An intermediate poly-dopamine layer for alginate coating on high-purity magnesium to achieve corrosion mitigation

Although magnesium (Mg) and its alloys are proposed as the next generation orthopedics transplanted materials, their clinical applications are limited by the fast degradation. To reduce the degradation rate, a strong adhesion poly-dopamine (PDA) layer was introduced as an intermediate layer for the subsequent alginate (ALG) spin-coating on high-purity Mg. The surface morphology and chemical composition were detected by scanning electron microscope, energy disperse spectroscopy, and Fourier transform infrared spectroscopy. The corrosion resistances of all samples were evaluated by electrochemical and 10-day immersion tests in Hanks’ balanced salt solution. Our results suggest that the thickness of the fabricated PDA/ALG composite coating is 8.58 ± 0.65 µm, and the intermediate PDA layer evidently enhances the adhesion between the substrate and ALG coating. The corrosion current density of Mg coated with the PDA/ALG composite coating decreases more than 10 times compared to that of the Mg substrate, and the charge transfer resistance is 12 times bigger than that of the bare Mg, which indicates the improved corrosion resistance. Moreover, the mechanism of corrosion protection of the composite coating is also discussed.