Artificial joints can be complex devices to mass produce. Traditionally, orthopedic device manufacturers rely on titanium because it’s a strong, lightweight material that is biocompatible with the human body. But, engineers at North Carolina State University think the future lies in foam.
A year ago, I wrote an article aboutorthopedic device manufacturing. Demand for replacement hips, knees, shoulders, spines and other old joints is skyrocketing as people live longer and enjoy more physically active lifestyles. By 2017, the orthopedic device industry is projected to be a $13 billion market.
Artificial joints can be complex devices to mass produce. For instance, knees must accommodate a range of motion up to 120 degrees, allowing them to naturally bend and rotate.
Traditionally, orthopedic device manufacturers rely on titanium because it’s a strong, lightweight material that is biocompatible with the human body. In addition, titanium can be welded using a wide variety of processes.
However, titanium poses numerous challenges to medical device engineers. Among other things, there’s a supply and demand problem. The titanium industry has experienced supply chain problems in recent years, due to extremely high demand and limited supply of raw materials. As a result, the race is on to develop an alternative.
Engineers at North Carolina State University think the future lies in foam. They recently created a “metal foam” that has a similar elasticity to bone but avoids the bone rejection that often results from using rigid implant materials, such as titanium.
The metal foam is lighter than solid aluminum and can be made of 100 percent steel or a combination of steel and aluminum using a powder metallurgy technique. Afsaneh Rabiei, an associate professor of mechanical and aerospace engineering at North Carolina State, believes it could lead to a new generation of biomedical implants.
The rough surface of the foam would foster bone growth into the implant, improving overall strength. In addition to the extraordinary high-energy absorption capability of composite foams, the modulus of elasticity of the foam is very similar to that of bone. Modulus of elasticity measures a material’s ability to deform when pressure is applied and then return to its original shape when pressure is removed.
“Modulus of elasticity is extremely important for biomedical implants,” says Rabiei. “Bone has a modulus of between 10 and 30 gigapascals, while titanium has a modulus of approximately 100 gigapascals. The new composite foam has a modulus that is consistent with bone and is also relatively light because it is porous.
“The rough surface of the metal foam will bond well with the new bone formed around it and let the body build inside its surface porosities,” claims Rabiei. “This will increase the mechanical stability and strength of the implant inside the body.”
If foam catches on, some day people with replacement hips and knees may be able to avoid setting off metal detectors when they go through airports. But, does anyone know if those controversial full-body scanners that are currently being installed at many U.S. airports can detect foam?
'Metal Foam' May Replace Worn-out Joints
By Austin Weber
Austin has been senior editor for ASSEMBLY Magazine since September 1999. He has more than 21 years of b-to-b publishing experience and has written about a wide variety of manufacturing and engineering topics. Austin is a graduate of the University of Michigan.