Corrosion resistance of HF-treated Mg alloy stent following balloon expansion and its improvement through biodegradable polymer coating

Magnesium (Mg) alloy has been actively investigated as a bioresorbable scaffold (BRS) for use as a next-generation stent because of its appropriate mechanical properties and biocompatibility. However, Mg alloy quickly degrades in the physiological environment. Hydrofluoric acid (HF) treatment and surface coating with biodegradable polymer are approaches for enhancing the corrosion resistance of Mg alloy. However, there are no studies that focus on the corrosion behavior of the Mg alloy stent after balloon catheter expansion, which results in mechanical stress and is required for stent placement. In this study, the corrosion behavior of a Mg alloy stent after expansion by a balloon catheter was investigated. Compared with the bare Mg alloy stent, the HF-treated Mg alloy stent showed excellent corrosion resistance without expansion. However, balloon catheter expansion caused small fragments and cracks to appear on the surface of the HF-treated Mg alloy stent and accelerated its corrosion rate. The HF-treated Mg alloy stent was therefore further coated with poly(d,l-lactic acid) (PDLLA). As a result, the high corrosion resistance of the coated stent was maintained after its expansion along with higher biocompatibility for endothelial cell adhesion than the stent without the polymer coating. The HF-treated and PDLLA-coated platform is expected to be a BRS candidate for clinical applications.