Synthetic Anatomy INDN 381 -
A study into multi-material 3D printing and its application in prosthetics.
Students Julian Goulding Simon Crane
Supervisor Bernard Guy
INDN 381 Trimester 2 2013
Introduction
This research project develops upon various anatomy centered projects done at the Faculty of Design at the Victoria University of Wellington. Previous projects have focused on creating products that fit on the body or replicate body movements. This project continues this shared knowledge to create new anatomy to fit and comply with the body. The research looks to create a base knowledge around the application of multi-material 3D printing, 3D scanning and MRI & CT scans to revolutionise the way prosthetics are fitted and created. The project targets surgical and cosmetic markets and how they can embrace future technology to improve their products and processes for customers. Cosmetic and reconstructive surgery in the areas of prosthetics, as well as movie prosthetics could all benefit from the speed, accuracy and tactile qualities of multi-material 3D printing.
Contents.
Research
01 Abstract
03 3d Scanning
04 MRI & CT Scanning
05 Fitting to the Body
02 Material Investigation
Development
06 Why Ears?
07 Software Development
08 Ear 2
09 Ear 3
10 Structure
10 Ear 4
11 Context Imagery
07 Ear 1
Additive Manufacture 3D Printing and digital scanning has potential to dramatically reduce the time and human labour needed to create prosthetics. It allows for real-time prototypes of form and style for instant visualisation. This means prototypes can be produced quicker and cheaper than current prosthetics. The focus of this research project is maxillofacial prosthetics, and specifically recreating anatomically correct ear prosthetics. However, the technology used in this project can be applied to any range of human prosthetics. It has the ability to transform the way examine prosthetic sites, record data, design and manufacture prosthetics. Additive manufacture presents unique value in the production of prosthetics. It requires less materials, no moulding and it digitises the entire process. This digital process of design will greatly improve accuracy, fit and allow for unique prosthetics for individuals. It allows the design of anatomically correct replacements for users and increases confidence in the wearer.
Abstract
The greatest value however may be in multi-material 3D printing. The creation of dynamic feeling prosthetics through multi-materials is a new area in prosthetic design. A new tactile experience could increase user acceptance and confidence in a more human behaving prosthesis.
Printed Prototypes A collection of the many ears and other body parts printed as form and structure tests.
Current Prosthetic Design
Existing processes
Current practices in the prosthetic design where investigated, including dentures, eyes and ears. What was found was an archaic process that has not developed with the rise of technology. The main reason for this was hand made techniques give control and compliance over the shape of the prosthetic for the best fit, where harder materials or computer created mold’s do not. The challenge is whether we can change this with 3D printing and digital scanning. This will aim to dramatically reduce the manpower, time taken and materials used to create prosthetics.
Current Prosthetics Dental and eye prosthetics. They are still made individually using hand made techniques.
Object - Connex 500 Multimaterial The Objet Connex 500 multi-material printer gives this research project the power to examine a range of materials, their performance and tactile quality to create precise maxillofacial prosthetics. The printer utilizes stereolithography technology to print in a range of rubber, plastic and digital materials. The key interest in multi-material printing is how can we combine different materials to create prosthetic experience that simulates the tactile qualities of the human body. Shore hardness The hardness of polymers, elastomers and rubbers is measured by a durometer. It measures a materials resistance to permanent indentation. The scale of measure is shore hardness and it measures the depth of indentation created by a standard force by a standard presser foot. There are different scales of shore hardness depending on the type of material being measured and the presser foot being used. The range of materials produced by the Connex are measured in shore hardness. We can transpose these material properties to the shore hardness of different body parts to create material compositions that simulate the tactile experience of the body.
