TiO2-HA bi-layer coatings for improving the bioactivity and service-life of Ti dental implants

A titania (TiO2) - hydroxyapatite (HA) bi-layered material, with a target surface design, was obtained by means of a two-step process on the surface of Ti substrates with three different pristine morphologies and topographies. A dense, compact and crystalline titania inter-layer was obtained via Metal Organic Chemical Vapor Deposition, and a homogeneously spread discontinuous calcium phosphate ceramic (hydroxyapatite) top-layer, with particular chemical composition, crystallinity, and morphology, was deposited by means of spray pyrolysis. A final thermal treatment at 600 degrees C was found as the best compromise between an adequate crystallinity, bioactivity and composite material features. The novelty of this work is that this synergic two-step approach allows the coexistence of both TiO2 and HA ceramics on the implant surface. This can help in increasing the surface bioactivity and improving the short(HA)- and long(TiO2)- term implant service-life. The influence of the two-step modification process was investigated. Coated surfaces exhibited better electrochemical performances in artificial saliva and reduced metallic ion release; also the mechanical properties at the nano-scale level of the composite materials were improved thanks to the functionalization. The composite material wettability was also studied: the freshly prepared surfaces always showed hydrophilicity. However, in air environments, the wettability decreased with ageing time due to hydrocarbon contamination. Acellular invitro bioactivity of all species was tested evaluating the ability of the materials to form a bone-like apatite layer after immersion in Dulbecco's Phosphate Buffer Saline solution at 37 degrees C. The obtained results showed that a bone-like apatite layer was effectively formed on the two-step functionalized Ti substrates, giving significant results just after 30 min incubation time.