Abstract
How to improve stent mechanical properties is a key issue for designing biodegradable polymeric stents (BPSs). In this study, a new design method of BPS was proposed based on the force analysis of supporting rings and bridges during stent implantation, and a novel BPS called open C-shaped stent (OCS) with superior comprehensive mechanical properties was developed accordingly. The key mechanical properties including radial force, radial recoil, and axial foreshortening of the OCS have been comprehensively studied and compared with those of the Abbott BVS using finite element analysis (FEA). In addition, the effects of the stent geometries on these mechanical properties have also been discussed in detail. Besides, in vitro mechanical tests including stent expansion and planar compression experiments have been performed to verify the simulation results. Based on the FEA results, it is found that the radial force and radial recoil of the designed OCS are 30% higher and 24% lower than those of the BVS, respectively. Meanwhile, the OCS is not shortened during expansion. Radial force and radial recoil are mainly dependent on the supporting ring structure, and the utilization of designed unequal-height supporting ring (UHSR) can effectively improve these two properties. Axial foreshortening is mainly determined by the bridge geometry as well as the connecting position of the bridge with the adjacent supporting rings. It is feasible to improve the axial foreshortening by using the bridges with a curved structure and locating the connecting position in the middle of the straight section of the supporting elements. The rationality of the proposed OCS and the effectiveness of the finite element method have been verified by in vitro experiments.
Highlights
Biodegradable vascular stents are hailed as the fourth revolution in coronary intervention [1]. ey provide temporary support to diseased blood vessels and disappears gradually, which overcome the core complications induced by the permanent retention of traditional metallic stents including vasomotor dysfunction, late in-stent restenosis and revascularization of advanced target lesions [2,3,4]
The open C-shaped stent (OCS) and BVS expanded uniformly without circumferential rotation and strut fracture with the increase of balloon inner pressure, which was consistent with the finite element analysis results
From the in vitro experimental results, it is concluded that all the mechanical properties including the radial force, radial recoil, and axial foreshortening of the OCS are better than those of the BVS, which further validates the rationality of the proposed OCS and the effectiveness of the finite element method to evaluate the mechanical properties
Summary
Biodegradable vascular stents are hailed as the fourth revolution in coronary intervention [1]. ey provide temporary support to diseased blood vessels and disappears gradually, which overcome the core complications induced by the permanent retention of traditional metallic stents including vasomotor dysfunction, late in-stent restenosis and revascularization of advanced target lesions [2,3,4]. Apart from the modification of build materials [10, 11], two strategies have been developed to improve the mechanical properties of BPSs: (1) increasing strut thickness [12,13,14] and (2) changing stent structure For the former one, the increase of strut thickness can effectively improve the radial force, while it results in the increase of the entire profile, which leads to the increasing risk of in-stent restenosis and limits the treatments for heavily curved or highly calcified diseased vessels [15]. Due to the complexity of the slide-lock stents, localized mechanical wear can happen during sliding, which increases the risk of artery wall damage [24] From these reported results, it can be seen that many BPSs with different structures have been proposed, these structures are only based on the improvement of one specific mechanical property.
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