Material Investiagtion
Digital Materials Digital materials are composite materials that are a combination of resins from the Connex that create a range of material properties. These properties vary in elasticity and shore hardness. This variation allows us to get as close as possible to simulating the tangible qualities of the human body. Vero White – Opaque Hard Photopolymer Tango Plus – Clear Rubber-like Elastomer. Standard Materials Shore A Tango Plus FLX930 Vero White Plus RGD835
Tensile Tear Resistance (kg/cm)
26-28 86 (Shore D)
4-6 -
35-45 45-50 55-66 65-75 80-90 90-100
4-9 5-7 7-9 12-14 25-27 45-47
35-45 45-50 57-63 68-72 80-95 92-95
5.5-7.5 7.5-9.5 11-13 15.5-17.5 23-25 41-44
Digital Materials Tango Plus + Vero White Plus FLX9740-DM FLX9750-DM FLX9760-DM FLX9770-DM FLX9785-DM FLX9795-DM Tango Plus + Vero Clear FLX9040-DM FLX9050-DM FLX9060-DM FLX9070-DM FLX9085-DM FLX9095-DM
Shore 00 0 Earlobe
10
3
20 Shore A
30 40 0 50
1
10
Soft Tissue
20
Above Concha
60 70
30 40
Shore D
80
Nose Cartilage
50 90
3
60
0
4
2
Articular (Hip) Cartilage 70
10
100 20 80
30 40
90 50 100
60 70 80 90 100
References 1 (Shahmiri, Aarts, Bennani, Das, & Swain, 2013) 2 (Wippermann, Kurtz, Hallab, & Treharne, 2008) 3 (Rasmussen) 5 (Schmitt, 2013)
3D Scanning
Scanning the body One path to recreating human anatomy through digital means is using exterior 3D scanning. Scanning allows the 3D capture of an object, such as body features. These are then built up to create a 3D surface, which can be manipulated through software. It is important to note that scanning creates a surface, not a solid object, so this is done in post processing. Microsoft Kinect The Microsoft Kinect is a cheaply available game controller that uses cameras and IR sensors to map body movements. Utilising Microsoft’s Kinect SDK 1.7 and developer package Fusion, the Kinect can be turned into a 3D scanner. Through this software we have been able to successfully scan human exteriors and create point clouds. These points can be vertex welded to create editable 3D meshes. To improve the detail of the Kinect, lenses were added in front of the camera. 2.0 strength lenses dramatically improved the detail captured by the Kinect. This enabled detailed scanning of much smaller objects such as hands and faces. The new scale was 1:31. Pro’s Free software available - Community support - Relatively cheap compared to other scanners - Gets good enough detail to fit prints to the body - No set up - Simple – Quick Con’s Not 100% perfect scans - Can never really get a full body scan - Needs a dedicated graphics card -Need a powerful computer to get quality scans. Not super high detail. Constantly updating software. Multiple scans need to be stitched together to create a solid surface.
Scan Experiments 3D scans of body parts where taken into 3DS Max, where the polygons where modified to create different surface patterns
Anatomically Correct To create anatomically correct prosthetics, we have utilised Magnet Resonance Imaging (MRI) scans and X-ray Computed Tomography (CT) scans. These scans allow us to get beyond the surface of the skin and delve into the body. Areas such as bone structure and cartilage are of interest to take prosthetics from a static shell to a dynamic addition to the body. Medical imaging files used in MRI and CT scans are called DICOM files. It is an image slice through the body. The resolution can vary and the steps between the slices can affect the final accuracy. The amount of radiation used in the scan can also vary the quality and the type of tissue most visible. An MRI is suited for examining soft tissue, (e.g. ligament and tendon injury, spinal cord injury, brain tumors etc.), while a CT scan is better suited for bone injuries, lung and chest imaging. DeVide is a DICOM file viewer developed by the Delft University of Technology. It is a powerful and free programme for visualizing MRI and CT scans. Different tissue densities are represented by different shades of back to white. These can then be extracted as different thresholds and turned into 3D images and exported as STL’s. Hounsdsfeild Scale The Houndsfeild Scale is a quantitative scale of radio-density. It directly relates to CT scans and the threshold level in DeVide. From the this scale, we can extract out anatomically correct body parts from patients such as cartilage, bone or muscle to turn into STL files for further design in prosthetics. Selecting the correct threshold for different body parts is different for every patient, therefore requires some trial and error. The amount of radiation in the scan depends on the quality of picture. This can mean it is hard to distinguish between colours and thresholds for getting the perfect extraction of body parts.
