两种覆膜支架的生物力学对比分析

目的应用数值模拟方法研究两种直管型覆膜支架在植入过程中自膨胀释放、平衡状态、支架弯曲3种工况下的生物力学特性,并对比支架结构变化对其各生物力学指标的影响。方法建立两款环状覆膜支架(支架Ⅰ、II,其中支架II各独立支架单元间添加连杆加固)和目标血管的有限元模型。使用输送鞘将支架输送到目标血管中,释放输送鞘使支架自膨胀释放,并建立血管和覆膜支架的接触关系;释放完全后,在支架内表面施加6.65~19.95 k Pa(50~150 mm Hg)动脉压;在支架两端施加角位移以使其弯曲变形。最后分析变形血管的等效应力峰值,覆膜支架在各工况下的最大主应变峰值、等效应力峰值及形态的变化。结果在自膨胀释放过程中,支架Ⅰ、II造成血管壁应力集中的峰值分别为0.349、0.371 MPa;平衡状态中,支架Ⅰ、II平均应变分别为0.086%、0.053%,振荡应变分别为0.049%、0.027%,覆膜应力峰值分别为2.098、2.430 MPa;支架弯曲变形时,支架Ⅰ、II最大主应变峰值分别为0.069%、0.101%,覆膜变化形态上支架Ⅰ褶皱更为严重。结论两种覆膜支架在各状态下应力应变都满足相应材料屈服极限;支架II由于单元间存在连杆而使其在释放过程中具有更大的径向支撑力,动脉压作用下具有较低应变水平,支架弯曲变形时也能具备更好的贴壁性。研究结果可以为覆膜支架的结构设计以及覆膜材料选择提供一种分析方法,并给临床覆膜支架介入手术操作提供直观、准确的技术指导。     

血管支架有限元优化设计

血管支架植入术是目前治疗冠心病的最流行手段,但现行支架较高的再狭窄率成为其进一步发展的最大障碍.通过对血管支架进行结构优化设计,改变其安放时的膨胀行为则是一个能够减少支架在植入时对血管内膜的损伤,从而降低支架内再狭窄率的有效途径之一.我们利用有限元技术,系统地模拟分析了支架不同环状支撑体宽度以及整体的非对称设计对其瞬时膨胀行为的影响.结果显示,在支架的结构参数中环状支撑体的宽度对支架膨胀压影响显著,在设计血管支架时,其环状支撑体结构的非对称设计,即环状支撑体的宽度从中部到端部依次逐渐递减变化,可以有效抑制了球囊伎架系统在瞬时膨胀过程中的"狗骨头"现象,从而达到减小对血管壁急性损伤的目的.     

形状记忆合金超弹性自扩张血管支架的优化设计

自扩张型镍钛合金血管支架由于其良好的生物相容性与超弹性,可以很好地解决支架植入后的再狭窄问题.利用有限元软件ANSYS对支架在血管中的自扩张行为进行模拟,并对支架的网格形状与尺寸进行优化设计.     

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。     

血管支架对颅内动脉瘤血液动力学的数值模拟

血管支架作为治疗颅内动脉瘤的新方法被广泛运用到临床中,而且越来越普遍。但由于某些支架植入后不能满足力学要求或对瘤内血液动力学无明显影响,反而更易形成血栓,造成动脉瘤破裂。本研究首先通过结构静力学分析比较矩形截面网格状支架和网丝编织成的圆形截面螺旋形支架的弯曲变形能力及扭转变形能力;然后将网格支架植入实际脑动脉瘤模型,进行流－固耦合模拟仿真,分析血流速度、壁面压力及壁面剪切力变化。结果表明：两种支架能够在不损失径向支撑力的情况下,提供良好的轴向顺应性,且网格状支架的变形能力高于螺旋状支架;支架植入后血液动力学各项指标明显降低。血管支架对颅内动脉瘤血液动力学有很大影响,可为临床治疗动脉瘤提供理论依据。     

靶向药物洗脱支架扩张过程力学性能研究

目的:药物洗脱支架(DES)的出现,在心血管狭窄治疗领域具有里程碑意义。DES扩张过程的力学性能对冠状动脉支架植入术的成功有着重要影响。球囊扩张冠脉支架的完整变形过程包括支架装配时往球囊上的压握过程、支架在球囊作用下的扩张过程、以及球囊撤出后支架受血管壁的周期性压缩过程3个阶段。研究两种不同结构的药物洗脱支架(DES)扩张过程的力学性能,以期对DES结构设计提供科学的指导。方法:采用Solidworks软件建立2种不同结构的支架模型(根据外表面刻槽与否分别称为II型支架和I型支架);使用Hypermesh软件对建立的几何模型进行六面体网格划分,并对网格进行优化;使用Abaqus有限元分析软件,对两种支架扩张过程中重要的力学性能指标进行了分析。结果:相对于I型支架,II型支架在减少载药量的同时,其径向回弹率、轴向回弹率、扩张不均匀性等力学性能并未降低。与II型支架相比,I型支架不仅在支撑体上存在面积更大的高应力区域,而且其最大应力值(585.5 Mpa)也要高于II型支架(446.2 Mpa)。结论:相对于传统药物洗脱支架,靶向药物洗脱支架在减少载药量的同时,力学性能并未降低,对心血管狭窄等疾病的治疗具有较好的临床应用前景。     

