (Simone and Okamura 2002).

Equation 3-8- Stiffness Force of a Membrane Deflecting

233

f stiffness

z < z1 ⎧ 0 ⎪ = ⎨a1 z + a2 z z1 ≤ z ≤ z2 ⎪ 0 z > z3 ⎩

z = position of needle tip z1 = position of membrane prior to needletouch z2 = position of membrane immediately before needle pierces membrane z3 = position of membrane after membrane has been punctured

Figure 3-37 Illustration of membrane behavior during pre-puncture, puncture, and post-puncture stages of needle insertion.

The frictional force is the force exerted on the needle as it passes through the material.

Frictional force is a combination of material adhesion and damping

between the material and the needle shaft. It can be modeled using a modified Karnopp Model (Equation 3-9) (Karnopp 1985, Richard, et al. 1999).

Equation 3-9- Frictional Force of a Needle Through a Membrane

234

z& ≤ −Δ2 v ⎧ Cn sgn( z& ) + bn z& ⎪ max( D , F ) −Δv & ⎪ n a 2 < z ≤0 f friction = ⎨ Δv ⎪ min( D p , Fa ) 0 < z& < 2 ⎪⎩C p sgn( z& ) + bp z& z& > Δ2v Cn , C p = negative & positive values of dynamic friction bn , bp = negative & positive values of damping coefficient Dn , D p = negative & positive values of static friction z& = relative velocity between needle & material ± Δ2v = value below which velocity is considered to be zero Fa = sum of non − frictional forces applied to the system The final force is the cutting force (Equation 3-10) (Simone and Okamura 2002). This is the force required for the needle tip to slice through the material. Ideally, cutting force is constant as the needle progresses through the material and is independent of needle depth into the material.

Equation 3-10- Cutting Force of a Needle Piercing a Membrane

⎧ 0 ntip ≤ z2 , t < t p f cutting = ⎨ ⎩ R ntip > z3 , t ≥ t p R = constant ntip = position of needle tip z2 , z3 = location of membrane, as defined for f stiffness t = time t p = time of puncture

3.3.1.9.3.2 Methods

235

The force required to insert and remove a single needle or needle array into a PDMS sample (thickness 2 mm Âą 0.1 mm) was measured using a Bose 3100 ElectroForce mechanical fatigue test instrument and custom-made laser-cut Plexiglas jigs. Measuring the stiffness, frictional, and cutting forces can be empirically obtained and compared to the theoretical values described in the above equations. The load-cell in the Bose machine can provide real-time measurements of the force exerted on a PDMS sample during the different stages of the needle insertion can isolate the stiffness and frictional forces. The cutting force is calculated by subtracting the frictional force from the total force measured after membrane puncture.

The insertion force to insert 1, 4 and 8 needles into the septum will be measured using a Bose 3100 ELF machine.

A custom-made jig is used to measure the

insertion force for multiple needles (Figure 3-38). The jig holds a PDMS membrane in place as the multiple needles are inserted into the membrane. For simplicity, a membrane is used instead of 4 or 8 individual PDMS pieces. Individual pieces are a more true-to-life representation of the arrayed interconnect system, however, the membrane is supported such that the stress on the membrane from each needle is independent of its neighbor. The drawing used to create the jigs can be found in Appendix WW.

The measured insertion force will be compared to the theoretical values. Theoretical values can be calculated in a manner similar to those discussed in Section 2.3.1.1.7.1.

236

Results using a single needle will be compared to the needle arrays to determine how the insertion force varies with respect to the number of needles.

Figure 3-38 Custom-made laser-machined jigs used to measure insertion force through PDMS using a A) 4 or B) 8 needle assembly.

The jigs held the sample PDMS piece between two Plexiglas plates. The plates had 2.54 mm spaced through holes (1, 4 or 8 holes) which guided the corresponding needles arrangements through the PDMS sample piece. The jig was attached to a load cell at the base of the Bose instrument; needles were lowered at a constant rate and the force required to puncture the PDMS sample (insertion force) and to remove the needles from the sample (pull-out force) were recorded.

Insertion force can be described as a combination of pre-puncture and post-puncture forces. The pre-puncture force, stiffness force (fstiffness), is the force due to material deformation. Post-puncture force is a combination of the force required to push a needle through the PDMS material (fcutting) and the friction force (ffriction) between the

237

needle shaft and the PDMS(Abolhassani, et al. 2007, Okamura, et al. 2004). Thus, the insertion force is expressed as:

Equation 3-11 Insertion force equation

f insertion = f stiffness + f cutting + f friction

The force required to remove the needle (pull-out force) is a combination of frictional and debonding forces (Gent and Liu 1991):

Equation 3-12 Removal force equation

f pull â&#x2C6;&#x2019; out = f debonding + f friction

A discussion of the pull-out force was previously presented for a single interconnect case(Lo and Meng 2008). In summary, Gent and Liu modeled debonding between a fiber (i.e. the needle) embedded in a matrix (i.e. the septa) using a modified theory based on the Griffith fracture energy criterion (Gent and Liu 1991). The debonding force is a function of the cross-sectional area of the matrix, fiber radius, the Youngâ&#x20AC;&#x2122;s modulus of the matrix, and the adhesive fracture energy between the matrix and the fiber. The frictional force varies linearly with respect to the coefficient of friction between the fiber and matrix, the compressive stress, and the contact area between the fiber and matrix.

238

The stiffness force can be determined by examining the resulting force versus displacement graph generated by the Bose machine. It has been reported that the force versus displacement curve will start at zero and reach a negative peak immediately before the initial puncture event. The lowest point corresponds to the maximum stiffness force.

The frictional force is determined by inserting the needle completely into the membrane. The needle is displaced in a sinusoidal pattern, however, the needle tip must remain on one side of the membrane (Figure 3-39) (O'Leary, et al. 2003, Simone and Okamura 2002). The measured force is purely the frictional force between the material and the needle shaft.

Figure 3-39 Illustration of needle tip displacement relative to the PDMS membrane for frictional force measurements.

The cutting force is the difference between the force measured by the Bose machine after puncture and the frictional force determined by the methods described above. The cutting force may also be verified by puncturing the membrane multiple times through the same hole.

239

As described in the Section 2.2.4.3.2.1 puncturing a location through the same location models the worst-case scenario.

The measured forces from multiple

puncture events in the same location may be correlated to sample strength. If the needle passes through the same hole, the cutting force would no longer be present for punctures after the initial puncture. Therefore, the force measured by the Bose machine for subsequent puncture events after the first puncture can be attributed to frictional forces. Each jig will be tested with 4 samples. The sample will be punctured multiple times with the measured puncture force recorded for each of the punctures.

Forces for each puncture event will be averaged across the four

membranes. Membrane puncture forces can also be affected by many variables. These variables need to be controlled or accounted for in order to compare the results. Parameters which may affect force include: needle tip shape, needle diameter, needle depth (in the case of frictional force), axial rotation of the needle, clamping forces on the membrane as the needle is inserted, and needle insertion velocity (Abolhassani, et al. 2007, O'Leary, et al. 2003, Okamura, et al. 2004, Richard, et al. 1999).

The relationship between insertion force and the number of needles (1, 4, or 8 needles), needle type (C: coring, or NC: non-coring), needle gauge (33, 30, or 27G), and insertion rate (0.5 or 1 mm/sec) was determined. All needles were obtained from Hamilton Company (Reno, NV). Additionally, needle insertion was completed multiple times on a single sample to examine magnitude of the insertion and removal 240

forces with each subsequent use. The two needle types used in this experiment are classified as coring (C) or non-coring (NC). The name describes the needle tip. The coring needle has a blunt tip which cores a cylindrical section from the material; the non-coring needle has a beveled tip and displaces material as the needle is pushed through the material.

The needle gauge describes the needle outer and inner

diameter; a higher gauge corresponds to a smaller diameter needle.

The insertion rates were selected based on the limitations of the Bose 3100 ElectroForce instrument. The maximum stroke distance of the displacement motor is 4 mm. A 1 mm/sec rate modeled a practical insertion rate while maintaining a high sample rate resolution from the Bose instrument. A second rate, which was half of the base rate value, was selected for comparison.

3.3.1.9.3.3 Results Stiffness, insertion (post-puncture insertion force is a combination of friction and cutting forces), and removal forces were identified for several needle arrangements (Table 3-10). Figure 3-40 shows a representative graph of the force measurement for a needle array insertion during needle array insertion and removal. The stiffness force was measured by identifying a slight dip in force between the needle touching the PDMS surface (Figure 3-40a) and full needle puncture (Figure 3-40b) (only present in single needle experiments and not for needle array graphs). The postpuncture force (cutting and frictional forces) was measured at Figure 3-40b. Frictional force was measured at Figure 3-40c; cutting force was calculated by subtracting the frictional force value (Figure 3-40c) from the post-puncture force. 241

The maximum pull-out force was measured at point Figure 3-40e. Previous work demonstrated that puncturing the same location multiple times decreased sealing ability of the material, compared to random insertion locations(Lo, et al. 2008). Therefore, needle insertion and removal cycles were performed at least 9 times at the same location in a PDMS slab to determine how multiple uses affect the insertion and removal forces.

Figure 3-40 Generic results from insertion force tests. a) needle touches surface of the PDMS sample, b) material being pierced by needle (combination of stiffness and puncture forces), c) needle

242

moving through PDMS material (friction force), d) needle stops moving and material relaxes, e) needle in process of being removed from material (max removal force), f) needle fully removed from material. Inset: needle displacement over time

As predicted from insertion force equations(Gent and Liu 1991), the forces for the 33G single, four needle array and eight needle array, on average, varied linearly with the number of needles (Figure 3-41). This result is also in agreement with the results presented by Okamura et al. where the forces of insertion in soft tissue was presented(Okamura, et al. 2004). Practically speaking, the maximum number of needles that can be simultaneously inserted is limited by overall device robustness as related to the magnitude of force necessary to insert the needle array.

243

Figure 3-41 Relationship of post-puncture insertion forces (friction and cutting forces) and removal forces with respect to the number of insertion needles.

Stiffness force increased with needle diameter (i.e. decreasing needle gauge). As expected, coring needles were associated with larger stiffness force due to the blunt profile compared to the beveled profile for non-coring needles. Stiffness force could not be determined for needle arrays because the needle tips are not aligned. Therefore, each tip punctured the PDMS sample at slightly different times and a reliable stiffness force could be determined.

The insertion force, the combination of friction and cutting forces, was also expected to increase with surface area. As surface area increases, frictional force should 244

likewise increase. Frictional force in 33 C was larger than 33G NC even though both have same outer diameter due to the area contributed by the lumen of the coring needle which was also in contact with the PDMS. Coring needles also had higher cutting force in general due to their blunt profile compared to the beveled tip of the non-coring needle.

A comparison of forces from differing insertion rates (1 and 0.5 mm/sec) identified a slight change in the frictional forces. The lower rate (0.5 mm/sec) had a small increase in insertion and removal forces; this may be caused by a change of dynamic frictional force between the needle and PDMS. As expected, the cutting force was not affected.

In all cases, multiple insertions reduced the insertion and removal forces, and therefore affected the sealing capability of the reusable arrayed interconnect. We previously presented information on the sealing capability of a PDMS slab that was punctured multiple times in the same location.

As the number of punctures

increased, the pressure at which induced leakage through the puncture site (leakage pressure) decreased. A decrease in sealing ability was attributed to damage of the PDMS from the repeated insertion and removal damage. However, the relative change in leakage pressure between each additional puncture and removal event decreased with each insertion/ removal event; this suggested a saturation of damage. The pull-out force of the first puncture for the 4 needle array (33G), normalized with respect to contact surface area between the needle and septa, was 0.52 to 0.48 N/mm2 245

for the tenth removal event. This result was similar to removal forces of comparable designs of other published reusable connectors, which range from 0.08 to 0.95 N/mm2 for the first removal event to 0.02 to 0.22 N/mm2 for the tenth removal(Chiou and Lee 2004, Li and Chen 2003, Lo and Meng 2008, Yao, et al. 2000).

