But a lot goes on under the surface of the various plastics in use in medtech—some examples of which are polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polymethyl methacrylate (PMMA). In the manufacture of plastics, fillers are used to improve performance and/or reduce production cost. For medical devices, often fibrous materials such as glass or carbon are added to resins to create reinforced grades with enhanced physical or mechanical properties. For example, adding 30 percent short glass fibers by weight to nylon 6 improves creep resistance and increases stiffness by 300 percent. However, these glass-reinforced plastics usually suffer some loss of impact strength and ultimate elongation, and are more prone to warping because of the relatively large difference in mold shrinkage between the flow and cross flow directions. Plastics with non-fibrous fillers such as glass spheres or mineral powders generally exhibit higher stiffness characteristics than unfilled resins, but not as high as fiber-reinforced grades. Resins with particulate fillers are less likely to warp and show a decrease in mold shrinkage. Particulate fillers typically reduce shrinkage by a percentage value roughly equal to the volume percentage of filler in the polymer, an advantage in tight tolerance molding.1
And then there are plasticizers, which have been the focus of scrutiny at least since the late 1990s when European regulators banned phthalate plasticizers from children’s toys. Plasticizers are used as additives to improve the fluidity of materials, and while they are sometimes used in other materials such as concretes or clays, they are most often used in plastic manufacturing. Phthalate plasticizers are used primarily to soften polyvinyl chloride (PVC), which is a form of plastic found in a wide range of medical devices including intravenous and blood bags, various types of tubing, and dialysis bags.
Due to concerns over the potential adverse effects on human health, the selection of di (2-ethylhexyl) phthalate (DEHP) as a plasticizer in flexible PVC has been a hotly debated issue for the last decade in the disposable medical device market. REACH legislation in the European Union (EU) has placed the phthalate DEHP on a list of Substances of Very High Concern (SVHC) for several years. Since February this year, DEHP can only be used for authorized applications; but essentially, DEHP use in the majority of industries within the EU has ceased. DEHP’s use within the medical industry is outside of the scope of the REACH legislation and is governed by the Medical Device Directive (MDD), so DEHP can continue to be used for medical applications.
Despite this exemption, due to the health concerns over DEHP, the medical device industry in the EU is gradually moving away from the use of DEHP. To address these concerns, Ridgefield, N.J.-based Colorite (a Tekni-Plex Inc. company), which manufactures in Europe, China and the United States, has adapted to these regulations by advancing their range of non-phthalate product platforms providing continuity in the global supply chains for U.S. medical device companies.
“As the Medical device industry transitions to non-phthalate plasticized PVC compounds, the first priority is to ensure that flexible PVC remains the material of choice for single use medical device applications,” Paul McShane, Ph.D., global technology director for Colorite, noted to Medical Product Outsourcing.
McShane also noted that Colorite has a dedicated global team of expert chemists supporting the transition, ensuring that the next generation medical PVC compounds matche the long term integrity, reliability, value and process versatility that has been characteristic of traditional DEHP compounds. He added that although non-phthalates have been used successfully in selected medical applications for many years, the transition to non-phthalates across the full spectrum of disposable medical devices has posed technical challenges. This includes extrusion, processing, assembly, biocompatibility, aging and sterilization requirements of the different industry segments and has caused medical device companies to re-evaluate their production and assembly technologies.
“There is a number of competing non-phthalate chemistries, including trimellitates, terephthalates, adipates and citrates, each with their advantages and disadvantages depending on the product requirement and end application,” McShane said. “Ultimately, there is no one size fits all solution like the traditional DEHP. “
Reprocessing and Recycling
But the elephant in the room with plastics is the issue of recycling plastic devices, and the environmental consequences of plastics manufacturing. For medical devices, this issue is often not at the forefront of discussion because the relative need and importance of devices in the medical space are high. It is one thing to reprimand populations for using too many plastic bottles or for not disposing of plastic toys correctly; but it is another to cause anxiety surrounding the use of plastic medical devices when their users need them to heal a disease or even to survive.
Because disposable devices are so often made of plastic, the issue of recycling for these devices is important. The flip side of that coin is improving the reprocessing of reusable devices, which may be made from plastics or metals. With better reprocessing, not only would hospital acquired infections be reduced, but the use of resusable devices could increase allowing for more savings for hospitals that do not have to restock disposables as much.
The U.S. Food and Drug Administration’s (FDA) Center for Devices and Radiological Health (CDRH) has made the improvement of reprocessing a priority for 2016. According to the FDA, reusable devices are commonly used in patient care and many reusable devices have evolved into more complex designs, making them more challenging to reprocess. To minimize patient harm from inadequately reprocessed devices and to enhance the safety, effectiveness, performance, and/or quality of these devices, it is critical to develop a comprehensive approach to address the effectiveness of reprocessing techniques.
