IN VITRO CHARACTERISATION OF HYDROXYAPATITE LAYERS DEPOSITED BY APS AND HVOF THERMAL SPRAYING METHODS

Titanium alloys are successfully used in medicine as implants due to their high mechanical properties and good biocompatibility. To improve implant osseointegration, they are covered with hydroxyapatite (HAp) because of its bioactive properties. Coating the implants with HAp by thermal spraying, due to the temperatures developed during the deposition process, the structure can be degraded, leading to the formation of secondary phases such as TCP, TTCP, and CaO. HAp layers were deposited by two thermal spraying methods: Atmospheric Plasma Spraying (APS) and High Velocity Oxy-Fuel (HVOF). The microstructures of the deposited layers was characterised by XRD and SEM. The bioactivity of the HAp layer was investigated in Simulated Body Fluid (SBF) by immersing the covered samples deposited by the two methods. In both cases, the coatings did not present defects as cracks or microcracks. XRD performed on HAp deposited layers shows that the structure was strongly influenced by plasma jet temperature, the structure consisting mainly of TCP (Ca3PO4)2. The samples deposited by HVOF after immersing in SBF reveal the formation of biological HAp, confirming the good bioactivity of the coatings.