Mg-Zn-Mn alloys degradation in pancreatic fluid: Trypsin disrupts passivation for stent design

Abstract

Biodegradable magnesium alloys show promising potential for pancreatic duct stents, yet their degradation varies significantly across physiological environments. This study compared the corrosion rates of extruded Mg-2Zn-xMn (x = 0, 0.5, 1.0, 1.5 wt. %) alloys in human pancreatic fluid. The results revealed that the alloys undergo different corrosion mechanisms in human pancreatic fluid, emphasizing the necessity of conducting evaluations under physiologically relevant conditions. Further investigations into the degradation mechanism in pancreatic fluid indicated that the alkaline pH (8.3–8.7), high bicarbonate concentration, and enzymatic activity significantly influence the corrosion process. Electrochemical and immersion tests showed rapid initial corrosion due to Cl⁻ attack, followed by the formation of a protective Mg(OH)₂, MgCO₃, and Ca₃(PO₄)₂ layer that slowed degradation. However, digestive enzymes, particularly trypsin, disrupt passivation by interacting with organic components, leading to pitting and filiform corrosion. Among the investigated alloys, Mg-2Zn-1.0Mn exhibited the most favorable combination of corrosion resistance, mechanical performance, and cytocompatibility. This study highlights the critical impact of pancreatic fluid on magnesium alloy degradation and stresses the need for physiologically accurate evaluations.