246

Table 3-10 Summary of relationship between insertion and removal forces and the needle type (coring vs. non-coring), needle gauge (27G or 33G), number of needles (1, 4, or 8), and rate of insertion (0.5 or 1 mm/sec) (mean ± SE, n=4). Insertion Needle Gauge # of Stiffness Insertion Friction Cutting Removal Needle # of Rate Insertions Force [N] Force [N] Force [N] Force [N] Force [N] Point Type Needles (O.D. [μm]) [mm/sec] 27G (406) Coring 1 1 1 1.87 ± 0.14 1.67 ± 0.16 1.3 ± 0.11 0.37 ± 0.07 1.4 ± 0.2 33G (203) Non-coring 1 1 1 0.18 ± 0.02 0.87 ± 0.02 0.74 ± 0.02 0.14 ± 0.04 0.6 ± 0.03 33G (203) Coring 1 1 1 0.83 ± 0.03 1.2 ± 0.01 0.83 ± 0.02 0.37 ± 0.02 0.89 ± 0.02 27G (406) Non-coring 4 1 1 N/A 5.41 ± 0.34 5.24 ± 0.49 0.18 ± 0.11 2.53 ± 0.17 33G (203) Non-coring 4 1 1 N/A 3.3 ± 0.05 2.81 ± 0.06 0.49 ± 0.04 2.65 ± 0.07 33G (203) Non-coring 4 0.5 1 N/A 3.48 ± 0.08 3 ± 0.05 0.49 ± 0.05 2.7 ± 0.1 33G (203) Non-coring 8 1 1 N/A 5.72 ± 0.15 4.88 ± 0.16 0.84 ± 0.02 4.6 ± 0.15 27G (406) Coring 1 1 9 N/A 1.25 ± 0.09 1.25 ± 0.09 0±0 1.11 ± 0.02 33G (203) Non-coring 1 1 10 N/A 0.61 ± 0.01 0.61 ± 0.01 0±0 0.54 ± 0.03 33G (203) Coring 1 1 9 N/A 0.66 ± 0.01 0.66 ± 0.01 0±0 0.71 ± 0.02 27G (406) Non-coring 4 1 10 N/A 4.67 ± 0.21 4.67 ± 0.21 0±0 2.64 ± 0.2 33G (203) Non-coring 4 1 10 N/A 2.45 ± 0.08 2.42 ± 0.07 0.03 ± 0.03 2.43 ± 0.09 33G (203) Non-coring 4 0.5 10 N/A 2.71 ± 0.07 2.7 ± 0.07 0.01 ± 0 2.49 ± 0.02 33G (203) Non-coring 8 1 10 N/A 4.42 ± 0.15 4.42 ± 0.13 0±0 4.37 ± 0.12

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As shown in the insertion and removal force tests, force scaled linearly with the number of needles and decreased for needles with 1) smaller diameters and 2) noncoring tip. The number of needles in an array can be maximized by using the smallest diameter non-corning needles possible. However, the needles must be rigid enough to penetrate the PDMS septa without buckling which may lead to needle misalignment.

3.3.1.9.4 Pressure Test 3.3.1.9.4.1 Maximum Leakage Pressure 3.3.1.9.4.1.1 Methods Pressurized DI H2O was applied to assembled microfluidic systems to determine failure pressures and modes. Failure pressures were obtained for all three septa designs (oval, oval overlap, and rectangular) in the 4 microchannel configuration. The design with the greatest failure pressure was compared to that of the matching the 8 microchannel design. Needles were inserted into the input and output septa. Dyed DI H2O was first introduced into the system to ensure the microchannel was open and free from obstructions. The output needles were removed; due to the selfsealing nature of PDMS, the pressure gradient required to cause leakage from the needle track is expected to be much higher than the leakage pressure of the insertion site or failure pressure of the device (Lo, et al. 2008, Lo and Meng 2008). Pressurized DI H2O was applied in increments of 0.5 psi (3.45 kPa) with a 5 minute hold period to allow system equilibration. The failure pressure was recorded when water leakage was observed. 248

3.3.1.9.4.1.2 Results The leakage pressure associate with each of the three septa designs were determined (Table 3-11). Several factors were identified to explain the wide range of failure pressures for each setpa design. The oval overlap may fail at lower pressures since septa delaminated from the substrate.

During needle array insertion, slight

adjustments to align a single needle in the array induced torque force on the other adjacent needles. This torque resulted in separation of the PDMS from the Parylenecoated substrate; the adhesion between these materials was poor. Parylene C was previously used as a release layer for PDMS because of their low adhesion strength (Lo, et al. 2008).

The oval design has distinct septa for each needle, therefore, the torque effect is minimized in this design. However, leakage pressure was determined by the weakest needle/septum pair. The data for this design in Table 3-11 were obtained for a single device. Failure occurred at the interface between the needle and septa (Figure 3-43a). Following failure of one pair (at 2 kPa), the septum was resealed using additional PDMS and repressurized. The same input location failed again at 26 kPa, whereas the other three input locations did not fail. Again, needle alignment affects sealing. If the needle was inserted at a large angle relative to the substrate surface, then the needle may contact the substrate. In this case, the needle is no longer sealed around its circumference by PDMS and causes the PDMS to partially delaminate from the substrate near the contact site. This â&#x20AC;&#x153;tentingâ&#x20AC;? effect creates a potential leakage path along the needle shaft (Figure 3-42). The failure point at 67 kPa was at 249

the output septum (Figure 3-43b). Needle alignment for the output septa has the same concerns as the input septa. However, this result indicated the input septa that did not fail at 2 and 26 kPa points were well aligned.

Figure 3-42 Illustration of â&#x20AC;&#x153;tentingâ&#x20AC;? effect.

The robustness of the rectangular septa interconnect was also highly dependant on needle alignment. The SU-8 anchoring posts in this design resulted in a narrow needle path through the septa area. Slight needle misalignment may result in needle tips lodging in the SU-8 posts or, with sufficient insertion force, dislodging SU-8 posts from the substrate. The 4 septa rectangular design failed at the device edge. This failure was not related to the interconnect portion of the device; instead it was an adhesion problem between the SU-8 and Parylene C or the SU-8 and substrate. The 4 septa rectangular design had a higher failure pressure than the 8 septa rectangular design because it was much simpler to align and insert 4 needles compared to 8. The additional force necessary to push 8 needles into the septa caused the needles within the array to buckle. The buckling resulted in the inserting force being redirected as torque.

The delamination between the septa and the

Parylene C, visible when the pressurized dyed water flows under the septa, was directly caused by this torque. Additionally, several SU-8 posts were dislodged from

250

the substrate, creating additional areas where the septa and substrate were not in contact.

Table 3-11 Summary of failure pressure and failure locations for all septa designs. Arrows indicate failure points. Channel Septa # of Failure Failure Location Material Type Septa Pressure [kPa] Insertion site, delamination at 3.79 septa/ substrate interface Oval SU-8 4 Delamination at Overlap setpa/ substrate 15.86 interface and Parylene C /substrate interface Edge input port (delamination 2.054 between septa and substrate) Edge input port 26.2 (delamination SU-8 Oval 4 between septa and substrate)

SU-8

Rectangular

67.57

Output port

36.54

Delamination between substrate and Parylene C interface

8.96

Insertion site, delamination at septa/substrate interface

Needle misalignment, leading to septa/substrate delamination, was the main cause of failure (Figure 3-43c,d). Needle guides in the SU-8 housing helped ensure the needles were inserted in the center of the septa, however, the needle guides could not prevent the needles from veering within the septa, or for the needle to be inserted at an angle relative to the substrate surface. Additionally, Okamura et al. demonstrated 251

needle bending is more prevalent for beveled tip needles (Okamura, et al. 2004). Beveled needles are necessary minimize insertion and removal forces, therefore, maximizing the reusability of this connector. Commercial bevel-tipped needles are readily available. Therefore, other methods to decrease instances or causes of needle misalignment need to be implemented.

Needle misalignment can be mitigated by improving needle stiffness, however, trade-offs need to be considered. The needles used to establish the microfluidic connections were 1 inch in length and the septa were 4 â&#x20AC;&#x201C; 4.5 mm in length. The needle length can be shortened to better match the septa length, however, needle length determines the maximum length of the septa which is linked to the achievable needle removal force.

Removal force is an indicator of the maximum leakage

pressure the septa can withstand. A smaller needle gauge (i.e. larger diameter) may be used. Larger needles require greater insertion force and greater septa thicknesses to accommodate the increased diameter. Finally, the needle guides can be altered (e.g. lengthened) to help establish and maintain the needle position and absorb any buckling effect, but lengthening the needle guides increases the device footprint. Septa and needle alignment can be more tightly controlled in precision commercial manufacturing. Therefore, needle alignment improvements may only be necessary in prototype and research devices.

Septa delamination from the Parylene C or the SU-8 was also failure mode (Figure 3-43a,b). Bonding between the septa to the SU-8 anchor and substrate package can 252

be improved. First, the Parylene C can be removed using oxygen plasma from the area within the SU-8 housing prior to adding the SU-8 layer. The glass surface can be treated with oxygen plasma in order to form irreversible bonds between the glass and PDMS (Bhattacharya, et al. 2005, Duffy, et al. 1998, McDonald, et al. 2000, McDonald and Whitesides 2002). The SU-8 sidewalls can also be roughened to increase the contact surface area.

Figure 3-43 Common failure modes of the arrayed interconnect. a) Leakage through needle insertion path between needle and septa, b) leakage at output septa through needle track, c) delamination between the septa and Parylene C coated substrate, d) delamination between the Parylene C coating and the substrate. Examples of needle misalignment are shown in c) and d).

3.3.1.9.4.2 Prolonged Pressure 3.3.1.9.4.2.1 Methods 253

Prolonged pressure will be applied to a device to ensure the arrayed interconnect can withstand pressure application for an extended period of time. The applied pressure will be determined by calculating 50% of the average maximum pressures of all tested interconnects. The pressure will be applied for 24 hours and observed to ensure no leakage during the entire 24 hours. 3.3.1.9.4.2.2 Results The oval design survived continuous application of pressure (25 kPa) for over 24 hours without any visible leakage.

This result demonstrated the interconnect’s

ability to be used in applications which require survival in extended pressurized conditions.

3.3.1.9.5 Electrolysis Pressure Generation 3.3.1.9.5.1 Theory Electrolysis reaction was previously presented in Section 2.3.1.1.2- Electrolysis Pump and Pump Chambe. The application of current to the electrolysis electrodes generates hydrogen and oxygen gas within the microchamber, thus driving liquid through the microchannel. The theoretical volume (Vtheoretical) can be calculated using Equation 3-13.

Equation 3-13 Volume of gas generation during electrolysis

⎛3 i ⎞ Vtheoretical = qtheoretical t = ⎜ Vm ⎟ t ⎝4 F ⎠

254

Given the theoretical gas generation rate, qtheoretical [m3/s], duration of applied current, t [sec], current, i [A], Faradayâ&#x20AC;&#x2122;s constant, F = 96.49x103 [C/mol], and the molar gas volume at 25 Â°C and atmospheric pressure Vm = 24.7x10-3 [m3/mol].

3.3.1.9.5.2 Methods Internal pressure can be generated using the electrolysis structures in the microfluidic device. The water within the device was converted to hydrogen and oxygen gas when current is applied to the electrolysis electrodes. The internal pressure was measured using a commercial pressure sensor (ASDX 015D44R, Honeywell International, Morristown, NJ).

3.3.1.9.5.3 Results The functionality of including an electrolysis structure for inducing pressure, or displacing water within the system was demonstrated.

The pressure generated

during electrolysis was measured using a pressure sensor. The electrolysis pressure that can be generated depends on the electrolysis variables (e.g. current, electrode design, electrolyte), the internal volume of the device, and volume of air already present in the device or testing setup.

A representative graph of the pressure change due to gas generation and recombination is shown in Figure 3-44. A baseline reading of atmospheric pressure was obtained prior to each test. Current was applied to the device until the entire device interior was voided of any visible water (approximately 100 sec). This is in good agreement with the theoretical time (97.4 seconds) to generate enough gas to 255

fill the entire internal volume of the microfluidic device (Equation 3-13, given

Vtheoretical = 5.61 mm3 and i = 0.3mA). The generated pressure within the device was well below the failure pressure of the septa (Table 3-11). Additionally, when the current was removed from the electrodes, recombination of the hydrogen and oxygen gases was observed. Complete recombination of generated gas occurred within 1 hour. This suggests that none of the generated gas escaped from the testing setup.

Figure 3-44 Internal pressure change due to electrolysis. Pressure increases when current (0.3 mA) is applied to the interdigitated electrodes, pressure decreases when current is turned off and the oxygen and hydrogen gas recombine into water.

3.3.1.9.6 Sideport Functionality 3.3.1.9.6.1 Methods The sideport feature on the SU-8 interconnects were demonstrated showing the combination of two input streams. Sideports allow multiple inputs to be combined 256

into a single microchannel.

One sideport was demonstrated in this arrayed

interconnect design, however, the sideport functionality can be extended to include multiple sideports for additional input lines, although at the expense of chip real estate.

To demonstrate the functionality and feasibility of the sideport, a 33G non-coring needles were inserted through the septa of the sideport and main channel. A 30G non-coring needle was inserted into the output port to minimize any fluidic resistance at the output. Syringes containing either deionized water (DI H2O) or dyed DI H2O were connected to each input needle. A syringe pump was used to deliver a constant steady flow to both needles (Figure 3-45).

