Research On Biological Composites Of Porous Calcium Phosphate Bone Cement

Porous calcium phosphate bone cement is prepared by an appropriate pore-making method from general calcium phosphate bone cement. It has excellent biocompatibility and greater structural advantages. Porous calcium phosphate bone cement has been more and more widely applied in tissue engineering, it represents a trend of the development of calcium phosphate bone cement.In this study, we made porous calcium phosphate bone cement owning interconnected pores by using pore-forming agent, and the diameter is about 200um. The pore-forming agent we selected was hydrogen peroxide, and the optimum amount was 6%. Meanwhile, to ensure the material owning penetrating nature, we invented a method of inserting soluble sucrose needles, and made a reserved hollow tube in materials. In the beginning of the material being implanted in, sucrose needles may play a role of strengthening, after a certain time, the sucrose needle will dissolve away, and a hollow tube will turn up, whose diameter is about 0.9mm. This structure of hollow tube structure matching with the ambient dispersive micropores can promote cell's adhesion, proliferation, differentiation, accelerate the bone cells'growth, climbing, running through the material, thus speed up the bone defect repairment.Although porous calcium phosphate bone cement has excellent biological properties and structure advantages, but it has a major drawback that the mechanical strength is low. And the higher the porosity is and the larger the pore size is, the lower the strength is. In order to strengthen the calcium phosphate bone cement, biological materials was composited, carboxymethyl chitosan and hydroxyapatite whiskers was applied to synergize with the bone cement, in which chemical enhancement combined with physical enhancement, and played a marked effect. Hydroxyapatite whiskers were prepared by template-mediated/homogeneous-precipitation, the SEM images showed that whiskers'morphology was complete, their lengths were in the range of 10 ~ 20μm, and the aspect ratio was among 5 to 20. The single optimal addition amount of carboxymethyl chitosan and hydroxyapatite whisker were determined respectively at 0.5% and 4%, and the highest flexural strength of their composites with bone cement were respectively 2.32MPa and 3.85MPa. Then adjusted their proportion appropriately, added both of them into the bone cement, and the result showed that the synergistic effect is indeed better than their single strengthening results. At last, the material's bending strength reached 4.14MPa.To further enhance the porous calcium phosphate bone cement, we modified its surface by coating a layer of gelatin, a kind of biological polymer material. The results showed that the gelatin layer played an evidable role in enhancing the porous bone cement material.As an implantation material, calcium phosphate bone cement should not only have considerable strength, but also certain degradability. In this study, we researched the process and mechanism of the porous bone cement samples'degradation in vitro initially. We got a conclution that the porous calcium phosphate bone cement has a faster degradation speed than conventional ones, and factors such as the pH value of body fluids, the porosity and pore size, the crystal form and doping of other materials have great influence on the degradation rate.