The Rise of Medical Polymers February 2013
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According to market analyst Frost & Sullivan, the market for engineering polymers in medical applications has grown considerably in the past decade, with global sales exceeding $2 billion in 2011 and demand set to double by 2018. One of the main reasons behind the increasing use of EPs in medical devices is the quest by engineers to replace traditional materials such as metals, ceramics, and glass with better materials. Some EPs have several advantages over traditional materials, which can include weight, biocompatibility, and cost. Concerns in 2012 surrounding the wear and corrosion of metal-on-metal (MoM) hip implants have also led to a surge in the medical community's uptake of implants containing EPs.
Engineering Polymers in Medical Implants
EPs such as polyetheretherketone (PEEK), polyetherimide, polyphenylsulfone, and polysulfone saw first use in experimental medical implants in the 1980s. Researchers then went on to conduct in-depth clinical studies in the 1990s that helped characterize the biocompatibility and in vivo stability of EPs. However, further progress was impeded by the reluctance of polymer manufacturers to supply the health-care market following a series of lawsuits against Dow Corning in the 1990s.
These lawsuits claimed that Dow Corning's silicone breast implants caused systematic health problems and eventually resulted in Dow Corning's agreeing to a multi-billion-dollar settlement for victims. To protect the chemical and plastics industry from future lawsuits, the US government established the US Biomaterials Assurance Act (BAAA) in 1998 and placed the burden of responsibility for any device failure on the manufacturer, not the material supplier.
The BAAA's reassurances to suppliers meant that the number of EP manufacturers seeking entry into the health-care market slowly grew in the next decade. In 2007, Solvay provided a notable entry by a leading EP manufacturer into the health-care market. Since then, the number of EP suppliers to follow suit has risen significantly, partly because of the relative stability of the health-care market, which has been sheltered from much of the impact of the global economic crisis that began in 2008.
Driving Force for Change
Although the strategic maneuvering of suppliers is indicative of an increase in demand for EPs, medical-device makers are the real driving force behind the growth in this sector. One indicator of medical-device manufacturers' growing interest in EPs is the rising number of US Food and Drug Administration (FDA) 510(k) clearances. FDA 510(k) clearances are necessary for companies introducing new medical devices into the US market. In 2001, only one FDA 510(k) clearance with a PEEK polymer featured in the registered name of an implantable device. Since 2001, the FDA has granted 97 such clearances, with the past two years (2011–12) accounting for 33% of these clearances.
One reason why device manufacturers are looking for a shift from traditional materials to EPs is that high-performance engineering polymers—such as PEEK—are less expensive than medical-grade metals such as titanium. Many EPs also have excellent chemical, thermal, and mechanical stability and are radiolucent, making implants compatible with a range of medical-imaging tools. Devices made from PEEK show the lowest wear rate of any counter metallic material.
An FDA enquiry in June 2012 called into question the safety and durability of MoM implants and concluded that it sees little use for MoM implants, favoring a greater use of ceramic and plastic alternatives in the future. Regulatory warnings from the FDA surrounding MoM implants may also become a significant contributory factor in future decision making about the type of material that goes into medical implants.
Applications of EPs in Medical Implants
The application of EPs in medical implants typically falls into three categories.
Device manufacturers use high-performance engineering polymers in a variety of spinal implants, including lumbar and cervical spacers. Surgeons typically use spacer units in spinal-fusion operations, a process in which surgeons fuse two or more vertebrae so that they can become a single strengthened unit—a procedure that helps protect the sensitive nerves running alongside the spinal column. Lumbar and cervical spacers typically contain a bone-graft material that, once implanted, promotes bone healing and facilitates the fusion. Many of the screws and rods that surgeons use to stabilize the spine further are also made of high-performance polymers. The use of EPs in spinal implants offer numerous advantages over the use of metals—such as titanium—including a similar elasticity to that of bone, helping to reduce jarring during situations of impact. Because of these advantages, the use of PEEK in spinal implants is becoming commonplace, with the number of FDA 510(k) clearances accelerating during 2012. Many of these clearances come from small start-up companies, such as Nexxt Spine and SpineNet, that specialize in the manufacture of unique cervical and lumbar spacers using Solvay's Zeniva PEEK.
