冠脉支架系统瞬时膨胀过程的有限元分析及其优化设计

经皮穿刺冠脉支架技术已成为治疗冠心病的有效手段，在实践该技术过程中，球囊与支架的配套情况和支架的设计影响着支架瞬时膨胀的效果，球囊／支架系统在病变处的瞬时非均匀膨胀，即Dogboning现象，是造成支架端部急性动脉损伤的主要原因之一。这种损伤与支架内再狭窄(in-stent restenosis)有着密切的联系。为减少这种损伤，降低支架植入再狭窄率。本研究利用有限元技术对六组不同搭配的球囊／支架系统的瞬时膨胀情况进行了对比分析。结果表明，在球囊、支架的搭配中，减小球囊有效长度的过盈量和增加支架端部支撑体的筋宽，这两种方法共同作用，可以有效抑制球囊／支架系统在瞬时膨胀过程中的Dogboning现象。验证实验与模拟结果比较吻合，说明有限元法可以胜任球囊／支架的优化设计工作。     

冠状动脉支架膨胀行为的有限元分析

冠状动脉支架作为经皮穿刺冠状动脉成形术中保持病变血管畅通的核心器件,其在手术过程中受球囊作用的扩张特性以及球囊撤出后的反弹行为对支架植入术的成功有着重要的影响。利用有限元的方法系统地研究了专利支架设计,其筋的尺寸变化和支架扩张尺度的不同对支架膨胀行为的影响。结果显示,增加支架筋的宽度或厚度提高了使支架迅速扩张所需的临界内压力,支架轴向长度的变化只与其结构和最终膨胀状态紧密相关。在结构一定的情况下,支架所用材料可能是影响支架反弹指标的主要因素。模型校核和SEM观察表明,有限元模拟可以在一定程度上替代支架原型测试工作。     

基于非对称孔结构的高性能血管支架设计

目的 设计一种新型高性能血管支架,使其能够在保证足够径向刚度的前提下减小支架厚度及金属覆盖率,并具有较好的轴向柔顺性,以达到减少支架内再狭窄的目的。方法 基于对称结构孔及非对称孔结构变形能力的研究,通过数值模拟方法对支架结构进行分析设计,并利用实验方法对加工后的支架进行径向刚度及弯曲刚度的测试。结果 新的支架结构具有较高的径向刚度、较小的金属覆盖率和较好的轴向柔顺性,对减少支架内再狭窄的产生具有一定意义。结论 基于非对称孔结构的支架设计方法是有效的,并且能够借此设计出高性能的血管支架结构。     

一种血管内支架的有限元模型及计算流体动力学分析

支架植入所造成的血栓、血管损伤及其对血流动力学的影响是造成支架内再狭窄的主要原因。我们利用有限元模型与计算流体动力学的方法,分析了一种支架在植入过程中与斑块、血管的相互作用及其对血流情况的影响。结果发现：支架植入后端部发生翘起,这容易损伤血管壁;支架植入模型所对应的即刻回缩率明显高于支架自身的回缩率,其结果分别为12.3%、3.1%;支架壁厚与连接筋设计能够引起血管壁面剪应力的明显变化。这对于血管内支架的设计具有一定的指导意义。     

不同形状血管中医用支架扩张力学行为的研究进展

血管支架介入术由于其微创性和高效性已经成为目前治疗由血管狭窄所引发的冠心病的主要治疗手段,但支架内再狭窄却是影响支架远期效果的最大障碍,严重制约了其实际疗效。首先从支架内再狭窄的形成机制出发,从固体力学角度回顾力学环境对再狭窄的影响,并主要阐述近年来支架在圆直、锥形、分叉、弯曲4种不同形状血管内扩张的研究进展,特别是从支架扩张对血管应力及血管形状的改变与再狭窄的相关关系方面进行综述。最后,针对不同血管形状对支架扩张的影响,提出一个旨在提高支架扩张性能及减少支架内再狭窄的血管支架多目标优化设计方法。     

有限元技术在心动脉支架设计中的应用

支架植入后再狭窄是限制支架应用的主要问题,大量研究表明支架设计对于再狭窄具有较大影响.有限元技术被认为是进行支架设计成本最低,且最适合的工具,本文综述了目前有限元技术在支架领域的应用情况,并提出了支架优化设计的方向.     

