Influence of strut cross-section of stents on local hemodynamics in stented arteries

Stenting is a very effective treatment for stenotic vascular diseases, but vascular geometries altered by stent implantation may lead to flow disturbances which play an important role in the initiation and progression of restenosis, especially in the near wall in stented arterial regions. So stent designs have become one of the indispensable factors needed to be considered for reducing the flow disturbances. In this paper, the structural designs of strut cross-section are considered as an aspect of stent designs to be studied in details. Six virtual stents with different strut cross-section are designed for deployments in the same ideal arterial model. Computational fluid dynamics(CFD) methods are performed to study how the shape and the aspect ratio(AR) of strut cross-section modified the local hemodynamics in the stented segments. The results indicate that stents with different strut cross-sections have different influence on the hemodynamics. Stents with streamlined cross-sectional struts for circular arc or elliptical arc can significantly enhance wall shear stress(WSS) in the stented segments, and reduce the flow disturbances around stent struts. The performances of stents with streamlined cross-sectional struts are better than that of stents with non-streamlined cross-sectional struts for rectangle. The results also show that stents with a larger AR cross-section are more conductive to improve the blood flow. The present study provides an understanding of the flow physics in the vicinity of stent struts and indicates that the shape and AR of strut cross-section ought to be considered as important factors to minimize flow disturbance in stent designs.     

新型可降解金属血管支架的有限元力学分析

近年来,镁合金血管支架被用于动物实验和临床研究.文献中报道,镁合金支架具有良好的生物相容性,植入血管后能够被逐渐腐蚀降解,但与不锈钢相比,镁合金材料脆性大,塑性变形能力差.根据Biotronik公司的两种镁合金血管支架建立有限元模型.有限元分析结果表明,扩张过程中支架中的最大应变达到20%,超过了目前市场上提供的镁合金的最大延伸率.因此,为了研制出可用的镁合金血管支架,需要优化设计血管支架的几何形状,避免应力集中,同时需要定制镁合金成分,并通过细化晶粒,提高材料的塑性变形能力.     

Finite element structural analysis of self-expandable stent deployment in a curved stenotic artery

A self-expandable stent is a tube-like structure that is expanded into the stenotic arteries to normalize the blood stream. Selfexpandable stents are expected to have superelastic properties of restoration after mechanical strain, restoring capability by at least 5% since the stents in operation may suffer large deformations, as each is folded and crimped into a catheter for insertion into a stenotic area in an artery and expands to the original diameter of the artery. Therefore, the shape of a stent is an important factor to control its desired tension and flexibility. In the present study, as a basic step to model the geometry of a stent and to design parameters for stent performance development, finite element analysis of a typical self-expandable stent was conducted to understand stent influence on arteries and plaques. A numerical analysis model to predict the stress and strain of the artery and plaque is presented with three steps of stent operation: Crimping the stent in a catheter, positioning the catheter in the stenotic area, and deploying the stent inside arteries with three different curvatures (κ = 0, 0.2 and 0.4). The results of this study showed the influence of the geometry of commercially available stents on an artery with plaque and the radial direction of plastic deformation of the plaque, which indicates the recovery of the stenotic artery.

     

高径向支撑性可生物降解聚合物血管支架结构设计与力学性能分析

在研究血管支架支撑单元夹角与其径向支撑强度关系的基础上,提出采用不等高支撑环以利于增大扩张后支撑单元夹角进而提高支架径向支撑强度的设计方法,根据该方法设计了三种可降解聚合物血管支架结构。采用有限元方法对比分析了该三种支架和雅培生物可降解支架(BVS)的径向支撑强度、径向回缩率、轴向短缩率与弯曲刚度,研究了支架结构对这些性能的影响规律。所设计的J型支架(JS)、开放式C型支架(OCS)和密闭式C型支架(CCS)的径向支撑强度相对BVS的径向支撑强度分别提高了14%、34%和42%,同时设计的三种支架的径向回缩率相对BVS的径向回缩率减小了约21%,且均未发生轴向短缩;采用开放式连接形式的JS、OCS的弯曲刚度与BVS的弯曲刚度相当,相比密闭式CCS减小了约73%。影响径向支撑强度和径向回缩率的主要因素是支撑环的结构形式,采用不等高支撑环可有效改善径向支撑强度和径向回缩率;影响轴向短缩率的主要因素是桥筋的结构形式和桥筋的连接位置,采用具有弯曲结构的桥筋且桥筋连接位置位于支撑单元直线段的中间处可避免支架发生轴向短缩;影响弯曲刚度的主要因素是桥筋与支撑环的连接形式,采用开放式连接的支架弯曲刚度...     

