Fabrication and Histological Evaluation of Porous Carbonate Apatite Block from Gypsum Block Containing Spherical Phenol Resin as a Porogen

The utility of carbonate apatite (CO3Ap) as a bone substitute has been demonstrated. The feasibility of fabricating macroporous CO3Ap was evaluated through a two-step dissolution–precipitation reaction using gypsum as the precursor and spherical phenol resin as the porogen. Porogen-containing gypsum was heated to burn out the porogen and to fabricate macroporous structures. Gypsum transformed into CaCO3 upon immersion in a sodium carbonate solution, while maintaining its macroporous structure. Next, CaCO3 transformed into CO3Ap upon immersion in a Na2HPO4 solution while maintaining its macroporous structure. The utility of the macroporous CO3Ap for histologically reconstructing bone defects was evaluated in rabbit femurs. After 4 weeks, a much larger bone was formed inside the macroporous CO3Ap than that inside non-macroporous CO3Ap and macroporous hydroxyapatite (HAp). A larger amount of bone was observed inside non-macroporous CO3Ap than inside macroporous HAp. The bone defects were completely reconstructed within 12 weeks using macroporous CO3Ap. In conclusion, macroporous CO3Ap has good potential as an ideal bone substitute.