| Titanium and titanium alloys are widely used in the field of dentistry due to the excellent material properties and biological activity.However,because of its upper structure exposed to the oral environment,it is easy to be invaded by tbe bacteria at the implant-soft tissue binding weak site.Secondly,intraoperative congestion and damaged implant sites provide an ideal environment for bacterial reproduction.Thirdly,the surface roughness of the lower part of the implant is not only easy to form bone bonding,but also facilitate bacterial adhesion and colonization.Fourthly,titanium and titanium alloys are a kind of inert materials.These factors will induce the occurrence of peri-implantitis.Therefore,how to make the surface modification of implant materials have biological activity and antibacterial property which is the focus and difficulty so as to improve the success rate of implant.In the study,the surface of pure titanium was obtained viaelectroplating and UV reduction methods to obtain the membrane and granular structure.The antibacterial activity of Ti surface coating was tested with common oral pathogenic bacteria.And the biological activity of Ti surface coating was evaluated.In a word,The properties of Ti surface coating were optimized in terms of antibacterial and biological activities.Part I Fabrication and characterization of GO-Ag-Ti multiphase nanocomposite on Ti surfaceObjective:To design and fabricate GO-Ag-Ti multiphase nanocomposite on Ti surface,and to evaluate their material properties.Methods:The process parameters were designed by orthogonal experiments.The pure Ti surface was modified by the different concentrations of GO(20 ?g/ml?50?g/ml?80?g/ml?100?g/ml)and silver nitrate solution(1 mol/L)via electroplating method and UV reduction method for 5 min at 20 V.The Ti-GO and Ti-GO-Ag surface morphologies were observed by FE-SEM.And the properties,contents and distribution of Ti-GO/Ti-GO-Ag were charactered by Raman and XPS.Also the surface profile,roughness and hydrophilicity of Ti-GO/Ti-GO-Ag were analyzed vith AFM and contact angle tester.Certainly the mechanical properties of surface coating were investigated by nanoindentation and nanoscratch,including elastic modulus,Vickers hardness and friction force,respectively.In addition,The release of silver ions was studied by ICP – MS.Results:20 V and 5 min,which were chosen by orthogonal experimental design.There were a kind of film and granular structure on the Ti surface,which were GO and Ag particles via electroplating method and UV reduction method,respectively.And the amounts of GO and Ag were proportional to the concentration of GO.The contour of surface coating was ups and downs.The roughness,elastic modulus and Vickers hardness were proportional tothe concentration of GO,and the friction was not related to concentration.Additionally,the amounts of Ag ions released of 4 groups showed similarities on the fourth day.Conclusions:The experimental process could be optimized by the orthogonal experimental design.Ti surface can be obtained in the form of film and granular modification.The morphology,contour,roughness,hydrophilicity,elastic modulus,Vickers hardness,friction of surface coating are different from the pure Ti substrate.And the general rule of silver ion release in the four experimental groups tends to decrease.Part II The studying on the antimicrobial activity of Ti-GO-Ag multiphase nanocomposite on Ti surface Objective:To study the antimicrobial activity of Ti surface coating on common oral pathogenic bacteria at different concentrations and amont of GO and Ag.Methods:Staphylococcus aureus,Streptococcus mutans and Porphyromonas gingivalis were studied.The ability of biofilm formation on the surface coating was evaluated at the concentrations of 20 ?g/ml?50?g/ml?80?g/ml?100?g/ml.And the bacterial morphology and bacterial cell membrane integrity were observed by FE-SEM and LSCM.The fluorescence intensity values and the three-dimensional morphology of the surface coating were analyzed by Image J software.Also bacterial apoptosis and bacterial internal structure were investigated by flow cytometry and TEM,respectively.In addition,the relative gene expression of bacteria was detected by real-time quantitative PCR.At last,the antimicrobial mechanism of surface coating was explored.Results:The antibacterial effects of four different concentrations of Ti-GO-Ag coating on Staphylococcus aureus,Streptococcus mutans and Porphyromonas gingivalis were morethan 89%,and the antibacterial effects of four experimental groups were better than the control group.The morphology and cell membrane integrity of three kinds of bacteria changed obviously.The red fluorescence intensity was higher than the green fluorescence intensity on the surface coating,and bacterial activity was lower than the control group.The three-dimensional morphology of the bacteria was also less,thinner and more loose than the control group.Bacterial apoptosis which planted on the surface coating was significantly different from the control group.Then through the observation of the internal structure,it was found that the destruction of bacteria was mainly the contact of silver ions and the passage of the membrane into the cell and the destruction of bacterial structure.Additionally,the relative expression of the three genes was lower than that of the control group.Conclusions:Different concentrations of GO and silver coating on three kinds of common oral bacteria have the antibacterial effect,and it have better effect on Gram negative bacteria than gram positive bacteria.The antibacterial mechanism is that the silver ion contacts and attacks the bacterial cell membrane,which makes the cell membrane structure perforation,cytoplasm leakage,and the bacteria crack death..Part III Evaluation the biological activity of Ti-GO-Ag multiphase nanocomposite on Ti surface Objective:To evaluate the bioactivity of surface coating at different concentrations and amounts of GO and Ag.Methods:The deposition of calcium and phosphorus on the surface of GO and silver coating with different concentrations was studied using SBF immersion test.And CCK-8 assay was used to evaluate the activity of the bone marrow mesenchymal stem cells on the surface coating at different concentrations and amounts of GO and Ag.Results:Surface coating could be deposited Ca and P elements at different concentrations and amounts of GO and Ag,and the control group,G20 group and G80 group had better effect.The activity of bone marrow mesenchymal stem cells was worse than that of the control group on the surface coating,but the effects of G20 and G50 group were better than G80 and G100 group.Conclusion:The surface coating has different degree of biomineralization,and has an effect on the activity of bone marrow mesenchymal stem cells at different concentrations and amounts of GO and Ag. |
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