MRI / CT
Patients with tattoos or metal implants can seriously distort the scan, creating a lot of noise and ruining the quality. HU
Substance
-1000 -500 -100 to -50 0 +15 +30 +30 to +45 +10 to +40 +37 to +45 +20 to +30 +40 to +60 +100 to +300 +700 to +3000
Air Lung Fat Water /Spinal Fluid Kidney Blood Muscle Grey Matter White Matter/J-O Blast Liver Soft Tissue/Contrast Bone Cancellous Bone to Dense Bone
Devide Thresholds Skin Fat Cartilage
-200 to 2500 -100 to -70 -30 to 300
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1. MRI layer 2. Thresholds extracted in DeVide 3. Extracted threshold layers as STL 4. Example of noise in an MRI Scan 5. STL of extracted skin and bone over layed 6. Extracted Bone STL
Lung Bronchi Extracted MRI data from DeVide and edited through 3DS Max.
Unique to you. 3d Printing and digital scanning gives us the potential to create unique objects that can fit exactly on the human skin. The first step towards creating anatomically correct prosthetics was to understand how we can fit objects to the body.
Body Fit
Experiments into various forms were undertaken, with shapes made to fit over the exact curvature of the skin. These forms represent a basis of potentially new structures to create prosthetics.
Lattice Glove 3D Scanning data from the Microsoft Kinect taken through 3DS Max to transform its from a flat surface into an interesting addition to the body.
Why Ears?
Tactile Quality and Custom Fit. Ears present a unique opportunity to multi-material printing and their development as prosthetics. Ears are currently made from molds and silicon casting. This archaic technique has not evolved in many years. Silicon ears, all though made to look identical to existing ears, their connection to the head is crude and the casting process has to be done every few years as they deteriorate over time. The most interesting area for multi-material printing is the tactile quality and intricacy of ears. yThe first goal of the project is to re-design an ear prosthetic that moves and feels like existing ears. The intricate material density of ears, from skin to cartilage, gives a great opportunity for different digital materials to be utilized to recreate anatomy. The second goal is to create an anatomically correct and unique ear for the user, with a perfect fit to the face. The unique value is in the tactile quality, durability and a anatomically correct replica of the human body. Delving inside the body and being able to extract data and print anatomy and organs.
Left A sample of the many test prints done on UP Plus printers to test shape’s and structure of the ear geometry.
CAD Process. The inherent organic nature of anatomy presents a number of difficulties when developing and problem solving in CAD. The sheer complexity and random nature of geometry from either 3D Scans or MRI’s mean they are prone to gaps and a number of other potential issues. This means not all programmes can be used for all applications. A number of software applications were used to create viable geometry for printing. 3DS Max This allowed us to directly modify the polygons from scans in STL format. It allowed for the scaling, sizing, deleting and transforming of polygons to create clean geometry.
Software Development
Maya Maya gave more precise control of individual polygons. We used vertex welding extensively to join different shapes together, close gaps and create our “manual boolean” operation Mudbox Mudbox is a 3D sculpting programme which allowed us to create the finishing touches to our models. Its sculpting tools allowed for free form smoothing and manipulation of polygons. We used this at the end stages of modelling to smooth polygons for clean transition between parts Solidworks Solidworks was used as a final check before printing. If the model could import into Solidworks with no faulty faces or gaps, it meant the geometry was good to print. We used the evaluate functions to test issues such as thickness and interference. 1. MRI data in 3DS Max. 2. Cleaned ear - skin. 3. Cleaned cartilage. 4. Separated cartilage and lobe. 5. Lining up cartilage inside skin. 6. Orientating new ear on head. 7. Extracting location of the new ear. 8. Lining up skin - head with ear. 9. Exploded view of skin-head, cartilage and skin-ear. 10. Vertex welding skin of ear and head together. 11. Ear in Mudbox for sculpting. 12. Smoothing cartilage polygons in Mudbox. 13. Cartilage lined up inside ear. 14. Full ear assembly in Solidworks. 15. Interference check. 16. Thickness analysis.
