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

Carbonate apatite (COAp) 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 COAp block was fabricated by hydrate expansion and carbonation of CaO granules, and the resulting CaCO was then converted to COAp. When CaO granules were exposed to 100% humidity CO in a closed vessel, the CaO granules were hydrated and expanded to form a porous Ca(OH) block. The block was then carbonated to form a porous CaCO block, which was then immersed in a NaHPO solution to convert it to a porous COAp block. The resulting COAp block possessed a fully interconnected porous structure. Histological analyses 4 and 8 weeks after implantation in rabbits revealed that the porous COAp block resulted in more significant material resorption and bone formation than the dense COAp block. Therefore, it was concluded that a fully interconnected porous COAp block fabricated by the hydrate expansion of CaO granules has potential value as a bone substitute.