Hip and knee implants have done wonders for improving people's mobility and quality of life, but they are a bit of a nuisance at the airport metal detector. Metal is much more dense than bone, so x-rays don't pass through it readily, which leads to queues and the inevitable pat-down.
Carbon fiber medical implants can change that. While work on carbon fiber replacements for hip and knee joints is continuing, there are many medical applications where this material is already having a dramatic impact. Understanding this exciting field begins with an appreciation of the medical value of carbon fiber, followed by a dive into implants and other applications.
Characteristics of Carbon Fiber Favorable to Medical Applications
Lighter and stronger than steel, carbon fiber has been put to work in aerospace, motorsports, and automotive applications for several decades. Starting out as tape or a sheet, carbon fiber can be molded into complex structures that are stiff, strong, light, and more fatigue-resistant than any metal equivalent, even titanium. This saves weight while creating stronger structures and components.
In addition to these properties, carbon fiber has three other characteristics that interest medical professionals. It is:
- Radiolucent: X-rays of the intensity used for medical imaging pass through it
- Biocompatible: The body accepts carbon fiber implants, and evidence shows they facilitate osseointegration better than metal equivalents
- Similar in density and elasticity to bone
Uses of Carbon Fiber in Medical Equipment
Strength and radiolucence make carbon fiber a preferred material in many imaging applications. For example, CT and MRI machines depend on taking a 360° scan around a patient's body. If the table patients lay on was metal, it would block much of the imaging. To prevent this, patients lay on a cantilevered carbon fiber medical table that slides into the imaging field. These tables can bear more than two hundred pounds without deflection and without restricting the radiologist’s view.
Another medical equipment application of carbon fiber is power tools. These require seals that don’t leak in either direction and that withstand clinical cleaning and sterilization regimens. Unlike elastomeric seals, those made with carbon fiber-filled PTFE have the temperature and chemical resistance needed to hold up to these processes.
Prosthetic Applications of Carbon Fiber
Amputees require prosthetics that are lightweight, yet strong and durable, which makes carbon fiber the ideal material. A number of manufacturers are producing prosthetic sockets and limbs from carbon fiber. Manufacturing techniques originally developed for aerospace and motorsports are most commonly used to create prosthetics. These entail forming the shape with pre-impregnated tape and compression or autoclave molding. However, the use of 3D printing is growing, as seen in this new prosthetic leg, which uses an Ultramid polyamide that’s reinforced with short carbon fiber.
An interesting, and somewhat controversial, prosthetic application of carbon fiber concerns feet. Athletes have found that carbon fiber offers greater energy storage and dynamic response than the human foot can provide. This means carbon fiber prosthetic feet give athletes with a disability an advantage. Carbon fiber can also provide performance gains when incorporated into sports footwear.
Carbon Fiber Medical Implants
Extensive research, such as that detailed in, “Carbon Fiber Biocompatibility for Implants,” confirms that carbon fiber is not only safe for medical implants, but confers several advantages over other implant materials. These include superior transfer of loads, which, in accordance with Wolff’s Law, helps strengthen bone, and electrical properties that encourage tissue formation.
Orthopedic implants are typically produced from carbon-fiber-reinforced polyetheretherketone (CFR-PEEK). PEEK is a thermoplastic polymer with excellent chemical resistance, a high melting point, and a glass transition temperature of around 289°F. Adding short length carbon fiber to the mix creates a composite that’s strong, fatigue-resistant, and lightweight. A composite flow molding process, which is a derivation of injection molding, is used to make CRF-PEEK implants.
CFR-PEEK has been used in bone screws and implants for several years. Spinal cages are another established application, and more recently, doctors have started using the material to replace spinal discs. Work is underway on using CFR-PEEK orthopedic implants as alternatives to titanium in knee and hip replacements.
Interestingly, implants are an application where the radiolucence of carbon fiber is not so beneficial. The issue here is that it doesn’t show up on X-rays, making it harder for medical professionals to determine location. Manufacturers of carbon fiber medical implants address this by adding materials that scatter X-rays, notably tantalum wire.
Making Life Better for Millions
The properties that make carbon fiber so attractive in aerospace, motorsports, and sporting goods, like footwear and bicycles, also make it an excellent candidate for a host of medical uses. This is further supported by carbon fiber being radiolucent and having similar mechanical properties to human bone. While medical equipment and prosthetic usage is booming, the implant applications have the greatest potential to improve clinical outcomes and improve quality of life. Maybe they’ll even put an end to delays at airport metal detectors!