Evaluation of carbonate apatite blocks fabricated from dicalcium phosphate dihydrate blocks for reconstruction of rabbit femoral and tibial defects

Abstract: This study aimed to evaluate in vivo behavior of a carbonate apatite (CO₃Ap) block fabricated by compositional transformation via a dissolution–precipitation reaction using a calcium hydrogen phosphate dihydrate [DCPD: CaHPO₄·2H₂O] block as a precursor. These blocks were used to reconstruct defects in the femur and tibia of rabbits, using sintered dense hydroxyapatite (HAp) blocks as the control. Both the CO₃Ap and HAp blocks showed excellent tissue response and good osteoconductivity. HAp block maintained its structure even after 24 weeks of implantation, so no bone replacement of the implant was observed throughout the post-implantation period in either femoral or tibial bone defects. In contrast, CO₃Ap was resorbed with increasing time after implantation and replaced with new bone. The CO₃Ap block was resorbed approximately twice as fast at the metaphysis of the proximal tibia than at the epiphysis of the distal femur. The CO₃Ap block was resorbed at an approximately linear change over time, with complete resorption was estimated by extrapolation of data at approximately 1−1.5 years. Hence, the CO₃Ap block fabricated in this study has potential value as an ideal artificial bone substitute because of its resorption and subsequent replacement by bone.