Improved corrosion performance of biodegradable magnesium in simulated inflammatory condition via drug-loaded plasma electrolytic oxidation coatings

Magnesium and its alloys are nowadays one of the most common biodegradable materials for orthopedic applications. Following the implantation of an orthopedic device, near the implant hydrogen peroxide and acidic environment are generated by an inflammatory reaction. In this study, a betamethasone sodium phosphate (BSP) layer as an anti-inflammatory drug was prepared on plasma electrolytic oxidation (PEO) coatings by a dip-coating process on magnesium alloys. X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR), field emission scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy (FESEM-EDX) and atomic force microscopy (AFM) were utilized for characterization studies. The results showed that the BSP layer successfully sealed the PEO coating. The corrosion resistance of the uncoated and coated samples was evaluated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests in normal and simulated inflammatory conditions. During the simulated inflammation, the samples indicated an enhanced corrosion rate compared to that of normal condition. The results in the inflammatory environment showed that the corrosion resistance of the PEO/BSP coating was remarkably improved by two or three orders of magnitude, compared with uncoated Mg alloy and the PEO coating. Immersion tests show that the BSP layer significantly improves the bioactivity of PEO-coated Mg alloy in simulated body fluid (SBF). Moreover, the in vitro release behavior of drug loaded PEO coating was evaluated.