Biocorrosion resistance and biocompatibility of Mg-Al layered double hydroxide/poly-L-glutamic acid hybrid coating on magnesium alloy AZ31

It is of necessity to seal porous layered double hydroxide (LDH) coating on bioabsorbable magnesium alloys to further enlarge its long-term protection using an organic top layer with good biocompatibility. An Mg-Al LDH coating sealed by poly-L-glutamic acid (PGA) is prepared on the AZ31 magnesium alloy. The LDH coating and PGA coating are synthesized by hydrothermal treatment and vacuum freeze-drying method. The structure and morphology of the coatings are characterized by means of X-ray photoelectron spectrometer (XPS), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, field-emission scanning electronic microscope (FE-SEM) and energy dispersive X-ray spectrometer (EDS). The corrosion protection afforded by the coatings is measured using electrochemical polarization and impedance spectroscopy and hydrogen evolution tests. The results indicate that the appropriate addition of PGA can postpone the time that pH values reach the minimum. The hybrid coatings effectively provide a corrosion protection for the AZ31 alloy. An acceptable cytocompatibility for mouse embryonic fibroblasts (NIH 3T3) of the hybrid coating is shown by methyl thiazolyl tetrazolium (MTT) assay and live/dead staining. Finally, a biodegradation mechanism of the coating is proposed and discussed.