McKenna Ciara G, Vaughan Ted J
Biomechanics Research Centre (BioMEC), Biomedical Engineering, School of Engineering, College of Science and Engineering, National University of Ireland Galway, Galway, Ireland.
Biomechanics Research Centre (BioMEC), Biomedical Engineering, School of Engineering, College of Science and Engineering, National University of Ireland Galway, Galway, Ireland.
J Mech Behav Biomed Mater. 2020 Mar;103:103549. doi: 10.1016/j.jmbbm.2019.103549. Epub 2019 Nov 21.
Self-expanding wire braided stents have been used in a wide-range of medical implant applications due to the distinct flexibility offered by the wide-range of tunable design parameters, which includes braid angle, wire diameter and braid pattern. Recently, there has been increasing attention on developing covered stent systems in endovascular repair, whereby the stent frame is wrapped with a graft or textile material, typically made from expanded polytetrafluoroethylene (ePTFE) or polyester (PET, Dacron). However, the addition of a polymeric cover to a wire braided stent fundamentally changes its mechanism(s) of deformation and there is distinct lack of understanding how the functional performance of these systems compares to their bare-metal counterparts. This paper presents the first systematic evaluation of the effect of a polymeric cover on braided stent mechanics using radial compression, axial compression and tension, kink deformation and stent elongation testing. Nitinol wire braided stents were manufactured with braid angles of α = 30°, α = 45°, and α = 60°, and subsequently covered with a polyurethane-silicone composite polymer with cover thicknesses of t = 25 μm and t = 100 μm. Results demonstrate that the response of both bare-metal and covered wire braided stents is heavily influenced by braid angle across all loading regimes. In particular, it was shown that the bare-metal stents exhibited higher stiffness under radial and axial loading when the direction of loading was closer aligned to the orientation of the wires. It was shown that covering stents with a polymeric cover led to a stiffer response across all braid angles and, in some cases, this could be up to two orders of magnitude greater when thicker covering systems were considered (t = 100 μm). Covered wire braided stents with braid angles of α = 30° and α = 45° show excellent potential for use in femoropopliteal applications, where the addition of 25 μm cover increased the radial resistive force but did not have any negative effects in terms of flexibility. The current analysis shows that use of a cover in braided stent mechanics is another variable parameter which can be used to produce optimum stent properties tailored to an application.
自膨胀金属丝编织支架由于其多种可调设计参数（包括编织角、金属丝直径和编织图案）所提供的独特柔韧性，已被广泛应用于各种医疗植入领域。最近，在血管内修复中开发覆膜支架系统受到越来越多的关注，在这种系统中，支架框架被移植片或纺织材料包裹，这些材料通常由膨体聚四氟乙烯（ePTFE）或聚酯（PET，涤纶）制成。然而，在金属丝编织支架上添加聚合物覆盖层从根本上改变了其变形机制，而且对于这些系统的功能性能与裸金属支架相比情况如何，人们明显缺乏了解。本文首次使用径向压缩、轴向压缩和拉伸、扭结变形和支架伸长测试，对聚合物覆盖层对编织支架力学性能的影响进行了系统评估。制造了编织角为α = 30°、α = 45°和α = 60°的镍钛诺金属丝编织支架，随后用覆盖厚度为t = 25μm和t = 100μm的聚氨酯 - 硅酮复合聚合物进行覆盖。结果表明，在所有加载方式下，裸金属和覆膜金属丝编织支架的响应都受到编织角的严重影响。特别是，研究表明，当加载方向与金属丝的取向更接近对齐时，裸金属支架在径向和轴向加载下表现出更高的刚度。研究表明，用聚合物覆盖层覆盖支架会导致在所有编织角下响应更硬，在某些情况下，当考虑较厚的覆盖系统（t = 100μm）时，这种情况可能会高出两个数量级。编织角为α = 30°和α = 45°的覆膜金属丝编织支架在股腘动脉应用中显示出极好的潜力，添加25μm的覆盖层增加了径向阻力，但在柔韧性方面没有任何负面影响。当前分析表明，在编织支架力学中使用覆盖层是另一个可变参数，可用于根据应用定制出最佳的支架性能。
