This work presents a novel method for directly forming highly-oriented Mg–Fe–CO₃ LDH coating on pure Mg samples by treating the sample in pH 5.6 aqueous Fe³⁺/HCO₃ ⁻/CO₃ ^{2 −} at 50 °C, and then immersing it in pH 9.5 aqueous HCO₃ ⁻/CO₃ ^{2 −} at 50 °C. The former step was performed to yield Mg²⁺ in aqueous solution at pH 5.6 by corroding the Mg sample. A two-layered thin film was thus formed on the Mg substrate, of which the outer layer (∼1 μm-thick) comprised fine platelet-like Mg–Fe–CO₃ LDH. The latter treatment in pH 9.5 aqueous HCO₃ ⁻/CO₃ ^{2 −} at 50 °C resulted in the growth of the fine LDH platelets into a strongly-oriented Mg–Fe–CO₃ LDH. The chemical formula of the Mg–Fe–CO₃ LDH is Mg_0.74Fe_0.26(OH)₂(CO₃)_0.13·mH₂O. The method used herein involves a metal salt-free system, which requires no addition of Mg(NO₃)₂ and Fe(NO₃)₃. Several in vitro tests of the Mg–Fe–CO₃ LDH coating on a Mg sample were performed. Based on the measured contact angle between the sample surface and human whole blood, the Mg–Fe–CO₃ LDH coating can improve the hydrophilicity of a pure Mg surface. According to the results of an in vitro corrosion test in revised simulated body fluid (R-SBF), the Mg–Fe–CO₃ LDH coated sample had a much higher corrosion resistance than the pure Mg substrate. The results of in vitro human mesenchymal stem cell adhesion tests showed that the Mg–Fe–CO₃ LDH coated sample had a better cell spreading and cell–cell interaction behavior than the pure Mg substrate.

Objective: To test the hypothesis that different nickel-titanium (NiTi) archwires may have dissimilar corrosion resistance in a fluoride-containing oral environment. Materials and Methods: Linear polarization test, a fast electrochemical technique, was used to evaluate the corrosion resistance, in terms of polarization resistance (R_p), of four different commercial NiTi archwires in artificial saliva (pH 6.5) with various NaF concentrations (0%, 0.01%, 0.1%, 0.25%, and 0.5%). Two-way analysis of variance was used to analyze R_p with the factors of archwire manufacturer and NaF concentration. Surface characterizations of archwires were analyzed using scanning electron microscopy, atomic force microscopy, and x-ray photoelectron spectroscopy. Results: Both archwire manufacturer and NaF concentration had a significant influence on R_p of NiTi archwires. Different surface topography was present on the test NiTi archwires that contained the similar surface chemical structure (TiO₂ and trace NiO). The surface topography did not correspond to the difference in corrosion resistance of the NiTi archwires. Increasing the NaF concentration in artificial saliva resulted in a decrease in R_p, or corrosion resistance, of all test NiTi archwires. The NiTi archwires severely corroded and showed similar corrosion resistance in 0.5% NaF-containing environment. Conclusions: Different NiTi archwires had dissimilar corrosion resistance in acidic fluoride-containing artificial saliva, which did not correspond to the variation in the surface topography of the archwires. The presence of fluoride in artificial saliva was detrimental to the corrosion resistance of the test NiTi archwires, especially at a 0.5% NaF concentration.