新型可回收血管支架的设计与有限元分析

目的针对药物洗脱支架植入后引起的早期再狭窄问题,对镍钛合金血管支架进行结构上的可回收设计和生物力学分析。方法建立可回收血管支架及其回收系统的几何模型,其中支架回收部为圆台形网状结构,由4个对称分布的回收筋组成;分析支架在压握过程中的最大主应变分布、压握及自膨胀均匀性等,并对支架的回收过程进行仿真实验。结果当支架被压握至最小尺寸时,其最大应变为3.7%,不均匀性指数为0.62%;当支架自膨胀结束时,其不均匀性指数为1.31%;当1/2支架被回收进外鞘管时,最大应变为1.52%;而支架在回收过程中并未发生断裂或"卡顿"情况。结论支架应变在其安全范围之内,且支架的压握及自膨胀过程较均匀,能够被安全、顺利地回收进外鞘管中。研究结果可以为可回收血管支架的结构设计、生物力学分析和临床应用提供重要参考依据。     

血管支架内再狭窄的研究进展

冠状动脉粥样硬化性心脏病是心血管疾病死亡的重要原因之一 ,血管支架植入治疗已经成为一个标准的血管成形术方法 ,但是支架内再狭窄仍然是制约其应用的一个主要的问题 ,据统计 ,冠状动脉血管支架植入在 6个月后的再狭窄率仍然高达 2 0～ 30 % ,成为制约支架临床应用的一个最主要的问题。本研究综述了血管支架内再狭窄机理以及再狭窄发生过程的研究进展 ,介绍了金属支架涂层以及高分子血管支架的最新研究进展。     

基于动脉系统旋动流原理的一种血管内支架旋流导引装置的优化

血管内支架是目前治疗心血管疾病的主要方法之一。但是支架植入后的血管再狭窄问题至今未获完全解决。研究表明,支架植入后导致的局部血流紊乱和流场异常是造成再狭窄的主要原因之一。基于动脉系统的旋动流原理,设计了一种能够引导血流产生旋动的血管内支架旋流导引装置,并用计算流体力学的方法,对其进行了优化设计。流场数值研究表明,优化设计得到的旋流导引装置可产生足够强度的旋动流。我们相信,该装置产生的旋动流可有效抑制支架结构对血流的扰动,从而达到减缓血管再狭窄的目的。     

血管支架柔顺性能的仿真模拟及灰色相关性分析

目的利用有限元法与灰色相关性理论的方法,分析并比较支架结构参数对支架植入后与血管同步运动能力的影响。方法选取S型闭环镁合金支架作为研究对象,应用Solid Works软件建立不同材料、周向支撑体数目、支撑体长度及初始直径共9款支架模型;应用Hyper Mesh软件进行支架模型网格的划分;应用ABAQUS软件模拟分析支架植入后与血管同步运动能力;利用灰色相关性理论研究并比较支架结构参数对弯曲刚度影响因子大小。结果材料对支架柔顺性的影响较明显,其中镁合金的柔顺性最好,对应弯曲刚度值为0.958 N·(rad·mm)~(-1);周向支撑体数目为5对应支架的柔顺性最好,其弯曲刚度值为0.853 N·(rad·mm)~(-1);支撑体长度为1.0 mm对应支架的柔顺性最好,其弯曲刚度值为0.829 N·(rad·mm)~(-1);初始直径为1.4 mm对应支架的柔顺性最好,其弯曲刚度值为1.024 N·(rad·mm)~(-1)。结论镁合金支架对应柔顺性最好,其次为不锈钢,钴铬合金支架对应柔顺性较差;柔顺性随着周向支撑体数目、支撑体长度、初始直径的增加而呈减小趋势变化;通过灰色相关性计算可知,材料对应柔顺性的影响最显著,其次为周向支撑体数目、支撑体长度,初始直径对其影响较小;分析支架结构参数对柔顺性的影响,可为支架的设计研发及临床治疗提供更加科学的参考。     

药物涂层支架的研究进展

药物涂层支架在介入心脏病治疗中存在着很大应用潜力,也是预防血管再狭窄的重要方法。首先论述了支架与血液相互作用的机理,分析了药物涂层支架缓释药物的基本原理,然后重点对药物涂层支架的缓释涂层、药物缓释体的设计以及药物涂层支架研究的最新进展进行了综合评述。     

