This project continues the work reported last year to identify and quantify the factors affecting the static mechanical and fatigue properties of the metal alloys commonly used in cardiovascular, orthopedic and dental implants. The alloys under study include 316L stainless steel, 6Al4V titanium, and several cobalt alloys, including L605, Elgiloy and MP35N, in both fine wire and bar stock form. Such cold working is common during the fabrication of interventional cardiology devices and is sometimes performed during surgery in orthopedic procedures. OST is completing those experiments by characterizing the hardness and grain structure of the virgin and prestretched wire and attempting to correlate the fatigue behavior with the results of stress-strain tests. However, microhardness measurements indicate that hardening is occurring, and manifesting itself in the change in fatigue behavior.
Experiments using non-contact video extensometry and other methodologies are underway.
OST scientists have also initiated a full-factorial experiment to evaluate the effects of test frequency and physiological environment on the fatigue behavior of 316L and 6Al4V titanium alloys. These alloys were selected as being the most and least susceptible to corrosion fatigue among the commonly-used implant alloys. The results of this project should allow OST to develop definitive guidance regarding the experimental protocols for characterizing the fatigue behavior of these implant alloys and devices made from them. The biological response to wear debris is complex, involving many cell types, including macrophages, which can phagocytize the wear debris. To date, in vitro studies have focused on the release of inflammatory mediators by phagocytic cells in the presence of particles.