Fabrication of carbonate apatite blocks from octacalcium phosphate blocks through different phase conversion mode depending on carbonate concentration

摘要

Carbonate apatite (CO(3)Ap) is an inorganic component of mature bone and is used as bone substitute instead of autografts. Recently, 100% pure CO(3)Ap granules formed from calcium carbonate via a dissolution-precipitation reaction have been used as a clinical precursor for bone. In this study, the feasibility of fabricating blocks of CO(3)Ap from blocks of octacalcium phosphate (OCP), which is an analog of the bone composition and serves as a precursor for bone, was investigated by immersion in NaHCO3. The macroscopic structure of the OCP block was retained upon conversion to CO(3)Ap. In addition, as the NaHCO3 concentration increased from 0.0 to 2.0 mol/L, the carbonate content increased in the resulting CO(3)Ap, reaching approximate to 14 wt% at maximum NaHCO3 concentration. Moreover, the morphology of the CO(3)Ap crystals varied as the NaHCO3 concentration increased up to 0.5 mol/L: they were pseudomorphic plate-like when the NaHCO3 concentration was low but formed particles ranging similar to 10 nm in size at high NaHCO3 concentrations. The different phase transformation modes depended on NaHCO3 concentrations closely related to CO(3)Ap crystal morphology and were associated with a decrease in the mechanical strength of the block.