球囊扩张式冠脉支架耦合扩张变形机理研究

完整的支架耦合扩张过程包括压握收缩、自由扩张和与动脉血管壁的综合作用过程。文中在不考虑血管内斑块的情况下,利用有限元方法(FEM)分析了两种材料(SUS-316L、CoCr-L605)的支架动静态连续变形过程,重点研究了支架受到脉流载荷时的作用机制。通过设定接触,边界条件和载荷等关键条件控制求解过程,比较了它们在几何变形、应力分布等方面的差异性,并利用轴向缩短率、径向回弹率、静态强度和疲劳强度等指标定量预测两种支架的生物力学性能。有限元模拟对支架的设计及其性能的评价有一定指导意义。     

Estimation of force on vascular wall caused by insertion of self-expanding stents

Stent placement is a minimally invasive procedure that has received considerable attention as a treatment option for vascular stenotic lesions associated with coronary atherosclerosis. However, the severe problem of in-stent restenosis has recently begun to occur in blood vessels in which long-term placement of stents has occurred. In-stent restenosis results from the increase in neointimal hyperplasia caused by the stimulus of the force on the vascular wall. In the present study, methods are proposed to compute the contact force and straightening force on a vascular wall. The force on the vascular wall is calculated using these methods. As an example, the force on the vascular wall created by the insertion of the stent into the carotid artery is calculated, and the concentration of the force at both ends of the stent is confirmed. Guidelines are presented to modify the stent shape based in order to remove this force concentration which may provoke the neointimal hyperplasia. The methods described in the present paper are easily applied to the shape design of stents and will be an effective tool for improving the stent shape.     

利用等离子弧熔覆的薄壁件快速成型工艺研究

介绍一种基于等离子弧熔覆的直接金属快速成型工艺。研究了薄壁件成型时成型轨迹截面形状对成型质量的影响、尾缩控制、成型温度控制,以及力学性能等关键工艺问题。研究结果表明,扁平截面的成型轨迹有利于保证成型质量;采用末端减速法可以有效地避免薄壁件的尾缩现象;采用减小热输入与直接水冷相结合的成型方式,能够避免成型时液态金属的过度流淌等缺陷;薄壁件的抗拉强度和延伸率与填充金属丝相当,水平方向的性能优于垂直方向。     

OPTIMIZATION OF CORONARY STENT STRUCTURE DESIGN FOR MAXIMIZING THE ANTI- COMPRESSION MECHANICAL PROPERTY

Excellent mechanical property of the anti-compression or high collapse pressure has become an essential feature of new coronary stents. How to determine the design parameters of stent becomes the key to improve the stent quality. An integrated approach using radial basis function neural network （RBFNN） and genetic algorithm （GA） for the optimization of anti-compression mechanical property of stent is presented in this paper. First, finite element simulation and RBFNN are used to map the complex non-linear relationship between the collapse pressure and stent design parameters. Then GA is employed with the fitness function based on an RBFNN model for arriving at optimum configuration of the stent by maximizing the collapse pressure. The results of numerical experiment demonstrate that the combination of RBFNN and GA is an effective approach for the mechanical properties optimization of stent.     

