The Study Of Calcium Phosphate Biomaterials Setting In Situ

Nowadays, with the development of biomaterial science, the bone defects repair materials developed from the traditional mechanical fixation to biomaterial implantation and the technique of surgery developed from traumatic to minimal invasive technology. However, most of the biomaterials used in oral clinical is particle and not good in shaping, biomechanics, handling and lack of osteoinductivity which always have to be used with biomembrane. In order to relieve the pain of patients and reduce the syndromes, seeking for a more ideal material such as calcium phosphate cement which could owns the properties of self-setting in situ, easy handling and bone inductivity became the most attractive point.Some of the calcium phosphate cement (CPC) has been used in clinic; however, the relatively low strength and susceptibility to brittle catastrophic fracture of the cement have severely limited its use to only non load bearingm applications. CPC sets to form hydroxyapatite which lack of osteoinductive ability, So we have to improve the the biomechanic and osteoinductive ability of the CPC.The aim of the study is to synthesize the CPC with improved mechanics and osteoinductivity. First theα-TCP particle and the CPC based onα-TCP was synthesized. Then the degummed silk is used to improve the strength and fracture resistance of materials. Ascorbic acid,β-glycerophosphate and dexamethasone are added in CPC liquid to improve the osteoinductivity of the materials. The results of the study show that:1.α-TCP was synthesized by the reaction between phosphoric acid and CaCO₃ slurry. The assist agents of CPC are CaCO₃ and DCPD. The miture powders were mixed with 0.25M 0.25MNaH₂PO₄/Na₂HPO₄. The initial setting time is about 7 min, the final setting time is about 17min. The compressive strength reached 7.46MPa and the bending strength reached 5.16MPa.2. Trypsin was picked out as degumming reagent for the ability of preserving the mechanic integrity of silk. The examination of degummed silk suggested that the sericin can be totally removed under our degumming protocols.The simple twisting method was adopted by us for the sake of adding the degummed silk in 3mm length. The CPC added with degummed silk can reach 12.54MPa of compressive strength and 8.882MPa of bending strength. The setting time is almost the same between the CPC group and the CPC added with degummed silk and osteoinductive agents.3. In vitro experiments were designed and carried out to evaluate the biological reaction of the CPC. The BMSCs cells were cultured on CPCsurfaces in vitro. Cell attachment, spreading, cell proliferation and differentiation were evaluated and there is no statistic difference between CPC and control group.4. The mRNA level of osteoblast-related genes ALP, Col-I and OCNwere examined using RT-PCR; The mRNA of ALP, Col-I and OCNwere expressed in all CPC groups and wasn't expressed in control group. The protein level of OCN was examined using ELISA, there is statistic difference between CPC and CPC+osteoinductive group. With the limitation of these findings,α-TCP with the assist agents of CaCO₃ and DCPD can almost meet the clinic demands. The compressive and bending stress were improved with the adding degummed silk fiber to CPC and the osteogenic ability of the CPC were improved by adding the osteoinductive agents to CPC.