Fabrication of Carbonate Apatite Block through a Dissolution–Precipitation Reaction Using Calcium Hydrogen Phosphate Dihydrate Block as a Precursor

Carbonate apatite (CO(3)Ap) block, which is a bone replacement used to repair defects, was fabricated through a dissolution–precipitation reaction using a calcium hydrogen phosphate dihydrate (DCPD) block as a precursor. When the DCPD block was immersed in NaHCO(3) or Na(2)CO(3) solution at 80 °C, DCPD converted to CO(3)Ap within 3 days. β-Tricalcium phosphate was formed as an intermediate phase, and it was completely converted to CO(3)Ap within 2 weeks when the DCPD block was immersed in Na(2)CO(3) solution. Although the crystal structures of the DCPD and CO(3)Ap blocks were different, the macroscopic structure was maintained during the compositional transformation through the dissolution–precipitation reaction. CO(3)Ap block fabricated in NaHCO(3) or Na(2)CO(3) solution contained 12.9 and 15.8 wt % carbonate, respectively. The diametral tensile strength of the CO(3)Ap block was 2 MPa, and the porosity was approximately 57% regardless of the carbonate solution. DCPD is a useful precursor for the fabrication of CO(3)Ap block.