The Corrosion Resistance And Antibacterial Properties Of Polydopamine-Graphene Oxide Coatings On NiTi Alloys

PurposeNickel titanium(NiTi)archwires generate forces that affect tooth movement by interacting with brackets and are commonly used in the alignment and leveling phases of orthodontic treatment.In the oral environment,the corrosion resistance and antibacterial properties of NiTi alloys are not ideal,which can increase friction between archwires and brackets and cause side effects such as enamel demineralization,affecting the orthodontic efficacy.This research intends to construct polydopaminegraphene oxide(PDA-GO)coatings on NiTi alloys and investigate the effect and mechanism of GO concentrations on the corrosion and antibacterial behaviors,which will provide a reference for optimizing the properties of dental metals.Methods(1)PDA-GO coated NiTi alloys with different concentrations were prepared by self-assembly technique,and their morphological structure and physicochemical composition were characterized by SEM,EDS,AFM,FTIR,and XPS.(2)Using three-point bending stress models in artificial saliva,the corrosion morphology and Ni2+ precipitation of NiTi archwires were observed;electrochemical tests were performed to obtain the polarization curves and corrosion performance parameters such as corrosion current density.(3)The antibacterial activity and mechanism of PDA-GO modified NiTi alloys against Streptococcus mutans were evaluated by SEM,bacterial plate count and live/dead staining tests.The effects of samples on the relative proliferation rate and ROS content of L-929 cells were detected by CCK-8 and ROS experiments,respectively.Results(1)The PDA-GO coated NiTi alloys were mainly composed of C,N,O,Ti,and Ni,and there are chemical bonds such as C=O,C=C,C-O,and N-H.With the increase of GO concentrations in a certain range,the well-adhesive coating is dense and uniform lamellar with decreased surface roughness.(2)Stress corrosion experiments showed that corrosion cracking and more Ni2+precipitation appeared on unmodified NiTi;the PDA-GO coated NiTi prepared at 0.2 mg/mL GO was unevenly distributed,and the Ni2+ release was not significantly different from that of the control group;no obvious pitting was seen on the surface structure of 0.5 mg/mL group;the 1.0 mg/mL group has a relatively intact surface under stress with the least ion precipitation.According to electrochemical tests,the Icorr value was reduced,indicating an enhanced corrosion resistance.(3)SEM and live/dead fluorescence staining indicated that the number of adhesion bacteria on the surface of modified samples decreased and dead bacteria increased compared with unmodified samples.The bacterial plate counts showed that the antibacterial rates of samples prepared at 0.2,0.5,and 1.0 mg/mL GO were 33.4%,77.7%and 93.1%,respectively.Although the 1.0 mg/mL GO group produced higher cellular ROS,the relative proliferation rate of L-929 cells in each modified group was greater than 80%after co-culture with the extract for 1,3,and 5 days,indicating that the self-assembly PDA-GO coating had good biocompatibility.ConclusionsIn this study,PDA-GO modified NiTi alloys were prepared and optimized using self-assembly.The suitable GO concentration could prepare uniform and dense PDAGO coatings with covalently C-N bonds,to improve the corrosion resistance of NiTi and significantly reduce the Ni2+precipitation.The special surface structures of PDAGO give NiTi alloy good resistance to Streptococcus mutans.PDA-GO coating had no cytotoxic effect on L-929 cells.The nanocomposite coating with corrosion resistance and antibacterial is expected to safely modify the orthodontic fixed appliance to improve orthodontic efficiency.