Transcatheter heart valve replacement is a key advancement in the cardiovascular device industry and provides an alternative to open surgical procedures for patients that suffer from severe symptomatic stenosis and/or regurgitation. The functions and boundary conditions of the four heart valves are unique and must be considered separately. It is essential that the structural durability of these high-risk valve replacement implants is thoroughly assessed through testing and analysis. As such, ISO 5840 outlines a comprehensive device durability approach that incorporates worst-case boundary conditions, computational stress/strain analyses, and benchtop fatigue testing. The present study is focussed on 100,000,000-cycle fatigue testing of custom-designed “diamond-shaped” coupons of process-optimized high purity VAR/EBR Nitinol. Benchtop testing was coupled with finite element analysis (FEA) and microstructural characterization to provide an in-depth understanding of durability.

Nitinol staples are in forefront of internal fixation devices. The application of staples in comparison with other fixation methods such as plates, screws or pins has benefits of being less invasive and simpler. There is a huge potential of using Nitinol in the orthopedic field, but so far only limited research done on material properties of Nitinol in combination with fatigue life of Nitinol staples. Earlier work has shown significant impact of grain size on fatigue life of Nitinol sheet. The aim of this study was a comparative investigation on the fatigue behavior of semi-finished Nitinol flat continuous rolled sheets with staple shaped samples and optimization of Nitinol sheet for the use in the biomedical implant under product-related conditions. Samples based on a generic staple design used in the internal fixation of the musculoskeletal system and four-point bend test methods were used to conduct this study. Monotonic force-displacement tests at different maximum force conditions were conducted, to understand the relationship between microstructure in Nitinol sheets and fatigue life. To get a better understanding of these correlations is primary objective of this investigation.

Nitinol is commonly used as a retention clip to prevent backout of fixation screws in spinal anterior cervical plates (ACP). During implantation, however, there is metallic contact between the screw and retention clip. The effects of this surface damage on corrosion resistance of the Nitinol clip have not been thoroughly investigated and may be dependent on the level of screw-clip interference in the construct design. Therefore, the goal of this study is to characterize the effects on the Nitinol corrosion resistance using varying levels of screw-clip interference in a modified ACP assembly.

Although improvements in fatigue performance with increasing Nitinol microstructural purity have been previously characterized, there is limited information on whether corrosion resistance is impacted by reductions in inclusion size and distribution. The objective of this study is to characterize the surface oxide for different Nitinol microstructural purities and determine its influence on corrosion susceptibility. To assess the surface oxide, X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS) were performed on Nitinol heart valve frames with a variety of purities and surface finishes.