Figure 3-45 Experimental setup for sideport testing

3.3.1.9.6.2 Results The functionality of the sideports was verified by introducing clear liquid stream through the sideport into a dyed liquid stream. Both streams were injected at a rate of 500 ÎźL/min. Due to laminar flow characteristics in microfluidic devices, distinct and adjacent streams were observed in the channel (Figure 3-46).

257

Figure 3-46 Time lapse images of sideport function: a) dyed water introduced in the main septum and un-dyed water through the sideport, b) close up image of the laminar flow within the microchannel.

The sideport allowed the injection of two distinct fluids into a single microchannel. However, the sideport feature can be extended to allow multiple inputs into the same microchannel, thus providing a modular design which uses none, some, or all of the sideports. Sideports can also be placed perpendicular to the microchannel; these sideports would allow samples to be drawn from any location along the fluidic stream, or for the introduction of sensors into the microchannel.

3.3.1.9.7 Parylene C Microchannel Functionality 3.3.1.9.7.1 Methods An arrayed interconnect with a Parylene C microchannel was placed in isopropyl alcohol (IPA) to remove the sacrificial photoresist in the Parylene C microchannel. The interconnect was removed from the IPA bath, the liquid front was observed over time to determine if the channel inlet and outlet orifices were open. Once the channel was completely dry, a drop of Rhodamine B dye was then placed at the channel opening. Channel functionality was verified through observing Rhodamine B movement in the channel via capillary action. 258

Next, a device was partially packaged where the channel inlet was packaged, as described in Section 3.2.2.3, while the outlet was not packaged. The outlet was not packaged in order to decrease the chances of damaging or clogging the microchannel during packaging; demonstration of channel functionality is still possible with partially packaged device. A 33G non-coring needle was inserted into the inlet septum and Rhodamine B dye was pushed into the device. Again, Rhodamine B flow was observed in the channel.

3.3.1.9.7.2 Results The liquid/ air interface within the Parylene C microchannel verified the inlet and outlet ports of the Parylene C microchannel were open. IPA evaporated from the channel opening and the air/ liquid front was seen advancing through the microchannel (Figure 3-47). Additionally, capillary action of Rhodamine B through the channel demonstrated the channel was open and was unobstructed (Figure 3-48).

Functionality of the partially packaged device was verified (Figure 3-49). However, because pressure was used to inject the Rhodamine B into the channel, time lapsed images were not fast enough to capture the movement of the Rhodamine B in the channel. However, Rhodamine B movement through the outlet port funnel was captured.

259

Figure 3-47 Time-lapsed images of IPA evaporating from within the arrayed interconnect Parylene C microchannel.

260

Figure 3-48 Time-lapsed images of Rhodamine B moving through the arrayed interconnect Parylene C microchannel via capillary action. Scale bar is 1 mm.

261

Figure 3-49 Time-lapsed images of Rhodamine B moving through the arrayed interconnect Parylene C microchannel in a partially packaged device. Scale bar is 1 mm.

3.3.2 Summary An arrayed interconnect design capable of rapid and multiple simultaneous connections to a microfluidic device. Additionally, this device is reusable, where connections can be established, broken, and re-established up to 10 times. Optimal needle size and style was determined (33G non-coring), and the linear relationship between insertion and removal forces and the number of needles was theoretically and experimentally verified. While the failure pressure of the arrayed interconnect 262

was limited by the weakest connection, up to 62 kPa of pressure was supported. Also, interconnects were able to maintain 25 kPa of pressure for over 24 hours. Connector spacings of 2.54 and 1 mm were fabricated, however, FEM analysis of stress distribution shows 33G needles can be spaced as close as 503 Îźm, center-tocenter. Functionality of additional features such as needle guides, sideports for combining two fluids, and electrolysis structures were demonstrated.

Modular arrayed interconnects are possible by chosing different combinations of the septa shape, septa spacing, side ports, needle guides, microchannel material, and metal structures. Additionally, the arrayed interconnect can be scaled to have any number of septa (not just limited to 1, 4 or 8 septa designs). Similar to the single interconnect, septa length can be increased or decreased based on available space and operating pressure requirements. Arrayed interconnects provide a rapid and standard means for connecting to microfluidic systems to laboratory setups or even to other microfluidic systems.

263

4 Conclusion Devices which can incorporate modular components are very powerful designs which increase the versatility, flexibility, and potential functionality of the device. Furthermore, if many of the parts are pre-fabricated, than any number of combinations are possible and available on-demand without the need of a cleanroom facility. The two devices presented in this work show how simple changes to a device can produce an entirely different set of operating characteristics.

providing the basic building blocks (much like a box of micro-Legos速) and having an understanding of how modular components can affect a system, the combinations of possible devices are endless.

264

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6 Appendices Appendix A- Fabrication Process for Silicon Masters 1. Dehydrate wafer at 100 °C for 30 minutes. 2. Vapor coat wafer with hexamethyldisilazane (HMDS) adhesion promoter. 3. Spin coat photoresist (AZ 4620) 2 krpm, 40 seconds results in 10 μm layer (Figure 2-12A, Figure 2-15A). 4. Pattern photoresist using bottom (Figure 6-2) or middle layer (Figure 6-3) masks (Figure 2-12B, Figure 2-15B). 5. Remove native oxide with 10% hydrofluoric acid dip. 6. Etch DRIE a. 100 μm etch for bottom layer (Figure 2-12C). b. 250 μm etch for middle layer (Figure 2-15C). 7. Strip photoresist (acetone, isopropyl alcohol, deionized water). 8. Clean with plasma oxygen (400 mTorr, 400 W, 4 minutes). 9. Clean with RCA-1 cleaning process. 10. Vapor deposit 5 μm Parylene C.

270

Appendix B- Steps to Mount Silicon Master to Glass Substrate 1. Clean a 5’’x 5’’ (127 mm x 127 mm) glass plate (IPA wipe). 2. Place glass plate on hotplate (90 °C), do not exceed 120 °C or Parylene C will thermally degrade. 3. Place a few scraps of paraffin wax in center of glass plate. 4. When wax is complete melted, place wafer (unpatterned side down) on melted wax. 5. Apply pressure on wafer (avoid patterned areas) so wafer is flush with glass surface. 6. Wipe excess wax that seeps out from underneath the wafer. 7. Turn off hotplate and allow setup to cool to room temperature. 8. Remove glass/ wafer setup from hotplate. 9. Create an aluminum foil boat around glass plate. a. A boat is made by placing the glass plate onto a sheet of aluminum foil. b. The foil sheet should extend beyond the glass slide edge by approximately 2’’ on all sides. c. The excess foil is turned up and the corners folded. The aluminum walls contain excess PDMS. The boat is also necessary in order to degas the PDMS. During the degassing process, PDMS may expand up to 4 times in volume as trapped air pockets are removed.

271

Appendix C- Fabrication Steps for Creating Acrylic Master 1. Laser-cut square pieces with rounded corners (6mm x 6mm, or 0.24’’ x 0.24’’) from a 0.8 mm (0.03 inches) thick piece of acrylic (Figure 6-1) 2. Clean acrylic pieces using IPA. 3. Clean glass microscope slide (1’’ x 2’’) with IPA 4. Mix 5 minute epoxy. 5. Using tweezers, carefully dip one side (6mm x 6mm face) into epoxy. 6. Wipe excess epoxy from square. 7. Place square onto glass slide, ensure square is at least 1 cm from edge of slide and no closer than 1 cm to another square. 8. Press down on the square, make sure no epoxy seeps out from underneath the square and that square does not shift (leaving an epoxy trail). Excess epoxy will result in leaks when the top layer is assembled with the rest of the layers. 9. Allow the epoxy to cure (24 hours). 10. After 24 hours, gently push on the edge of each square to test if the square is securely fastened to the slide. 11. Create an aluminum foil boat around each glass slide.

Figure 6-1 6 mm x 6 mm acrylic squares to form the acrylic mold of the device reservoir. Note, image is not shown true to scale.

272

Appendix D- Mask Used to Fabricate Bottom Layer Silicon Master

Figure 6-2 Mask used to create silicon master for the bottom layer of the drug delivery device. The white sections are etched 100 Îźm into the silicon substrate to create a negative of the desired structure.

273

Appendix E- Fabrication Steps for Creating Bottom and Middle Layers 1. PDMS was prepared for creating the base layer. 2. Pour small puddle (approximately 15 g) of PDMS on center of wafer. 3. Spread PDMS over entire wafer by manually tipping the wafer (Figure 2-12D). 4. Ensure each component is fully covered with PDMS. 5. Tip wafer so excess PDMS is removed from wafer. 6. Place wafer in vacuum oven for 30 minutes at less than -30 inHg, or until bubbles within PDMS are fully removed. 7. Place wafer into oven (30 minutes, 70 °C). When PDMS is fully cured, remove wafer from oven. Alternately, PDMS can be cured for 24 hours at room temperature (make sure glass substrate is placed on flat surface). 8. Using a razor blade, cut the PDMS following the outer diameter of the wafer. 9. Clean a 5’’ x 5’’ glass plate (IPA wipe). 10. With a clean pair of tweezers, slowly lift the PDMS layer from the wafer (Figure 2-12E). 11. If fabricating middle layer: a. Obtain two additional 5’’ x 5’’ glass plates (clean with IPA). b. Place the plates adjacent to each other with a 1cm gap between the plate edges. c. Place the PDMS sheet onto two glass plates with the side that had been in contact with the wafer facing up. Align the PDMS sheet such that the pattern for the cannula and check valve is over the 1cm gap. d. Using a clean 33 gauge coring needle (OD 203 μm), align the needle over the mark which indicates the location of the check valve. e. Press down on the needle until it punctures the PDMS sheet. Visually inspect the puncture location to ensure the needle did not tear the PDMS sheet. f. Using the tweezers, lift the PDMS sheet and realign another set of check valve orifices over the gap. Continue until all of the check valve orifices are created. 12. Place the PDMS sheet onto the glass plate with the side that had been in contact with the wafer facing up. (i.e. the patterned side of the PDMS sheet is packing up) 13. Using a clean and fine-tipped blade, separate out each bottom or middle layer piece from the PDMS layer (cutting under the microscope leads to more precise cuts) by cutting along the outline of each piece. 14. Place pieces into a Petri dish and cover for later use.

274

Appendix F- Mask Used to Fabricate Middle Layer Silicon Master

Figure 6-3 Mask used to create silicon master for the middle layer of the drug delivery device. The white sections are etched 250 Âľm into the silicon substrate to create a negative of the desired structure.

275

Appendix G- Fabrication Process for Creating Top Layer from Acrylic Master 1. Prepare PDMS. 2. Pour PDMS into the boat. Pour enough PDMS such that the PDMS extends beyond the top of each acrylic square by 1 mm (0.04 inches). 3. Degas the PDMS. 4. Place mold in oven (70 °C for 20 minutes). 5. Check PDMS to see if the PDMS is “half-cured.” To check if PDMS is halfcured, gently touch surface of PDMS with a mixing rod. Lift the rod, if the PDMS sticks to the rod and deforms slightly then the PDMS is half-cured. If piece is not half-cured, replace mold into oven and check every minute. Be careful not to fully cure the PDMS. 6. Remove the glass side from the aluminum boat. Remove any excess PDMS that is on the bottom surface of the slide. 7. Place slide on the cutting pattern (Appendix H). 8. Align the acrylic square to the inner square on the pattern. 9. Using a fine-tipped blade, separate the top layer from the mold by cutting along the outer square on the pattern. 10. Get a bottom and middle layer that have already been oxygen plasma treated, aligned and bonded. 11. Lift the piece from the mold using clean tweezers. 12. Carefully align the reservoir on the bottom/middle layer structure. Make sure the edges of the reservoir match the edge on the middle layer. 13. Place assembled device into a Petri dish and cover. Let reservoir finish curing in room temperature (24 hours).

276

Appendix H- Pattern to Cut PDMS Reservoirs 1. 2. 3. 4. 5.

6. 7. 8. 9.

Remove the glass slide from the aluminum boat. Remove any excess PDMS that cured to the underside of the glass side. Place slide on the cutting pattern (Figure 6-4). Align the acrylic square to the inner square on the pattern. (Align 6 mm x 6mm acrylic square over the 6mm x 6mm pattern.) Using a fine-tipped blade, separate the top layer from the mold by cutting along the outer square on the pattern (7 mm x 7 mm square). Tip: it is easier to lift the square out if an extra piece is removed to create a hollow area next to the square (i.e. cut a small rectangular piece from one of the sides of the 7mm x 7mm cut). Get a bottom and middle layer that have already been oxygen plasma treated, aligned and bonded. Lift the piece from the mold using clean tweezers. Carefully align the reservoir on the bottom/middle layer structure. Make sure the edges of the reservoir match the edge on the middle layer. Place assembled device into a Petri dish and cover. Let reservoir finish curing in room temperature (24 hours).