Mesenchymal stem cell seeding promotes reendothelialization of the endovascular stent

This study is designed to make a novel cell seeding stent and to evaluate reendothelialization and anti-restenosis after the stent implantation. In comparison with cell seeding stents utilized in previous studies, Mesenchymal stem cells (MSCs) have advantages on promoting of issue repair. Thus it was employed to improve the reendothelialization effects of endovascular stent in present work. MSCs were isolated by density gradient centrifugation and determined as CD29(+) CD44(+) CD34(-) cells by immunofluorescence and immunocytochemistry; gluten and polylysine coated stents were prepared by ultrasonic atomization spray, and MSCs seeded stents were made through rotation culture according to the optimized conditions that were determined in previous studies. The results from animal experiments, in which male New Zealand white rabbits were used, show that the reendothelialization of MSCs coated stents can be completed within one month; in comparison with 316L stainless steel stents (316L SS stents) and gluten and polylysine coated stents, the intimal hyperplasia and in-stent restenosis are significantly inhibited by MSCs coated stents. Endovascular stent seeded with MSCs promotes reendothelialization and inhibits the intimal hyperplasia and in-stent restenosis compared with the 316L SS stents and the gluten and polylysine coated stents.     

The influence of physical stent parameters upon restenosis

In this paper we examine whether the structure, geometry and dimensions of coronary stents influence the occurrence of restenosis. Whilst many consider these parameters to be less important since the advent of drug-eluting stents, this view reveals a poor appreciation of the technological development of stents over the last 18 years. Early 'slotted tube' stents were completely inflexible and posed major problems for delivery; and early 'coil' stents had poor radial strength, allowing considerable tissue prolapse. Nowadays, we are used to greatly improved physical stent parameters, which provide better deliverability, visibility, procedural success and scaffolding performance. Many of these physical parameters also impact upon restenosis, even in the current era of drug-eluting stent. In this paper we examine the contribution of mode of expansion (self vs. balloon-expandable), design (coil vs. tube), length and width to restenosis. We also consider the more subtle influence of advanced slotted tube vs. modular design, percent metal coverage, strut thickness, strut shape, surface smoothness and alloy composition.     

血管内支架治疗鼻咽癌放疗后颈部血管狭窄或闭塞病变的效果

目的探讨血管内支架置入术治疗鼻咽癌放疗后的颈动脉狭窄或闭塞病变的疗效。方法对3例鼻咽癌患者放疗后出现严重动脉狭窄或闭塞病变的颈部血管行球囊成形术及支架置入术并进行随访。结果 3例患者均为男性,其中1例为双侧颈动脉闭塞,进行了一侧颈动脉闭塞病变再通术;1例为双侧颈动脉重度狭窄,进行了左侧颈动脉支架成形术;1例右颈内动脉起始段严重狭窄,左侧颈动脉闭塞,对右侧颈动脉严重狭窄处进行了血管内支架治疗;经过随访并未发现有支架内再狭窄。结论血管内支架置入术是治疗鼻咽癌放疗后颈部血管重度狭窄或闭塞病变的有效手段。     

Demonstrating the Influence of Compression on Artery Wall Mass Transport

The development of restenosis within the coronary arteries after a stenting procedure has been addressed with the development of the drug eluting stent device. However, in recent times the superiority of the drug eluting stent over bare metal stents has been brought into question. A lack of knowledge regarding the behavior of drug transport from the drug eluting devices contributes to this uncertainty. Questions arise as to whether drug eluting stents deliver sufficient amounts of therapeutic agents into the artery wall to suppress restenosis. Published investigations in this area have focused primarily on trends associated with how variations in stenting conditions affect mass transport behavior. However, experimentally validated numerical models that simulate mass transport within the artery wall are lacking. A novel experimental model was developed to validate computational predictions of species diffusion into a porous medium and an investigation into how stent strut compression influences mass transport was conducted. The study revealed that increased compressive forces on a porous media reduced the ability of species to diffuse through that media, and in relation to drug eluting stents will contribute to a reduction in therapeutic levels of drugs within the wall.     

