Effect of number of crowns on the crush resistance in open-cell stent design

Our group is developing novel preferential covered carotid stents aimed at preventing friable parts from atherosclerotic plaques from dislodging into the cerebral blood flow, and also preserving external carotid artery (ECA) perfusion through slits on the membrane. Enhanced ECA flow rates can be achieved by designing bare metal stents with larger cells that can accommodate more slits for enhanced blood flow to the ECA where the stents have fewer crowns in the circumferential direction. The general perception is that the stent stiffness and thereby the crush resistance will decrease with fewer crowns in the circumferential direction. However, we observed the opposite effect. To study the effect of crown number on crush resistance of stents, finite element analysis (FEA) was used to evaluate the crush resistance of open-cell stent designs by varying the number of crowns. From FEA simulation results, it was found that the crush resistance of the open-cell stent design actually increases with fewer crowns. To verify this effect, three stent designs with different crown numbers were fabricated and subjected to crush resistance experimental testing. The experimental testing further confirmed the effect observed by FEA. Finally, a simplified analytical model was proposed to explain why the crush resistance of stent increases with a reduction in the number of stent crowns. From this study, we can infer that the stent's crush resistance increases with reduction in the number of stent crowns in the circumferential direction.