NiTi心血管支架的疲劳断裂性能分析

目的对NiTi合金心血管支架进行疲劳寿命的预测研究。方法采用疲劳断裂的有限元分析方法,建立了三维空间NiTi心血管支架结构的模型,并分析了在生理脉动循环载荷作用下的心血管支架结构。结果有限元分析发现支架结构结点附近区域的正应力大、疲劳寿命低、损伤大;同时,支架结构的疲劳寿命预测发现,用结构表面进行氮化、喷丸硬化等方法处理的支架疲劳寿命较高。相关的实验结果显示疲劳裂纹或断裂总是发生在支架结点附近区域。结论生理载荷下的模拟结果与相关的实验结果相吻合,最终为心血管支架结构的安全性指导和设计提供了理论依据。     

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。     

球囊扩张式支架扩张过程的数值模拟

目的求解支架扩张过程中的应力、形变分布云图,以及压强-直径变化曲线,获取球囊扩张式支架整体性能数据。方法使用"体积控制"球囊-支架模型,运用有限元分析软件ANYSY进行数值模拟,并与实验数据进行比较。结果支架-球囊模型可以很好地模拟支架扩张全过程;当球囊膨胀至最大直径,支架模型的主体结构与加强筋连接位置会发生塑性形变,而最大应力也分布在连接位置。结论通过有限元分析可以对支架性能进行优化。     

镍钛合金冠脉支架纵向柔顺性数值分析

目的利用有限元方法分析自主设计镍钛合金冠脉支架的结构特征与纵向柔顺性的关系。方法通过Soildworks设计一种新型支架的几何模型,运用Hypermesh、MATLAB及ABAQUS软件构建出支架的有限元模型,在ABAQUS中对支架一个结构周期内的9个弯曲方向上分别施加转角位移,使支架保持纯弯曲状态。结果支架柔顺性在自接触前差异性不明显;当自接触发生后,支架的柔顺性表现出明显的各向异性,同时支架在平面内的纯弯曲载荷作用下发生弯曲变形,并伴随着平面外的偏转及围绕自身轴线的扭转变形。结论支架的结构特征决定了其弯曲行为,连接体的螺旋和自接触使支架的柔顺性始终表现出各向异性,为支架在临床上的应用提供科学指导。     

Characterizing the Expansive Deformation of a Bioresorbable Polymer Fiber Stent

Polymeric vascular stents must employ other strategies than malleable deformation, as generally practiced with metal stents, to expand and withstand compressive stresses in situ. The stent expansion strategy must further consider induced flow perturbations and wall stresses that may injure the vessel wall and promote thrombogenesis. Analyzing the stresses furled stents undergo during balloon-assisted expansion is an important first step in achieving a better understanding of stent–wall mechanical interactions, thereby to improve stent function. To this end, we performed finite element (FE) analysis of the balloon-induced unfurling of an internally coiled, bioresorbable polymeric stent employing a 3D FE solid model of a 120° symmetric stent segment and a large deformation finite strain formulation. Uni-axial tensile testing of stent fiber elastic to plastic yielding provided the mechanical property information, and the von Mises criterion was employed to establish the elastic–plastic transition in the FE model. The model was validated with pressure and deformation measurements obtained during stent expansion tests. The internal coils of this inner coil–outer coil design twisted as the stent expanded, leading to plastic yielding at the point of tangency of the inner and outer coils. The remaining stent fiber portions underwent elastic bending. Cross-sections revealed only the outside surface layer of the coiled fiber underwent plastic yielding. The interior elastic fiber was supported by this plastic shell. The analysis suggests that during balloon-induced expansion, local plastic yielding in torsion “sets” the stent fibers, imparting high radial collapse resistance. The results further suggest that the stent exerts non-uniform mechanical forces on the vessel wall during expansion.     

A predictive study of the mechanical behaviour of coronary stents by computer modelling

Intravascular stents are small tube-like structures expanded into stenotic arteries to restore blood flow perfusion to the downstream tissues. The stent expansion is an important factor to define the effectiveness of the surgical procedure: it depends on the stent geometry and includes large displacements and deformations, geometric and material non-linearity. Numerical analyses seem appropriate to study such a complex behaviour after a free stent expansion. In this study the finite element method (FEM) was applied to a new generation coronary stent. Results from computations were compared with those from a laboratory experiment in terms of radial expansion and elastic recoil. By means of a scanning electronic microscopy the area of plastic deformation were also detected and compared with those obtained in the numerical simulation. Matching between the different measurements was quite satisfactory even if some discrepancies were present due to the absence of the balloon in the numerical model.     

