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 °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 co-existence 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 in-vitro 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 °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.