Larger surface area can reduce nitinol corrosion resistance

Abstract

Surface area has long been thought to influence the corrosion behavior of medical devices although this phenomenon has not been systematically investigated. Because many nitinol implants are offered in a range of sizes, understanding the influence of device surface area on corrosion susceptibility is key to ensuring nitinol devices are safe. This study evaluates the corrosion susceptibility of amber oxide, mechanically polished and chemically etched nitinol wires with surface areas ranging from 0.05 to 10.0 cm2 using a standard test method, ASTM F2129. The corrosion testing shows that as the surface area increased the breakdown potential decreased. Results from the amber oxide and chemically etched samples show a plateauing of breakdown potential at larger surface areas, which suggests that there may be a minimum surface area threshold that could predict the performance of larger devices. Additional testing on electropolished wire and modified laser-cut stents shows a similar decrease in breakdown potential with increased surface area thus corroborating the trend observed with nitinol wires. Overall, surface area was found to affect corrosion susceptibility as measured per ASTM F2129 for a range of nitinol samples.