Corrosion Behavior of Biodegradable Mg-Zn-Ca Alloy under Simulated Severe Post-implantation Inflammatory Conditions

Magnesium alloys are promising candidates for temporary implant materials due to their biocompatibility, biodegradability, and ability to support tissue regeneration while gradually dissolving in physiological environments. However, the inflammatory environment near implants, characterized by the presence of reactive species and acidic conditions, can significantly influence their corrosion behavior. This study investigates the electrochemical corrosion performance of Mg-2.1wt% Zn-0.6wt% Ca alloy in three simulated physiological conditions: (1) normal medium (phosphate-buffered saline, pH 7), (2) inflammatory medium (PBS with H₂O₂ and HCl, pH 5), and (3) severe inflammatory medium (PBS with H₂O₂, HCl, bovine serum albumin [BSA], and lactic acid, pH 3).

Electrochemical tests, including potentiodynamic polarization and electrochemical impedance spectroscopy, were employed to systematically evaluate the corrosion rates and underlying mechanisms of the alloy in the three simulated media. The results demonstrated that the presence of H₂O₂ and an acidic pH significantly accelerated the corrosion rate of the Mg-Zn-Ca alloy, owing to the oxidative stress induced by H₂O₂, which promoted the formation of reactive oxygen species (ROS) that destabilized the magnesium hydroxide protective layer. The acidic pH further exacerbated the corrosion by dissolving the passivating Mg(OH)₂ layer, exposing fresh magnesium to the corrosive medium.

In addition, the inclusion of BSA and lactic acid in the severe inflammatory medium amplified the corrosion process. BSA, a protein that simulates the role of extracellular proteins, binds to the alloy surface and alters the local electrochemical environment by forming complexes with magnesium ions. This chelation effect destabilizes the surface and promotes ion release. Similarly, lactic acid, a byproduct of cellular metabolism during inflammation, acts as a weak organic acid that enhances the dissolution of magnesium hydroxide through acidification and ion chelation mechanisms. Together, BSA and lactic acid simulate conditions that reflect the inflammatory response and metabolic activity near implants, highlighting their synergistic impact on accelerating corrosion.