Readying Medical Device Composite Materials for Takeoff

From wings and stabilizers to fuselages and landing-gear doors, carbon-fiber-based composite materials have become a standard feature of modern aircraft. And while they are also employed in a variety of medical devices, such as surgical instruments, tables, and external fixators, they have yet to come into their own in implantable medical device applications. The Center of Innovation for Biomaterials in Orthopedic Research (CIBOR; Wichita, KS), part of the National Institute for Aviation Research at Wichita State University, is determined to change this.

"From our inception, we have had a lot of knowledge of the aviation industry," explains Joel White, research engineer at CIBOR. "Home to Cessna, Beechcraft, Learjet, and Spirit AeroSystems, the Wichita area is known as the aviation capital of the world, and it is also one of the few capable hubs in the world for manufacturing composite materials." At the same time, because Wichita has a strong healthcare sector, CIBOR wanted to bridge the gap between the aviation and medtech sectors, applying its aviation knowledge to the design and development of medical devices.

The future use of composite materials in medical device applications is attractive for several reasons. In addition to being radiolucent, they boast high strength-per-weight and stiffness-per-weight ratios, are corrosion resistant, and are not prone to scratching other sensitive materials such as orthopedic implant bearing surfaces." And because they are not isotropic, homogeneous materials, they can also be tailored to meet the needs of specific medical devices. "For this reason, composites are often referred to as designer materials," White comments.

Carbon foam, a material used in aerospace composites that CIBOR is exploring for use as a bone scaffold, has additional beneficial properties, rendering it suitable for implantable medical device applications. "This material," White notes, "has proven to be biocompatible and has slightly osteoinductive properties. It also readily binds bone morphogenic proteins and stem cells, increasing their bioactivity." Consequently, the center has tested this material successfully in small-animal studies and is poised to test it in a large-animal study, demonstrating its potential promise in orthopedic applications.

Despite their undoubted benefits, however, composite materials can undergo degradation resulting from moisture ingression. They can also experience tissue discoloration--a phenomenon that occurs when tissue is exposed to unencapsulated carbon fiber and wear environments. Thus, to fully characterize the risks associated with the use of composite materials in medical device applications, CIBOR engineers are studying how they react to repeated sterilizations. In addition, they are studying the long-term biocompatibility of coated or uncoated composite materials in the body and the effects of motion and wear debris on tissue discoloration.

Although composite materials are used in mission-critical aviation applications, adapting them for use in the body has been challenging. "One of our main objectives is to increase our understanding of the materials' use in the context of the body," White remarks. Thus, one of the major hurdles holding back their adoption in implantable medical device applications is the need to develop new testing standards. Meanwhile, understanding the characteristics of composite materials and using them in applications for which they are suited can mitigate many of the risks associated with them. "Risks," White adds "can be avoided by better understanding the benefits of composite materials, knowing which applications can be most improved by their use, and properly designing devices specifically for them."

Bob Michaels is managing editor of Medical Product Manufacturing News.