Fabrication and evaluation of interconnected porous carbonate apatite from alpha tricalcium phosphate spheres

Carbonate apatite (CO 3 Ap) blocks have attracted considerable attention as an artificial bone substitute material because CO 3 Ap is a component of and shares properties with bone, including high osteoconductivity and replacement by bone similar to autografts. In this study, we fabricated an interconnected porous CO 3 Ap block using α‐tricalcium phosphate (TCP) spheres and evaluated the tissue response to this material in a rabbit tibial bone defect model. Interconnected porous α‐TCP, the precursor of interconnected porous CO 3 Ap, could not be fabricated directly by sintering α‐TCP spheres. It was therefore made via a setting reaction with α‐TCP spheres, yielding interconnected porous calcium‐deficient hydroxyapatite that was subjected to heat treatment. Immersing the interconnected porous α‐TCP in Na–CO 3 –PO 4 solution produced CO 3 Ap, which retained the interconnected porous structure after the dissolution–precipitation reaction. The diametral tensile strength and porosity of the porous CO 3 Ap were 1.8 ± 0.4 MPa and 55% ± 3.2%, respectively. Both porous and dense (control) CO 3 Ap showed excellent tissue response and good osteoconductivity. At 4 weeks after surgery, approximately 15% ± 4.9% of the tibial bone defect was filled with new bone when reconstruction was performed using porous CO 3 Ap; this amount was five times greater than that obtained with dense CO 3 Ap. At 12 weeks after surgery, for porous CO 3 Ap, approximately 47% of the defect was filled with new bone as compared to 16% for dense CO 3 Ap. Thus, the interconnected porous CO 3 Ap block is a promising artificial bone substitute material for the treatment of bone defects caused by large fractures or bone tumor resection. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 107B: 269–277, 2019.