A silicate-loaded MgAl LDH self-healing coating on biomedical Mg alloys for corrosion retardation and cytocompatibility enhancement

Abstract

Clinical application of magnesium (Mg) alloys such as bone fracture fixation is hindered by the fast degradation rate under physiological conditions. In this work, a magnesium‑aluminum layered double hydroxide coating intercalated with silicate (LDH-SiO3) is fabricated on the anodized AZ31B Mg alloy by a hydrothermal technique and anion exchange process to tailor the corrosion rate and cytocompatibility. The LDH-SiO3 coating comprising a porous outer layer and compact inner layer adheres strongly to the anodized Mg alloy substrate. Electrochemical tests reveal that the LDH-SiO3 coating reduces the corrosion current density by 266 times to 0.8 ± 0.1 μA cm−2 in addition to yielding a large charge transfer resistance of 4.98 × 104 Ω cm2 in the simulated body fluid (SBF), revealing decreased corrosion because of inhibition of diffusion of aggressive ions through the compact and adherent inner LDH layer on the Mg alloy substrate. Immersion tests in SBF for 360 h reveal that the LDH-SiO3 coating mitigates corrosion propagation, Mg release, hydrogen evolution, and pH variation, indicating the notable long-term protection ability resulting from the self-healing LDH-SiO3 coating after localized corrosion occurs on the Mg alloy substrate. The self-healing mechanism mainly stems from SiO32− released from the LDH coating in conjunction with Mg leaching during natural degradation, resulting in the formation of Mg silicate precipitate that covers the corroded areas. Biologically, the LDH-SiO3 coating enhances attachment and proliferation of MC3T3-E1 pre-osteoblasts suggesting good cytocompatibility stemming from the favorable outcome including inhibited Mg leaching and alkalization as a result of the LDH-SiO3 coating. The self-healing LDH-SiO3 coating is very promising in expanding the clinical application of Mg-based implants by offering a viable approach to control corrosion and improve cytocompatibility.