Medical Plastics
Plastics use surging in medical applications Widely used in the medical sector now, plastics have evolved in use and composition, for instance, plastic implants are implanted in the body to introduce treatment or enhance the function of a certain device. Plastics in the medical sector have now become a staple and essential material, says Angelica Buan in this report.
Elasto, part of the Hexpol TPE family, has developed a Mediprene TPE compound for use in the Happy Ears earplugs, which are said to reduce noise while effectively reproducing sound
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M
etals, glass and ceramics used to be the materials that made up most medical devices, but with surging healthcare costs, the demand for lower-cost equipment and devices has gone up. Thus, polymers have become a viable material option due to the potential for design flexibility, weight savings and cost efficiency. A US market analysis by Frost & Sullivan suggests that the total market volume of plastics in medical devices is about 600,000 tonnes. With such a volume, revenue turn out is expected to reach US$1.45 billion by 2018, at a CAGR of 5.2%. The report also indicates that commodity plastics such as PVC, PE and PE account for most of the total volume. Healthy growth in Western markets The US remains to be the main driver of growth for medical plastics, according to Frost & Sullivan. This finding is reaffirmed by Lucintel, a global management consulting and market research firm, that says the US accounts for 46% of the global market. Lucintel also reported that technological advancements, nanotechnology applications as well as robotics will create a new segment in the medical device industry. Meanwhile, Southeast Asia’s medical device markets have had marked growth, especially in imports of medical devices and increasing healthcare expenditures amongst end-consumers, according to a study published by UK-based Epsicom Business Intelligence. It also noted that although demand is strong, impeding factors, such as tariff regulations imposed through free trade agreements with the more developed economies, will affect market expansions. Maintaining a safety check Material safety has set the stage for comparison: which is the best material that could ensure a patient’s safety? Several incidences of complications with metallic devices, such as knee replacements and transvaginal mesh, have been reported. Recently, the US FDA recalled a metal hip replacement made by Johnson & Johnson's subsidiary, DePuy Orthopaedics. It was found to be releasing fragments of metal, causing tissue damage and at times seeping into the bloodstream. Nevertheless, plastics are not without their problems. For instance, health-risk concerns have prompted companies such as Kaiser Permanente to ban DEHP plasticiser-containing PVCs, amidst claims of leeching. Last year, the French government passed a law unilaterally banning the use of tubing containing DEHP phthalate from paediatric, neonatal and maternity wards. The ban will come into force in 2015. Typically 20-40% content of DEHP is used to soften PVC blood bags. Nevertheless, the European Council of Vinyl Manufacturers (ECVM) claims that there is currently no viable plastic material that could be used to replace PVC, which has been used for manufacturing blood bags for over 50 years. The PVC-DEHP combination has proven itself highly suitable for the manufacture of blood bags because DEHP stabilises red blood cells, minimising hemolysis (the rupturing of red blood cells).
Medical PLASTICS Thus, it is not surprising that increasing regulatory requirements are in place for plastics, against the backdrop of widespread environment concerns, awareness for safety and shelf life of consumables and rising allergy threats. These concerns have, thus, put pressure on polymer manufacturers and engineers to come up with viable solutions. For instance, Teknor Apex has developed three new TPE wire and cable compounds as alternatives to PVC that can be used by hospitals for meeting stringent medical standards, the company says. Medalist 8421, 8431, and 8451 elastomers can be used for insulation, jacketing, and moulded fittings and connectors. They have Shore A hardness levels of 92, 69, and 82, respectively, a flammability classification of HB (UL-94), and a maximum continuous operating temperature rating of 105ºC (UL-1581). The three compounds retain high levels of tensile strength, tensile modulus and elongation after autoclave, gamma irradiation, and EtO sterilisation. They are resistant to the cleaning solutions commonly used in medical facilities. The new TPEs are analogs to specific Elexar non-medical wire and cable compounds from Teknor Apex and provide comparable properties but are manufactured in an ISO-13485 facility dedicated to Medalist medical elastomers. A patient with electromonitoring wires made of Teknor Apex’s TPE
Citing the Frost & Sullivan study on polymers in medical devices, there has been an ongoing focus now on engineered polymers such as co-polyether-ester elastomers (COPE), polyether block amides (PEBA) and acetal chemistries that are suitable for advanced applications like implants and tissue engineering. PEEK developments in spinal implants US-based Solvay Specialty Polymers says that TranS1, a supplier of minimally invasive spinal implants and medical devices, has commercialised the VEO Direct Lateral Access and Interbody Fusion System that incorporates a lumbar fusion cage implant made of Solvay’s Zeniva PEEK resin. The VEO system also features a tubular retractor made of Solvay’s Radel PPSU resin for radiolucency and the ability to withstand repeated steam sterilisation.
