Carbonate Hydroxyapatite and Silicon-Substituted Carbonate Hydroxyapatite: Synthesis, Mechanical Properties, and Solubility Evaluations

The present study investigates the chemical composition, solubility, and physical and mechanical properties of carbonate hydroxyapatite (CO(3)Ap) and silicon-substituted carbonate hydroxyapatite (Si-CO(3)Ap) which have been prepared by a simple precipitation method. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF) spectroscopy, and inductively coupled plasma (ICP) techniques were used to characterize the formation of CO(3)Ap and Si-CO(3)Ap. The results revealed that the silicate (SiO(4) (4−)) and carbonate (CO(3) (2−)) ions competed to occupy the phosphate (PO(4) (3−)) site and also entered simultaneously into the hydroxyapatite structure. The Si-substituted CO(3)Ap reduced the powder crystallinity and promoted ion release which resulted in a better solubility compared to that of Si-free CO(3)Ap. The mean particle size of Si-CO(3)Ap was much finer than that of CO(3)Ap. At 750°C heat-treatment temperature, the diametral tensile strengths (DTS) of Si-CO(3)Ap and CO(3)Ap were about 10.8 ± 0.3 and 11.8 ± 0.4 MPa, respectively.