Degradation Performance of Poly-Lactic Acid Membrane for WE43 Alloy Under Flow Condition

The poly-lactic acid (PLA) coating was widely applied to the WE43 alloy to modulate its degradation for biomedical implants, a strategy whose long-term efficacy is critically dictated by the coating’s protective and ion-permeation properties under dynamic physiological flow. This work systematically investigates the corrosion performance under the such flow condition using a novel in situ monitoring method. This method enables a direct, in situ assessment of both the ion-permeation rate across the PLA membrane acted as the coating and the concurrent evolution of the electrochemical properties of the membrane as well as the WE43 alloy substrate. Results revealed that the applied flow accelerated the formation of micro-cracks in the PLA membrane, which facilitated the permeation of Na+ and Cl− ions and thereby intensified the corrosion of the underlying substrate. During the initial 15 days, the ion permeation rates for Na+ and Cl− ions under the flow condition were 0.097 and 0.042 mmol/(L·h), respectively. The degradation rate of the substrate exhibited a strong positive correlation with the concentration of permeated Cl− ions. In contrast, the deposition of calcium-containing compounds was identified as a time-dependent process, governed by the permeation kinetics of Ca2+ ions through the membrane.