Biological and mechanical response of laser shock peening orthopaedic titanium alloy (Ti-6Al-7Nb)

This paper focuses on the evaluation of mechanical and biological properties of laser shock peening (LSP) orthopaedic grade Ti-6Al-7Nb alloy. LSP surface treatment was conducted at laser energy of 3 to 7 J with overlaps of 33%–67%, and with a 3 mm laser spot size. Cell viability on laser shock peened surface was evaluated through in-vitro MTT assay, using osteoblast-like MG63 cells for the first-time. Residual stresses, microhardness, microstructure, sliding wear and wetting properties were investigated. Compressive residual stresses were found at various depths due to controlling the LSP parameters, compared to the as-received surface. The laser shock peened surfaces were hardened from 365HV(0.05) to 405HV(0.05), while the as-received surface was 320HV(0.05). The average sub-grain size was refined from 14% to 36% after LSP. The wear resistance was also controllable by altering LSP parameters. The MTT results show that the cell viability on the laser shock peened surfaces was comparatively lower than that of the untreated surface after 24 h. However, after 72 h, the cell viability on modified surfaces were significantly improved. This work indicated that laser shock peened surfaces have a strong potential to decrease the pain from orthopaedic implant failures and promote the cytocompatibility between the bone and implant.