A new in vitro-in vivo correlation for bioabsorbable magnesium stents from mechanical behavior

Correlating the in vitro and in vivo degradation of candidate materials for bioabsorbable implants is a subject of interest in the development of next-generation metallic stents. In this study, pure magnesium wire samples were corroded both in the murine artery (in vivo) and in static cell culture media (in vitro), after which they were subjected to mechanical analysis by tensile testing. Wires corroded in vivo showed reductions in strength, elongation, and the work of fracture, with additional qualitative changes between tensile profiles. The in vivo degradation was 2.2±0.5, 3.1±0.8, and 2.3±0.3 times slower than corrosion in vitro in terms of effective tensile strength, strain to failure, and sample lifetime, respectively. Also, a combined metric, defined as strength multiplied by elongation, was 3.1±0.7 times faster in vitro than in vivo. Consideration of the utility and restrictions of each metric indicates that the lifetime-based multiplier is the best suited to general use for magnesium, though other metrics could be used to deduce the mechanical properties of degradable implants in service.