Corrosion kinetics of magnesium alloys for bioresorbable biomedical implants coated by plasma electrolytic oxidation

Magnesium alloys are currently employed in the development of bioresorbable medical devices, such as osteosynthesis implants and cardiovascular stents. For the successful application of these devices, it is essential to precisely control the degradation rate by tailoring the corrosion kinetics through alloying strategies and/or the application of biocompatible coatings, for instance via plasma electrolytic oxidation (PEO). The aim of this study is to evaluate the effect of PEO coatings produced in phosphate-based electrolytes on the corrosion kinetics of Mg-RE and Mg-Y-RE alloys (EV31A and WE43B, respectively), and commercially pure magnesium (Mg-CP), which was used as a reference. For all materials, oxygen- and phosphorus-rich coatings with thickness in the 20-30 µm range were obtained. Hydrogen evolution corrosion tests, carried out in isotonic solution (0.9% NaCl) at 37 °C, revealed a reduction in corrosion rates for the coated specimens compared to their uncoated counterparts, but mainly in alloys with intrinsically lower corrosion resistance.