Multilayer hybrid coatings on bioresorbable magnesium alloy: enhanced corrosion resistance and biocompatibility through inhibitor and polymer treatment

This study presents a systematic investigation of anticorrosion layers formed via plasma electrolytic oxidation (PEO) of a bioresorbable Mg alloy with following treatment using corrosion inhibitor—stearic acid (SA) and polycaprolactone (PCL). Composite coatings (PEO, PCL-impregnated, or inhibitor-impregnated) provided moderate corrosion protection but exhibited localized degradation and limited self-healing capacity. A novel hybrid coating (HC-2SP), fabricated by sequential application of inhibitor and polymer layers (two-stage application), demonstrated superior performance: mass loss after 7 days in MEM (minimum essential medium) was reduced to 1.46 ± 0.4%—over fivefold lower than unmodified PEO-coatings. Local electrochemical study (SVET/SIET) of the sample with artificial defects revealed that inhibitor-containing coatings actively suppress corrosion through self-healing, with maximum local current densities equal to 4 µA‧cm –2 for HC-2SP. SEM-EDX confirmed preservation of surface integrity and pore-filling by the biodegradable polymer. The hybrid coating (HC-2SP) promoted the highest adhesion and maturation of the mesenchymal stem cells and had no cytotoxic effect on FLEH-104 fibroblast cells. In vivo experiments showed that HC-2SP coating demonstrated favorable biocompatibility and remodeling process of the pre-implant tissues. These findings establish that two-stage hybrid coatings offer an effective strategy providing the combination of high corrosion resistance, self-healing functionality, and biocompatibility of bioresorbable magnesium implants.