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

The utility of carbonate apatite (CO(3)Ap) as a bone substitute has been demonstrated. The feasibility of fabricating macroporous CO(3)Ap 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 CaCO(3) upon immersion in a sodium carbonate solution, while maintaining its macroporous structure. Next, CaCO(3) transformed into CO(3)Ap upon immersion in a Na(2)HPO(4) solution while maintaining its macroporous structure. The utility of the macroporous CO(3)Ap for histologically reconstructing bone defects was evaluated in rabbit femurs. After 4 weeks, a much larger bone was formed inside the macroporous CO(3)Ap than that inside non-macroporous CO(3)Ap and macroporous hydroxyapatite (HAp). A larger amount of bone was observed inside non-macroporous CO(3)Ap than inside macroporous HAp. The bone defects were completely reconstructed within 12 weeks using macroporous CO(3)Ap. In conclusion, macroporous CO(3)Ap has good potential as an ideal bone substitute.