| Objectives:Increased use of reconstruction procedures in orthopedics has improved the life of patients undergoing surgery.However,surgical site infection remains a major challenge.Efforts were made to fabricate antibacterial surfaces with good biocompatibility.This present study aimed to fabricate zinc-incorporated chitosan/gelatin(CS/G)nanocomposite coatings on the titanium substrates via electrophoretic deposition(EPD).And a further step was taken into the morphogenesis of Sr/CS/G aggregates and biomimetic apatite formation ability in vitro.Methods:Zinc/chitosan/gelatin composite coatings were fabricated via EPD where the final concentrations of zinc ions in the EPD solutions were 0.5,5,and 50 mM.Morphology characteristics of the coatings were observed by fluorescence microscopy,field emission scanning electron microscope(FESEM)and transmission electron microscopic(TEM).X-ray energy dispersive analysis(EDX),X-ray photoelectron spectroscopy(XPS),fourier transform infrared spectroscopy(FTIR)and X-ray diffraction analysis(XRD)were applied for physiochemical characterization of the coatings.The tensile and shear bond strength tests were conducted using an electrical mechanical Instron Model.Zinc ion release profile was analyzed using plasma-optical emission spectrometer(ICP-OES).Anti-planktonic and anti-adherent bacteria test were conducted using E.coli and S.aureus.Furthermore,rat BMSCs were used to evaluate the in vitro biocompatibility and osteogenic effect of the coatings.The second part of the experiment took a further step into the morphogenesis of Sr/CS/G aggregates grown under different external parameters(polymer concentration,time,EPD current)through scanning electron microscope(SEM),transmission electron microscope(TEM),X-ray diffraction(XRD)and-Fouriertransform infrared(FTIR).The apatite formation ability of these aggregates is explored,as well as the primary biological study of these apatites.Results:In the first part of the experiment,physicochemical characterization confirmed that zinc was successfully deposited in a metallic oxide/salt complex status.Transmission electron microscopic(TEM)results observed formation of core-shell nanosized particles released from the coatings.The selected-area electron diffraction(SAED)pattern of the particles presented faces of ZnO with organic background.Mechanical tests showed improved tensile and shear bond strength between substrates and zinc-incorporated coating surfaces.Zinc-incorporated CS/G coatings presented antibacterial abilities against both Gram-negative E.coli and Gram-positive S.aureus in a concentration-dependent manner.The generation of ZnO/Zn2+ complex in the coatings may contribute to bacteria inhibition.In vitro study demonstrated that appropriate concentration of zinc could promote proliferative and osteogenic activities of rat bone marrow stromal cells.In the second part,when different amount of gelatin was brought to the EPD suspension,the morphology of the aggregates changed from branched structure to flower-like and sphere-like structure,the growth of the aggregates presented branched structure externalized the self-similarity of fractal structure.Chitosan serves to bridge these nanoparticles,while gelatin plays vital role in forming spherical structure from microscope to nanoscale.XRD confirmed the formation of SrC03.To further explore the biomineralization behavior,the apatite formation capacity of the aggregates is investigated in PBS and SBF solution.When Sr/CS/G coated Ti plate was immersed in SBF,the spherical apatite formation was observed,XRD diffraction patterns detected characteristic peaks at 26° and 32°.The morphology of apatite forming without calcium was explored by immersing the coating in PBS,lamellar crystals of nanosize were observed in the aggregates,which was the result of secondary crystallization of SrCO3 nano cells,XRD patterns confirmed the formation of SrHAp.The Sr/CS/G aggregates showed satisfactory in vitro biocompatibility when co-culturing with rBMSC,the coatings can improve cell adhesion,proliferation and calcium intake after immersing in PBS and SBF.Conclusion:Based on the findings in this study,it can be concluded that an organic-inorganic nanocomposite coating was electrophoretic deposited on substrate.Metal oxide nanoparticles could form and be released continually from the coatings.Moreover,this organic-inorganic coating showed inhibitory action against both gram positive and negative bacterial strains,and was also biocompatible under in vitro conditions and promoted osteoblast differentiation.Inexpensiveness and convenience of the strategy,green routs for synthesis would make it a promising candidate for surface modification of biomedical materials.The organic molecules as crystal modifiers play an important role in controlling the shape and architecture of crystallizing and growing inorganic materials.The identification of the biomimetic strontium-chitosan-gelatin composite led us to a detailed investigation of the material from atomic to the mesoscale level... |
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