Fabrication of low-crystalline carbonate apatite foam bone replacement based on phase transformation of calcite foam

Carbonate apatite (CO₃Ap) foam may be an ideal bone substitute as it is sidelined to cancellous bone with respect to its chemical composition and structure. However, CO₃Ap foam fabricated using α-tricalcium phosphate foam showed limited mechanical strength. In the present study, feasibility of the fabrication of calcite which could be a precursor of CO₃Ap was studied. Calcite foam was successfully fabricated by the so-called "ceramic foam" method using calcium hydroxide coated polyurethane foam under CO₂+O₂ atmosphere. Then the calcite foam was immersed in Na₂HPO₄ aqueous solution for phase transformation based on dissolutionprecipitation reaction. When CaO-free calcite foam was immersed in Na₂HPO₄ solution, low-crystalline CO₃Ap foam with 93-96% porosity and fully interconnected porous structure was fabricated. The compressive strength of the foam was 25.6±6 kPa. In light of these results, we concluded that the properties of the precursor foam were key factors for the fabrication of CO₃Ap foams.