Si-doping Biomimetic Bone Substitutes Via Bi-template Stratage And Its In Vitro And In Vivo Evaluation

Bone is a composite material composed of an interpenetrating organic-inorganic matrix that exhibits excellent mechanical properties,hierarchical structure from nano to macro,and intriguing function of self-remodeling,derived from the biomineralization process during natural bone formation.With the exploration and understanding of the native biomineralization,it reveals that the natural bone is co-assembly induced by many organic molecular template headed by collagen.Therefore,it is a very popular thesis to synthesis the bio-inspired materials based on template self-assembled strategy.Template-induced materials not only involve component simulation,but also pay more attention on the structural bionics.Compared with the single template self-assembly,the biomimetic bone substitutes induced through the strategy of bi-template show much more close to the natural bone.Thus,the bi-template-induced strategy as a beneficial supply and great advance of single-template self-assembly has been attracted a wide attention in the field of biomineralization.With the rapid development of biomedical materials,materials that solely mimicking composition and microstructure of natural bone are unable to fit the higher demands of people,especially on bone repair biomaterials.Functionalization of the biomaterials with bionic component and structure,giving it more excellent properties for bone repair,can well adapt to the development of modern medicine.Silicon(Si),an essential trace element in the human body,has been extensively recognized to play an important role in regulating bone metabolism,and promoting bone repair.It is well documented that the addition of silicon can significantly improve the bone repair ability of materials.In this study,we firstly synthesized a series of hybrid bone composites,Silicon-Hydroxyapatites/Silk fibroin/Collagen,based on a specific molecular assembled strategy.Silk fibroin and collagen were selected as the bi-template due to their similar structure and compensative properties.Then the compositions,physical and chemical properties,as well as biocompatibilities of the materials were investigated.(1)Ethylsilicate was used as silicate source,a series of Si-doping bone composites with different silicon content were fabricated by bi-template-mediated self-assembly method.X-ray diffraction(XRD),X-ray photoelectronic spectroscopy(XPS),thermogravimetric analysis(TGA)and Transmission electron microscope(TEM)were used to analyze the physiochemical properties of materials.The results indicated that the Si-doping content in the biomimetic bone substitutes varied from 0 to 1.2%,and contained about 70%of the inorganic components that was similar to the natural bone.The inorganic crystals were needle-like hydroxyapatite,and the crystallinity of crystal was decreased with increase of Si content.(2)After co-cultured with rat bone marrow mesenchymal stem cells(rMSCs),Si-doping bone substitutes exhibited a good biocompatibility,and enable to well support the adhesion and proliferation of rMSCs.The cell proliferation and adhesion were increased with the enhancement of Si content in Si-doping bone substitutes.The results of alkaline phosphatase activity analysis and staining,RT-PCR,immunofluorescence staining and calcium nodules staining demonstrated that the group containing 0.8wt%of Si was able to promote rMSCs differentiation into osteoblasts comparing with other groups.(3)Poly(lactic-co-glycolic acid)shows good biocompatibility and strong plasticity.Therefore Si-doping bone composites and PLGA were mixed to prepare porous scaffolds with ordered pore structure and high porosity by ice-templating technology.The porosity of scaffolds were about 80～90%,and the range of pore diameter were 150～200 microns,with good connectivity between inner pores.The cell experiment revealed that the composite scaffolds containing biomimetic bone substitutes was able to well support the adhesion and proliferation of rMSCs(4)Rats subcutaneous implantation experiment and rat cranial defect model were further used to estimate the histocompatibility and bone repair capacity of the porous scaffolds in vivo.After 3 weeks of subcutaneous implantation,the scaffolds were partially degraded,and well integrated with the adjacent tissue.Results of histological staining and micro-CT analysis indicated that the implanted scaffold with 0.8wt%Si exhibited a great potential for bone defect repair.