In Vitro and In Vivo Biocompatibility Testing of Absorbable Metal Stents

Summary: Permanent metallic stent implants are the most frequently applied treatment option in angioplastic interventions. Here we report in vitro and in vivo characteristics of the newly developed absorbable metal stent (AMS), consisting of magnesium (Mg) with yttrium and rare earth additives, in comparison to the clinically applied steel stent (316L). Viability and proliferation of smooth muscle cells (SMC) and endothelial cells (EC) exposed to various Mg‐alloys were analyzed. AMS and 316L were implanted into coronary arteries of Göttingen minipigs (n = 17) and explanted after 28 and 56 days. Stented arterial segments were analyzed prior to explantation by angiography and ex vivo by micro‐computer tomography (micro‐CT), by histology, and by immunohistochemistry. Exposure to the alloy in vitro resulted in reduced viability and proliferation of smooth muscle cells. Consistently, larger luminal diameter and less neointimal formation were found in AMS both 28 and 56 days after implantation. Histological analysis revealed no significant differences in the number of macrophages and Ki‐67 positive cells, yet a significantly higher number of proliferating cells around 316L struts at the earlier time point. The reduction in neointima formation and a larger vessel lumen indicates the superiority of the recently developed AMS over commercial available steel stents. Furthermore, AMS is absorbable, and thus will not cause stress to the stented vessel for the lifetime of the recipient.