Sodium alginate coating on biodegradable high-purity magnesium with a hydroxide/silane transition layer for corrosion retardation

Fast degradation of magnesium (Mg) and its alloys in the physiological environment has impeded their clinical use as temporary implants. To control degradation of Mg in the physiological environment, a sodium alginate coating is fabricated on alkalinized high-purity Mg with a silane transition layer by spin coating. The surface morphology and composition are investigated by scanning electron microscopy, energy-dispersive X-ray spectrometry, X-ray diffraction, and Fourier transform infrared spectroscopy. Electrochemical and immersion tests are performed in the simulated body fluid (SBF) at 37 °C. The composite coating with a thickness of 10.3 µm is uniform and adheres well to the Mg substrate. Compared to the bare substrate, the corrosion current density of the sample with the composite coating decreases from 130.9 ± 6.2–1.3 ± 0.3 μA cm⁻² and the charge transfer resistance increases by 190 times. The average degradation rate in SBF drops to 0.80 ± 0.26 mm year⁻¹ from 3.47 ± 0.25 mm year⁻¹ of the pristine Mg substrate and the composite coating is demonstrated to impede corrosion of the Mg substrate after immersion in SBF for 14 days. The excellent protection rendered by the composite coating is ascribed to the effective barrier effects of the dense and adhering sodium alginate coating and blocking effect of chelate compounds of sodium alginate and Mg ions formed during the corrosion process.