Influence of Active Af on the Fatigue Performance of Peripheral Stents Subjected to Physiological Loading Conditions

The temperature difference between active austenite finish temperature, Af, and the intended operating temperature in the range of 3.2 °C to 20.8 °C. has been reported to have an influence on the fatigue lifetime of a pseudoelastic shape-memory device. The negative effect on fatigue life increases with the temperature difference between active Af and, in case of a biomedical device, 37 °C body temperature. In this study, samples were prepared and processed in a manner to replicate aspects of the complex manufacturing process, device design, and geometry of state-of-the-art stents, and physiological loading conditions. Following explantation from the mock vessels after fatigue testing, the stents were inspected using optical microscopy to detect and document the location and number of strut fractures. The fatigue results were compared and assessed for statistical significance between the groups with various active Af temperatures. The variations in the heat treatments, as part of the manufacturing process, resulted in three distinct groups of samples with varying target active Af temperatures. These variances corresponded to differences in fatigue damage.