Structural Optimization and Finite Element Analysis of Variable-Stiffness Biodegradable Vascular Stents

Premature structural failure of biodegradable vascular stents (BVSs) induced by stress corrosion cracking (SCC) remains a critical challenge. Heterogeneous plaques compress the stent, leading to inadequate expansion and inducing stress concentration that exacerbates SCC. This study proposes variable-stiffness stents to improve radial support and mitigate non-uniform degradation. The stents were designed with shortened axial ring segments and selective strut widening at the stenotic regions for targeted stiffness enhancement. They were virtually deployed in arteries with non-calcified and calcified plaques to evaluate immediate performance, while long-term service behavior was assessed via degradation simulation under combined electrochemical corrosion and SCC effects. The results show that variable-stiffness stents exhibited comparable residual stenosis to uniform-stiffness stents with identical local structures at plaque regions. Dual-stiffness designs yielded a smoother luminal profile than uniform-stiffness counterparts, and gradient-stiffness designs achieved further improvements. Local strut widening extended full recoil time, with a more marked effect on high-stiffness segments, by 52.6% and 41.2% in non-calcified and calcified plaques, while simultaneously increasing volume loss to mitigate non-uniform degradation. In addition, widened gradient-stiffness designs further prolonged the stable support time by 9.7%. These findings show variable-stiffness stents with widened gradient-stiffness design exhibit a more favorable immediate and long-term performance.