Evaluation and characterization of nitinol stents produced by selective laser melting with various process parameters

Various studies have reported 3D printing of superelastic nitinol parts. However, the sizes of samples are several scales larger than those in the biomedical applications, which provides insufficient values for the industry use. To investigate the feasibility of SLM fabrication of thinner nitinol medical devices, i.e., stent, this study has systematically explored how the process parameters affect the final quality of the printed parts. Firstly, the nitinol powders have been validated through various testings on flow property, powder behavior, and size distribution to ensure the reproducibility of nitinol devices. Then the process-microstructure-property relation of nitinol wire was investigated experimentally based on the phase transformation temperature, microstructures, phase or crystalline structures, and nickel-titanium atomic weight percentage. In the last, novel superelastic nitinol stents with two different closed-cell designs were successfully printed using the selected process parameters. A comprehensive mechanical/material characterization and biocompatibility assessment have been conducted on these 3D printed stents. In summary, this preliminary study provided a guideline on how to print thin nitinol medical devices, also demonstrated that with the suitable process parameter, it is highly feasible to use SLM to accurately print thin nitinol devices with high density, uniform strut diameters, adequate superelasticity, and excellent biocompatibility.