Influence of tissue suturing on the corrosion behavior of nitinol: insights into mechanisms and implications

Nitinol is widely used in cardiovascular implants due to its superelasticity, fatigue strength and corrosion resistance. In many cardiovascular devices, such as transcatheter heart valves or endovascular prostheses, biological tissues or polymers are manually sutured onto Nitinol frames to serve as a functional substitute for native tissue. In these devices, the Nitinol frame is intended to provide structural support and corrosion resistance throughout the device’s lifetime. Because the attached tissue could influence corrosion testing, assessing corrosion resistance in such devices can be challenging. To investigate the influence of the attached tissue as well as the suturing processes on corrosion performance, potentiodynamic polarization tests were performed on a simplified Nitinol stent ring with two different surface finishes (electropolished and thermally oxidized). For each Nitinol surface finish, four different test specimen preparation conditions were examined: as-manufactured, tissue attached, tissue removed, and simulated needle strikes. Results for electropolished Nitinol specimens suggested that deeper scratches may act as initiation sites for pitting corrosion, although there were many instances of observed needle strikes that did not corrode. Overall, pitting corrosion depended on the interplay between surface finish and the test specimen preparation, underscoring the importance of accounting for these effects in device development and testing.