| Part I Characteristics of Injectable Calcium Phosphate Cement Reinforced By Silk Fibroin[Objective]To evaluate the compressive strength and setting time of a silk fibroin reinforced calcium phosphate cement(CPC)with different mass fractions of silk fibroin(SF)and using different liquid/solid(L/S)ratios. And to explore the possibility of a novel injectalbe filler material for kyphosplasty.[Methods]The experiment was performed by using biomechanical testing-machine and measuring instrument for setting time(Vicat apparatus) under the simulated body fluid environment (namely,37±0.5℃, humidity 100%).①the CPC with different mass fractions of SF (0.5%,1.0%,1.5%,2.0%,2.5% and 3.0%) and pure calcium phosphate cement(control group)were mixed with a L/S ratio of 0.400 ml/g.②the calcium phosphate cement with a 2% mass fraction of SF were mixed with different L/S ratios(0.350,0.375,0.400,0.425,0.450 and 0.475). Then, the compressive strength and setting time(initial setting time, final setting time) were measured(n=5).[Results]The compressive strength of injectable calcium phosphate cement would increase gradually along with the mass fraction of SF. However, the compressive strength starts to reduce as the SF content reaches 3%.Additionally,the compressive strength of calcium phosphate cement with 1.0%,1.5%,2.0%,2.5% and 3.0% mass fractions of SF were statistically different in t-test(p<0.05) compared with control group.And the compressive strength of injectable CPC would increase when decrease the L/S ratio. However, it would decrease when L/S ratio was 0.350.The initial setting time and the final setting time would decrease gradually as the mass fraction of SF increases. The initial setting times of CPC with 1.0%,1.5%,2.0% and 2.5% mass fractions of SF and the final setting times of CPC with 0.5%,1.0%,1.5%,2.0%and 2.5% mass fractions of SF were statistically different in t-test(p<0.05) compared with control group respectively.The initial setting time and the final setting time would gradually decrease accordingly along with the L/S ratio's reducing.[Conclusions]The calcium phosphate cement reinforced by silk fibroin(SF/CPC) is a promising kyphoplasty filler for it's good compressive strength, however the SF content and L/S ratio would be considered to gain an appropriate setting time. Part II Cell Compatibility of Injectable Calcium Phosphate Cement Reinforced By Silk Fibroin[Objective]To evaluate the cell compatibility of the injectable CPC reinforced by SF,which used as a foundation for further researches in vivo.[Methods]Human bone marrow mesenchymal stem cells(hBMSCs) were isolated by combining density gradient centrifugation with plastic adherence and cultured in specified culture medium.Cell phenotype was detected by flow cytomety.hBMSCs cultured with extracted liquid of SF/CPC and CPC were used to detect the relative growth rate and evauate the cytotoxicity on 1st,3rd,5th and 7th day with the help of MTT assay. hBMSCs cultured with extracted liquid of SF/CPC and CPC were used to detect cell cycles on 4th day by flow cytomety. hBMSCs were seeded onto prepared SF/CPC to observe the adhesion and growth by scanning electron microscope.[Results]Higher purity of hBMSCs could be achieved by density gradient centrifugation.hBMSCs highly express cell phenotype such as CD29,CD44 and CD105 and lowly express CD34 and CD45.hBMSCs cultured with extracted liquid of SF/CPC and CPC had excellent activities. The classification of cytotoxicity of SF/CPC and CPC on 1st,3rd,5th and 7th day were grade 0 to 1.No abnormal DNA contents were observed by flow cytomety.The G0/G1 stage,S stage,G2/M stage and proliferation index(PI) of hBMSCs cultured with extracted liquid of SF/CPC and CPC had no difference (p>0.05).hBMSCs seeded on SF/CPC had good adhesion and proliferative ability.[Conclusions]The injectable calcium phosphate cement reinforced by silk fibroin has good cell compa- tibility in vitro.And it can be applied in experiment in vivo.
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