球囊扩张式冠脉支架的动静态扩张过程的变形机理研究

研究冠脉支架在压握收缩、压握卸载、自由扩张、球囊卸载等植入过程的静态扩张变形强度和在冠脉内受到脉流循环载荷时的疲劳强度。建立冠脉支架系统的有限元模型,全面考虑冠脉支架、压缩壳、球囊和冠脉血管之间的相互作用,定量评价冠脉支架的静态强度和疲劳强度。为了检验冠脉支架受到脉流循环载荷时的疲劳强度,将冠脉支架植入到人工血管中,实施加速寿命疲劳试验。试验结果表明,支架结构完整,支架表面无破损和裂纹等失效形式。所提出的冠脉支架系统的有限元建模方法,将为冠脉支架的优化设计与失效评价提供可靠的科学依据。     

Mechanism of wavy wear of high speed railway trolley wires

Wavy wear of the sliding surface of a high speed railway trolley wire develops through a sequential sliding contact between the trolley wire and a pantograph. Results of research on wavy wear on the new Tokaido line are presented. An appropriate mathematical model of the dynamic evolution mechanism of wavy wear of the trolley wire and pantograph system is introduced to interpret the transition in the power spectral density of the sliding surface unevenness of the wire obtained from research on the actual conditions. In the model, wear is assumed to be proportional to the contact force acting on the wire. The harmonics of wavy wear correspond to an interval between two contact points of a pantograph in a higher frequency range. A design method for pantographs to suppress the evolution of wavy wear is proposed.     

A numerical analysis on the curved bileaflet mechanical heart valve (mhv): leaflet motion and blood flow in an elastic blood vessel

In blood flow passing through the mechanical heart valve (MHV) and elastic blood vessel, hemolysis and platelet activation causing thrombus formation can be seen owing to the shear stress in the blood. Also, fracture and deformation of leaflets can be observed depending on the shape and material properties of the leaflets which is opened and closed in a cycle. Hence, comprehensive study is needed on the hemodynamics which is associated with the motion of leaflet and elastic blood vessel in terms of fluid-structure interaction. In this paper, a numerical analysis has been performed for a three-dimensional pulsatile blood flow associated with the elastic blood vessel and curved bileaflet for multiple cycles in light of fluid-structure interaction. From this analysis fluttering phenomenon and rebound of the leaflet have been observed and recirculation and regurgitation have been found in the flow fields of the blood. Also, the pressure distribution and the radial displacement of the elastic blood vessel have been obtained. The motion of the leaflet and flow fields of the blood have shown similar tendency compared with the previous experiments carried out in other studies. The present study can contribute to the design methodology for the curved bileaflet mechanical heart valve. Furthermore, the proposed fluid-structure interaction method will be effectively used in various fields where the interaction between fluid flow and structure are involved.     

Operation and Force Analysis of the Guide Wire in a Minimally Invasive Vascular Interventional Surgery Robot System

To develop a robot system for minimally invasive surgery is significant,however the existing minimally invasive surgery robots are not applicable in practical operations,due to their limited functioning and weaker perception.A novel wire feeder is proposed for minimally invasive vascular interventional surgery.It is used for assisting surgeons in delivering a guide wire,balloon and stenting into a specific lesion location.By contrasting those existing wire feeders,the motion methods for delivering and rotating the guide wire in blood vessel are described,and their mechanical realization is presented.A new resistant force detecting method is given in details.The change of the resistance force can help the operator feel the block or embolism existing in front of the guide wire.The driving torque for rotating the guide wire is developed at different positions.Using the CT reconstruction image and extracted vessel paths,the path equation of the blood vessel is obtained.Combining the shapes of the guide wire outside the blood vessel,the whole bending equation of the guide wire is obtained.That is a risk criterion in the delivering process.This process can make operations safer and man-machine interaction more reliable.A novel surgery robot for feeding guide wire is designed,and a risk criterion for the system is given.     

