In-vitro behaviour of titania-hydroxyapatite functionally graded coatings

The in vitro behaviour of titania–hydroxyapatite graded coatings obtained by plasma sprayingwas investigated by a microstructural and mechanical point of view. To verify the bioactivity of thegraded coatings, as sprayed and after thermal treatment, in vitro tests were performed insimulated body fluid. Furthermore, since the mechanical properties of the coatings may bealtered by the immersion in simulated body fluid, the local elastic properties were measured onthe cross-section by means of a depth sensing Vickers microindentation technique beforeimmersion (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 toaccount for the compositional gradient. The results proved that the presence of titania in thecoating did not suppress the bioactivity, which, on the contrary, was inhibited by the heattreatment. However, the heat treated samples showed higher mechanical properties and reduceddissolution rates.