封闭式取栓支架的生物力学研究

The biomechanical study of the close-type stent retrievers

目的机械取栓术(mechanical thrombectomy,MT)是治疗急性缺血性脑卒中(acute ischemic stroke,AIS)的有效方法,治疗中使用的封闭式取栓支架的结构及力学特性对手术效果有重要影响。为了提高取栓支架的安全性及有效性,本研究对封闭式取栓支架的压握入管、自膨胀释放和迁移取栓3个阶段进行生物力学研究,分析取栓支架结构及其力学特征。方法首先建立支撑单元个数不同(3、4、5)的B3、B4和B5取栓支架的几何模型,然后建立压握工具、模拟血管和血栓的有限元模型。在压握工具的径向施加位移载荷对取栓支架进行压握;恢复其位移,使取栓支架自膨胀与血管接触;再通过在取栓支架的近端施加轴向位移,让取栓支架带动血栓进行迁移。评价参数分别为取栓支架的最大主应变及应力、取栓支架径向支撑力、血管Mises应力和支架的回撤力。结果压握过程中3款封闭式取栓支架的最大主应变峰值分别为9.10%、10.41%和8.61%,都处于安全范围内。支架外径为3 mm时(等于血管内径),B3支架的径向支撑力最大。自膨胀释放过程中,B5支架对血管造成的Mises应力值为1.757 MPa,超过了已知的正常血管的极限。迁移取栓阶段发现,取栓支架的支撑单元数越多,对应血管的Mises应力值越大;取栓支架的回撤力在迁移取栓的初始阶段达到最大值,后渐渐下降趋于平稳,其中B5支架的回撤力最大。结论虽然B5支架拥有最大的回撤力,但B3支架在径向支撑性能、结构完整性能、与血管作用的安全性等方面表现更优。该研究结果可以为取栓支架的结构优化设计提供一种分析方法,为取栓支架的性能提高提供一些参考。

Objective Mechanical thrombectomy(MT)is an effective method for the treatment of acute ischemic stroke(AIS).The structure and mechanical properties of the close-type stent retrievers used in the treatment are related to the therapeutic effect.In order to improve the safety and effectiveness of stent retrievers,this study carries out biomechanical analysis on the three stages of close-type stent retrievers:compression and insertion tube,self-expanding release,and migration thrombus removal,and analyzes the structure and mechanical characteristics of the stent retrievers.Methods First,we established finite element models of B3,B4 and B5 stent retrievers with different supporting cells(3,4,5),and then established finite element models of crimping tools,simulated blood vessels and thrombus.We applied displacement load on the radial direction of the crimping tool to crimp the stent retrievers,restored displacement to make the stents self-expand and contact the blood vessel,and then applied axial displacement at the proximal end of the stent retrievers to make the thrombus to migrate.The evaluation parameters are the maximum principal strain(MPS)and von Mises stress(VMS)of the stent retrievers,the radial force of the stent retrievers,the vascular VMS and the stent withdrawal force.Results During the crimping process,the MPS peaks of the three close-type stent retrievers were 9.10%,10.41%,and 8.61%,which were all within the safe range.When the outer diameter of the stent was 3 mm(equal to the inner diameter of the blood vessel),the B3 stent’s radial force was the largest.During the self-expanding and release process,the VMS caused by the B5 stent to the blood vessel was 1.757 MPa,which exceeded the limit of normal blood vessels.It was found in the migration and removal stage that the larger the number of support cells,the greater the VMS of the corresponding blood vessel.The withdrawal force of the stents reached the maximum value at first,then gradually decreased.The withdrawal force of the B5 stent was the largest.Conclusions Although the B5 stent has the largest withdrawal force,the B3 stent performs better in terms of radial support performance,structural integrity,and safety in vascular interaction.The research results can provide an analysis method for the structural optimization design of the close-type stent retrievers,and certain references for the performance improvement of the close-type stent retrievers.