Fabrication of porous carbonate apatite based on setting reaction of carbonate apatite granules

Abstract

Event Abstract Back to Event Fabrication of porous carbonate apatite based on setting reaction of carbonate apatite granules Kunio Ishikawa1, Kanji Tsuru1 and Song Chen1 1 Kyushu University, Department of Biomaterials, Faculty of Dental Science, Japan Introduction: Carbonate apatite (CO3Ap) was found to up-regulate differentiation of the osteoblastic cells and resorbed by the osteoclasts[1],[2]. Thus, CO3Ap demonstrated much higher osteoconductivity than hydroxyapatite (HAp) and replaced to bone. Replacement to bone is expected to be accelerated by the introduction of interconnected porous structure. In this study, therefore, interconnected porous CO3Ap was fabricated based on setting reaction of CO3Ap granules, and tissue response to the interconnected porous CO3Ap was evaluated histologically. Materials and Method: CO3Ap granules with 100-200 µm in diameter were exposed to acidic calcium phosphate solution (acidic Ca−P: Ca(HPO4)2·H2O − H3PO4) in the presence and absence of the loading. Then, porous body was further immersed in NaHCO3 solution. Composition was analyzed with XRD and the structure was evaluated by micro-CT and SEM. Mechanical strength was evaluated using a universal testing machine. For histological evaluation, porous CO3Ap was placed in the bone defect made at tibiae of rabbit for 4 and 12 wks, and observed after Villanueva Goldner staining. Result and Discussion: When CO3Ap granules were exposed to acidic Ca-P solution, CO2 bubble was formed and no setting reaction was observed even though surface of the CO3Ap was coated with dicalcium phosphate dihydrate [DCPD: CaHPO4·2H2O]. In contrast, interconnected porous body was fabricated when CO3Ap was exposed to acidic Ca-P solution under loading. DCPD crystals formed on the surface of CO3Ap granules bridged the CO3Ap granules one another. These difference indicated that contact of CO3Ap granules one another is the key for the bridging of CO3Ap granules with the DCPD crystals. The DCPD formed on the surface of CO3Ap granules was converted to CO3Ap when immersed in NaHCO3 solution. The pore was interconnected pore and the porosity was 42%. And the compressive strength was approximately 2MPa. When implanted in the rabbit tibiae, bone penetration inside the porous structure was confirmed within 4 wks whereas no bone penetration was observed in the case of dense CO3Ap as shown in Fig. 1. After 12 wks, larger amount of bone was found inside the porous CO3Ap, and CO3Ap was replaced to the bone. In contrast, replacement to bone was limited in the case of dense CO3Ap. Conclusion: Interconnected porous CO3Ap was fabricated based on the setting reaction of CO3Ap granules with acidic Ca-P solution. Interconnected porous CO3Ap elicited the bone tissue penetration interior to the CO3Ap body and accelerated its replacement to bone. Japan Agency for Medical Research and Development.