Enhancing biocompatibility and corrosion resistance of PEO-treated magnesium alloys with polylactic acid coatings for degradable bone implants

Magnesium alloys stand as promising candidates for orthopedic implants due to their biodegradability, which eliminates the need for secondary removal surgery and potentially reduces hospital care costs. However, the biodegradation of magnesium alloys AZ31 and ZK60A in vivo may occur before bone implants stabilize. Therefore, the objective of this study was to enhance the corrosion resistance and cytocompatibility of two magnesium alloys through coating treatments. Specifically, both alloys, AZ31 and ZK60A, were exposed to surface modification by plasma electrolytic oxidation (PEO) in a sodium metasilicate and potassium hydroxide-based electrolyte. Subsequently, polylactic acid (PLA) was applied using a dip-coating method. Comprehensive physical and chemical characterizations of the materials were conducted. The coatings exhibited a thickness of approximately 3.7 µm with pore sizes ranging from 0.8 to 1.4 µm. The PEO-PLA coatings significatively reduced the degradation rate. In particular, PEO-AZ31and ZK60-PEO exhibited a 93 % and 95 % reduction, respectively, in hydrogen evolution compared to bare metals. In addition, the AZ31 coating demonstrated superior corrosion resistance in a simulated biological fluid (SBF). Moreover, the coated ZK60 and AZ31 alloys displayed enhanced cell viability when compared to the uncoated alloys. The AZ31-PEO-PLA and ZK60-PEO-PLA samples exhibited mitochondrial activity greater than 80 % at dilutions greater than 1:2. As a result, PEO-PLA films were proposed as a physical barrier to corrosion.