Fabrication of Selenium-Doped Hydroxyapatite Coatings by Suspension Plasma Spraying: Characterization and Improvement of Coating Properties

Biological hydroxyapatite (HA) coatings have been used to repair damaged bone exhibiting fluorosis. However, they are often inappropriate and have some undesirable effects. Consequently, modified HA coatings with functional elements have become popular. In the present work, selenium-doped HA (Se-HA) powders were first synthesized by chemical coprecipitation. A Se-HA nanostructure coating was then fabricated on the surface of a titanium (Ti) substrate by suspension plasma spraying. Energy-dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy, and x-ray powder diffraction demonstrated the homogeneous presence of Se within a Se-HA coating made from the appropriately doped powder. The Se was incorporated into the HA lattice by replacing some of the phosphate groups with selenite groups. The chemical stability of the coating was assessed by immersing samples in a citric acid-modified phosphate-buffered saline solution. The solubility of the Se-HA coating increased slightly owing to the introduction of Se. According to electrochemical tests, the dense Se-HA coating provided the Ti substrate with a reliable biocorrosion barrier. The in vitro bioactivity of the coating was characterized by immersing the samples in simulated body fluid for various times. The results suggested that the Se-HA coating had similar bone-like apatite formation capability to that of a conventional HA coating. Compared with the HA coating, the Se-HA coating effectively promoted the adhesion, proliferation, and differentiation of osteoblasts in the presence of fluoride ions. These results suggest that Se-HA coatings have some potential for improving bone regeneration in fluorosis patients.