Investigation of microstructure, microhardness and biocompatibility characteristics of yttrium and fluoride doped hydroxyapatite

In this study, microstructural, mechanical properties and biocompatibility of hydroxyapatite (HA) doped with constant yttrium (Y³⁺) and varying fluoride (F^-) compositions were investigated. HA was synthesized by precipitation method and sintered at 1100°C for 1 hour. Y³⁺ doping led to increase in material densities while F^- doping led to decrease. In x-ray diffraction (XRD) analysis, no secondary phases were formed in pure and doped samples. Decrease in lattice parameters were observed upon substitutions of ions. Scanning electron microscopy (SEM) results showed that addition of doping ions resulted in smaller grains. In Fourier transform infrared (FTIR) spectroscopy analysis, novel bands were observed in F^-ion doped samples in addition to characteristic HA bands, indicating the substitution of F^- ions. The highest microhardness was obtained for the sample doped with 2.5%Y³⁺, 1%F^-. Lower microhardness values were obtained with increased F^- doping. In methylthiazolyldiphenyltetrazolium (MTT) assay, which was performed for cell proliferation, Y³⁺ and F^- incorporation was found to improve cell proliferation on discs. In SEM analysis cells were found to attach and proliferate on disc surfaces. Alkaline phosphatase (ALP) assay showed that it was possible to improve differentiation of cells on the discs by doping the HA with an optimum amount of F^- ion. Dissolution tests revealed that structural stability of HA was improved with F^- ion incorporation.