Stephanie Lachapelle for Medtech1
Researchers at North Carolina State University have developed a metal foam material that may be used in bone implants.
Two common failures of conventional bone replacements are bone rejection and stress shielding. Bone rejection occurs when a rigid implant material like titanium metal is used to replace all or part of a bone, and the body rejects the material. Stress shielding occurs when an implant is unable to handle the amount of stress naturally placed on the limb. "If the modulus of elasticity of the implant is too much bigger than the bone, the implant will take over the load bearing and the surrounding bone will start to die. This will cause the loosening of the implant and eventually ends in failure”, says Dr. Afsaneh Rabiei, an associate faculty member of biomedical engineering at North Carolina State University and one of the researchers working on the new implant material. "When this happens, the patient will need a revision surgery to replace the implant,” he explains.
The new foam material is structured to avoid both of these common complications. This new material is lighter than solid aluminum, and can be made fully of steel or a combination of steel and aluminum. The material was designed to absorb the shock that a natural bone is subjected to during movement, and to foster new bone growth into the implant to improve the strength of the implant.
The material also has a high “modulus of elasticity”, which is a measure of the ability of a material to deform when pressure is applied, and to reform when pressure is removed. Measured in gigapascals (GPa), natural bone has a modulus between 10 and 30 GPa, whereas titanium has a modulus of approximately 100 GPa. The foam metal has a modulus closer to that of natural bone while maintaining a low mass due to its porous nature.
Researchers hope that this new metal foam will increase mechanical stability and the strength of the implant while decreasing the failure rate of bone implants.