Study On Osteoinductive Calcium Phosphate Ceramcs And Bone Histo-engineering In Vivo

With the progress in material science, molecular biology and medicine, the repair of bone defects has been developed from simply fixing by metal, polymer and bioceramics mechanically to regenerating or reconstructing new bone tissues by means of inducing biomaterials. The key to realize this goal is to endow bone substitutes or devices with bionic structure and biological functions of inducing bone tissue regeneration, thereby, the advantage of body' s health ability themselves could be taken. Calcium phosphate, mainly hydroxyapatite, is the inorganic composition of biological bone. There is a kind of typical bioactive material with excellent biocompatibility and the ability to form chemical bond with newly formed bone tissue, which make it the best choice for develop a new generation of bone substitute. Traditional hydroxyapatite and tricalcium phosphate ceramics have not the potential of inducing bone regeneration. In order to endow them with this ability, bone tissue engineering has been established in recent years. There are usually two approaches for bone tissue engineering. That is: 1. To take biomaterials as scaffold and to cultivate osteoblasts and other bone tissue cells within it to fabricate living devices in vitro. 2. To add some bone growth factors or other bone growth signal molecules into biomaterials as carrier of a controlled release system and then to implant them in vivo. In the first case, cells existed in biomaterials can naturally secrete cytokines, bone growth factors and enzymes which can stimulate or induce bone regeneration. In the second case, the biomaterial carriers can control the release of the biochemical molecules, which induce mesenchymal cells to differentiate into osteoblasts and further develop into new bone tissue. In the former approach, problems arise such as standard cell lines and their multiplication and cultivation as well as maintaining their activity in vivo because the conditions for cell differentiation, multiplication and growth are different between in vitro and in vivo. Therefore, cells cultivated under certain conditions in vitro are not absolutely viable in vivo. The later approach involves immunity and safety of growth factors. Meanwhile, the price of growth factors is expensive. These problems must be solved through bone tissue engineering studies.At the beginning of the 90s in the 20th century, a hypothesis was put forward by Professor Zhang, that is, by controlling material factors themselves or optimizing their design, calcium phosphate ceramics could be endowed with biological function of inducing bone regeneration. Under the principle of this hypothesis, a series ofnew porous calcium phosphate ceramics were fabricated and the osteoinductive effect of them was demonstrated by Zhang, Yamasaki and Ripomonti respectively, which settled a base for developing a new generation of osteoinductive biomaterials.Based on the review to a number of references and the previous work of Professor Zhang, blocks of porous HA/TCP without any growth factors were implanted into muscles of dogs to verify whether the material possess osteoinductivity. The results suggested that three kinds of HA/beta-TCP blocks with different porosity held osteoinductivity. They could make the active stage of bone formation in bones be ahead of schedule. The speed of bone forming in the materials with smaller pore size was faster than in materials with larger pore size and thus the repair was completed earlier. The ultimate strength that the implanted samples could reach was closely related with porosity of the materials. In the samples with lower porosity, the ratio of living bone was also lower comparatively. The higher the porosity, the higher the ratio of the living bone and strength closed to biological bone could obtain. Eight months after implantation, the strength of the samples with proper porosity could reach the level of biological bone. Although the osteoinductivity of these materials was proven, it did not meet the demand for time limit of bone repair clinically.To...