Figure 6-4 Pattern used to cut uniform reservoirs from molded PDMS sheet.

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Appendix I- Cleaning Process for Device Layers Prior to Oxygen Plasma Treatment 1. Wipe two beakers using IPA, and place into fume hood. 2. Prepare diluted HCl solution in one beaker (1:10 DI H2O:HCl). Fill other beaker with DI H2O. 3. Using plastic tweezers, gentle place all of the bottom and middle PDMS layers that are to be cleaned into the dilute HCl solution for 30 minutes. (Make sure that the number of bottom layers to be cleaned equals the number of middle layers.) 4. Remove the pieces using the tweezers and place into DI H2O beaker to rinse. 5. Clean glass microscope slides (IPA wipe). The number of glass slides needed equals the number of bottom pieces that are cleaned. 6. Remove one bottom piece from the DI H2O, dry using N2 gas and place onto glass slide with the patterns facing up (this side will be treated with oxygen plasma). 7. Remove one middle piece from t he DI H2O, dry using N2 gas and place onto glass slide so that piece is orientated in a â&#x20AC;&#x153;mirror-imageâ&#x20AC;? of the bottom slide (Figure 2-20). This placement expedites assembly after oxygen treatment. 8. Place glass slide into Petri dish and cover.

278

Appendix J- Oxygen Plasma Treatment Process for Bonding Bottom and Middle Layers 1. 2. 3. 4. 5. 6.

Place one slide into RIE machine. Setup RIE machine and expose slide to 100 mTorr, 100 W, 45 seconds. Remove the slide from the RIE machine. Squirt a small amount of 95% ethanol onto each piece. Gently lift the middle piece and place onto bottom piece. Use microscope to help align check valve orifice over the check valve seat and edge of both layers. Alignment must be completed within 1 minute of removing pieces from RIE machine. 7. Bake assembly for 30 minutes at 75째C to increase the strength of the bonds. 8. Place aligned pieces and glass slide into covered Petri dish.

279

Appendix K- Process for Making PDMS Members of a Certain Thickness 1. Obtain a clean 5’’x5’’ glass plate. 2. Make an aluminum foil boat which encloses the glass plate. 3. Determine how much PDMS is necessary to obtain desired thickness (estimated value is a guide, but remember that some PDMS is loss inside the mixing cup and along the edge between the glass plate and Al boat) 4. Make PDMS according to PDMS SOP. 5. Pour PDMS on glass plate. Spread PDMS on plate evenly either by tipping the plate or using a clean glass slide to help spread PDMS. 6. Place glass plate into vacuum oven to remove the bubbles from the PDMS. 7. Remove plate from vacuum, place plate into oven (70°C for 20 minutes). 8. Remove plate from oven. Remove aluminum foil. 9. Align plate over cutting pattern. 10. Using a fine-tipped blade, cut 0.5’’x0.5’’ PDMS squares from PDMS slab. 11. Measure 2 clean glass cover slips using thickness gauge, record thickness. 12. Place PDMS square between cover slips, measure thickness and record thickness. 13. Place PDMS square onto a marked glass slide to help catalog square and for storage. 14. Repeat steps 12 and 13 until all squares are measured. 15. Subtract thickness of glass cover slips from cover slip and PDMS square stack to obtain thickness of PDMS square. 16. Note if the prepared amount of PDMS resulted in squares of desired thickness, if not, adjust the amount of PDMS in step 3.

280

Appendix L- Mask Used to Make Metal Alignment Marks for All of the Modular Valve Processes

Figure 6-5 Mask used to create the metal alignment marks. This mask patterns a photoresist layer. Metal is then deposited on the photoresist; the photoresist is removed using acetone, isopropyl alcohol, and water.

281

Appendix M- Mask Used to Pattern First Layer of SU-8 Valve Plate/ Pressure Limiter

Figure 6-6 Mask used to pattern the bottom layer of the SU-8 valve seat and pressure limiter. SU-8 is a negative resist, therefore, the white areas indicate locations where SU-8 structures will remain, while the black areas will be removed.

282

Appendix N- Mask Used to Pattern Second Layer of SU-8 Valve Plate/ Pressure Limiter

Figure 6-7 Mask used to pattern the top layer of the SU-8 valve seat and pressure limiter. SU-8 is a negative resist, therefore, the white areas indicate locations where SU-8 structures will remain, while the black areas will be removed.

283

Appendix O- Fabrication Process for SU-8 Valve Seat and Pressure Limiter Metal Alignment Marks 1. Dehydrate glass wafer (120 ºC, 20 minutes) 2. Spin HMDS on wafer a. Prespin 5sec 1k b. Spin 30 sec 3k 3. Spin AZ 4400 a. Prespin 5sec 1k b. Spin 30 sec 4k 4. Softbake at 90 ºC, 3 minutes 5. Expose (387 mJ/cm2) using Metal Mark Mask (Appendix L) 6. Develop a. 1:4 AZ 351: DI H2O b. Rinse in DI H2O 7. Check pattern 8. RIE (only descum immediately before metal dep) a. ASH machine: 100 W, 100mT, 20 minutes b. Descum 60W, 100mT, 1 minute 9. Metal deposition of Cr a. 300 Å of Cr (follow Metal Dep SOP) 10. Liftoff PR in acetone, may need to ultrasound the wafer 11. Check pattern

Bottom and Top SU-8 Plate 1. Clean substrate 2. Dehydrate substrate (90 ºC, 20 minutes) 3. Apply OmniCoat a. Dispense 1-4 mL of OmniCoat b. Prespin 500 rpm for 5 sec (acceleration of 100rpm/sec) c. Spin 3000rpm for 30 sec (acceleration of 300 rpm/sec) d. Bake for 1 min at 200 ºC 4. Repeat step 2 a total of three times for triple coat of OmniCoat (as per recommendation from MicroChem, Rob) 5. Spin SU-8 2100 to get ~160 µm thickness (thickness here does not have to be precise, additional thickness makes structure stronger but need to make sure exposure energy is enough to develop) a. Coat wafer in SU-8 2100 b. Prespin at 500 rpm for 10 sec (acceleration 100rpm/sec) c. Spin 1750 rpm for 30 sec (acceleration of 300rpm/sec) 284

d. e. f. g. h.

Let sit at room temp for 2 hours to Place wafer on hot plate, ramp from room temp to 65 ºC at 3 ºC/min Stay at 65 ºC for 5 minutes Ramp from 65 ºC to 95 ºC at 3 ºC/min Stay at 95 ºC for 30 minutes (might need to reduce this time because this layer gets double-baked) i. Turn off heater and allow hotplate and wafer to slowly cool to room temp 6. Expose SU-8 (~260 mJ/cm2 * 1.5 if on glass, 390 mJ/cm2) a. Apply mask for Bottom SU-8 Disk 1 (Appendix M) b. Consider apply energy in 50 mJ/cm2 doses to prevent overheating of SU-8 7. Post exposure bake for 160 µm thick SU-8 a. Place wafer on hot plate, ramp from room temp to 65 ºC at 3 ºC/min b. Stay at 65 ºC for 5 minutes c. Ramp from 65 ºC to 95 ºC at 3 ºC/min d. Stay at 95 ºC for 12 minutes e. Turn off heater and allow hotplate and wafer to slowly cool to room temp 8. Spin SU-8 2050 to get 40 µm thickness (times are adjusted for a total thickness of 200 µm) a. Coat wafer in SU-8 2050 b. Prespin at 500rpm for 10 sec (acceleration 100rpm/sec) c. Spin 4000rpm for 30 sec (acceleration of 300rpm/sec) d. Let sit at room temp for 1 hour e. Place wafer on hot plate, ramp from room temp to 65 ºC at 3 ºC/min f. Stay at 65 ºC for 7 minutes g. Ramp from 65 ºC to 95 ºC at 3 ºC/min h. Stay at 95 ºC for 39 minutes i. Turn off heater and allow hotplate and wafer to slowly cool to room temp 9. Expose SU-8 for 40 µm (~160 mJ/cm2 * 1.2 if on SU-8, 192 mJ/cm2) a. Apply mask for Bottom SU-8 Disk 2 (Appendix N) 10. Post exposure bake for 200 µm thick SU-8 a. Place wafer on hot plate, ramp from room temp to 65 ºC at 3 ºC/min b. Stay at 65 ºC for 5 minutes c. Ramp from 65 ºC to 95 ºC at 3 ºC/min d. Stay at 95 ºC for 14 minutes e. Turn off heater and allow hotplate and wafer to slowly cool to room temp 11. Develop SU-8 a. Pour SU-8 developer into one tray b. Pour IPA into another tray c. Place substrate into developer, mark time it takes to develop (will take ~17 minutes according to spec sheet) 285

d. Rinse in IPA (of white substance appears in unexposed portions, development is not done) 12. Hard bake (optional) a. Bake for 10 minutes at a temp 10 ยบC higher than final device operation temp. May need to do this if SU-8 reacts unfavorably during heat shrink 13. Liftoff SU-8 structures by using Remover PG a. Place wafer in heated Remover PG (40-60 ยบC) b. As soon as structures lift from wafer, remove from Remover PG c. Rinse with IPA d. Rinse with water

286

Appendix P- Mask Used to Pattern SU-8 Spacer Plate

Figure 6-8 Mask used to pattern the SU-8 spacer plate. SU-8 is a negative resist, therefore, the white areas indicate locations where SU-8 structures will remain, while the black areas will be removed.

287

Appendix Q- Fabrication Process for SU-8 Spacer Plate SU-8 Spacer Plate 1. Clean substrate 2. Dehydrate substrate (90 ºC, 20 minutes) 3. Apply OmniCoat a. Dispense 1-4 mL of OmniCoat b. Prespin 500 rpm for 5 sec (acceleration of 100rpm/sec) c. Spin 3000rpm for 30 sec (acceleration of 300 rpm/sec) d. Bake for 1 min at 200 ºC 4. Repeat step 2 a total of three times for triple coat of OmniCoat (as per recommendation from MicroChem, Rob) 5. Spin SU-8 2050 to get 40 µm thickness a. Coat wafer in SU-8 2050 b. Prespin at 500rpm for 10 sec (acceleration 100rpm/sec) c. Spin 4000rpm for 30 sec (acceleration of 300rpm/sec) d. Let sit at room temp for 1 hour e. Place wafer on hot plate, ramp from room temp to 65 ºC at 3 ºC/min f. Stay at 65 ºC for 3 minutes g. Ramp from 65 ºC to 95 ºC at 3 ºC/min h. Stay at 95 ºC for 6 minutes i. Turn off hotplate and allow substrate to slowly cool to room temp 6. Expose SU-8 (~160 mJ/cm2 * 1.5 if on glass, 240 mJ/cm2) a. Apply mask for Center SU-8 Disk (Appendix P) 7. Post exposure bake for 40 µm thick SU-8 a. Place wafer on hot plate, ramp from room temp to 65 ºC at 3 ºC/min b. Stay at 65 ºC for 1 minutes c. Ramp from 65 ºC to 95 ºC at 3 ºC/min d. Stay at 95 ºC for 6 minutes e. Turn off heater and allow hotplate and wafer to slowly cool to room temp 8. Develop SU-8 a. Pour SU-8 developer into one tray b. Pour IPA into another tray c. Place substrate into developer, mark time it takes to develop (approximately 5 minutes) d. Rinse in IPA (of white substance appears in unexposed portions, development is not done) 9. Hard bake (optional)

288

a. Bake for 10 minutes at a temp 10 ยบC higher than final device operation temp. May need to do this if SU-8 reacts unfavorably during heat shrink 10. Liftoff SU-8 structures by using Remover PG a. Place wafer in heated Remover PG (40-60 ยบC) b. As soon as structures lift from wafer, remove from Remover PG c. Rinse with IPA d. Rinse with water

289

Appendix R- Mask Used to Pattern SU-8 Mold for Silicone Valve Plate

Figure 6-9 Mask used to pattern the SU-8 mold used to cast the silicone valve plate. SU-8 is a negative resist, therefore, the white areas indicate locations where SU-8 structures will remain, while the black areas will be removed.

