Tissue Engineering With Porous Calcium Phosphate Bone Cement Materials

Tissue engineering is a new method of repairing defects of bone, and one of focus of research in medicine. The purpose for tissue engineering is that the cells can propagate on the surface of scaffolds made up with degradable materials, and then new tissues grow out. Calcium phosphate cement is a new type of self-setting cement. It is perfect material for bone substitution and repair, which shows excellent biocompatibility, osconductibility, biodegradability, plasticity and less reaction thermal. But its mechanical property is not enough when it is used as scaffolds. The higher the porosity is, the bigger the pores are and the lower the strength is. Because of all of above the material cannot be used widely. As a result the research on calcium phosphate used as scaffolds is of importance.We prepared monoclinic powder by sintering at high temperature. A series of experiments upon different sintering temperature and holding time were carried out. The procedure of bone cement powder was optimized. The production had high purity and stable performance. When the time for mixing the raw materials was prolonged, the orthorhombic powder was obtained, and then the formation process of that was analyzed theoretically. The compressive strength and bending strength of orthorhombic powder were 26.71MPa and 15.16MPa, respectively.The gelatin mixed with the bone cement powder was removed as the result of its water-solubility, and then the porous material was obtained. The research on the effect of particle-size and a mount of gelatin on the mechanical strength, setting time and porosity, and the effect of liquid to powder ratio on the mechanical properties and porosity of setting products, were carried out. Also the effect of Na₂HPO₄, which was used as setting accelerator, on the setting time was one of the aspects we studied. When the amount of gelatin was increased, the mechanical strength declined, and the setting time and the porosity increased. When the liquid to powder ratio increased, the porosity increased and while the mechanical strength declined. The main crystal phase of the powder mixed with gelatin was hydroxyapatite (HA), the same as that without gelatin. The grain tangled with each other and composed reticulation, which might improve the mechanical properties of the setting products. The model of HA growing with gelatin was built by means of analyzing mechanism of the formation of pores. At first of mixing the gelatin swelled, and at last as the form of small molecule after 4h placed in ultrasonic cleaner. As a result the space was remained and the pores were formed.The result was found in slurry when detected by X-ray diffractometer for liquid metal that at first the reaction rate was low and accelerated after 120min, and decreased finally. The conclusion was elicited that the amount of HA increased and α_H-TCP was depleted in the products after different setting time when detected by X-ray diffractometer, α_H-TCP disappeared after 24h. The hydration of α_H-TCP was the process of dissolution and precipitation. The ions of CPC dissolved in water when α_H-TCP was mixed with water. After that the setting product was formed.