<i>In Vivo</i> Dissolution Rate and Bone Regeneration Efficiency of Porous Carbonated Apatite Scaffolds: Comparative Study with Hydroxyapatite Scaffolds

Hydroxyapatite (HAp) is widely used as an artificial bone graft material in orthopedic and dental surgeries because of its excellent biocompatibility. However, the slow biodegradation rate of HAp scaffolds can increase the risk of infection at implanted sites and hinder bone tissue regeneration. Carbonated apatite (CA), which is a substituted HAp with carbonate ions replaced by phosphate ions in the HAp lattice, has been demonstrated to exhibit higher solubility than that exhibited by HAp. Therefore, this study investigated porous CA-based blocks fabricated by sintering a mixture of CA powder and organic beads. The synthesized CA, identified as B-type CA, had a carbonate content of 8%, which is close to that present in natural bones. The fabricated CA block, with over 60% porosity, promoted osteoblast activity and new bone formation within the pores. The porous CA blocks were implanted into the holes/defects created at different sites in the rabbit femur, and the in vivo behavior of the porous CA blocks was compared with that of the porous HA blocks. At one and three months after implantation, changes in the blocks and new bone formation were observed in different sites—cortical, cancellous, and bone marrow. At three months post-implantation, the HAp block hardly dissolved, whereas the implanted CA block dissolved in the cancellous bone and bone marrow, which have high blood flow. Additionally, at three months post-implantation, the CA blocks exhibited superior bone formation in the cortical bone and similar bone growth as compared to that exhibited by the HAp blocks. This study demonstrates that porous CA blocks are suitable alternatives to porous HAp blocks for use as bone scaffolds because of their superior osteoconductivity and biosolubility.