290

Appendix S- Fabrication Process for SU-8 Mold to Create PDMS Valve Plate Metal Alignment Marks 1. Dehydrate glass wafer (120 ºC, 20 minutes) 2. Spin HMDS on wafer a. Prespin 5sec 1k b. Spin 30 sec 3k 3. Spin AZ 4400 c. Prespin 5sec 1k d. Spin 30 sec 4k 4. Softbake at 90 ºC, 3 minutes 5. Expose (387 mJ/cm2) using Metal Mark Mask (Appendix L) 6. Develop e. 1:4 AZ 351: DI H2O f. Rinse in DI H2O 7. Check pattern 8. RIE (only descum immediately before metal dep) g. ASH machine: 100 W, 100mT, 20 minutes h. Descum 60W, 100mT, 1 minute 9. Metal deposition of Cr i. 300 Å of Cr (follow Metal Dep SOP) 10. Liftoff PR in acetone, may need to ultrasound the wafer Check pattern

SU-8 Mold (flat membrane, no overlap, no bossed structure) 1. Clean substrate 2. Apply A174 adhesion promoter 3. Deposit ~5 µm Parylene C on substrate 4. Dehydrate substrate (90 ºC, 20 minutes) 5. Spin SU-8 2050 to get 75 µm thickness a. Coat wafer in SU-8 2050 b. Prespin at 500rpm for 10 sec (acceleration 100rpm/sec) c. Spin 2000 rpm for 30 sec (acceleration of 300rpm/sec) d. Let sit at room temp for 1 hour e. Place wafer on hot plate, ramp from room temp to 65 ºC at 3 ºC/min f. Stay at 65 ºC for 3 minutes g. Ramp from 65 ºC to 95 ºC at 3 ºC/min h. Stay at 95 ºC for 8 minutes i. Turn off heater and allow hotplate and wafer to slowly cool to room temp 291

6. Expose SU-8 (205 mJ/cm2 * 1.5 if on glass, 308 mJ/cm2) a. Apply mask for SU-8 PDMS Mold 3 (Appendix R) 7. Post exposure bake for 75 µm thick SU-8 a. Place wafer on hot plate, ramp from room temp to 65 ºC at 3 ºC/min b. Stay at 65 ºC for 2 minutes c. Ramp from 65 ºC to 95 ºC at 3 ºC/min d. Stay at 95 ºC for 7 minutes e. Turn off heater and allow hotplate and wafer to slowly cool to room temp 8. Develop SU-8 a. Pour SU-8 developer into one tray b. Pour IPA into another tray c. Place substrate into developer, mark time it takes to develop (~ 7 minutes according to spec sheet) d. Rinse in IPA (of white substance appears in unexposed portions, development is not done) 9. Hard bake a. Bake for 10 minutes at 150 ºC (ramp from room temp to 150 ºC at 3 ºC/min), turn off heater and allow hot plate and SU-8 to return to room temp slowly. b. May help SU-8 survive if need to accelerate PDMS curing in oven using this mold PDMS Layer 1. Pour PDMS onto SU-8 PDMS Mold 2. Vacuum PDMS to remove bubbles 3. Scrap off excess PDMS slowly (try to prevent meniscus from forming) 4. Cure PDMS 5. Liftoff molded PDMS, separate individual pieces, remove lift-off tab

292

Appendix T- Mask Used to Pattern SU-8 Mold for Silicone Valve Plate with Optional Bossed Feature

Figure 6-10 Mask used to pattern the optional second layer for an SU-8 mold used to cast the silicone valve plate with bossed feature. SU-8 is a negative resist, therefore, the white areas indicate locations where SU-8 structures will remain, while the black areas will be removed.

293

Appendix U- Fabrication Process for SU-8 Mold to Create Silicone Valve Plate with Bossed Feature Metal Alignment Marks 1. Dehydrate glass wafer (120 ºC, 20 minutes) 2. Spin HMDS on wafer j. Prespin 5sec 1k k. Spin 30 sec 3k 3. Spin AZ 4400 l. Prespin 5sec 1k m. Spin 30 sec 4k 4. Softbake at 90 ºC, 3 minutes 5. Expose (387 mJ/cm2) using Metal Mark Mask (Appendix L) 6. Develop n. 1:4 AZ 351: DI H2O o. Rinse in DI H2O 7. Check pattern 8. RIE (only descum immediately before metal dep) p. ASH machine: 100 W, 100mT, 20 minutes q. Descum 60W, 100mT, 1 minute 9. Metal deposition of Cr r. 300 Å of Cr (follow Metal Dep SOP) 10. Liftoff PR in acetone, may need to ultrasound the wafer Check pattern PDMS Mold (flat membrane, with 40 µm bossed structure, no overlap) 1. Clean substrate 2. Apply A174 adhesion promoter 3. Deposit ~5 µm Parylene C on substrate 4. Dehydrate substrate (90 ºC, 20 minutes) 5. Spin SU-8 2050 to get 40 µm thickness a. Coat wafer in SU-8 2050 b. Prespin at 500rpm for 10 sec (acceleration 100rpm/sec) c. Spin 4000 rpm for 30 sec (acceleration of 300rpm/sec) d. Let sit at room temp for 1 hour e. Place wafer on hot plate, ramp from room temp to 65 ºC at 3 ºC/min f. Stay at 65 ºC for 3 minutes g. Ramp from 65 ºC to 95 ºC at 3 ºC/min h. Stay at 95 ºC for 6 minutes (may want to adjust because this layer gets double baked when second layer added) 294

i. Turn off heater and allow hotplate and wafer to slowly cool to room temp 6. Expose SU-8 thickness 40 µm (160 mJ/cm2 * 1.5 if on glass, 240 mJ/cm2) a. Apply mask for SU-8 PDMS Mold 1 (Appendix T) (this is the bossed structure layer) 7. Post exposure bake for 40 µm thick SU-8 a. Place wafer on hot plate, ramp from room temp to 65 ºC at 3 ºC/min b. Stay at 65 ºC for 1 minutes c. Ramp from 65 ºC to 95 ºC at 3 ºC/min d. Stay at 95 ºC for 6 minutes e. Turn off heater and allow hotplate and wafer to slowly cool to room temp 8. Spin SU-8 2050 to get 75 µm thickness a. Coat wafer in SU-8 2050 b. Prespin at 500rpm for 10 sec (acceleration 100rpm/sec) c. Spin 2000 rpm for 30 sec (acceleration of 300rpm/sec) d. Let sit at room temp for 1 hour e. Place wafer on hot plate, ramp from room temp to 65 ºC at 3 ºC/min (times adjusted for a total of 115 µm thickness) f. Stay at 65 ºC for 5 minutes g. Ramp from 65 ºC to 95 ºC at 3 ºC/min h. Stay at 95 ºC for 20 minutes i. Turn off heater and allow hotplate and wafer to slowly cool to room temp 9. Expose SU-8 thickness 75 µm (205 mJ/cm2 * 1.2 if on SU-8, 246 mJ/cm2) a. Apply mask for SU-8 PDMS Mold 2 (Appendix R) (this is the valve plate layer) 10. Post exposure bake for 115 µm thick SU-8 a. Place wafer on hot plate, ramp from room temp to 65 ºC at 3 ºC/min b. Stay at 65 ºC for 5 minutes c. Ramp from 65 ºC to 95 ºC at 3 ºC/min d. Stay at 95 ºC for 10 minutes e. Turn off heater and allow hotplate and wafer to slowly cool to room temp 11. Develop SU-8 a. Pour SU-8 developer into one tray b. Pour IPA into another tray c. Place substrate into developer, mark time it takes to develop (~ 11 minutes according to spec for 115 µm thickness) d. Rinse in IPA (of white substance appears in unexposed portions, development is not done) 12. Hard bake a. Bake for 10 minutes at 150 ºC (ramp from room temp to 150 ºC at 3 ºC/min), turn off heater and allow hot plate and SU-8 to return to room temp slowly. 295

b. May help SU-8 survive if need to accelerate PDMS curing in oven using this mold PDMS Layer 1. Pour PDMS onto SU-8 PDMS Mold 2. Vacuum PDMS to remove bubbles 3. Scrap off excess PDMS slowly (try to prevent meniscus from forming) 4. Cure PDMS 5. Liftoff molded PDMS, separate individual pieces, remove lift-off tab

296

Appendix V- Mask (1 of 3) Used to Pattern SU-8 Mold for Silicone Valve Plate with Optional Bossed and Overhang Features

Figure 6-11 Mask used to pattern the first layer for an SU-8 mold used to cast the silicone valve plate with bossed and overhang feature. The thickness of this layer determines how far the overhang will extend beyond the valve plate. SU-8 is a negative resist, therefore, the white areas indicate locations where SU-8 structures will remain, while the black areas will be removed.

297

Figure 6-12 Mask used to pattern the second layer for an SU-8 mold used to cast the silicone valve plate with bossed and overhang feature. This layer defines the bossed structure. SU-8 is a negative resist, therefore, the white areas indicate locations where SU-8 structures will remain, while the black areas will be removed.

298

Figure 6-13 Mask used to pattern the third layer for an SU-8 mold used to cast the silicone valve plate with bossed and overhang feature. This layer is used to define the thickness of the valve plate and the shape of the valve plate arms (i.e. through-holes). SU-8 is a negative resist, therefore, the white areas indicate locations where SU-8 structures will remain, while the black areas will be removed.

299

Appendix W- Fabrication Process for SU-8 Mold to Create Silicone Valve Plate with Bossed and Overhang Features Metal Alignment Marks 1. Dehydrate glass wafer (120 ºC, 20 minutes) 2. Spin HMDS on wafer a. Prespin 5sec 1k b. Spin 30 sec 3k 3. Spin AZ 4400 c. Prespin 5sec 1k d. Spin 30 sec 4k 4. Softbake at 90 ºC, 3 minutes 5. Expose (387 mJ/cm2) using Metal Mark Mask (Appendix L) 6. Develop e. 1:4 AZ 351: DI H2O f. Rinse in DI H2O 7. Check pattern 8. RIE (only descum immediately before metal dep) g. ASH machine: 100 W, 100mT, 20 minutes h. Descum 60W, 100mT, 1 minute 9. Metal deposition of Cr i. 300 Å of Cr (follow Metal Dep SOP) 10. Liftoff PR in acetone, may need to ultrasound the wafer Check pattern

SU-8 Mold (flat membrane, with 40 µm bossed structure, with overlap) 1. Clean substrate 2. Apply A174 adhesion promoter 3. Deposit ~5 µm Parylene C on substrate 4. Dehydrate substrate (90 ºC, 20 minutes) 5. Spin SU-8 2100 to get 260 µm thickness a. Coat wafer in SU-8 2100 b. Prespin at 500rpm for 10 sec (acceleration 100rpm/sec) c. Spin 1000 rpm for 30 sec (acceleration of 300rpm/sec) d. Let sit at room temp for 3 hours e. Place wafer on hot plate, ramp from room temp to 65 ºC at 3 ºC/min f. Stay at 65 ºC for 7 minutes g. Ramp from 65 ºC to 95 ºC at 3 ºC/min 300

h. Stay at 95 ºC for 56 minutes (may want to adjust because this layer gets double baked when second layer added) i. Turn off heater and allow hotplate and wafer to slowly cool to room temp 6. Expose SU-8 thickness 260 µm (365 mJ/cm2 * 1.5 if on glass, 548 mJ/cm2) a. Apply mask for SU-8 PDMS Mold 1 (Figure 6-11) (this is the overhang layer) b. Consider apply energy in 50 mJ/cm2 doses to prevent overheating of SU-8 7. Post exposure bake for 260 µm thick SU-8 a. Place wafer on hot plate, ramp from room temp to 65 ºC at 3 ºC/min b. Stay at 65 ºC for 5 minutes c. Ramp from 65 ºC to 95 ºC at 3 ºC/min d. Stay at 95 ºC for 19 minutes e. Turn off heater and allow hotplate and wafer to slowly cool to room temp 8. Spin SU-8 2050 to get 40 µm thickness a. Coat wafer in SU-8 2050 b. Prespin at 500rpm for 10 sec (acceleration 100rpm/sec) c. Spin 4000 rpm for 30 sec (acceleration of 300rpm/sec) d. Let sit at room temp for 1 hour e. Place wafer on hot plate, ramp from room temp to 65 ºC at 3 ºC/min (times adjusted for a total of 300 µm thick) f. Stay at 65 ºC for 8 minutes g. Ramp from 65 ºC to 95 ºC at 3 ºC/min h. Stay at 95 ºC for 64 minutes (may want to adjust because this layer gets double baked when second layer added) i. Turn off heater and allow hotplate and wafer to slowly cool to room temp 9. Expose SU-8 thickness 40 µm (160 mJ/cm2 * 1.2 if on glass, 192 mJ/cm2) a. Apply mask for SU-8 PDMS Mold 2 (Figure 6-12) (this is the bossed layer) 10. Post exposure bake for 300 µm thick SU-8 a. Place wafer on hot plate, ramp from room temp to 65 ºC at 3 ºC/min b. Stay at 65 ºC for 5 minutes c. Ramp from 65 ºC to 95 ºC at 3 ºC/min d. Stay at 95 ºC for 21 minutes e. Turn off heater and allow hotplate and wafer to slowly cool to room temp 11. Spin SU-8 2050 to get 75 µm thickness a. Coat wafer in SU-8 2050 b. Prespin at 500rpm for 10 sec (acceleration 100rpm/sec) c. Spin 2000 rpm for 30 sec (acceleration of 300rpm/sec) d. Let sit at room temp for 1 hour 301

