Bone Induction Of Ca, P Department Of Ceramic Materials In The Bone-like Apatite Layer Formation, Characterization And In Vitro Dynamic Research Model Initially Established

Bone-like apatite formation on the surface of calcium phosphate ceramics has been believed to be the necessary step of new bone growth on the ceramics and to be relative to the osteoinductivity of the material. The research of the factors effecting bone-like apatite formation is a great help to the understanding of the mechanism of osteoinduction.A comparative study of the in vitro formation of bone-like apatite on the surface of dense calcium phosphate ceramics was finished in a simulated body fluid (SBF) flowing at different rates. The dynamic condition was realized by controlling the SBF flowing in/out of the sample chamber of 100ml. The flow rate of 2ml/min is closed to the flow rate of body fluid in human muscle environment. The pH and inorganic ionic composition of SBF are close to those of human body fluid. Bone-like apatite formation was relatively easier in static SBF than in dynamic SBF. The apatite formed faster in 1.5 SBF than in SBF. Roughing of the surfaces would facilitate bone-like apatite formation. Bone-like apatite did not been formed on the dense smooth surface in dynamic SBF. All these demonstrated local supersaturating concentration of Ca2+ HPO42- PO43- near nucleation site was critical for nucleation of apatite .Bone-like apatite formation on the wall of porous calcium phosphate ceramics was investigated in static SBF and dynamic SBF flowing at different rate. The results of a 14-day immersion of samples in static SBF showed that the formation of bone-like apatite was occurred both on the surface and in the wall of the pores of materials. When SBF flowed at the physiological rate of the tissue fluid in muscle (2ml/l 00ml.rnin). bone-like apatite can be detected only in the pores of the materials. There was no bone-like apatite formation on both in the pores and on the surface of the materials when SBF flowed at rate higher than the normal rate of tissue fluid (IGml/lOOml.min). By increasing the concentration of Ca2+ and HPO42" in SBF to111.5 fold of the standard SBF, a 7-day immersion experiment result showed that bone-like apatite could be found in the pore of the materials. The result that bone-like apatite formation could only be found in the pores of the materials when SBl- flowing at physiological rate was coordinated with that of in vivo implantation of calcium phosphate ceramics: most of the ectopic bone formation was detected inside the pore of the porous calcium phosphate ceramics. This result demonstrated that dynamic model used in this study was better than usually static immersion model in mimicking the physiological condition of in vivo formation of bone-like apatite. Dynamic SBF method is very useful for understanding the in vivo formation of bone-like apatite and the mechanism of ectopic bone formation of calcium phosphate ceramics.Ca and P ion concentrations in body fluid are too low for spontaneous apatite nuclcution but it is sufficient for the growth of apatite crystal. Ca2+ can induce bone-like apatite tarnation in a dose-dependent manner; there is a threshold of Ca2+ local concentration for the formation of bone-like apatite. The threshold of Ca2+ for bone-like apatite formation in static SBF is different from dynamic SBF. The threshold of static SBF is lower than that of dynamic SBF.Five kinds of SBF were prepared according to the Ca2+ ions concentration in body fluids of human, dog, pig. rabbit and monkey. After 14-day immersion in SBFs, bone-like apatite formed on the pore wall with micro pores while no apatite was observed on the smooth pore wall. The bone-like apatite grew faster in SBF of dog and rabbit than in other SBF. In animal experiment, the same phenomena were also observed: bone-like apatite formed faster on specimens implanted in dog and rabbit than in other animals. This sequence is different from the order of osteoinductivity of biphasic calcium phosphate ceramics implanted in these animals. The results show the formation of bone-like apatite on materials is an important factor but not the only factor for their osteoinduction.The b...