Mechanical behaviour of nanolayer hydroxyapatite (HA) coating developed through superplastic embedment of titanium (Ti) alloy (Ti6Al4V)

• Hydroxyapatite (HA) superplastically embedded to Ti6Al4V substrate.
• Nanolayer HA produced.
• Newly grown HA layer produced after immersion in simulated body fluid.
• HA layer is strongly intact both to each other and to the substrate.

Ti6Al4V is superplastically embedded with HA powder after being submitted to a heat treatment process designed to produce an HA embedded layer with improved strength and good biocompatibility. The surface properties of the produced HA embedded layer, having 249 nm thickness and 660 HV hardness, have been studied and correlated according to their biological and mechanical behaviour in vitro. A scratch test comprising two maximum applied scratch loads of 100 mN and 500 mN has been performed. This was carried out in order to reveal the degree of adherence between the surface layer and substrate both before and after immersion in a simulated body fluid (SBF) for 1, 3, 7, 14, 21, 28 and 35 days, respectively. The results obtained demonstrate that the HA embedded layer is sufficiently intact to the substrate, and that its stability is maintained even after immersion in SBF for a period of 35 days. Further, the newly grown HA layer starts to develop in the early stages of immersion through precipitation of the HA particles. It later becomes thicker upon the relevant immersion duration, which suggests that its biocompatibility remains sound.