e. Place wafer on hot plate, ramp from room temp to 65 ºC at 3 ºC/min (adjusted for 375 µm thickness) f. Stay at 65 ºC for 8 minutes g. Ramp from 65 ºC to 95 ºC at 3 ºC/min h. Stay at 95 ºC for 81 minutes i. Turn off heater and allow hotplate and wafer to slowly cool to room temp 12. Expose SU-8 thickness 75 µm (205 mJ/cm2 * 1.2 if on SU-8, 246 mJ/cm2) a. Apply mask for SU-8 PDMS Mold 3 (Figure 6-13) (this is the valve plate layer) 13. Post exposure bake for 375 µm thick SU-8 a. Place wafer on hot plate, ramp from room temp to 65 ºC at 3 ºC/min b. Stay at 65 ºC for 5 minutes c. Ramp from 65 ºC to 95 ºC at 3 ºC/min d. Stay at 95 ºC for 23.5 minutes e. Turn off heater and allow hotplate and wafer to slowly cool to room temp 14. Develop SU-8 a. Pour SU-8 developer into one tray b. Pour IPA into another tray c. Place substrate into developer, mark time it takes to develop (~ 23.5 minutes according to spec sheet for 375 µm) d. Rinse in IPA (of white substance appears in unexposed portions, development is not done) 15. Hard bake a. Bake for 10 minutes at 150 ºC (ramp from room temp to 150 ºC at 3 ºC/min), turn off heater and allow hot plate and SU-8 to return to room temp slowly. b. May help SU-8 survive if need to accelerate PDMS curing in oven using this mold

PDMS Layer 1. Pour PDMS onto SU-8 PDMS Mold 2. Vacuum PDMS to remove bubbles 3. Scrap off excess PDMS slowly (try to prevent meniscus from forming) 4. Cure PDMS 5. Liftoff molded PDMS, separate individual pieces, remove lift-off tab

302

Appendix X- Assembling Second Generation Heat Shrink Valve SOP Preparing the valve plate 1. Use mold with valve plate of 900 μm diameter pieces “squeegee 900 μm membrane only” 2. Select the type of valve you want (Figure 6-14)

Figure 6-14 Three valve plate types: a) hole, b) straight arm, c) s-shaped arm

3. Gentle cut around valve plate and tab using x-acto knife (Figure 6-15a) 4. Lift valve plate with needle tweezers using tab and place on glass slide with excess PDMS facing up (Figure 6-15b) 5. Gently open through-holes by removing excess PDMS (Figure 6-15c) 6. Cut excess PDMS from around the valve plate using x-acto knife (Figure 6-15d) 7. Remove tab (Figure 6-15e)

303

Figure 6-15 Steps to prepare valve plate

Assembling Valve

Figure 6-16 Items needed to packaging valve

1. Gather required pieces a. 2 valve seat/ pressure limiter b. 1 valve plate c. 1 spacer plate d. Needle tweezers e. Assembly jig f. 22G FEP heatshrink g. Glass slide with PDMS square (assembly area) 304

2. Place valve seat, pressure limiter, valve plate, and spacer plate on assembly area 3. Place assembly area under Lynx microscope 4. Check valve seat/ pressure limiter to make sure raised portion is facing up

Figure 6-17 Front and side views of SU-8 pieces

5. Align valve plate over valve seat. Make sure valve seat has raised portion facing up and that the through-holes on the valve plate are not over the through-hole in the valve seat) 6. Align spacer plate on valve plate 7. Align pressure limiter with raised portion facing down

Figure 6-18 Aligning pieces (top view) : valve plate only, valve plate with valve seat, valve plate & valve seat & spacer plate, valve plate & valve seat & spacer plate & pressure limiter

Figure 6-19 Aligning pieces (side view) : valve plate only, valve plate with valve seat, valve plate & valve seat & spacer plate, valve plate & valve seat & spacer plate & pressure limiter

8. Cut a section of 22G FEP heat-shrink tubing and place over needle on the jib base. FEP tubing needs to be shorter than the needle 305

9. Place jig top onto jig bottom to make sure needles align, bend needles if necessary, remove jig top 10. Place jig bottom on Teflon sheet

Figure 6-20 Process needed to shrink FEP tubing around valve

11. Lift stack and place on the tip of the needle with the FEP tubing, try to center on needles as much as possible 12. Place jib top on and push top needle down on top of stack 13. Lift FEP tubing so it surrounds valve and is touching the top of the jig

Figure 6-21 Assembled valve in heat shrink prior to placing in the oven

14. Take sheet to cleanroom, and place in vacuum oven 15. Remove air from vacuum oven 16. Set temp to 215 ยบC with 1.5 ยบC/min ramp a. Turn on oven with switch on front of machine b. Use arrow button to change target temp 306

c. Press the enter button to accept new temp d. Set overtemp control i. Hold enter button down until menu appears ii. Set the valve to 5 ยบC more than target iii. Hit enter to accept e. Set ramp i. Hold enter button down until menu appears ii. Press enter button until LoC appears iii. Change LoC valve to -1 iv. Press enter button until Upr appears v. Change value to 1.5 vi. Press enter button until dpr appears vii. Change value to 1.5 17. When oven reaches 215 ยบC, decrease temp to 20 ยบC 18. Remove jigs from oven when oven is cool 19. Remove valves from jigs, take pictures of top and side view, label valves (description of which membrane inside and valve #)

Figure

6-22

Side

and

top

view

packaged

valve

307

Appendix Y- Procedure to Test Heat-Shrink Packaged Valve Pressure System 1. Gather the following materials a. Blank pressure test form b. Valve c. Silicone tubing (Standard Silicone Tubing REF 60-411-44, 0.04’’ ID, 0.085’’ OD) d. 50 μL pipette (has a green tip) e. Upchurch parts: luer connector (black and brown), brown tubing, small brown screw to connect luer and tube f. Ruler g. 16G non-coring needle h. Timer 2. Make sure images have been taken of the valve prior to testing 3. Attach Upchurch setup to pressure system

Figure 6-23 Testing setup to apply pressure to packaged valves or solid disks.

4. Place 16G needle on end of Upchurch luer connector 5. Cut ~ ¾’’ length of silicone tubing and connect one end to the 16G needle and other end to the packed valve inlet. Push both parts into the tube as far as possible to reduce the amount of compliant tubing 6. Prefill pipette with some water (so you can see meniscus) 7. Cut ~ ½’’ length of silicone tubing; put output end of packaged valve into silicone tubing and connect other end to the 50 μL pipette 8. Tape ruler below the pipette 9. Fill out the pressure table with the information about the valve 10. Apply pressure to the valve a. Make sure pressure system outlet valve is closed b. Change pressure to target value c. Mark location of meniscus in pipette d. Set time to 3 minutes 308

e. Open pressure system outlet valve f. When timer beeps, mark location of meniscus 11. If valve worked, try to test again immediately after first test is complete and repeat as many times as you can. If the valve does not behave the same way, try testing the valve after waiting 24 hours between tests 12. If valve seems to be stuck closed, try applying pressure to the outlet side and try again 13. Examine valve under a microscope and see if you can observe any changes/ damage to the valve after testing is complete (take pictures).

309

Appendix Z- File Used To Make Custom-Designed Cut Puncture Jig

Figure 6-24 The three custom-designed laser-machined layers that are stacked to form the puncture jig.

1. The 30 gauge hole (lower right) is placed at the top of the stack to guide the needle. 2. The 30 gauge hole with the membrane outline (upper right) is the middle layer, this piece aligns the membrane such that the holes puncture the center of the membrane. 3. The 20 gauge hole (lower left) is placed on the bottom of the stack. The hole allows the needle to keep penetrating through the membrane until the luer portion of the needle comes into contact with the top plate. This ensures that each puncture is identical.

310

Appendix AA- File for Making the Puncture Force Jigs and Illustration of the Jig Assembly

Figure 6-25 Corel Draw files to create puncture force jigs. Jig assembly is also shown. The colors are just used to indicate corresponding layers and are not present in the laser file.

311

Appendix BB- Laser File for Making the Molds for Possible Layouts for Version 1 of the Solid Surgical Shams.

Figure 6-26 Corel draw files used to create custom-made, laser-machined molds of various shapes and sizes for the first version of the solid surgical shams. The 0.75 mm to 2 mm labels indicate the thickness of the sham.

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Appendix CC- Laser File User to Create Solid Surgical Sham v2_large and v2_small

Figure 6-27 File used to fabricate the redesigned solid surgical sham molds (v2_large and v1_small). The dimensions are the same as in version 1 with additional sutures on the 1 mm thick sham and the sutures removed from the silicone cannula from both shams.

313

Appendix DD- Laser File Used to Create Solid Surgical Sham Mold v3_1

Figure 6-28 Drawing used to create solid sham mold v3_1. The mold is a convex dome which was filled with silicone, leveled, and cured to create a solid sham.

314

Appendix EE- Laser File Used to Create Hollow Surgical Sham Molds v3_2, v3_2, and v4_1

Figure 6-29 Drawing used to create hollow sham molds v3_2, v3_3, and v4_1. Shaded portions are etched to create domes or flat surfaces.

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Appendix FF- Laser File Used to Create Hollow Surgical Sham Molds v5_1 and v6_1

Figure 6-30 Drawing used to create hollow sham molds v5_1 and v6_1. Shaded portions are etched to create domes or flat surfaces.

316

Appendix GG- Laser File Used to Create Hollow Surgical Sham Mold v7

Figure 6-31 Drawing used to create hollow sham mold v7. Shaded portions are etched to create domes or flat surfaces.

317

Appendix HH- Fabrication Process for Making Hollow Shams 1. Obtain acrylic molds: reservoir dome concave mold, reservoir dome convex mold, device base mold. (Figure 2-71A). 2. Make PDMS and pour into reservoir dome concave and device base molds (Figure 2-71B). 3. Cut a piece of silicone tubing (0.305 mm ID, 0.61 mm OD), thread a stripped piece of wire-wrap wire (0.254 mm diameter) into the silicone tube. Ensure that the wire extends beyond both sides of the tube. 4. Place stainless steel washer into bottom of reservoir dome concave mold (Figure 2-71C). 5. Place molds in the vacuum oven and degas PDMS. 6. Gently place the PEEK baseplate into the device base mold, take care not to introduce any bubbles into the PDMS. Place the wired silicone tube into tube location indentation on the reservoir dome mold. 7. Place 2 glass cover slips on the reservoir dome mold, gently place the reservoir dome convex mold on top of the reservoir dome concave mold (Figure 2-71D), do not introduce any bubbles. 8. Place both molds into the oven at 70째C for 30 minutes. 9. Remove PDMS from molds (Figure 2-71E). 10. Cut extra PDMS from the pieces (Figure 2-71F). Reservoir dome concave mold has a guiding groove to help cut the piece to the oval shape. 11. Align PDMS dome over PDMS base piece. Seal with a thin layer of PDMS prepolymer (Figure 2-71G). 12. Optional- coat entire system with Parylene C.

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Appendix II- Surgical Protocol for In Vivo Implantation of Hollow Surgical Shams 1. Pre-surgical preparation: a. Fill hollow shams with saline solution. b. Manually-depress the device to verify functionality. c. Fill the device with phenylephrine. d. Pinch off the silicone tube by tying a suture around the base of the tube (as close to the device body as possible). 2. Remove the conjunctiva. 3. Create a scleral tunnel, 3 mm wide and 2 mm posterior to the limbus. 4. Measure the appropriate length for the cannula. 5. Cut the device cannula to the desired length. Cut the cannula at an angle to create a beveled tip. This tip shape aides insertion through the scleral tunnel. 6. Insert the cannula into the anterior chamber. 7. Suture the device to the sclera using the suture tabs. 8. Measure the baseline pupil size (horizontal and vertical). 9. Release the suture closing the cannula. 10. Manually press the device using blunt forceps. Mark time of dispensation. 11. Measure immediate pupillary response, mark time. 12. Replace conjunctiva. 13. Measure pupillary response at 10 minutes following dispensation. 14. Inject (subconjunctival) steroids and antibiotics were administered inferior nasally.

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Appendix JJ- Fabrication Process to Create the Interconnect Test Structure 1. 2. 3. 4. 5. 6.