VEO’s interbody cage is made from Zeniva PEEK rod stock that TranS1 offers in various sizes, including widths of 17 mm and 22 mm and lengths from 40-60 mm. The implant has a large centre channel to allow bone growth through the device, fusing the adjacent bony surfaces of the vertebrae. Zeniva PEEK has a modulus very close to that of bone plus toughness and fatigue resistance. It is certified to meet the full requirements of the ASTM F2026 standard for PEEK used in implantable surgical devices. The VEO brings clear and direct visualisation to lateral fusion surgery, thus minimising iatrogenic trauma to the psoas muscle and the nerve plexus to help reduce the risk of post-operative complications. German chemical firm Evonik's Vestakeep PEEK that has been used by US-based K7 for its K7C Cervical Spacer spinal implant device has received the FDA’s 510(K) approval for use as an Intervertebral Body Fusion (IBF) device, a first for the material for this kind of product. The material is known for its biocompatibility and biostability as well as sterilisation resistance and good combination of stiffness and ductility. The Vestakeep PEEK material also has regulatory clearance for spinal implants in Europe and Asia. With this 510(K) approval, customers will now have easier access to regulatory approvals in the US market. Meanwhile, complementing innovations for polymer implants, researchers from the North Carolina State University have developed and successfully implemented a bioactive film coating for PEEK polymer implants used in spinal surgeries. The film coating enhances the efficacy of PEEK polymer implants, since the researchers say PEEK does not bond well with bone or other tissues in the body. Over time, the implant rubs against the surrounding tissues and this can cause complications. The technique coats the implant with a thin film of yttria-stabilised zirconia (YSZ) and thereafter a coating of hydroxyapatite, which is a calcium phosphate that bonds well with bone. The hydroxyapatite layer is then heated using microwaves. The YSZ layer acts as a heat shield, preventing the PEEK from melting. Meanwhile, North Carolina University: the top scanning electron microscope image (b) shows a cross section of the bioactive hydroxyapatite/YSZ coating without heat treatment. Note how the two layers are distinct. The bottom image (f) shows the coating after heat treatment and the layers that are now integrated
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Medical PLASTICS the heat gives the hydroxyapatite a crystalline structure that makes it more stable in the body, enabling bonding with the surrounding bone. The University says it has received funding from the National Institute of Health to proceed with animal testing to fine-tune the technique. Medical-grade plastics Supporting the use of appropriate materials for medical devices, French chemicals firm Arkema says that it only recommends special, higher-priced grades of MED resins for medical applications. The castor oil-based speciality polyamides have a distinct set of properties such as good chemical resistance, compared to fossil fuel-based materials. Most polymers used in minimally invasive surgical devices are hydrophobic and create friction against moist bodily tissue. Hydrophilic coatings are often applied to these polymer components to reduce friction and avoid tissue trauma, yet they add additional manufacturing steps and may provide more lubricity than necessary. Arkema’s hydrophilic Pebax MV 1074 SA 01 MED polymer absorbs up to 48% of moisture from the surrounding environment and forms hydrogen bonds that create a wet film on the component surface that enhance lubricity against bodily tissue. Comparatively, in the same conditions, Pebax SA 01 MED copolymers commonly used for medical devices absorb only 1.2% moisture. Meanwhile, Pebax MV 1074 SA 01 MED is a flexible thermoplastic elastomer with a 40 Shore D hardness and 80 MPa flexural modulus. Ease of processing and melt compatibility with traditional polyether block amide and polymers offer excellent opportunities in co-extrusion applications. Pebax MV 1074 SA 01 MED polymer can be extruded as a hydrophilic polymer layer in a multi-layer tube or film extrusion for surfaces directly in contact with bodily tissue that require high moisture absorption. Germany-based Bayer MaterialScience (BMS) has also introduced a PC-grade Makrolon Rx2440 for medical devices. The material is said to offer a faster recovery time in colour shift and can also be sterilised with high-energy radiation (gamma or e-beam) and ETO. It is suitable for applications requiring biocompatibility that meet ISO 10993-1 and USP Class VI. According to BMS, its new PC material can be used in a variety of medical device applications, such as IV access, respiratory, surgical and renal care. Elsewhere, US-based speciality chemicals firm Lubrizol has recently launched eight new medical materials that are available in four clear grades and four radiopaque grades that include a 20% loading of barium sulphate. An extension of the Carbothane line of PC-based TPUs, the materials are designed to feature improved chemical/creep resistance and are suitable for long-term implant applications, including catheters and devices that will remain in the body for more than 30 days, and for permanent spinal and orthopedic implants.
