Tribological characterization of biocompatible HAp-TiO2 coatings obtained by high velocity oxy-fuel spray

Bioceramic coatings have been employed for many years to improve the biological, and consequently the mechanical, properties of bone implants. However, only a few studies have focused on wear behavior, which has been considered of secondary importance compared to other properties. The present study demonstrates that contrary to this assumption, it is important to guarantee the integrity of the coatings during and after implantation, a process that subjects the surface to high wear. Reciprocating ball-on-flat tests were performed to characterize the wear properties of HAp-TiO2 coatings, which have previously been shown to present other good mechanical and biological properties. An alumina ball was used as counterface and the tests were conducted at 37 °C immersed in Hank's solution, to simulate physiological conditions. Three loads were employed: 5 N, 10 N and 15 N. The results show a clear advantage of more compact coatings, with a lower percentage of amorphous phases, since they present a higher friction coefficient. That could indicate, according to the literature, better implant fixation and a lower wear rate, and thus ensure the integrity of the coating.