In vitro behaviour of titania–hydroxyapatite functionally graded coatings

Abstract The in vitro behaviour of titania–hydroxyapatite graded coatings obtained by plasma spraying was investigated by a microstructural and mechanical point of view. To verify the bioactivity of the graded coatings, as sprayed and after thermal treatment, in vitro tests were performed in simulated body fluid. Furthermore, since the mechanical properties of the coatings may be altered by the immersion in simulated body fluid, the local elastic properties were measured on the cross-section by means of a depth sensing Vickers microindentation technique before immersion (reference materials) and after soaking for 1 week (short term response) and 4 weeks (long term response), separately investigating the titania and the hydroxyapatite rich zones to account for the compositional gradient. The results proved that the presence of titania in the coating did not suppress the bioactivity, which, on the contrary, was inhibited by the heat treatment. However, the heat treated samples showed higher mechanical properties and reduced dissolution rates.