Electrodeposition of Sacrificial Layer, Al2O3/ZnTPP film, onto NiTi Orthodontic Wire: Surface Characterizations and Electrochemical Investigations

Abstract

Background: NiTi (nickel-titanium) alloy wires are widely used in orthodontics due to their unique properties, such as shape memory and superelasticity. However, these wires can be susceptible to corrosion in the oral environment, which can compromise their mechanical performance and longevity. Zinc tetraphenyl porphyrin (ZnTPP) is a corrosion inhibitor that forms a protective layer on the aluminum oxide (Al2O3) surface, acting as a barrier against corrosive agents. Objective: The electrodeposition of a sacrificial layer of Al2O3 with ZnTPP was carried out onto Ni- Ti orthodontic wire to enhance the corrosion resistance. Methods: 10 mM aluminum nitrate was dissolved in 10 mL of 0.1 M phosphate buffer solution (PBS), which was used as an electrolyte. Firstly, electrodeposition of Al2O3 on NiTi wire was carried out by using cyclic voltammetry by potential scanning between 0 and -2.0 V at a scan rate of 50 mV/s for 50 cycles. Secondly, 10 mL of 1 mM ZnTPP in 0.1 M PBS and ethanol (1:1) was prepared and used as an electrolyte. Electrodeposition of ZnTPP onto Al2O3/NiTi wire was achieved by cyclic voltammetry through the potential window of 0 to -2.0 V at a scan rate of 50 mV/s for 50 cycles. Results: The ZnTPP/Al2O3/NiTi wire displayed a potentiodynamic polarization resistance of 412931 Ω, with high stability compared to the bare NiTi wire (396421 Ω). Additionally, the corrosion rate for the ZnTPP/Al2O3/NiTi wire was measured as 0.254 mm/year, which was notably lower than that of the bare NiTi wire (0.540 mm/year). This decrease in corrosion rate can be attributed to the presence of the ZnTPP/Al2O3 film, which renders the NiTi wire electrically insulative and significantly increases its impedance compared to the bare NiTi wire. Conclusion: The bilayer coating of Al2O3 and ZnTPP has proven to significantly improve the corrosion resistance and stability of the wires. Thus, these materials can be considered for coating orthodontic archwires with improved corrosion stability.