Effect of different shape-set parameters on functional properties of ePTFE coated Nitinol stents

Expanded polytetrafluoroethylene (ePTFE) has gained increasing attention in recent years as a bio-inert barrier cover for NiTi stents. Its application helps prevent or delay tissue ingrowth, thereby maintaining luminal patency for extended periods following initial stent deployment. The ePTFE cover is typically sintered onto the electropolished NiTi stent using a combination of heat and pressure. However, the sintering temperature and duration fall within a range that can potentially alter the functional properties of the Nitinol stent.

Despite this, no systematic study has been conducted to evaluate how variations in the austenite finish temperature (Af) of the starting material, along with different shape-setting heat treatment histories, influence the stent’s functional performance after exposure to a standardized sintering process. In this study, various shape-setting heat treatment combinations were applied to two types of starting materials—characterized by low (cold ingot) and high (warm ingot) Af values. The functional properties of the devices, including transformation temperatures, device stability, tensile strength, and radial resistive force, were assessed both before and after the sintering step.