Improving the inflammatory-associated corrosion behavior of magnesium alloys by Mn₃O₄ incorporated plasma electrolytic oxidation coatings

Biodegradable magnesium alloys for orthopedic bone fixation have been introduced for various fields of application. The corrosion resistance of magnesium implants weakens in physicochemical environments and is further compromised during post-implantation inflammation. In this study, Mn₃O₄-incorporated plasma electrolyte oxidation (PEO) coatings were developed on Mg-Zn-Ca substrate through two approaches: the addition of KMnO₄ salt and the inclusion of Mn₃O₄ nanoparticles into the electrolyte composition. Incorporating additives into electrolytes led to a reduction in surface porosity and an increase in coating thickness in both synthesis approaches. The electrochemical and immersion corrosion tests were conducted under simulated normal conditions and inflammatory conditions, where inflammatory solutions were prepared with the addition of hydrogen peroxide (H₂O₂) and hydrochloric (HCl) acid. Both corrosion studies revealed that inflammation significantly increased the corrosion rate of the uncoated Mg-Zn-Ca biomaterial, escalating from approximately 2 mm·y^-1 to 16 mm·y^-1. Moreover, corrosion studies showed that the composite PEO coatings, incorporating Mn₃O₄ nanoparticles (MnPR-PEO), demonstrated superior corrosion performance among all coated samples. Potentiodynamic polarization results indicated a substantial reduction in corrosion current density, decreasing from 73.9 μA·cm^{- 2} for basic PEO coatings to 5.5 μA·cm^{- 2} for MnPR-PEO coatings. The improved performance of Mn₃O₄-incorporated PEO coatings, attributed to their catalytic H₂O₂ scavenging, suggests promise for magnesium implants, offering enhanced corrosion resistance and potential biomedical application benefits.