The efficiency of the green inhibitors (sodium salts of fumarate, glycolate and gluconate) in suppressing corrosion of the structural MA8 magnesium alloy ((Mg–Mn–Ce) and the biomedical Mg0.8Ca alloy was studied using the hydrogen evolution measurements, mass loss test, EIS, PDP, SVET/SIET. The analysis of the morphology, chemical composition, and growth kinetic of corrosion films formed in 0.9 wt% NaCl solution with and without corrosion inhibitors was carried out. The most compact surface film with the smallest thickness was formed in a saline solution with sodium fumarate. The Mg alloy samples exhibited the highest polarization resistance, the lowest localized electrochemical activity, and the lowest corrosion rate in saline with the addition of sodium fumarate and sodium glycolate. The efficiency of the applied inhibitors was up to 81 %. The model of the corrosion mechanism based on the sorption of molecules of organic inhibitors is proposed. The results show the high compatibility of the used inhibitors with the calcium-phosphate PEO-matrix, indicating the possibility of forming a self-healing coating by means of these active substances.

In this study, the biocompatible protective coating was formed using plasma electrolytic oxidation (PEO) on bioresorbable Mg-0.8Ca alloy. The composition of the formed coating was studied using XRD, SEM-EDX analysis, and micro-Raman spectroscopy. The uniform distribution of hydroxyapatite over the thickness of protective PEO-layer was established. Using traditional (EIS, PDP, OCP) and local scanning electrochemical methods (SVET, SIET with H⁺-selective microelectrode), the level of protective properties of PEO-layer in a biological environment (mammalian cell culture medium, MEM) was determined. It was established that modification of Mg-0.8Ca alloy surface by PEO contributes to a significant increase in the corrosion resistance of the surface layer, making it possible to control the process of material‘s biodegradation. The maximum local electrochemical activity was recorded after 72 h of testing, while for the uncoated sample, intense corrosion degradation was recorded in the first 12 min of exposure to the cell culture medium. Formation of the PEO-coating results in a twofold decrease in the corrosion current density (2.8·10⁻⁶ A cm⁻²) and an increase in the impedance modulus measured at a low frequency (1.7·10⁴ Ω cm²) in comparison with the uncoated material (9.5·10⁻⁶ A cm⁻²; 8.1·10³ Ω cm²). The mechanism of material bioresorption was established and a model for biodegradation process of Mg-0.8Ca alloy with hydroxyapatite-containing PEO-coating in MEM was proposed. Analysis of these results and comparing with others obtained by various scientific groups indicate the prospects for application of biocompatible PEO-coating on Mg-Ca alloy in implant surgery.

A new method of the formation of composite coatings with the function of active corrosion protection of magnesium alloys was developed using the plasma electrolytic oxidation (PEO) method. Susceptibility of PEO-layers to pitting formation was evaluated using localized electrochemical methods (SVET/SIET). The morphological features and electrochemical properties of composite coatings were studied using SEM/EDX, XRD, micro-Raman spectroscopy and EIS/PDP measurements, respectively. The effect of surface layers impregnation with corrosion inhibitor on their protective properties in a corrosive environment was established. Additional protection was achieved using controllable coating pore sealing with polymer. It was found that the polymer treatment of the PEO-layer does not reduce the inhibitor's efficiency. The formed protective composite inhibitor-and-polymer-containing layers decrease the corrosion current density of a magnesium alloy in a 3 wt.% NaCl solution to three orders of magnitude. This predetermines the prospect of new smart coatings formation that significantly expand the field of application of electrochemically active materials. The mechanism of smart composite coating corrosion degradation was established. The antibacterial activity of the inhibitor-containing coatings against S. aureus methicillin-resistant strain was proved using the in vitro model. These protective layers are promising for reducing the incidence of implant-associated infections.