Electrochemical corrosion properties of a novel sodium hyaluronate and zinc oxide nanoparticle-coated stainless steel orthodontic arch wire – an in-vitro study

Background: Nanoparticle-based surface modifications of orthodontic arch wires have been extensively investigated for antimicrobial and frictional properties. However, their effect on corrosion behaviour remains largely unexplored. Objectives: To evaluate the electrochemical corrosion resistance properties (corrosion potential [Ecorr], polarisation resistance [Rp], corrosion current density [icorr], corrosion rate [CR] and the impedance-derived charge-transfer resistance [Rct]) of zinc oxide and sodium hyaluronate (ZnO-SH)-coated and -uncoated stainless steel (SS) orthodontic arch wire in three simulated pH environments.Materials and methods: Thirty commercially available 19 × 25” SS arch wires were divided into coated (n = 15) and uncoated (n = 15) groups. The samples were immersed in neutral, acidic and alkaline pH at 37°C for 2 h. Electrochemical testing included potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS). Statistical comparison was done using Welch’s t-test and two-way Analysis of variance (ANOVA) with Bonferroni-corrected post-hoc comparisons.Results: The effect of the ZnO–SH coating was strongly environment dependent, with a highly significant coating-to-environment interaction for all rate parameters (p < 0.001). In the neutral and alkaline environments, the coated wires showed significantly higher Rp and lower corrosion icorr and CR than the uncoated wires (p < 0.001). In the acidic medium, the opposite was observed: the uncoated wires had significantly higher Rp (822 vs. 91 kΩ·cm²) and significantly lower icorr (0.019 vs. 0.273 µA/cm²) than the coated wires (p < 0.001). Post-corrosion scanning electron microscopy confirmed an intact coating in the neutral and alkaline environments and extensive coating breakdown, pitting and cavitation in the acidic medium.Conclusion: The ZnO–SH coating improved the corrosion resistance of SS orthodontic arch wires in the neutral and alkaline but not in the acidic environment.