Research On Biofunctional Coating Based On Gelatin Nanospheres And Its Effects On Promoting Bone Repair

There are more than 10 million patients with bone defects in China every year.Artificial bone implantation is the most effective clinical treatment.Biomedical metallic materials have become a versatile and economical alternative used as bone repair implants because of their high mechanical strength,corrosion resistance,flexible structure and properties.At present,the metallic bone implant materials commonly used still have some problems that need to be solved urgently.For example,metallic materials lack biological activity,which makes it difficult for osteointegration;fast degradation and weak corrosion resistance of metallic materials in physiological environments can easily cause potential lesions;post-implantation inflammation causes delayed healing and causes implant failure.Therefore,research and development for new metallic implant materials with excellent biocompatibility and better performance is an effective way to reduce the pain of patients,surgical revision and cost.Surface modifications of metallic implants materials could be a promising approach for improving the biocompatibility of materials.The bioactive surface coating can improve the interface between the implants and the organism,and promote osseointegration.Furthermore,the incorporation of antibacterial agents into the coating can effectively inhibit the formation of biofilm,giving the coating multiple functions,which is the critical development direction for activating the surface of metallic materials and improving the efficiency of bone regeneration.In this paper,the commonly used biomedical metal in clinical,titanium and magnesium alloy was the object of research.Firstly,gelatin nanospheres were prepared by a two-step desolvation method.The gelatin nanospheres/chitosan(GNs/CTS)composite coatings made of natural polymer with excellent biocompatibility,biodegradability and low immunogenicity were prepared on the surface of biomedical metal by electrophoretic deposition(EPD).According to the drug release behavior of drug-loaded GNs and composite coatings,the dual biological functions of anti-inflammation and osteogenic differentiation were explored.Furthermore,the interaction between materials and cells,cells and cells,and the mechanism of promoting osteogenic differentiation and vascularization by the two sides' functional coating coated magnesium alloy in multicellular environment were investigated.The main research contents and conclusions are as following:(1)GNs were prepared by a two-step desolvation method.GNs(? 200 nm)with narrow size distribution and negative surface charge were prepared through optimized parameters,and the high efficient loading(? 130 ?g·mg-1)and slow release(> 28 d)of GNs were realized.The thermosensitive polymer was introduced to prepare two kinds of temperature responsive gelatin nanocarriers,and the temperature was 36.0 °C and 40.5 °C,respectively.The regulation of drug release through the changes of ambient temperature lay the foundation for the on-demand release of drugs in vivo.(2)Preparation and performance research of dual function coating on titanium surface.GNs loaded with dexamethasone(DEX)were used to prepare composite coatings with chitosan on the surface of titanium by EPD.GNs were distributed homogeneously on the surface and inside the coating,and the thickness of the composite coating was about 10 ?m.The DEX-loaded coating showed a burst release manner at the initial period followed by a sustained release period for up to 28 d.Biological assessments demonstrated that the DEX-loaded coating possessed the function of inhibiting inflammation during the burst release period and stimulating osteogenesis in the sustained release period with the help of DEX release profile,which endows the dual biological functions of the composite coatings on titanium.(3)Preparation and performance research of two sides coating on the surface of magnesium alloy.According to the characteristic of magnesium alloy's easily oxide surface,through the optimization of the EPD process,a GNs/CTS two sides composite coating on the WE43 substrate was fabricated with simvastatin(SIM)loaded into the GNs.The thickness of the composite coating was about 50 ?m,and the contact angle was about 55°,which is suitable for cell adhesion.Both the degradation and corrosion rates of the coated substrate were significantly minimized in contrast to bare WE43.Additionally,the release of SIM in the composite coating sustained up to 28 d,which could promote osteogenic differentiation and inhibit the activity of osteoclasts.(4)Mechanism research of promoting osteogenic differentiation and vascularization by the functional coating on the two sides of magnesium alloy.SIM-loaded GNs/CTS composite coating modified magnesium alloy could promote the osteogenic differentiation of BMSCs.BMSCs and HUVECs were co-cultured through Transwell systems,and the release of SIM from the coating could increase the secretion of chemokine and angiogenic factors from BMSCs,which could promote the migration and tube formation of HUVECs,respectively.Bone morphogenetic protein secreted by HUVECs could be increased by the release of SIM from the coating,which could promote the osteogenic differentiation of BMSCs.The secretion of chemokine from HUVECs could promote the migration of BMSCs.In summary,GNs were carriers for loading different drugs in this paper,and it was obtained two kinds of functional coating on the surface of metallic implants.GNs/CTS composite coating on the surface of titanium loaded with DEX played a dual biological function of anti-inflammation and osteogenic differentiation in different release concentrations.The two sides composite coating modified magnesium alloy loaded with SIM could not only slow down the degradation rate and enhance the corrosion resistance,but also regulate the osteogenic differentiation of osteoblasts and mesenchymal stem cells,and promote vascularization of HUVECs.In this paper,the methods of bioactive coatings based on GNs loaded with drugs and the obtained research results,through the modification of metallic implants to promote bone regeneration,providing research basis and references for the design of bone repair materials,which has the basis of theoretical significance and clinical application value.