Bioactive Ca-P coatings on WE43 alloy via soft sparking PEO: Structure, electrochemical performance and cytotoxicity studies

• Coatings containing Ca and P were successfully formed on WE43 alloy. • Coatings were prepared with different duty ratios of 15, 25 and 50 % and negative-to-positive current ratios - 2 or 1.6. • The onset of soft sparking regime was faster for the processes conducted at higher duty and current ratios which corresponded to rougher, thicker and more porous coatings. • Optimization of the current ratio allowed to obtain a coating with a stable degradation progression. • The proposed surface modifications significantly reduced the cytotoxic effects observed in direct contact with the material while still maintaining the cell proliferation-promoting effects of the material eluents. Plasma electrolytic oxidation is a well-known technique for surface modification of biomedical magnesium alloys, with good corrosion protection and the ability to produce biocompatible and bioactive coatings. In this study, calcium-phosphate coatings were produced on WE43 magnesium alloy for use, as orthopedic implants. Coating formation was prepared using different oxidation parameters with various duty ratios (DR) of 15, 25 and 50 % and current ratios (R)-2 or 1.6. Application of R with excess cathodic current ( R > 1) in processes with DR≥25 % allowed attaining the soft-sparking regime (SSR) that resulted in thicker oxide coatings with higher degree of crystallinity compared to the films obtained without SSR. The results of the corrosion tests contributed to a noticeable improvement in the corrosion resistance of the magnesium alloy. Optimization of the oxidation parameters allowed the selection of the variants with the most favorable degradation behavior over the tested immersion period, indicating a successful modification of the magnesium alloy surface to obtain an implant biomaterial capable of providing controlled degradation. Furthermore, biological evaluation of the produced coatings showed that the proposed surface modifications significantly reduced the cytotoxic effects observed in direct contact with the material while still maintaining the cell proliferation-promoting effects of the material eluents.