Carbon Fiber Innovations for the Medical Industry

Hip and knee implants have done wonders for improving people's mobility and quality of life, but they are a bit of a nuisance in airport metal detectors. Metal is much denser than bone, so X-rays don't easily pass through it, which can lead to lines and the inevitable pat-down searches.

Carbon fiber medical implants can change that. While work continues on carbon fiber replacements for hip and knee joints, this material is already making a huge impact in many medical applications. Understanding this exciting field begins with understanding the medical value of carbon fiber before delving into implants and other applications.

Knee Joint

Carbon fiber properties favorable for medical applications

Lighter and stronger than steel, carbon fibers have been useful in aerospace, motorsports and automotive applications for decades. Starting with tapes or sheets, carbon fibers can be molded into complex structures that are stiffer, stronger, lighter and more fatigue resistant than any metal equivalent or even titanium. This allows for weight savings while creating stronger structures and components.

In addition to these properties, carbon fiber has three other properties that are of interest to medical professionals. It is

Radiopaque: X-rays of the intensity used for medical imaging pass through it

Biocompatibility: the body accepts carbon fiber implants and there is evidence that they promote osseointegration better than their metal equivalents

Density and elasticity similar to bone.

Four Bar Hip Joint

Carbon fiber uses in medical devices

Strength and ray permeability make carbon fibers the material of choice for many imaging applications. For example, CT and MRI machines rely on a 360° scan of the patient's body. If the patient is lying on a table that is metal, it can block much of the imaging. To prevent this, patients lie on a cantilevered carbon fiber medical table that slides into the imaging area. These tables can support over 200 pounds without deflection and without restricting the radiologist's view.

Another medical device application for carbon fiber is power tools. These require seals that do not leak in either direction and can withstand clinical cleaning and sterilization protocols. Unlike elastomeric seals, seals made from carbon fiber-filled PTFE have the temperature and chemical resistance needed to withstand these processes.

Four Bar Pneumatic Knee Joint

Prosthetic applications for carbon fibers

Amputees need lightweight, strong and durable prostheses, which makes carbon fiber an ideal material. Many manufacturers are producing prosthetic nests and limbs from carbon fiber. Manufacturing techniques originally developed for aerospace and motorsports are most commonly used to create prosthetic limbs. These require the use of pre-impregnated tape and compression or autoclave molding to form the shape.

One interesting and controversial application of carbon fiber for prosthetics involves the foot. Athletes have found that carbon fiber provides greater energy storage and dynamic response than the human foot can provide. This means that carbon fiber prosthetic feet offer an advantage to athletes with disabilities. Carbon fibers can also provide performance enhancements when incorporated into athletic footwear.

Carbon Fiber Storage Energy Sach Foot

Carbon Fiber Medical Implants

Extensive research, such as that detailed in "Carbon Fiber Biocompatibility for Implants," has confirmed that carbon fiber is not only safe for medical implants, but also offers several advantages over other implant materials. These include superior load transfer, which, according to Wolff's Law, helps strengthen bone, and electrical properties that promote tissue formation.

Orthopedic implants are typically made from carbon fiber-reinforced polyetheretherketone (CFR-PEEK), a thermoplastic polymer with excellent chemical resistance, a high melting point, and a glass transition temperature of approximately 289°F. The addition of short lengths of carbon fiber to the blend results in a strong, fatigue-resistant and lightweight composite. The composite flow molding process is a derivative of injection molding and is used to make CRF-PEEK implants.

Stainless Steel Single Axis Mechanical Hip Joint

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 of people

The same properties that make carbon fiber so attractive in aerospace, motorsports and sporting goods such as footwear and bicycles also make it a great candidate for many medical uses. This is further supported by the fact that carbon fibers are ray-permeable and have mechanical properties similar to those of human bone. While the use of medical devices and prosthetics is booming, implant applications have the greatest potential to improve clinical outcomes and enhance quality of life. Maybe they'll even put an end to airport metal detector delays!