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MRI Data & Boolean Operations The first attempt at re-creating an ear was from MRI data. MRI scans were taken into DeVide where skin and cartilage were extracted as STL files using thresholds based on the Houndsfeild scale. The STL parts were brought into 3DS Max and the excess geometry was deleted to leave a clean ear. The cartilage was placed inside the skin and then put into Solidworks to check the files had no errors.
Ear 1-MRI
However we misunderstood the boolean requirements for printing on the Connex printer. A shape must booleaned out of another when the internal shape is being printed in the secondary material. Primary will generally be a Tango material (rubber) and the secondary a Vero (solid). Primary material will always take priority over the secondary material if the shapes are not separated. This meant our ear printed as all rubber and no internal cartilage was printed. Software DeVide 3DS Max Solidworks
3D Scan Instead of using MRI data, this ear used 3D scanned data of an exterior surface of an ear. This 3D scan was then cleaned in 3DS Max. Without cartilage available from an MRI scan, cartilage was created in 3DS Max. This was created using a “manual boolean� operation. This involved shelling the surface of the ear, cutting out the internal surface and then stitching this surface back together in Maya. This meant this cartilage now had and open void inside the ear to sit inside. Cartilage was then created from a replica of the internal surface. An empty space was left at the bottom of the ear to re-create the tactile quality of the earlobe. The ear was then put into Solidworks for pre-printing checks. The result was successful print of skin and cartilage to create an ear. The ear had great tactile quality but the cartilage needed a lower shore hardness to be more malleable. This print proved that a cheap 3D scanner has the ability to produce correct geometry for creating anatomically correct prints.
Ear 2
Software Microsoft Kinect SDK 3DS Max Maya Solidworks
Succsessfull MRI Print This ear re-visits the process undertaken in first Ear print to create successful print from MRI data. The “Manual Boolean� operation was re-created successfully to create a perfect fit for cartilage. This time it was with existing cartilage rather than creating our own, which was a more complex task. Maya was used extensively to weld the open skin and cartilage as well as creating the void lobe.
Ear 3 - MRI
Software DeVide 3DS Max Maya Solidworks
New Flexibility The current shore hardness of materials provided by the Connex 500 printer are not soft enough to get a true representation of the feeling of skin and the flexibility of cartilage. To combat this we undertook a range of experiments to create new forms from lighter structures. These structures were designed to remove material while keeping the basic the shape and to enhance the tactile experience of the ear. The shapes where based of the polygon structure of the ear and then iterated upon.
Structure
Software Rhino Grasshopper
BREP Structure This unique structure of the ear goes further the just a surface representation. This structure interlinks between its-self to create a complex shape and defined strength area’s.
Invisible and unique. The final ear represents the culmination of many prototypes and software experiments to realise the potential of 3D printing in creating an ear prosthesis. This ear stems from MRI data to create an anatomically identical ear for a patient. MRI data is extracted to form the outer ear skin and cartilage. These two are then combined through Maya and 3DS Max to create an assembly of the two parts. The lobe is made void to allow for a softer feel. The exterior head location for the ear is 3D scanned or brought in from existing MRI data. A section of this is then welded to the existing ear and then sculpted out to create an invisible transition between the patients head, the added skin and the ear. The result is unique ear for each patient.
Ear 4
An ear that will work with the body not against it. It is designed directly off existing body data to become your ear. It fits in seamlessly with the shape of the body and can be easily covered with make up to hide the transition between body and prosthetic. Overall, this ear becomes not an extension of the body, but rather fits in with the body, invisibly and confidently.
Left Final ear fitted upon an FDM print of the head location.
Final Ear The final ear in its entirety. The lighting of this image shows the variable thickness of the materials used and how 3d sculpting has made smooth transitions between parts.
Underside of Ear The back of the ear holds 3 magnets that hold the ear in place. This clicks on to the existing plate used to hold ear prosthetics.
Context
Everyday Prosthetic These images represent where we believe the prosthetic industry should be heading. A prosthetic that becomes an everyday item. A piece of the body people are proud of and becomes a natural item around the household.