Fabrication of carbonate apatite honeycomb and its tissue response

Carbonate apatite (CO₃ Ap) block can be used as a bone substitute because it can be remodeled to new natural bone in a manner conforming with the bone remodeling process. Among the many porous structures available, honeycomb (HC) structure is advantageous for rapid replacement of CO₃ Ap to bone. In this study, the feasibility to fabricate a CO₃ Ap HC was studied, along with its initial tissue response in rabbit femur bone defect. First, a mixture of Ca(OH)₂ and a wax-based binder was extruded from a HC mold. Then the fabricated HC was heated for binder removal and carbonation at 450°C in a mixed O₂ -CO₂ atmosphere, forming a CaCO₃ HC. When the CaCO₃ HC was immersed in 1 mol/L Na₃ PO₄ solution at 80°C for 7 days, its composition changed from CaCO₃ to CO₃ Ap, maintaining the structure of the original CaCO₃ HC. Compressive strengths of the CaCO₃ and CO₃ Ap HCs were 65.2 ± 7.4 MPa and 88.7 ± 4.7 MPa, respectively. When the rabbit femur bone defect was reconstructed with the CO₃ Ap HC, new bone penetrated the CO₃ Ap HC completely. Osteoclasts and osteoblasts were found on the surface of the newly formed bone and osteocytes were also found in the newly formed bone, indicating ongoing bone remodeling. Furthermore, blood vessels were formed inside the pores of CO₃ Ap HC. Therefore, CO₃ Ap HC has good potential as an ideal bone substitute. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1014-1020, 2019.