Biocompatibility of Titanium After Nano-hydroxiapatite Coating by Friction Stir Processing

Objectives: Determine the biocompatibility by inflammatory response and repair connective tissue around titanium dental implants after nano-hydroxiapatite coating by friction stir processing
Methods: This study was approved by the Ethics Committee in animals (CONS-CIEA 018-2016). Titanium dental implants after nano-hydroxiapatite coating by two different friction stir processing implants and uncoated controls were simultaneously implanted subcutaneously in rats for 2, 14 and 30 days. Samples were prepared using the computer control HAAS machine; which incorporates pure hydroxiapatite nanoparticles with 97% purity, diameter <200nm and surface area >9.4m 2/g on Titanium disks. Both friction stir processing implants differs on the nano-hydroxiapatite surface roughness. Group 1: Ra 1.38-2.08 um, Group 2: Ra 2.02-4.5 um, Group 3: Ti uncoated. The peri-implant tissue was qualitatively analyzed by histopathologic examination for healthy connective tissue, granulation tissue, macrophages, inflammatory cells, and proliferating cells.
Results: No remarkable difference was found between group 1 (Nano-hydroxiapatite Ra 1.38-2.08um) and the control group (Titanium). The peri-implant tissue of all the surface samples from group 2 were necrotic at day 4 in all the rats. So we decided to withdraw those samples before the study ends. Those samples were not contaminated, we confirmed the absence of oxides, so it is concluded that the nanohydroxiapatita surface roughness influences the inflammatory reaction. Friction stir processing should leave smooth surfaces.
Conclusions: This study demonstrates the biocompatibility of titanium after nano-hydroxiapatite coating by friction stir processing when the surface roughness is between 1.38-2.08 um.