An intriguing design concept to enhance the pulsatile fatigue life of self-expanding stents

Intravascular stenting has emerged as the primary treatment for vascular diseases and has received great attention from the medical community since its introduction two decades ago. The endovascular self-expanding stent is used to treat peripheral artery diseases; however, once implanted, these stents suffer from various cyclic motions caused by pulsatile blood pressure and daily activities. Due to this challenging environment, fatigue performance has become a critical issue for stent design. In this paper, a simple yet intriguing concept of stent design aimed at enhancing pulsatile fatigue life is investigated. The concept of this design is to shift the highly concentrated stresses/strains away from the crown and re-distribute them along the stress-free bar arm by tapering its strut width. Finite element models were developed to evaluate the mechanical integrity and pulsatile fatigue resistance of the stent to various loading conditions. Results show that the fatigue safety factor jumped to 2.5–3.0 times that of the standard stent with constant strut width. This is astonishing considering that the stent profile and scaffolding were not compromised. The findings of this paper provide an excellent approach to the optimization of future stent design to greatly improve stent fatigue performance.     

端部形状对支架-食管耦合系统力学行为的影响

目的研究食管支架不同端部形状对支架-食管系统力学行为的影响。方法通过有限元仿真,对不同端部形状(直筒形、杯球形和双喇叭形)的编织型食管支架及其与食管腔道构成耦合系统之间力学行为进行分析,并比较3种不同端部形状的裸支架和覆膜支架对食管内壁应力分布和食管狭窄区扩张的影响。结果裸支架使食管狭窄率降低的程度比覆膜支架高,并且裸支架使食管的等效应力和食管内壁的接触应力都远大于覆膜支架植入后的情况;支架不同的端部形状对食管健康区域内的等效应力和接触应力有很大影响,在食管与杯球形支架的杯端中部和双喇叭形支架端部边缘所接触的区域内出现应力集中;3种不同端部的编织型食管支架都具有良好贴壁性能。结论不同的支架端部形状使食管内壁产生不同应力状态。应力越大,食管组织增生的可能性越大,但支架移位的可能性越小。了解支架端部形状对支架性能的影响,可为支架的优化设计和临床选型提供重要的理论依据。     

Stents: Biomechanics,Biomaterials, and Insights from Computational Modeling

Coronary stents have revolutionized the treatment of coronary artery disease. Improvement in clinical outcomes requires detailed evaluation of the performance of stent biomechanics and the effectiveness as well as safety of biomaterials aiming at optimization of endovascular devices. Stents need to harmonize the hemodynamic environment and promote beneficial vessel healing processes with decreased thrombogenicity. Stent design variables and expansion properties are critical for vessel scaffolding. Drug-elution from stents, can help inhibit in-stent restenosis, but adds further complexity as drug release kinetics and coating formulations can dominate tissue responses. Biodegradable and bioabsorbable stents go one step further providing complete absorption over time governed by corrosion and erosion mechanisms. The advances in computing power and computational methods have enabled the application of numerical simulations and the in silico evaluation of the performance of stent devices made up of complex alloys and bioerodible materials in a range of dimensions and designs and with the capacity to retain and elute bioactive agents. This review presents the current knowledge on stent biomechanics, stent fatigue as well as drug release and mechanisms governing biodegradability focusing on the insights from computational modeling approaches.     

Comparison of Two Stents in Modifying Cerebral Aneurysm Hemodynamics

There is a general lack of quantitative understanding about how specific design features of endovascular stents (struts and mesh design, porosity) affect the hemodynamics in intracranial aneurysms. To shed light on this issue, we studied two commercial high-porosity stents (Tristar stent and Wallstent) in aneurysm models of varying vessel curvature as well as in a patient-specific model using Computational Fluid Dynamics. We investigated how these stents modify hemodynamic parameters such as aneurysmal inflow rate, stasis, and wall shear stress, and how such changes are related to the specific designs. We found that the flow damping effect of stents and resulting aneurysmal stasis and wall shear stress are strongly influenced by stent porosity, strut design, and mesh hole shape. We also confirmed that the damping effect is significantly reduced at higher vessel curvatures, which indicates limited usefulness of high-porosity stents as a stand-alone treatment. Finally, we showed that the stasis-inducing performance of stents in 3D geometries can be predicted from the hydraulic resistance of their flat mesh screens. From this, we propose a methodology to cost-effectively compare different stent designs before running a full 3D simulation.