Poly(lactic acid) coating with a silane transition layer on MgAl LDH-coated biomedical Mg alloys for enhanced corrosion and cytocompatibility

Fast degradation of magnesium (Mg) - based alloys in the physiological environment has hampered their application to bone fracture fixation devices. Herein, a poly(lactic acid) (PLA) coating and (3-aminopropyl)triethoxysilane (ATS) transition layer are fabricated on the AZ31B Mg alloy pre-deposited with a magnesium-aluminum layered double hydroxide (LDH) coating to mitigate corrosion rate and improve the cytocompatibility. The porous outer layer of the LDH coating is sealed by the compact PLA coating and with the aid of the ATS layer, the PLA coating adheres well to the LDH coating. The corrosion current density of the Mg alloy substrate coated with the hybrid coating declines to 0.6 A cm⁻² in the simulated body fluid (SBF). It is approximately one order of magnitude smaller than that of the Mg alloy with the LDH coating and 386 times smaller than that of the bare Mg alloy. The hybrid coating increases the charge transfer resistance to 1.05 × 10⁵ Ω cm² which is one and three orders larger than those of the Mg alloy with and without the LDH layer, respectively. The corrosion propagation along the surface, hydrogen evolution, and pH variation during immersion in SBF for 7 days are also reduced by the hybrid coating. The excellent protection is ascribed to pore sealing in the LDH layer, barrier effect of the compact PLA coating against aggressive solutions, and good adhesion between the LDH and PLA coatings with the aid of the ATS transition layer that avoids coating delamination. Besides retarded hydrogen evolution and smaller pH variation, good cytocompatibility is demonstrated by culturing with MC3T3-E1 cells. Our study suggests an effective strategy to tailor the corrosion rate and cytocompatibility of Mg alloys by the combination of the LDH and PLA coatings in conjunction with the ATS transition layer.