Investigation Of Rheological Properties And Cohesion Of Calcium Phosphate Cement And A Novel Preparation Method

Due to its excellent biocompatibility, self-setting and facility to be shaped, calcium phosphate cement (CPC) is a promising biomedical material for hard tissue repair. Because of wide applications of injectable CPC, improvement of its injectability becomes the hot issue of the research. CPC with good injectability should have excellent flow ability and stability, which are largely dependent on rheological properties. However, there are limited related researches. Cohesion time (CT) and remaining percentage (RP) are two parameters evluating cohesion of CPC. Only when these two parameters meet clinical requirements, can uneasiness to disintegrate of CPC paste be ensured, which will lead to the success of surgery.In this dissertation, with HAAKE MARS Rheometer, we investigated effects of compositions of TTCP/DCPA CPC on rheological properties and the results shows that viscosity, yield stress and thixotropy of CPC paste increased with increasing powder-to-liquid, but they didn't increase directly when the content and molecular weight of dextran were raised. The viscosity, yield stress and thixotropy of CPC paste became the strongest with 0.2wt% dextran or dextran with molecular weight of 5×105.Then a new testing method was designed to measure cohesion time and remaining percentage of CPC paste at the same time. Two kinds of disintegration mechanisms were observed: a rapid disintegration of a large number of particles within a short time and a continuous but slow disintergrations process. According to the test results, we found that increasing the concentration of the incubation liquid or the mixing liquid is the effective measure to ensure the two cohesion parameters of cohesion to meet clinical requirements at the same time.In addition, we explored the possibility of using natural bone powder which had good biocompatibility to synthesize solid phases of CPC. With this novel method, high purity solid phases of CPC were successfully synthesized. Furthermore, the setting process of TTCC/DCPA CPC was studied and we found that the conversion percentage of HAP of this kind of CPC and the compressive strength were relative low. The possible reason was that the impurity Mg of CPC introduced by natural bone powder inhibited the growing of HAP crystal and further research was needed.