Fabrication of B-type carbonate apatite blocks by the phosphorization of free-molding gypsum-calcite composite

Abstract

B-type carbonate apatite (CO₃Ap) block may be an ideal artificial bone substitute because it is closer in chemical composition to bone mineral. In the present study, the feasibility to fabricate CO₃Ap blocks was investigated using compositional transformation, which was based on the dissolution-precipitation reaction of a gypsum-calcite composite with free-molding behavior. For the compositional change, or phosphorization, gypsum-calcite composites of varying CaCO₃ contents were immersed in 1 mol/L (NH₄)₃PO₄ aqueous solution at 100°C for 24 hours. No macroscopic changes were found after the treatment, whereas microscopic change was observed at SEM level. X-ray diffraction, Fourier transform infrared spectroscopy and CHN analysis indicated that the composites were B-type CO₃Ap containing approximately 6–7 wt% of CO₃, a value similar to that of biological bone apatite. Diametral tensile strength of the CO₃Ap block was approximately 1–3 MPa. Based on the results obtained, it was therefore concluded that gypsum-calcite was a good candidate for the fabrication of CO₃Ap blocks, coupled with the advantage that the composite can be molded to any shape by virtue of the setting property of gypsum.