Physico-chemical properties, in vitro bioactivity of carbonate- fluoride- substituted apatite

Carbonate (CO3) is the chief minor substituent in bone apatite. Fluoride (F) has been shown the ability to stimulate osteoblastic activity and inhibit osteoclastic activity. Independently, CO3 or F substitution causes decrease in the a-axis dimension of the apatite; have opposite effects on crystallite size and in the solubility. Simultaneously substituted carbonate and fluoride apatite (CFA) has been considered as a possible bone graft material for orthopedic and dental applications. Objective: The purpose of this study was to determine the effect of simultaneous substitution of fluoride and carbonate on the physico-chemical properties of synthetic apatites and in vitro bioactivity. Methods: Hydroxyapatite (HA), F-substituted apatite (FA), CO3-substituted apatite (CHA) and CFA were prepared by precipitation method. Physico-chemical properties (crystallite size, lattice parameters, spectral properties, morphology and dissolution) were characterized using X-ray diffraction, FT-IR spectroscopy, scanning electron microscopy, thermogravimetry and chemical analyses. CFA, HA, CHA and FA pellets were exposed to the fetal bovine serum (FBS) to test in vitro bioactivity reflected by the formation of CHA on the pellet surfaces. Results: Simultaneous incorporation of F and CO3 ions in the apatite had additive effects on the a-axis dimension, crystallite size and dissolution properties. Greater amount of apatite deposited on the CFA compared to HA, CHA and FA pellet surfaces. Conclusion: Simultaneous incorporation of fluoride and carbonate in apatite (CFA) enhances in vitro bioactivity and may promote greater bone formation in vivo.