“A 2016 FDA Top 10 regulatory science priority is to improve the quality and effectiveness of reprocessing reusable medical devices,” said Tim Cabot, president of DCHN LLC., a Woonsocket, R.I.-based provider of metal and anodizing finishing services. “This formalizes a need that has been apparent for quite some time about how devices need to be engineered for cleaning and sterilization and have validated processes that demonstrate the effectiveness of these processes. While some companies are further ahead than others in implementing these requirements, all companies will be impacted. What we are interested in is how to protect aluminum devices and the printing on these devices through repeated cleaning, disinfecting, and sterilization cycles. Anodizing is commonly used for aluminum parts used for handles, couplings, housings, and other components of surgical power tools, scopes, and a range of ancillary equipment such as cases and trays. While anodizing initially looks great and can be decorated to meet a wide range of branding needs, it doesn’t perform with many common cleaning chemistries and a variety of sterilization methods. This is the area that we are really excited about as we are working with some of the top medical device companies to upgrade their aluminum finishing specs and meet the FDA’s challenge.”
With advancements in blending materials, biomimicry and hyper-customization is becoming commonplace as a feature of medical devices. Nitinol, for instance, has emerged in recent years as a sort of wonder-metal with the ability to retain “shape memory”—i.e., nitinol can undergo deformation at one temperature, and then recover its original, undeformed shape upon heating above its transformational temperature. Superelasticity occurs at a narrow temperature range just above its transformation temperature; in this case, no heating is necessary to cause the undeformed shape to recover, and the material exhibits enormous elasticity, some 10-30 times that of ordinary metal. Nitinol is an almost equal-measure alloy of nickel and titanium. While nickel poses some concern regarding allergies and carcinogens, modern methods of electropolishing and passivation have alleviated some of that concern by forming very effective protective barriers between the metal and its environment. Nitinol’s use in implanted self-expanding stents, such as the Epic Vascular Self-Expanding Stent System from Boston Scientific Corporation, has proven successful with no evidence of corrosion or nickel release; and the outcomes in patients with and without nickel allergies are indistinguishable.
“What’s exciting today is that there is much more of a focus on trying to better mimic the behavior of natural biological systems and materials,” Gemma Budd, business manager of Healthcare for Lucideon Ltd., a materials technology company based in Staffordshire, United Kingdom, and Raleigh, N.C. “For example, self healing polymers, bioresorbable composites, cellular scaffolds, etc. which often also have a therapeutic effect—they are not just inert physical structures that simply sit in the body. They are bioactive, either inherently, e.g. via release of ionic species that trigger cellular pathways or having surface functionality that attracts cellular attachment or stimulates behaviors; or by acting as carriers for drugs, whether that is small molecules or larger protein based therapies. Many existing materials can’t offer the right balance between physical integrity and biological activity, so there is a lot of work being done to try and develop new ones or to combine the best of multiple materials by engineering new processing technologies as well as exploiting natural processes.”
Materials such as nitinol fall under the category of smart materials—materials that can be significantly changed in a controlled fashion by stimuli such as heat, changes in pH, stress, moisture, or even electric and magnetic fields. A recognizable example are the photochromes in certain eyeglasses that allow them to change to sunglasses in the presence of sunlight. A range of piezoelectric materials, which generate electricity in response to stress, comprises the functional component of ultrasound and echocardiograph probes. Their ability to act as a transducer between voltage and pressure at elevated frequency makes them highly useful for biomedical imaging.
“Smart materials are a very interesting new sector of the advanced flexible materials industry,” Brianna Sporbert, director of Sourcebook Engineering for Lee, Mass.-based Boyd Technologies Inc., a precision converter of flexible materials. “They pose many new challenges, but also opportunities to advance the point-of-care and home care markets. To me, this is a crucial area of medicine that must continue to thrive and develop. Smart materials have the ability to increase global health by providing access to medical care in the developing world, and increase the ease of preventative care in the developed world. With our company’s ongoing development of Sourcebook, a material sourcing platform, we have had the opportunity to work closely with many of these new novel materials as they are added to the database and incorporate into our customers’ products. The more these materials are tested and used the more applications we seem to be finding for them, which makes for an exciting future for smart materials.”
Boyd Technologies’ Sourcebook is a material sourcing website that allows customers to search, compare, and sample thousands of flexible materials. The Sourcebook sample library is filled with samples of all the materials available on the company’s website. Samples ship directly to the customer overnight to help projects stay on track.
