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>Fabrication of porous carbonate apatite based on the bridging of calcite granules followed by the phase transformation to carbonate apatite
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Fabrication of porous carbonate apatite based on the bridging of calcite granules followed by the phase transformation to carbonate apatite
Introduction: Carbonate apatite (CO_3Ap) has attracted much attention for artificial bone substitutes becuse it can be replaced to new bone due to the resorption by osteoclasts, followed by the deposition of bone mineral by osteoblasts. Introduction of interconnected porous structure to the CO_3Ap is thought to enhance the ability of bone replacement because cells and tissues can penetrate into the pores. Since piling and bridging of p granules are one of methods to fabricate interconnected porous material, calcite granules as precursor for CO_3Ap fabrication were piled and bridged each other owing to the interlocking of calcium hydrogen phosphate dihydrate (DCPD) crystals that could be precipitated by the reaction with acidic calcium phosphate solution. Then, it was immersed into the solution containing carbonate and phosphate ions for phase transform to CO_3Ap in order to fabricate interconnected porous CO_3Ap. Experiment: Calcite granules (＜p100-300 μm) were put into split stainless steel mold (Φ6 mm ×12 mm in height) and exposed to monocalcium phosphate monohydrate (MCPM)-saturated phosphoric acid solution (H_3PO_4:0.6 mol/l and MCPM: 1.0 mol/l). Subsequently, 0.4 MPa of pressure was loaded externally for 5 minutes. The set porous body was immersed into 1.0 mol/L Na_3H_2CO_3PO_4 solution at 80°C up to 7 days. Characterization of the obtained specimens was done by X-Ray diffraction (XRD) measurement, scanning electron microscope (SEM) observation and compressive strength measurement. Porosity was calculated using Archimedes' principle. Results and Discussion. SEM observation indicated that many small crystals were observed on the surface of calcite granules after being reacted with acidic calcium phosphate solution. These substances were assigned to DCPD by XRD analysis. Interconnected porous structure could be observed even after being immersed in 1.0 mol/l Na_3H_2CO_3PO_4 solution at 80°C for 7 days. XRD analysis indicated that calcite granules with DCPD crystals could be transform into CO_3Ap after the reaction. Porosity and mechanical strength of the obtained porous CO_3Ap were 21 ±12% and 1.5±0.4 MPa, respectively. This mechanical strength is enough for handling in clinical situation. Conclusion: Fabrication of porous CO_3Ap could be achieved by bridging of calcite granules using the DCPD crystals that were formed by the reaction to acidic calcium phosphate solution, followed by the reaction of 1.0 mol/l Na_3H_2CO_3PO_4 solution.
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