Fabrication and Histological Evaluation of a Fully Interconnected Porous CO₃Ap Block Formed by Hydrate Expansion of CaO Granules

Carbonate apatite (CO3Ap) fabricated by a dissolution-precipitation reaction from a precursor exhibits excellent osteoconductivity and is readily replaced by bone. In the present study, a fully interconnected porous CO3Ap block was fabricated by hydrate expansion and carbonation of CaO granules, and the resulting CaCO3 was then converted to CO3Ap. When CaO granules were exposed to 100% humidity CO2 in a closed vessel, the CaO granules were hydrated and expanded to form a porous Ca(OH)2 block. The block was then carbonated to form a porous CaCO3 block, which was then immersed in a Na2HPO4 solution to convert it to a porous CO3Ap block. The resulting CO3Ap block possessed a fully interconnected porous structure. Histological analyses 4 and 8 weeks after implantation in rabbits revealed that the porous CO3Ap block resulted in more significant material resorption and bone formation than the dense CO3Ap block. Therefore, it was concluded that a fully interconnected porous CO3Ap block fabricated by the hydrate expansion of CaO granules has potential value as a bone substitute.