Metal Implant Liability Invigorates Advances in Polymer Alternatives


metal-on-metal medical device materials

The risk of exposure to wear debris from commonly used metal-on-metal implants has led to renewed interest in developing new polymer medical devices.

By Crystal Morrison, Ph.D.

Recalls, regulatory warnings, and legal actions in the United States and abroad have called into question the safety and durability of traditional metal-on-metal (MoM) medical device materials. Hip replacements, for example, have been under intense scrutiny because wear debris for titanium implants pose patient health risks, such as tissue damage at the device site and potentially high metal ion levels entering the bloodstream. Due to these concerns, the U.S. Food and Drug Administration (FDA) has assessed the safety and effectiveness of MoM hip replacements, issued orders for post-market surveillance studies, and established a committee of scientific and clinical experts. Despite the warnings, recalls, and litigation surrounding MoM hip replacements, the market size and medical need for implants have been constant and will likely increase due to an ageing population. At the same time, polymer suppliers are ramping up production capacity of medical device materials, pursuing R&D initiatives, and pursuing acquisitions to ensure they are poised to meet polymer demands.

The shift to polymer devices from traditional metal-on-metal (such as titanium implant) medical device materials provides numerous advantages.

titanium aluminum wear debris particle

Secondary electron image of a titanium aluminum wear debris particle from a spinal implant screw that underwent life cycle testing. This type of debris can cause potentially negative health effects, such as tissue damage.

First, polymeric materials are less expensive than medical grade metals such as titanium. Polymers are also ideal for medical applications because of their tunable properties ranging from soft, flexible and permeable to rigid with excellent impact and wear resistance. Polymers are compatible with medical imaging tools and have excellent chemical, thermal and mechanical stability. Many polymers are even biodegradable, alleviating the need for expensive and invasive device removal. Highly promising features are continually being developed including materials engineered to mimic bone or soft tissue, polymer hydrogels with biocompatible degradation properties, and emerging composites and nano coatings for future devices. At every stage of the implant life cycle including device design, material selection, structural requirements, and clinical tests, multiple iterations of these devices may be necessary to determine the intricate relationship between implant structure, materials, and environment. With an array of possible materials and application, manufacturers must understand in vivo environments as well as material properties and testing requirements from nanoscale to device function.

Medical device manufacturers must operate in a litigious environment of ever-increasing regulatory scrutiny. The litigation-induced bankruptcy of Dow Corning sparked a re-evaluation of supplier risk in the medical device industry. After years of litigation claiming health concerns from silicone implants, the major breast implant manufacturers and material suppliers settled class action litigation for $3.4 billion in 1994. Subsequently, the Biomaterials Access Assurance Act (BAAA) of 1998 was created to offer protection for suppliers providing raw materials and polymers to the medical device industry. Legal risks still remain. Medical device manufacturers must accept more responsibility, and liability, for the performance of their devices. This responsibility requires manufacturers to guarantee high quality materials are received from suppliers prior to producing their devices.

The medical and regulatory landscape will change in the coming years as the medical device market continues to grow. To avoid many of the pitfalls associated with medical device issues, materials suppliers and device manufacturers must be aware of the scientific intricacies involved with introducing new materials into the human body. A challenge with any material, including polymers, is that their application must address specific device properties and functional requirements without adversely impacting other areas of performance. To allow polymeric materials to fully realize their substantial medical value, experts must understand the complete device life cycle, as well as the legal implications and regulatory changes that will evolve in the future.

REFERENCES

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Fries, R.C. Reliable Design of Medical Devices, 3rd Ed. CRC Press, 2012.

Colas, A.; Curtis, J. “Silicone Biomaterials: History and Chemistry & Medical Applications of Silicones” in Biomaterials Science, 2nd Ed. Edited by Ratner, B.D.; Hoffman, A.S.; Schoen, F.J.; Lemons, J.E. Elsevier Academic Press, 2004.

Reisch, M.S. “Resurgence for Medical Polymers.” Chemical &Engineering News, September 24th, 2012, p.19. http://cen.acs.org/articles/90/i39/Resurgence-Medical-Polymers.html?h=1982005040

“Plastics win, metals and glass lose in medical device material battle.” Plastics Today, August 8th, 2012. http://www.plasticstoday.com/articles/plastics-win-metals-and-glass-lose-medical-device-material-battle-080820122

Densmore, C.G.; Robison, T.W.; Smith, B.F.; Lewis, R.E. “Controlled Release and Adsorption of Cetylpyridinium Chloride Using Polymer Hydrogels.” Journal of Applied Polymer Science, 2006, 99(6), p. 3153. http://onlinelibrary.wiley.com/doi/10.1002/app.23210/abstract

Kalogerou, B. “Assessing Protections for Biomaterials Suppliers 12 Years After the Biomaterials Access Assurance Act.” McDermott Will & Emery, November 18, 2010. http://www.mwe.com/publications/uniEntity.aspx?xpST=PublicationDetail&pub=5876&PublicationTypes=d9093adb-e95d-4f19-819a-f0bb5170ab6d

Medical Device Alert MDA/2012/036 on all metal-on-metal (MoM) hip replacements. Medicines and Healthcare products Regulatory Agency (MHRA), June 25th, 2012 http://www.mhra.gov.uk/Publications/Safetywarnings/MedicalDeviceAlerts/CON155761

“DePuy ASR™ Hip Recall Guide” on DePuy Orthopedics website http://www.depuy.com.

Case MDL No. 2244 Document 811 Filed 09/27/12 UNITED STATES JUDICIAL PANEL on MULTIDISTRICT LITIGATION IN RE: DePUY ORTHOPAEDICS, INC., PINNACLE HIP IMPLANT PRODUCTS LIABILITY LITIGATION Patricia M. Gentry, et al. v. DePuy Orthopaedics, Inc., et al., C.D. California, C.A. No. 2:12-4446 (MDL No. 2244)

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