The influence of laser surface remelting on the in vitro cell viability of additively manufactured Ti–6Al–4V plates

Additive manufacturing (AM) technologies, for instance, selective laser melting (SLM), have been used to produce orthopaedic metal implants to cater to the customised bone replacement needs of patients. The as-built implants fabricated by SLM are limited by the surface asperities and surface defects introduced by the layered deposition process, thus post-processes must be adopted to address these problems. As one of the potential post-processes to improve the surface quality, laser surface remelting (LSR) can be applied to eliminate surface pores and residual powder by remelting them into a thin and dense surface layer over the substrate. In this study, a 1064 nm wavelength, 100 W, nanosecond-pulsed fibre laser was used to remelt the surfaces of a cuboid Ti-6Al-4 V test plate placed in argon gas protection. A dense, pore-free and crack-free surface layer of over 300 µm in thickness was formed, demonstrating a phase transition from α + β to α′ phase Ti after the LSR process. Subsequent in vitro cell viability tests presented an improvement of human osteoblast-like SAOS2 cells’ viability subject to the LSR, which could be linked to the laser-remelted surface layer essentially slowing down the release of toxic vanadium ions. The results demonstrated a potential of the LSR technique to improve the biocompatibility of SLM produced Ti–6Al–4V implants in vivo.