Obtain 2’’ x 3’’ glass slides or soda lime wafer (Figure 3-6A). Clean the slides using a piranha clean procedure. Treat the slides with A-174 adhesion promoter. Vapor deposit Parylene C onto the slides (Figure 3-6B). Dehydrate the slides at 90°C for 30 minutes. Spin 300 μm layer of SU-8 2100 (MicroChem Corp., Newton, MA) using a two step process (complete substep “a” for steps10-13 first before repeating “b” substeps for steps 10-13): a. First layer: spin at 1.5 krpm (approximately 200 μm thick). b. Planarization layer: spin at 3 krpm (for an additional 100 μm) (Figure 3-6C). 7. a,b Leave applied SU-8 layer rested at room temperature for 3 hours to improve planarization. 8. Softbaked layers at 90 °C. Baking steps were all performed on a programmable hotplate (Dataplate Series 730, Barnstead International, Debuque, IA) set to ramp at 3 °C/min.: c. First layer softbaked for 90 minutes. d. Planarization layer for 3 hours. e. The lower softbake temperature was selected to avoid thermal degradation of the underlying Parylene C. 9. a,b Slowly cool SU-8 to room temperature after each bake step to avoid thermal stress cracks in the SU-8 (repeat steps 10-13 for substeps “a” and then substeps “b”). 10. Pattern SU-8 (600 mJ/cm2). 11. Post-exposure baked for 30 minutes at 90 °C 12. Developed using SU-8 developer (MicroChem Corp., Newton, MA) (Figure 3-6D). 13. Final hardbake step was performed at 90 °C for 30 minutes.

For the Parylene C deposition step (step #4) the slides were placed in a commercial Parylene C vapor deposition chamber. Parylene C is a pin-hole free, biocompatible, and conformal material. Normally, the slides would be placed on the base of the machine, however, to increase the capacity of the deposition chamber, a slide holder was custom-designed and laser-cut. The slide holder is a modular design containing 320

6 levels, where each level is capable of holding 4 slides or wafers (for a maximum of 24 slides or wafers). Furthermore, both sides of the slide and/or wafer can be coated. The file to laser-cut the acrylic needed to fabricate each level can be found in Appendix LL.

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Appendix KK- Fabrication Process to Create Integrated Interconnect System 1. The substrate, either a 76 mm (3 inch) soda lime wafer (Silicon Quest International, Santa Clara, CA) or soda lime slide substrate (75 mm x 50 mm, Corning Glass Works, Corning, NY), was spin coated with AZ 4400 photoresist (AZ Electronic Materials, Branchburg, NJ) (4 krpm, 40 s, 4 μm) (Figure 3-7A). 2. Expose PR and develop to create liftoff mask of metal layer. 3. E-beam evaporate Ti/Pt (200 Å/2000 Å) (International Advanced Materials, Spring Valley, NY). 4. Liftoff metal in an acetone bath. Use a cleanroom swab to gently remove extra metal. Last bits of metal can be removed by placing the substrate in an acetone bath and quickly place the acetone bath into an ultrasound sonicator. standard liftoff processes by removing the photoresist layer in acetone. Rinse substrate/metal in isopropyl alcohol and deionized water (Figure 3-7B). 5. Vapor deposit Parylene C (Specialty Coating Systems, Inc., Indianapolis, IN) (2 μm thick) to electrically isolate the metal traces (Figure 3-7C). 6. Spin coat AZ 4400 was spin coated ( m, krpm, 40 s) to pattern Parylene C. 7. Pattern PR and develop. 8. Use oxygen plasma to remove Parylene C to reveal the contact pads (Figure 3-7D). 9. Remove PR in acetone, isopropyl alcohol and deionized water. 10. Spin 300 μm layer of SU-8 2100 (MicroChem Corp., Newton, MA) using a two step process (complete substep “a” for steps10-13 first before repeating “b” substeps for steps 10-13): a. First layer: spin at 1.5 krpm (approximately 200 μm thick). b. Planarization layer: spin at 3 krpm (for an additional 100 μm) (Figure 3-7E). 11. a,b Leave applied SU-8 layer rested at room temperature for 3 hours to improve planarization. 12. Softbaked layers at 90 °C. Baking steps were all performed on a programmable hotplate (Dataplate Series 730, Barnstead International, Debuque, IA) set to ramp at 3 °C/min.: a. First layer softbaked for 90 minutes. b. Planarization layer for 3 hours. c. The lower softbake temperature was selected to avoid thermal degradation of the underlying Parylene C. 13. a,b Slowly cool SU-8 to room temperature after each bake step to avoid thermal stress cracks in the SU-8 (repeat steps 10-13 for substeps “a” and then substeps “b”). 14. Pattern SU-8 (600 mJ/cm2). 322

15. Post-exposure baked for 30 minutes at 90 째C 16. Developed using SU-8 developer (MicroChem Corp., Newton, MA) (Figure 3-7F). 17. Final hardbake step was performed at 90 째C for 30 minutes.

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Appendix LL- File for Creating a Layer of the Parylene C Deposition Holder

Figure 6-32 Corel Draw file to create Parylene C deposition holder. 6 layers using this pattern were cut. The assembled holder is modular and can be placed in the Parylene C deposition chamber with up to all six layers in place. The Parylene C deposition holder layers are separated using plastic standoffs.

1. The dark areas are etched down to show indentations for where the slides and wafers are placed. 2. Tabs are cut to allow the wafers and slides to be removed easily. 3. Through holes are cut to encourage Parylene C circulation to other layers.

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Appendix MM- Masks Used to Fabricate the Single Interconnect Designs The masks used to create the single interconnect are presented in the order they are used. There are three masks for each interconnect design: 1. Metal Liftoff 2. Parylene C Etch 3. SU-8 Patterning a. 300 Îźm channel b. 500 Îźm channel

Figure 6-33 Mask used to pattern photoresist to create a metal liftoff layer for the single interconnect design.

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Figure 6-34 Mask used to pattern photoresist to create an etch mask for the Parylene C and expose the metal electrodes and electrolysis structure on the single interconnect deign.

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Figure 6-35 Mask used to pattern SU-8 layer to create a 300 Îźm channel. This produces a structure that is compatible with using a 33 gauge needle to pierce the septum.

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Figure 6-36 Mask used to pattern SU-8 layer to create a 500 Îźm channel. This produces a structure that is compatible with using a 30 gauge needle to pierce the septum.

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Appendix NN- Wafer Level Pictures of Arrayed Interconnect Four distinct wafers of designs that combine similar connector designs were fabricated. The first two wafers contain SU-8 microchannels designs (Figure 6-37). The remaining two wafers have designs that utilize Parylene C microchannels (Figure 6-38). Each pair of wafers is further delineated by combining structures that are integrated with metal structures (electrolysis and conductance) (Figure 6-37B, Figure 6-38B).

Table 3-5summarizes the possible combinations which can be

achieved using the masks to fabricate the four wafers presented in Figure 6-37 and Figure 6-38.

Figure 6-37 Wafers with SU-8 microchannels, A) which do not contain metal structures, and B) microchannels integrated with electrolysis and conductance structures. The blue areas identify the septum locations.

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Figure 6-38 Wafers with Parylene C microchannels, A) that do not contain metal structures, and B) microchannels integrated with electrolysis and conductance structures.

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Appendix OO- Mask Used To Fabricate Arrayed Interconnect SU-8 Wafer 1 The mask used to create the SU-8 Wafer 1 of the arrayed interconnect designs is presented in the order they are used. There is one masks for the SU-8 Wafer 1 layout: 1. SU-8 Patterning

Figure 6-39 Mask used to pattern SU-8 layer for the SU-8 microchannel arrayed interconnects found in Figure 6-37A.

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Appendix PP- Masks Used to Fabricate Arrayed interconnect SU-8 Wafer 2 The masks used to create the SU-8 Wafer 2 of the arrayed interconnect designs are presented in the order they are used. There are three masks for the SU-8 Wafer 2 layout: 1. Metal Liftoff 2. Parylene C Etching 3. SU-8 Patterning

Figure 6-40 Mask used to pattern photoresist to create a metal liftoff layer for the SU-8 microchannel arrayed interconnects found in Figure 6-37B.

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Figure 6-41 Mask used to pattern photoresist to create an etch mask for the Parylene C and expose the metal electrodes and electrolysis structure on the SU-8 microchannel arrayed interconnects found in Figure 6-37B.

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Figure 6-42 Mask used to pattern SU-8 layer for the SU-8 microchannel arrayed interconnects found in Figure 6-37B.

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Appendix QQ- Masks Used to Fabricate Arrayed interconnect Parylene C Wafer 1 The masks used to create the Parylene C Wafer 1 of the arrayed interconnect designs are presented in the order they are used. There are three masks for the Parylene C Wafer 1 layout: 1. Sacrificial PR for Channel Definition 2. Parylene C Etching 3. SU-8 Patterning

Figure 6-43 Mask used to pattern photoresist to create a sacrificial photoresist structure that defines the microchannel interior for the Parylene C arrayed interconnect designs found in Figure 6-38A.

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Figure 6-44 Mask used to pattern photoresist to create an etch mask for the Parylene C covering the microchannel opening of the Parylene C microchannel designs found in Figure 6-38A.

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Figure 6-45 Mask used to pattern SU-8 layer for the Parylene C microchannel arrayed interconnects found in Figure 6-38A.

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Appendix RR- Masks Used to Fabricate Arrayed interconnect Parylene C Wafer 2 The masks used to create the Parylene C Wafer 2 of the arrayed interconnect designs are presented in the order they are used. There are three masks for the Parylene C Wafer 2 layout: 1. 2. 3. 4. 5.

Parylene C Etching 1 Metal Liftoff Sacrificial PR for Channel Definition Parylene C Etching 2 SU-8 Patterning

Figure 6-46 Mask used to pattern photoresist to create an etch mask which etches the Parylene C for the Parylene C microchannel arrayed interconnects found in Figure 6-38B. The etched areas will allow the electrodes of the metal structure to come into direct contact with the glass substrate.

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Figure 6-47 Mask used to pattern photoresist to create a metal liftoff layer for the Parylene C microchannel arrayed interconnects found in Figure 6-38B.

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Figure 6-48 Mask used to pattern photoresist to create a sacrificial photoresist structure that defines the microchannel interior for the Parylene C arrayed interconnect designs found in Figure 6-38B.

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Figure 6-49 Mask used to pattern photoresist to create an etch mask for the Parylene C covering the microchannel openings, electrodes, and electrolysis structures for Parylene C microchannel designs found in Figure 6-38B.

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Figure 6-50 Mask used to pattern SU-8 layer for the Parylene C microchannel arrayed interconnects found in Figure 6-38B

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Appendix SS- Fabrication Process for Arrayed Interconnects with SU-8 Microchannels 1. If necessary, clean substrate, 76 mm (3 inch) soda lime wafer (Silicon Quest International, Santa Clara, CA), using standard piranha clean (1:4-5, H2O2: H2SO4) (Figure 3-26A). 2. Treat substrate with A-174, an adhesion promoter. 3. Cover the back of the wafer with dicing saw tape. 4. Vapor deposit Parylene C (Specialty Coating Systems, Inc., Indianapolis, IN) (2 μm thick) to prevent the SU-8 from delaminating (Figure 3-26B). 5. Spin 300 μm layer of SU-8 2100 (MicroChem Corp., Newton, MA) using a two step process (complete substep “a” for steps12-15 first before repeating “b” substeps for steps 10-13) (Figure 3-26C): a. First layer: spin at 1.5 krpm, 30 sec (approximately 200 μm thick). b. Planarization layer: spin at 3 krpm, 30 sec (for an additional 100 μm). 6. a,b Leave applied SU-8 layer rested at room temperature for 3 hours to improve planarization. 7. Softbaked layers at 90 °C. Baking steps were all performed on a programmable hotplate (Dataplate Series 730, Barnstead International, Debuque, IA) set to ramp at 3 °C/min. A lower softbake temperature than the manufacturer suggested value was selected to avoid thermal degradation of the underlying Parylene C. c. First layer softbaked for 90 minutes. d. Planarization layer for 3 hours. 8. a,b Slowly cool SU-8 to room temperature after each bake step to avoid thermal stress cracks in the SU-8 (repeat steps 12-15 for substeps “a” and then substeps “b”). 9. Pattern SU-8 (600 mJ/cm2) ((Figure 3-26D). 10. Remove dicing saw tape. 11. Post-exposure baked for 30 minutes at 90 °C. Ramp temperature from RT to 90˚C at 3˚C/min to avoid thermal stress. Once the post-exposure bake is completed, slowly ramp down the temperature as well. 12. Developed using SU-8 developer (MicroChem Corp., Newton, MA). Be sure to agitate the developer to speed up the development process. 13. Final hardbake step was performed at 90 °C for 30 minutes. Again, ramp temperature from RT to 90˚C at 3˚C/min to avoid thermal stress. Once the post-exposure bake is completed, slowly ramp down the temperature as well. 14. Dice designs from wafer. 15. Fill septa with PDMS (Figure 3-26E). 16. Cap device with glass slide (Figure 3-26F).