基于有限元模拟的支架扩张、血流动力学及支架疲劳分析

目的利用有限元方法研究支架在狭窄血管内的扩张性能、支架内血流动力学状况和支架的疲劳寿命。方法采用ANSYS模拟支架在狭窄血管内的扩张过程,提取扩张后相关节点数据,建立血流动力学分析模型,并建立与之对应的简化模型,模拟分析支架内血流动力学状况。分别基于Goodman图表和累计损伤法,对支架的疲劳寿命进行评估。结果 (1)支架上绝大部分部位发生塑性变形,主要应力发生在镂空孔的角点。(2)支架附近流动紊乱,血流流入端的桥接支柱附近应力最高。(3)Goodman图表法表明该支架是安全的,累计损伤法表面支架在血流流入端桥接支柱所在的第2个横截面上累计损伤最大。结论有限元方法能有效地应用于支架扩张、支架内血流动力学以及支架的疲劳模拟仿真。     

冠状动脉支架抗压缩性能的有限元分析

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。其对病变动脉壁的支撑作用如何是支架植入术成功的先决条件之一。依据冠脉支架抗压缩性能的实际测试原型，建立起对应的有限元模型，并利用此方法系统地研究了专利支架设计，其扩张尺度的不同和筋的尺寸变化对支架抵抗两平面压缩性能的影响。结果显示，随支架扩张直径的增大，其抵抗两平面压缩的作用减小，增加支架筋的宽度或厚度能够提高支架的抗压缩性能，且这两个方向尺寸的增加对提高抗压缩性能的作用相当。模拟与实验结果一致，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。     

Cell Area and Strut Distribution Changes of Bent Coronary Stents： A Finite Element Analysis

Coronary stents are metal coils or mesh tubes delivered to blocked vessels through catheters, whic Recently, special drugs h are expanded by balloons to reopen and scaffold target vessels. are carried by stents （drug-eluting stents） to further reduce instent restenosis rate after stenting procedure. However, continual study on biomechanical characteristics of stents is necessary provide a more suitable drug loading for better interactions between stents and tissue, or to platform for drug-eluting stents. The purpose of this paper is to show how finite element methods can be used to study cell area and strut distribution changes of bent coronary stents. A same bending deformation was applied to two commercial coronary stent models by a rigid curved vessel. Results show that the stent design influenced the changes of cell area and strut distribution under bending situation. The stent with links had more cell area changes at outer curvature, and the stent with peak-peak （ 〉 〈 ） strut design could have strut contact and overlapping at inner curvature. In conclusion, this finite element method can be used to study and compare cell area and strut distribution changes of bent stents, and to provide a convenient tool for designers in testing and improving biomechanical characteristics of new stents.     

Studying the non-uniform expansion of a stent influenced by the balloon

Non-uniform expansion of cardiovascular stents, which exists widely in experiments, has a large influence on stent safety, but has seldom been studied in depth until now. In this paper we use a folded balloon with friction to expand a stent through finite element method (FEM), and study how this influences non-uniform expansion of the stent. The simulations were carried out using ABAQUES software. The results show that the stent expands non-uniformly only when the fold and friction are considered together in the FEM model. The extent of non-uniformity during expansion increases with rising friction coefficient values; with the same friction coefficient but different stent locations on the balloon the extent of non-uniform deformation is different. On the other hand, compared to a tri-folded balloon, a six-folded balloon clearly decreases the expansive non-uniformity, which means that by increasing the number of the folded parts of balloon the stent expands more uniformly.     

考虑尺寸效应的聚合物血管支架力学性能

目的 研究考虑尺寸效应的聚合物血管支架力学性能,分析支架结构对支架力学性能和支架变形过程中尺寸效应的影响规律,为支架的结构设计提供理论依据。 方法 建立考虑尺寸效应的聚乳酸的 Cosserat 理论模型,并结合有限元法,通过三点弯和平板压获得支架弯曲刚度和径向刚度,进一步分析支架筋厚和筋宽、支撑单元曲率半径和轴向间距对支架径向支撑性能和尺寸效应的影响规律。 结果 聚合物血管支架在弯曲和压缩过程中均存在明显的尺寸效应现象;支架径向刚度与支撑单元曲率半径和轴向间距均呈负相关,与筋厚和筋宽均呈正相关;支撑单元曲率半径、轴向间距以及支架筋厚和筋宽越小,聚合物血管支架压缩过程中的尺寸效应越大。 结论 支架的径向支撑性能主要由结构的刚度决定,并受支架变形过程中尺寸效应的影响;支架几何结构的特征尺寸越小、支架弯扭变形的程度越大,则尺寸效应越明显,对支架径向支撑性能的增幅越大。