“When you optimize the right material or composite materials, you can significantly improve the performance and reliability of the finished device,” Jens Troetzschel, vice president of Advanced Technologies for St. Paul, Minn.-based Heraeus Medical Components (Heraeus Deutschland GmbH & Co. KG), told MPO. “And we are seeing some impressive breakthroughs in unlocking the potential of materials. There have been huge steps made in manufacturing technology to produce greater precision and accuracy, for example. Improving materials also enables the industry to raise quality standards, which is a critical requirement for the industry. All of these developments are encouraging, but we aren’t there yet as an industry. But I am confident that we will see continued progress in these areas.”
According to Troetzschel, Heraeus is seeing a trend towards composite and more complex materials that offer superior functionality—for instance, through integrated sensors—better biocompatibility, and increased miniaturization. The company’s newest innovation, CerMet Composites, is an example of where materials science is moving. The composites, which are mixtures of ceramic and metallic materials, offer complete electrical integration, biocompatible hermetic encapsulation and 3D design functionality in one solution.
“[CerMet] is a game-changer for us, because it is going to enable our device customers to deliver more effective therapy for the patient, greater reliability and safety and an increased yield in production,” Troetzschel added.
Sporbert, too, noted the prevalence and importance of composite materials in the medical device manufacturing space. “In recent years manufacturers have been working hard to develop cost efficient, high performing tapes and composites,” she said. “Several years ago there was a movement in industry towards using silicone adhesives, but because of the high material costs its demand has diminished. This has given manufacturers of other medical grade adhesives the opportunity to develop low trauma adhesives at a more feasible price that has the same functionality as silicone adhesives. This has resulted in an impressive new generation of adhesives that can be used for medical devices and advanced wound care applications.
“As the industry moves forward I foresee that manufacturers will begin to integrate the functions of the other material components of the product into the adhesive material,” Sporbert continued. “We have already seen the beginnings of multi-functional adhesives that are in development. These materials have particulates that act as an antibacterial substance as well as materials that actually aid in the healing of the wound.”
Materials in 3 Dimensions
Today, 3D printing technology can handle plastics, metals and ceramics—and universities and research institutions are experimenting with various live-tissue 3D printing. Most often, 3D printing (also known as rapid prototyping) is used for prototyping medical devices, and plastics are often used for mockups because they are cheap and lightweight. Direct metal laser sintering (DMLS), on the other hand, has been in use for over two decades in the medical device industry. Munich, Germany-based EOS Gmbh, for instance, provides an entire line of DMLS machines that can create the most complex metal medical components and devices through additive manufacturing.
MPO asked our expert sources for their perspectives on 3D printing materials in use today, and what their future might hold:
“3D printing is potentially turning into a Pandora’s box at the moment,” Lucideon’s Budd said. “There is undoubtedly a lot it can offer, but it is being dubbed the answer to the world’s problems…and the truth is, it is causing a lot of problems as well! We are spending a lot of time working with medical device manufacturers using metal and even ceramics for 3D printing because we realize that they are gaining some features at the expense of others. What industry doesn’t know yet is whether the ‘lost’ features are critical to performance or whether they have been previously over-engineered. Using our expertise in materials science and engineering, we look at the fundamental properties, e.g. microstructure of the 3D printed materials vs. traditional processing routes, and give more informed insight into whether they do need to be concerned—and how to overcome some of those concerns by modifying the process/materials. For example, a key issue is that 3D printing relies on the joining of lots of discrete particles—which means there are lots of potential defect points vis-à-vis normal processes—and ensuring those potential defects don’t lead to actual defects is a challenge that spreads from medical devices through to aerospace. Customers are now starting to look at post-processing as well as taking more control over their raw materials, to limit these risks moving forward—and we are helping to design and validate these processes.”
“3D printed materials align well with the advanced flexible materials industry because often these materials and components are used in single use products,” said Boyd Technologies’ Sporbert. “The advancements that have been seen in additive manufacturing make the use of 3D parts much more economically and dimensionally feasible. This provides our customers with additional access to single use technology and increases their ability to develop more innovative products.”
“3D printing shows lots of promise and potential, but it’s still in its infancy as an emerging process,” Heraeus’ Troetzschel said. “Additive manufacturing has a huge potential to revolutionize every industry and the medical field is no exception. Noteworthy are especially orthopedic implants that could potentially be tailored and custom-made for a patient—something that would be otherwise hard to achieve by conventional methods. The potential of 3D printing for the field of active implantable medical devices is yet to be revealed. Heraeus is highly active in the field of 3D printing materials, and we have formed a global team focused on additive manufacturing. 3D printing and manufacturing has a lot of opportunities within medical/healthcare even if it is still in its early stages. Our scientists, engineers and researchers are taking on this opportunity whether by the use of own 3D manufacturing facilities or by research into novel materials for this technology.”