Failure signal of high orientation Poly(L-lactic acid) monofilament for self-expanding stent during lifetime: Disappeared amorphous connections

Abstract

The premature failure of bioresorbable self-expanding stents for peripheral arterial disease could lead to form thrombosis and threaten patients′ lives. Predicting the time and cause of mechanical and structural failure is crucial to prevent premature failure of implanted stents. Herein, we report a situ accelerated hydrolysis to investigate the degradation properties of self-expanding stents braided by high-performance Poly(L-lactic acid) (PLLA) monofilaments in an accelerated term over a formal long one. Degradation, microstructure, and mechanical properties were comprehensively evaluated to identify key factors of the failure during lifetime. The results show that the upper temperature limit for accelerated hydrolysis is 50 °C. The mechanical properties undergo multiple stages of functional holding, decreasing, and eventual failure. It is attributed to uneven degradation and distribution of crystalline and amorphous regions. Specifically, the disappearance of amorphous chains between fibrils at 6 months leads to mechanical failure. Further disappearance of amorphous chains within fibrils at 18 months results in structural disintegration. Additionally, the degradation behavior of the stents and potential effects of degradation products on vascular tissues are validated for predictive accuracy. These insights provide valuable experimental references for optimizing design and clinical application of PLLA-based self-expanding stents.