| Background and ObjectionThe strontium-containing a-calcium sulfate hemihydrate(Sr-a-CSH)has successfully synthesized through the previous research work in our laboratory,which not only maintains the good biocompatibility and osteoconductivity of the original calcium sulphate,but also makes the material have osteoconductivity.However,there is still a defect in its rate of degradation that does not match the rate of new bone formation.The purpose of this study is through compound Sr-a-CSH and nano-hydroxyapatite(nHA)to develop a novel composite bio-ceramic materials,which could have good biocompatibility,moderate degradation rate,and combines osteoconductivity and osteoinductive properties.Method1.The physical characterization and in vitro degradation of novel Sr-a-CSH/n-HA composites.Firstly,Sr-?-CSH was prepared by coprecipitation and hydrothermal method.Then mixed with the n-HA in a fixed proportion and liquid-solid ratio,the cylindrical composite sample was obtained after being modeled,fixed and dried.X-ray diffraction(XRD),fourier transform infrared spectroscopy(FT-IR),compressive strength test and surface scanning electron microscopy(SEM)were used to observe the physicochemical properties and characterization of the composites.The in vitro degradation experiments of composite materials were carried out by soaking in simulated body fluid(SBF).2.The effect of novel Sr-a-CSH/n-HA composite on proliferation,differentiation and migration of bone marrow-derived mesenchymal stem cells(BMSCs)in rats.The preparation of strontium-containing composite extract following international standards,and the concentration of strontium,calcium in extract liquid was determined.The BMSCs were cultured in the extract solution,and the cell proliferation and migration ability were detected by CCK-8 assay and scratch assay.The expression of related osteogenic genes(ALP,RUNX2,OCN,BSP)was detected by real-time quantitative PCR(qRT-PCR).The difference of osteoblast mineralization was analyzed by alizarin red and Von Kossa staining.3.Experimental study on repair of rat critical tibial bone defects with Sr-a-CSH/n-HA composite.We used SD rats to establish the critical tibial bone defect and implanted different concentrations of strontium-containing composite material to fill the bone defect.Serum strontium and calcium concentrations were measured 4 weeks after operation.X-ray and Micro CT were used to observe the bone defect repair,and the morphology of bone trabecula was analyzed.Histomorphology of hematoxylin-eosin(HE)and goldner trichrome staining was used to investigate the osteogenesis and material degradation in vivo.The CFU experiments were used to observe the differences in the induction of BMSCs by different materials in vivo.Results1.XRD and FTIR analysis showed that the overall peak intensity of composite was reduced compared with Sr-a-CSH indicated that with the addition of n-HA particle the intensity of the correspond diffraction peak of a-CSH is decreased,but there was no significant shift in the absorption peak of CSH,nHA and Sr ions.The SEM observation shows that the surface of the material is rough,polyporous,and the crystals are tightly combined.With the gradual increase of strontium content,the compressive strength of composites was declined slowly,but still reaches the level of compressive strength of normal cancellous bone.Degradation rate of composites can be kept relatively stable after being degraded in vitro for two weeks.2.The concentration of calcium ion in the extract was not significantly different among the groups.Strontium ion concentration was significantly higher in the 10%Sr-a-CSH/n-HA group than in the 1%and 5%groups.CCK-8 was used to detect the relative proliferation activity of cells,no significant difference between the groups.The expression of osteoblast-related genes(ALP,RUNX2,OCN,BSP)in BMSCs was significantly up-regulated after intervened with extracts.The scratch healing assay showed that the healing rate increased with the rise of strontium in the composites.Osteogenic differentiation tests showed that the number of mineralized nodules increased gradually with the increase of strontium content.3.X-ray and Micro CT showed that reactive new bone formation was observed in CSH group at 4 weeks after operation,but the material was almost absorbed.At 4 weeks and 12 weeks after operation,the formation of trabecular and BV/TV,Tb.Th analysis of each experimental group:10%Sr-CSH/n-HA group>5%group>CSH/n-HA group>CSH group.Tissue sections showed that the bone repair of 5%and 10%groups was significantly better than CSH/n-HA and CSH groups,and more overall repair effect.Conclusion1.Sr-a-CSH can be combined with n-HA to form a new type of composite material,the composite material has certain chemical bonds between the phases,and has good porosity.The compressive strength of the composites is comparable to normal cancellous bone,and the rate of in vitro degradation is also between that of pure CSH and HA.The composite material can release high concentration of calcium and strontium ions during the degradation and has the potential to promote osteogenesis.2.The novel strontium-containing composite has no cytotoxic effect,has good cell compatibility in vitro and has the effect of promoting osteogenic differentiation andmigration of BMSCs cultured in vitro.It can effectively promote the expression of osteoblast-related genes and the mineralization process of BMSCs cells,and has some osteoinductive properties.3.The novel strontium-containing composites can have the effect of overall repair in the process of bone remodeling in vivo,and have good tissue compatibility and osteoconductivity.The porous lamellae formed after in vivo degradation are more favorable to bone repair and reabsorption of residual nHA.In the process of material degradation will be accompanied with the release of strontium and calcium ions,the change of local microenvironment,these will be have synergistic promotion effect on the migration,recruitment and osteogenic differentiation of BMSCs in vivo. |
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