Development of novel hybrid PEO-PLA coating on biodegradable ZK60 magnesium alloys

This study presents the development of novel hybrid coatings composed of plasma electrolytic oxidation (PEO) and poly(lactic acid) (PLA) on biodegradable ZK60 magnesium alloy. PEO coatings were fabricated using phosphate-based electrolytes under optimized parameters (0.4 A/cm2, 50 Hz, 50% duty cycle) and treatment durations of up to 2 min, resulting in porous ceramic layers approximately 70 µm thick, primarily composed of MgO and Mg3(PO4)2. Subsequent dip-coating with PLA (5 g in 55 mL dichloromethane) effectively sealed the PEO pores, forming a uniform polymer layer approximately 23 µm thick. Corrosion tests demonstrated that the hybrid PEO + PLA coating substantially improved corrosion resistance. The sample treated with a 2-minute PEO process followed by PLA coating exhibited a polarization resistance (Rp) approximately 246 times higher than that of untreated ZK60 after 168 h, and it maintained significant protection after 13 weeks of immersion (Rp ≈ 6.1 × 104 Ω·cm2). Molecular dynamics simulations supported the strong adsorption of PLA on the MgO surface, correlating with improved sealing performance. Overall, this work demonstrates that PEO/PLA duplex coatings markedly enhance the corrosion resistance and mechanical stability of biodegradable ZK60 magnesium alloy, making them highly promising for use in bioabsorbable medical implants.