Fabrication of a PEO-ZIF8@8HQ Multilayer Coating with Enhanced Corrosion Resistance for Biodegradable Mg-Zn-Gd Alloy

Biodegradable magnesium alloys are promising candidates for temporary orthopedic implants, yet their rapid corrosion in physiological environments remains a critical challenge. Herein, we report a novel hierarchical composite coating, designated PEO/ZIF-8/8-HQ, fabricated on a Mg–1Zn–1Gd (ZG11) alloy via a three-step strategy combining plasma electrolytic oxidation (PEO), hydrothermal synthesis of zeolitic imidazolate framework-8 (ZIF-8) and solvothermal coordination of 8-hydroxyquinoline (8-HQ). The PEO layer provides a porous ceramic base, which is subsequently sealed by a dense ZIF-8 nanocrystalline film, followed by the formation of a continuous Mg(8-HQ)2 coordination overlayer. Microstructural and compositional analyses (SEM, XRD, XPS) confirm the successful integration of each layer with strong interfacial bonding. Electrochemical measurements in simulated body fluid (SBF) demonstrate that the PEO-ZIF8@8HQ coating reduces the corrosion current density from [Formula: see text] A/cm 2 (bare alloy) to [Formula: see text] A/cm 2 — a four-order-of-magnitude improvement. Scanning electrochemical microscopy (SECM) further reveals a uniform and significantly suppressed local corrosion current. The enhanced corrosion resistance is attributed to the synergistic effect of physical pore sealing by ZIF-8, chemical passivation via 8-HQ chelation and improved interfacial integrity. This work provides a feasible and effective surface engineering strategy for advancing the clinical applicability of biodegradable magnesium implants.