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

A Mg-Al layered double hydroxide (Mg-Al-LDH) coating was firstly synthesized via an in-situ steam coating growth method on the AZ31 Mg alloy, and then was modified with poly(L-lactic acid) (PLLA) via dipping and vacuum freeze-drying. The microstructure and composition of LDH/PLLA hybrid coating were analyzed by XRD, SEM, EDS and FT-IR. The biocorrosion behavior of hybrid coating was evaluated by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and hydrogen evolution test in the Hank’s solution. The results showed that LDH/PLLA coatings exhibited a much dense layer compared to the unmodified Mg-Al-LDH coating with unobvious boundary between PLLA and LDH coatings. The corrosion current density of the LDH/PLLA-10 hybrid coating decreased three orders of magnitude in comparison to its substrate. It was proven that the existence of the PLLA coating further prolonged the service life of the Mg-Al-LDH coating. What’s more, the MTT assay and live/dead staining showed that the LDH/PLLA-10 coating had good biocompatibility for Mouse NIH3T3 fibroblasts. The formation mechanism and the anti-corrosion mechanism of hybrid coatings were proposed.