Shape memory alloys (SMA) offer unique shape memory (SME) or superelastic (SE) effects that have attracted the interest of different industrial sectors, such as aerospace, automotive, robotics, and biomedical devices. NiTi, also referred to as nitinol, is the most extensively used SMA in the biomedical field, due to its excellent biocompatibility, corrosion resistance and mechanical properties, specially to manufacture self-expandable devices for cardiovascular applications. However, current methods for manufacturing NiTi-based cardiovascular devices only allow for simple geometries and prevent the manufacturing of patient specific personalized devices.

In recent years, laser powder bed fusion (LPBF) is emerging as an additive manufacturing technique that should allow both the production of complex-shaped and custom-made NiTi devices. However, LPBF presents several drawbacks, which include the need to precisely control the processing parameters to ensure both a low level of porosity and an optimum microstructure, as well as the lack of knowledge on how the surface finish might affect the biological compatibility of the final part. As a matter of fact, the biological activity is expected to be affected both by the geometrical roughness of the surface, which it is typically large in the case of non-treated LPBF parts, as well as by the surface chemical composition and the nature of the passivation oxide that is formed on the surface. This passivation oxide is critical to prevent the release of Ni ions in the body that can cause severe allergic reactions, metallosis and cell mutations in the long term. In this context, this study evaluates the surface finish of potential post-printing surface modification techniques that could be used in LPBF parts, including chemical etching, electropolishing and combinations of both, with respect to the surface finish of the as-printed components. In particular, the impact of surface condition on the final geometrical roughness and surface chemistry will be presented and related to long-term cytotoxic studies carried out in each case using human endothelial cells, including viability, proliferation and migration studies.