Fabrication of silica-substituted carbonate apatite blocks through phase transformation process from silica-substituted octacalcium phosphate blocks

Abstract

Although silica substitution into apatites is an attractive method for improving biocompatibility and their bone-remodeling stimulation abilities, residual organic matter from organic silica as a silica source is a disadvantage for silica doping. In this study, we fabricated silica-substituted apatite blocks from silica-substituted octacalcium phosphate (OCP-silica) blocks by immersion in (NH₄)₂CO₃ solutions. At below 1-mol/L (NH₄)₂CO₃, the treated blocks retained their original OCP-silica block shapes while being converted to apatites containing both silica and CO₃. As the (NH₄)₂CO₃ concentration in the treated solutions increased, the CO₃ content of the apatite blocks increased, whereas their silica content decreased. The formed carbonate apatite (CO₃Ap) phase was categorized as AB-type CO₃Ap. The mechanical strength of the fabricated silica-substituted CO₃Ap blocks was approximately 150 kPa in diametral tensile strength (DTS) values.