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Appendix TT- Fabrication Process for Arrayed interconnects Components

with SU-8 Microchannels and Metal

1. If necessary, clean substrate, 76 mm (3 inch) soda lime wafer (Silicon Quest International, Santa Clara, CA), using standard piranha clean (1:4-5, H2O2: H2SO4) (Figure 3-27A). 2. Dehydrate substrate, 120˚C for 20 min. 3. Spin coated with AZ 4400 photoresist (AZ Electronic Materials, Branchburg, NJ) (4 krpm, 40 s, 4 μm) (Figure 3-27B). 4. Expose PR and develop to create liftoff mask of metal layer (Figure 3-27C). 5. Descum surface of substrate with oxygen plasma to remove any residues prior to metal deposition. 6. E-beam evaporate Ti/Pt (200 Å/2000 Å) (International Advanced Materials, Spring Valley, NY) (Figure 3-27D). 7. Liftoff metal in an acetone bath. Use a cleanroom swab to gently remove extra metal. Last bits of metal can be removed by placing the substrate in an acetone bath and quickly place the acetone bath into an ultrasound sonicator. standard liftoff processes by removing the photoresist layer in acetone. Rinse substrate/metal in isopropyl alcohol and deionized water. Dry with N2 gas (Figure 3-27E). 8. Treat substrate with A-174, an adhesion promoter. 9. Cover backside of wafer with dicing saw tape. 10. Vapor deposit Parylene C (Specialty Coating Systems, Inc., Indianapolis, IN) (2 μm thick) to electrically isolate the metal traces and to prevent the SU-8 from delaminating (Figure 3-27F). 11. Spin coat AZ 4400 (4 μm, 4 krpm, 40 s) to pattern Parylene C (Figure 3-27G). 12. Pattern PR, removing dicing saw tape, and develop photoresist. 13. Etch Parylene C using oxygen plasma (Figure 3-27H). 14. Remove PR in acetone, isopropyl alcohol and deionized water (Figure 3-27I). 15. Spin 300 μm layer of SU-8 2100 (MicroChem Corp., Newton, MA) using a two step process (complete substep “a” for steps12-15 first before repeating “b” substeps for steps 10-13) (Figure 3-27J): e. First layer: spin at 1.5 krpm (approximately 200 μm thick). f. Planarization layer: spin at 3 krpm (for an additional 100 μm). 16. a,b Leave applied SU-8 layer rested at room temperature for 3 hours to improve planarization. 17. Softbaked layers at 90 °C. Baking steps were all performed on a programmable hotplate (Dataplate Series 730, Barnstead International, Debuque, IA) set to ramp at 3 °C/min. A lower softbake temperature than the 344

manufacturer suggested value was selected to avoid thermal degradation of the underlying Parylene C. g. First layer softbaked for 90 minutes. h. Planarization layer for 3 hours. 18. a,b Slowly cool SU-8 to room temperature after each bake step to avoid thermal stress cracks in the SU-8 (repeat steps 12-15 for substeps “a” and then substeps “b”). 19. Pattern SU-8 (600 mJ/cm2) (Figure 3-27K). 20. Post-exposure baked for 30 minutes at 90 °C. Ramp temperature from RT to 90˚C at 3˚C/min to avoid thermal stress. Once the post-exposure bake is completed, slowly ramp down the temperature as well. 21. Developed using SU-8 developer (MicroChem Corp., Newton, MA). 22. Final hardbake step was performed at 90 °C for 30 minutes. Again, ramp temperature from RT to 90˚C at 3˚C/min to avoid thermal stress. Once the post-exposure bake is completed, slowly ramp down the temperature as well. 23. Dice structures from wafer. 24. Fill septa with PDMS (Figure 3-27L). 25. Cap entire structure with a glass slide (Figure 3-27M). .

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Appendix UU- Fabrication Process for Arrayed Interconnects with Parylene C Microchannels 1. If necessary, clean substrate, 76 mm (3 inch) soda lime wafer (Silicon Quest International, Santa Clara, CA), using standard piranha clean (1:4-5, H2O2: H2SO4) (Figure 3-28A). 2. Treat wafer with A-174 adhesion promoter. 3. Cover one side of the wafer with dicing saw tape so that Parylene C will only coat one side of the wafer. This will help the dicing process easier. 4. Vapor deposit Parylene C (Specialty Coating Systems, Inc., Indianapolis, IN) (2 μm thick) to define the bottom layer of the microchannel (Figure 3-28B). 5. Remove dicing saw tape. 6. Spin coat AZ 4400 (4 μm, 4 krpm, 40 s) and pattern to define interior of Parylene C microchannel (Figure 3-28C-D). 7. Apply dicing saw tape to backside of the wafer. 8. Vapor deposit Parylene C (Specialty Coating Systems, Inc., Indianapolis, IN) (4 μm thick) to define the bottom layer of the microchannel (Figure 3-28E). 9. Remove dicing saw tape. 10. Anneal two Parylene C layers without reflowing PR (if possible) (Figure 3-28F). 11. Apply dicing saw tape to the backside of the wafer, this helps with controlling the exposure dosage for the photoresist and SU-8 (prevents reflected UV light from overexposing the bottom of the photosensitive layer). 12. Spin coated with AZ 4903 photoresist (AZ Electronic Materials, Branchburg, NJ) (4 krpm, 40 s, 6 μm) (Figure 3-28G). 13. Remove dicing saw tape. 14. Pattern PR and develop to create Parylene C etch mask to etch microchannel opening (Figure 3-28H). 15. Parylene C removed using oxygen plasma (Figure 3-28I). 16. Remove PR in acetone, isopropyl alcohol and deionized water (Figure 3-28J). 17. Spin 300 μm layer of SU-8 2100 (MicroChem Corp., Newton, MA) using a two step process (complete substep “a” for steps12-15 first before repeating “b” substeps for steps 10-13) (Figure 3-28K): 18. First layer: spin at 1.5 krpm (approximately 200 μm thick). 19. Planarization layer: spin at 3 krpm (for an additional 100 μm). 20. a,b Leave applied SU-8 layer rested at room temperature for 3 hours to improve planarization. 21. Softbaked layers at 90 °C. Baking steps were all performed on a programmable hotplate (Dataplate Series 730, Barnstead International, Debuque, IA) set to ramp at 3 °C/min. A lower softbake temperature than the manufacturer suggested value was selected to avoid thermal degradation of the underlying Parylene C. 346

22. First layer softbaked for 90 minutes. 23. Planarization layer for 3 hours. 24. a,b Slowly cool SU-8 to room temperature after each bake step to avoid thermal stress cracks in the SU-8 (repeat steps 12-15 for substeps “a” and then substeps “b”). 25. Apply dicing saw tape to the backside of the wafer, this helps with controlling the exposure dosage for the photoresist and SU-8 (prevents reflected UV light from overexposing the bottom of the photosensitive layer). 26. Pattern SU-8 (600 mJ/cm2) (Figure 3-28L). 27. Remove dicing saw tape. 28. Post-exposure baked for 30 minutes at 90 °C. Ramp temperature from RT to 90˚C at 3˚C/min to avoid thermal stress. Once the post-exposure bake is completed, slowly ramp down the temperature as well. 29. Developed using SU-8 developer (MicroChem Corp., Newton, MA). 30. Final hardbake step was performed at 90 °C for 30 minutes. Again, ramp temperature from RT to 90˚C at 3˚C/min to avoid thermal stress. Once the post-exposure bake is completed, slowly ramp down the temperature as well. 31. Dice structures from wafer using dicing saw. 32. Place structure in isopropyl alcohol in room temperature for 3 days to remove sacrificial photoresist inside the microchannel (Figure 3-28M). 33. Fill septa with PDMS (Figure 3-28N). 34. Cap entire structure with a glass slide (Figure 3-28O).

347

Appendix VV- Fabrication Process for Arrayed Interconnects with Parylene C Microchannels with Metal Components 1. If necessary, clean substrate, 76 mm (3 inch) soda lime wafer (Silicon Quest International, Santa Clara, CA), using standard piranha clean (1:4-5, H2O2: H2SO4) (Figure 3-30A). 2. Place dicing saw tape on one side of the wafer so that Parylene C only coats one side of the wafer. This will help when dicing the setups apart. 3. Vapor deposit Parylene C (Specialty Coating Systems, Inc., Indianapolis, IN) (2 μm thick) to define the bottom layer of the microchannel (Figure 3-30B). 4. Spin coated with AZ 4400 photoresist (AZ Electronic Materials, Branchburg, NJ) (4 krpm, 40 s, 4 μm) (Figure 3-30C). 5. Expose PR and develop to create Parylene C etch mask. The electrodes must be deposited on the substrate in order for it to be robust enough to withstand electrical connections (Figure 3-30D). 6. Etch Parylene C using oxygen plasma (Figure 3-30E). 7. Remove PR in acetone, isopropyl alcohol and deionized water (Figure 3-30F). 8. Spin coated with AZ 4400 photoresist (AZ Electronic Materials, Branchburg, NJ) (4 krpm, 40 s, 4 μm). 9. Expose PR and develop to create metal liftoff layer (Figure 3-30G). 10. E-beam evaporate Ti/Pt (200 Å/3000 Å) (International Advanced Materials, Spring Valley, NY) (Figure 3-30H). 11. Liftoff metal in an acetone bath. Use a cleanroom swab to gently remove extra metal. Last bits of metal can be removed by placing the substrate in an acetone bath and quickly place the acetone bath into an ultrasound sonicator. standard liftoff processes by removing the photoresist layer in acetone. Rinse substrate/metal in isopropyl alcohol and deionized water. Dry with N2 gas (Figure 3-30I). 12. Spin coat AZ 4400 (4 μm, 4 krpm, 40 s) and pattern to define the interior of Parylene C microchannel (Figure 3-30J-K). 13. Vapor deposit Parylene C (Specialty Coating Systems, Inc., Indianapolis, IN) (4 μm thick) to define the bottom layer of the microchannel (Figure 3-30L). 14. Spin coated with AZ 4903 photoresist (AZ Electronic Materials, Branchburg, NJ) (6 μm, 4 krpm, 40 s) (Figure 3-30M). 15. Pattern PR and develop to create Parylene C etch mask to etch microchannel opening (Figure 3-30N). 16. Parylene C removed using oxygen plasma (Figure 3-30O). 17. Remove PR in acetone, isopropyl alcohol and deionized water (Figure 3-30P). 348

18. Spin 300 μm layer of SU-8 2100 (MicroChem Corp., Newton, MA) using a two step process (complete substep “a” for steps12-15 first before repeating “b” substeps for steps 10-13): (Figure 3-30Q) 19. First layer: spin at 1.5 krpm (approximately 200 μm thick). 20. Planarization layer: spin at 3 krpm (for an additional 100 μm). 21. a,b Leave applied SU-8 layer rested at room temperature for 3 hours to improve planarization. 22. Softbaked layers at 90 °C. Baking steps were all performed on a programmable hotplate (Dataplate Series 730, Barnstead International, Debuque, IA) set to ramp at 3 °C/min. A lower softbake temperature than the manufacturer suggested value was selected to avoid thermal degradation of the underlying Parylene C. 23. First layer softbaked for 90 minutes. 24. Planarization layer for 3 hours. 25. a,b Slowly cool SU-8 to room temperature after each bake step to avoid thermal stress cracks in the SU-8 (repeat steps 12-15 for substeps “a” and then substeps “b”). 26. Pattern SU-8 (600 mJ/cm2) (Figure 3-30R). 27. Post-exposure baked for 30 minutes at 90 °C. Ramp temperature from RT to 90˚C at 3˚C/min to avoid thermal stress. Once the post-exposure bake is completed, slowly ramp down the temperature as well. 28. Developed using SU-8 developer (MicroChem Corp., Newton, MA). 29. Final hardbake step was performed at 90 °C for 30 minutes. Again, ramp temperature from RT to 90˚C at 3˚C/min to avoid thermal stress. Once the post-exposure bake is completed, slowly ramp down the temperature as well. 30. Dice structures from wafer. 31. Place structure in isopropyl alcohol in room temperature for 3 days to remove sacrificial photoresist inside the microchannel (Figure 3-30S). 32. Fill septa with PDMS (Figure 3-30T). 33. Cap entire structure with a glass slide (Figure 3-30U).

349

Appendix WW- 4 and 8 Needle Insertion Force Jigs and Assembly

Figure 6-51 Corel Draw file used to create custom-made, laser-machined, jigs to measure insertion force of 4 and 8 needles arrays. Jig assembly is also shown.

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351