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In other news, Lubrizol has a new formulation of synthetic biochemically absorbable polymers, or “bioabsorbable polymers,” which are plastic-based materials that dissolve into compounds the body can safely absorb or eliminate. Absorbability is useful in a wide variety of applications, as it enables the safe internal use of medical With the development of advanced devices, wound care technology, Lubrizol says its implements and drug bioabsorbable polymers are delivery systems, set to become valuable tools in without requiring orthopaedic treatments, wound removal. By being care and tissue engineering truly “tunable,” Lubrizol’s bioabsorbable polymers overcome the strength and longevity challenges that have prevented the widespread use of existing bioabsorbable materials in some applications. Currently, bioabsorbable polymers are used for operative assistance, damage healing and drug release. With the development of advanced technology from Lubrizol, bioabsorbable polymers are set to become valuable tools in orthopaedic treatments, wound care and tissue engineering. Another US-based materials firm Styron has introduced two new compounds: Emerge PC/ABS 7700 and Magnum Mass ABS for medical equipment housings. The PC/ABS blend used for powered medical devices offer ignition resistance and longer colour stability, whilst the ABS resins are manufactured in a continuous mass production process that offers improved lot-to-lot consistency, natural whiteness and easy processing characteristics. Meanwhile, US compounder RTP developed a custom RTP 2900 Series polyether-block-amide thermoplastic elastomer (PEBA) compound for Pl sticos y Materias Primas (PyMPSA), a Mexican manufacturer of medical devices and components, for a new catheter for epidural anesthesia. The firm had first specified a biocompatible nylon material that was radiopaque so it could be readily observed during x-ray imaging to ensure proper placement but Catheter produced from RTP's PEBA compound
Medical Plastics the efforts were disappointing with the extruded nylon ending up with a lot of air bubbles. RTP says its material has passed ISO 10993 biocompatibility testing conducted by PyMPSA. It solved the air bubble problem, leading to the successful development of the new SET ESPICAT catheter. The success of the catheter project has led to PyMPSA working with RTP on producing the catheter in several different colours to help medical and manufacturing personnel quickly identify different diameter versions. Bone growth using plastic scaffolds Growing bones using plastic scaffold has been made possible with a group of British scientists from the University of Southampton having developed a honeycomb scaffold using biomedical implantable PC. This could lead to revolutionary bone repair therapies for people with bone fractures or those who need hip replacement surgery due to osteoporosis and osteoarthritis. The structure was created in a nano-topographical pattern that funnels the human embryonic stem cells toward the bone cells. It is also porous so that it allows blood to flow through, thus enabling stem cells from a patient’s bone marrow to attach to the scaffold and grow new bone cells. As the new bone grows, the scaffold gradually decomposes. Welding made safe in medical devices US-based Eastman Chemical says that a new technology from IPG Photonics for welding clear-toclear polymers with fibre lasers is available to weld products made with its Tritan copolyester, including medical devices. Eastman says that welding techniques typically require an energyabsorbing additive to be added to the polymer, and with medical applications, there is always the question of biocompatibility with the polymer. Thus, the new technique eliminates the A new welding technology from IPG need for additives Photonics is able to weld and because the components made with Eastman’s welding work is Tritan done via laser, no tools come into contact with the medical device material, making this a highly clean and controllable process. Other benefits are a fully hermetic leak-proof precision joint that has a smooth weld that will not entrap bio-burden.
Antimicrobial plastics use silver technology Sabic Innovative Plastics has introduced new silver technology antimicrobial compounds to help medical device manufacturers reduce healthcare-acquired infections (HAIs) amongst patients and clinicians. The compounds have been tested for long reduction values, with the level of microbes eliminating from a surface, based on the ISO 22196-2007 standards. The company offers nine different antimicrobial grades across four product families, namely Lexan EXL copolymer, Lexan PC, Xenoy PC/PBT and PP resins with and without fibreglass reinforcement. Of these grades, five have a high antimicrobial effect and four have a low antimicrobial effect. These variations will allow users to choose the right formulation they require for their end-product application. According to Sabic, the silver technology is widely accepted as a broad-spectrum antimicrobial, with activity against many pathogens including gramme-positive and gramme-negative bacteria, moulds and fungi. Potential applications include fluid and drug-delivery applications, surgical instruments, monitoring and imaging devices as well as hospital furniture such as hospital beds and operating tables. Germany-headquartered chemical company BASF has also developed a medical device technology that prevents infectious germ build-up on surfaces, utilising the silver-based antimicrobial technology. Included in its solutions line is the HyGentic antimicrobial technology that prevents bacterial growth on surfaces and protection against bacterial colonisation on a variety of polymeric surfaces. Also available is HyGentic SBC, a transparent injectionmouldable styrene butadiene block (SBR) copolymer material; HyGentic PA, glass fibre-reinforced, injection-mouldable polyamide; and HyGentic NW, synthetic non-woven technology with builtin antimicrobial activity that is ideal for medical applications such as surgical masks, drapes, gowns and surgical kit wraps. Meanwhile, a novel research suggests that needles of the Douglas fir (Pseudotsuga menziesii), a common pine tree in the US can be used to sterilise nano devices meant for medical applications. The research led by Poushpi Dwivedi from India, which was published in the International Journal of Biomedical Nanoscience and Nanotechnology, detailed that from these needles, nanoparticles with silver nitrate solution are able to be extracted. The derived self-sterilising composite material - silver/ chitosan bionano composite - can be used to safely coat medical implants and surgical devices to prevent microbial growth. The scientists explained that bacterial infection in implanted medical devices, prosthetics and sensors happens despite advances in sterilisation procedures. The antimicrobial composites could thwart the disease causing microbes to permeate biomaterials and tissues. MARCH / APRIL 2013
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