| Calcium phosphate cement can be easily operated and shaped at will, it is a self-setting cement which can solidify in-situ. When implanted in human body, it grow spontaneously, the chemical component of the products are similar to the inorganic component of the bone, the structure of the crystals are also similar to the bone structure. The hydrated products have biodegradability, after injection, they are absorbed by the human body gradually, the Ca and P ions take part in the formation of the damaged bone, so it is a perfect material for bone substitution and repair. But calcium phosphate cement has low strength and mechanical properties, it can't endure load because of its brittleness, which restrict its use. Researches are carried out to resolve these problems. First is solid powder, including the arrangement in-group for different calcium phosphate and the addition of additives. Second is liquid, including citric acid, malic acid and phosphate natrium. Crystal whisker, organic materials, chopped fiber were also used to strengthen the materials.In this paper, calcium phosphate powders were prepared by solid-state sintering, the influence of the cooling method on the purity of the powder was studied. We choose a proper cooling method to prepare powder with high purity.Carbon nanotubes possess unique properties such as small measure, high strength, the great modulus of elasticity and specific surface area. The CNTs, which were used to strength the materials, were added to the powders by ball milling. Different content of CNTs were added, the disperse condition were studied by SEM photographs, the flexural strength and the compressive strength of the composite with different content of CNTs were also compared. At last, we got CNTs/CPC composite powder with uniform dispersion of CNTs and high mechanics strength after setting.We did research about the influence of the granularity of raw powder, the ratio of liquid to solid and the content of HA crystal seed on the setting time and the mechanics strength of the composites. The experiments showed that reducing the diameter of the powder, adding HA crystal seeds and reducing the ratio of liquid to solid can shorten the setting time of the composite, the shortest setting time is T_I=5.5min, T_F=6.4min when the diameter of the powder is the minimum. The mechanics strength changed with the parameter and when the ratio of the liquid to solid is 0.35, we got the maximum of flexural strength, which was 16.81MPa. Observing the microstructure, we found that the addition of HA crystal seed will induce the morphology of the hydrated product to become grain-like.Two method were used to add chitosan, the result showed that the hydrated product have rod-like morphology, part showed plate-like. When the content of the chitosan is 0.5%, we got short setting time but high mechanics strength. Thermosensitive chitosan-based hydrogel were used as liquid and mixed with calcium phosphate powder, compared with pure calcium phosphate cement, the mechanics strength was improved. The SEM photographs showed that the structure is net-like, which can be used to prepare tissue engineering scaffold material.The setting mechanism of the composite were studied, we used solid reaction kinetics and principle of nonhomogeneous diffusion to explain that the smaller of the raw powder, the shorter of the setting time. The variety of ratio of liquid to solid will change the distance of the powders, which cause the change of the reaction time between powders. The addition of HA crystal seeds could decrease the potential barrier for nucleation and therefore accelerate nucleation and growth of the product. The addition of chitosan will increase the viscosity of the liquid, decelerate nucleation, therefore the setting time is prolonged. It showed that chitosan molecule have kinds of functions, which lead the product to grow to a certain direction, therefore part of hydrated product show plate-like. |
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