Fabrication, characterization, and in vitro studies of Selenium-substituted hydroxyapatite coatings

Abstract The increasing demand for hydroxyapatite (HA) coatings with enhanced functionality have led to novel materials with compositions that are more closely resembling those of natural bone apatites. In the present study, selenium-substituted (Se–HA) powders with various Se quantities were prepared by chemical precipitation. By applying suspension plasma spray (SPS), the surface of Ti substrates was coated with corresponding Se-HA coatings. The microstructural and physicochemical properties of the powders and the coatings were studied. Analysis by X-ray diffraction indicates that SeO32− replaced the PO43− groups, affecting the crystal structure and crystallinity of HA. As the extent of Se substitution increases, the lattice volume expands and the crystallinity decreases. The synthesized Se–HA powders were confirmed to be calcium-deficient apatite through energy-dispersive X-ray spectroscopy. However, the high temperature of SPS accelerated volatilization of P, increasing the Ca/(P + Se) ratio of the coatings, whereas the chemical valence state of Se remained unchanged. The Se–HA coating exhibited a high bonding strength of >33 MPa, fully meeting the requirement of 15 MPa as coating implant materials. Dissolution behavior tests indicate that the Se–HA coatings had high solubility in comparison to the HA coating. As the substitution degree of Se increased, the dissolution rate also increased, which greatly enhanced the capacity to generate a bone-like apatite layer. In vitro cell experiments indicate that the Se–HA coatings exhibited excellent biocompatibility, and facilitated adhesion and proliferation of osteoblast MC3T3-E1, even in the presence of fluorine. Furthermore, antibacterial properties of Se–HA coatings were also indicated by inhibition of Staphylococcus aureus, which is the main cause of most infections after orthopedic surgeries. Thus, the Se–HA coatings have potential as implant coating materials for orthopedic applications.