| PurposeOrthodontic composite arch wires(CAWs)are made of nitinol alloy shape memory(NiTi-SMA)alloy and stainless steel(SS),and are produced by laser welding with copper(Cu)serving as the interlayer.The NiTi-SMA segment exerts the appropriate orthodontic force on dislocated teeth,and the SS segment provides anchorage for anchoring teeth.Previous studies have shown that the CAWs have excellent mechanical properties.However,the CAWs made of heterogeneous alloys by welding may be affected by corrosion in the complex oral environment,leading to increased surface roughness,which influences the effect of orthodontic treatment.Moreover,the oral cavity is an environment rich in flora,which is easy to adhere to the surface of arch wire and form biofilm.On the one hand,the growth of cariogenic bacteria could lead to enamel demineralization and caries around the orthodontic appliances;on the other hand,the adhered bacteria increases the friction of arch wire,resulting in poor effect of tooth movement.Therefore,this study intends to prepare lysozyme coatings with different concentrations by surface modification method,and explore the corrosion resistance and antibacterial properties of modified CAWs.Methods(1)The CAWs were welded by laser with a copper interlayer.Different concentrations of lysozyme were coated on the surface of CAWs by liquid phase deposition(LPD)technology.Electron microscope(SEM)and atomic force microscope were used to analyze the surface micromorphology of CAWs.(2)Artificial saliva was used to simulate the oral environment for corrosion tests.The corrosion microstructure was observed by SEM;Potentiodynamic polarization was used to evaluate electrochemical corrosion;Ion precipitation detection and weight loss experiment were used to evaluate static corrosion.(3)The antibacterial properties of coated CAWs were evaluated by bacterial plate counting and live/dead bacterial staining kit and the biosafety of coated CAWs was evaluated by cell counting kit-8.Results(1)Preparation and characterization of CAWs:the results showed that the welding area of CAWs was smooth without obvious cracks,and CAWs coated with different concentrations of lysozyme showed different three-dimensional morphology.(2)Corrosion resistance test:the morphology of uncoated CAWs was rough with many pitting;the coating of CAWs coated with 20 g/L lysozyme was unevenly distributed,and some small corrosion pits could be seen in exposed areas;the surface coated with 40 g/L lysozyme was relatively smooth without obvious pitting corrosion;though the CAWs coated with 60 g/L lysozyme showed a rough surface due to partial stripping,there were no obvious corrosion pits on the surface.Results of Cu ion release and weight loss:both the Cu ion release and the weight loss in coated CAWs were decreased compared to uncoated CAWs.As the increase of lysozyme concentration,the Cu ion release in coated CAWs was further reduced.Electrochemical results:both the values of Ecorr and Epit in coated CAWs were higher than the uncoated CAWs.With the increase of lysozyme concentration,the value of Epit and Icorr increased markedly,while no significant change in Ecorr was observed.(3)Antibacterial activity of CAWs and in vitro cytotoxicity assay:the colony counts of lysozyme coated CAWs were 41.33±10.53%(20 g/L lysozyme CAWs),33±9.63%(40 g/L lysozyme CAWs)and 19±6.80%(60 g/L lysozyme CAWs),respectively;fluorescence staining of living/dead bacteria showed that the green/red fluorescence ratio decreased with the increase of lysozyme coating concentration;the biosafety test showed that the cell proliferation activity of lysozyme coating group did not decrease significantly.ConclusionsLysozyme coatings for CAWs can be prepared by LPD.In this study,these coatings improved the resistance against corrosion,reduced the precipitation of Cu ion and endowed CAWs surfaces with certain degrees of anti-S.mutans activity.In addition,different concentrations of lysozyme had different effects on the corrosion resistance,antibacterial properties,and cytotoxicity of CAWs.Among them,40 g/L may be the more appropriate lysozyme modified concentration for CAWs coatings.This study will provide new ideas for improving the corrosion resistance and antibacterial properties of oral metal materials. |