The cranial-implant market is dominated by a number of medical-device manufacturers, including Synthes, which has been providing custom-fit cranial implants since 2004. The cranial implants themselves have traditionally been made from metals—such as titanium—and customized using patients' computed tomography data and computer-aided design/computer-aided manufacturing. Manufacturers such as Synthes are now starting to move away from the use of metal in preference for high-performance EPs because of their lower cost and improved biocompatibility.
Choice of material is not the only aspect of implants that medical-device manufacturers are changing. The means of manufacture is also changing, with 3D printing seeing increasing use. In December 2011, the Custom IMD group, an EU–backed initiative, designed and manufactured the first laser-sintered PEEK cranial implant. Working in conjunction with EOS, the Custom IMD group used a unique sintering system that operated at temperatures up to 385°C, necessary for processing PEEK. One of the advantages of using 3D printing to manufacture these implants is that surgeons can design implants to include highly complex structures. The prototype designed by the Custom IMD group comprised a structured PEEK mesh that was subsequently filled with a bioabsorbable polymer/ceramic hybrid material. The Custom IMD group demonstrated that the combination of the mesh and the bioabsorbable polymer allowed the gradual infiltration of a patient's own bone cells and promoted natural bone growth. The demand for custom-made implants using additive-manufacturing techniques is likely to increase as the capabilities of 3D printing continue to expand.
Hip and Joint Replacements
Researchers at the Fraunhofer Institute for Manufacturing and Automation in Stuttgart, Germany, part of the EU-backed ENDURE (Enhanced Durability Resurfacing Endoprosthesis) project, are currently working on the final design of a prototype hip replacement. The project's design comprises a hip socket made of carbon-fiber-reinforced PEEK in combination with a ceramic femoral head.
The prototype has several distinct advantages over traditional hip replacements. Aside from being metal free, the prototype hip replacement works with the natural shape of the joint instead of removing large sections of the existing bone structure. In doing so, the transmission of force through the PEEK hip socket to the pelvic bone is modeled on natural conditions, thus avoiding any potential adverse bone adaptation.
In a separate study in September 2012, researchers at the University of Glasgow (Scotland) published their findings about the use of PEEK in hip implants. In traditional hip-replacement surgery, surgeons remove the head of the femoral bone and replace it with an implant, which is held in place by a rod fixed inside the marrow along the length of the bone. One of the problems associated with using this technique with a metal rod is that stem cells in the bone marrow tend to differentiate into soft tissue, leading to the loosening of the implant, typically limiting the lifetime of the implant to about 20 years. The researchers at Glasgow found that PEEK implants may potentially go some way to solving this problem and creating an "implant for life."
In collaboration with the University's James Watt Nanofabrication Centre, the researchers at Glasgow produced a PEEK sample with nanopatterns of tiny holes—about 120 nanometers in diameter—along the surface. When they placed stem cells on the surface of the PEEK sample, the stem cells diffused into the pores and, unlike metal, preferentially differentiated into bone cells, creating a much stronger bond between the PEEK and the surrounding tissue. The researchers believe that this technique could apply to a wide range of joint replacements and other orthopedic surgeries and are hoping to see a prototype ready for use within a decade.
Conclusions and Implications
The medical-device market is becoming increasingly aware of the capabilities of high-performance EPs. Suppliers' ability to tailor the physical and chemical properties of EPs grants device manufacturers the capability to fine-tune the functionality and biocompatibility of their products. Complementary manufacturing technologies—such as 3D printing—extend their capabilities, enabling custom-fit implants, which further help to drive demand for EPs in health-care applications.
The demand for EPs within the health-care market will be driven not only by advances in manufacturing and new applications but also by the growing markets of Asia: Japan, with its high-age population, will be a large target audience for medical implants and devices, and China is set to become one of largest marketplaces for medical devices and implants, driven by radical health-care reform and a rapidly growing middle class able to afford implant surgeries.