Comparative Effects of Post-Extrusion Annealing and PLLA Surface Modification on the Degradation Behavior and...

Biodegradable magnesium alloys have emerged as attractive materials for cardiovascular stents due to their mechanical compatibility with vascular tissues and inherent biocompatibility. Despite these advantages, their clinical translation is hindered by rapid and localized degradation in physiological environments. To address this challenge, the present study systematically compares the effects of bulk postprocessing and surface modification on the degradation behavior and biological performance of extruded ZK60 magnesium alloy. Hot-extruded ZK60 (E-ZK), postextrusion annealed ZK60 (A-ZK), and poly-(l-lactic acid)-coated ZK60 (P-ZK) were investigated through a stepwise experimental design. The influence of annealing on intrinsic mechanical properties was first examined, followed by electrochemical analysis, immersion degradation testing, and endothelial cell evaluations across all material conditions. While postextrusion annealing altered the mechanical response of ZK60, it showed limited effectiveness in mitigating degradation or enhancing endothelial interactions. In contrast, the PLLA surface coating significantly reduced electrochemical reactivity. It decreased the corrosion current density from approximately 151-223 μA/cm² to around 22 μA/cm². Additionally, the corrosion rate was reduced from approximately 3.46-5.09 mm/year to about 0.51 mm/year. This enhanced corrosion resistance contributed to improved surface integrity and more favorable endothelial responses, with cell viability reaching approximately 140% on day 3 for P-ZK, compared to around 125% for the uncoated samples. Collectively, these results demonstrate that surface modification plays a more decisive role than bulk annealing in optimizing degradation control and endothelial compatibility of magnesium-based biodegradable stents.