Understanding Corrosion in Medical Implants

Innovation in materials chemistry and engineering has led to wider use of medical implants, including dental, orthopedic, cardiovascular, and neurological implants, to improve patient quality of life.

Research characterizing the potential corrosion of biomedical metal alloys used in these implants can help the healthcare industry understand the risks of incorporating specific alloys into distinct applications, such as the potential for adverse patient reactions or impairment of implant functionality.

In his article "Pit initiation on biomedical alloys — A review," published in the Journal of Biomedical Materials Research, Exponent's Bruce Pound explores published research regarding pitting corrosion — a localized form of corrosion  —  that can produce pits on an implant surface and greatly increase the release of dissolved metals into surrounding fluid and tissue.

In his review focusing on biomedical alloy pitting sites, which generally tend to be inclusions or other particles present in the alloy, Dr. Pound found that pitting in stainless steel can initiate at sulfide and oxide inclusions and that pitting related to nitinol, a nickel-titanium alloy, can initiate at carbide and oxide inclusions, as shown in his own research.

The review article also explores cobalt-chromium (CoCr) alloy pitting, including in cobalt-chromium-molybdenum (CoCrMo) and cobalt-nickel-chromium-molybdenum (CoNiCrMo) alloys, and concludes that, in CoNiCrMo alloys, repassivation — which occurs when the corroding site becomes inactive — "is likely to occur and block any pit growth" in these materials.

From the publication: "There is some evidence to suggest that carbide inclusions may be more effective than oxide inclusions for pitting on nitinol."