轻质点阵结构的参数化建模及力学性能研究

针对点阵材料结构设计困难的问题,建立了由长方体空间衍生的胞元结构数学模型,并构建了胞元结构和试件的参数化模型及力学性能研究系统。对5种典型胞元构成的试件通过改变胞元尺寸大小及数量或支柱截面半径,使其具有相同几何形状、外形尺寸以及质量;采用有限元法分析试件分别受到拉伸/压缩、弯曲、扭转载荷及模态的力学性能。通过研究得到胞元结构试件力学性能的数据,提出在各种载荷下点阵材料的设计方法,并通过实例验证该方法的正确性及可靠性。     

机械传动原理方案设计目录及智能设计平台的研究

探讨了机械传动原理方案设计目录的开发以及基于设计目录的机械传动原理方案智能设计平台的研究。提出了“三级递进式”的机械传动原理方案设计目录结构形式，并以设计目录的研制和系统化设计法为基础，研制了一个智能化设计平台。本平台能够自动生成并选择最优的机械传动的原理方案，在实际的应用中取得了很好的效果。     

新型电缆牵引机双摩擦卷筒应力分析与仿真

针对电力特种装备——新型自驱动式牵引机的关键装置双摩擦牵引卷筒设计缺乏设计依据等关键问题,采用微积分及有限元仿真分析结合的方法进行了力学分析,得到牵引钢丝绳沿双摩擦卷筒绳槽的张力变化函数关系,进而建立了卷筒的力学分析模型,研究在不同载荷条件作用下卷筒的应力状态与关系.最后,基于ANSYS软件对卷筒进行有限元建模分析,并将仿真结果与理论计算结果进行分析比较.结果证明了所采用的单元梁力学模型应用于卷筒的应力计算的可靠性与有效性,可为摩擦卷筒类零件的强度设计提供重要的理论依据,具有一定的工程意义.     

机械加工设备的功能方案设计

在分析机械零件成形方法和加工设备工艺范围的基础上,得出功能原理的设计是机械零件加工设备设计的核心任务。设计机械零件加工设备,首先要完成的工作是功能方案设计。文中对机械零件加工设备运动功能的描述、表达以及包含的机理作了深入探讨,提出了机械加工设备功能方案设计的一般方法,这为机械零件加工设备开展总体结构设计增加了一种辅助手段。     

基于递归分割的机械零件三维形状结构检索方法

为实现设计重用,须对已有设计实例进行检索,实例检索中最为困难的是形状的相似性比较,为此提出基于递归分割的机械零件三维形状结构检索方法。生成模型凸包围盒获取机械零件的初始位置并对其进行归一化变换,再生成自适应有界分割面对实体进行分割,检测分割过程中实体的几何和拓扑参数变化,递归建立有序满二叉树,结合工程特征构建特征矢量,比较特征矢量的相似性获得非根结点实体的相似度,按广度优先变权遍历有序满二叉树,通过非根结点实体的相似度比较,获得各机械零件三维形状结构的相似度。将基于递归分割的机械零件三维形状结构检索方法在原型系统中对不同粒度的设计基元进行验证和应用,结果表明,该方法具有较高的计算效率和判断精度,能够快速准确地反映机械零件的总体轮廓形状和局部细节结构,对于实现设计重用提高设计效率具有重要意义。     

自膨式医用支架径向力学性能的测试技术

支架技术是广泛应用于临床的高科技医学工程技术,但目前支架成品力学性能检验技术不成熟,造成支架质量检验缺少力学及安全性能试验方法。本文介绍了应用张力法测定自膨式医用内支架成品径向力学性能的检测方法,讨论了医用内支架的径向力学性能,为控制支架设计及质量提供了新的手段,同时对支架技术规范的制订具有重要意义。     

接触式二维形貌测量仪

在机械行业中,轴承、光学器件、计算机芯片等的运行状况均取决于其表面形貌的实际情况,采用二维形貌测量仪可以精密地对其进行测量.介绍了二维形貌测量仪的测量原理和结构设计,并提出了一整套设计思路和数据处理方法.     

仿形技术中一类新的有效方法

本文从机械工程、天线的外形设计和各种测试数据的分析中,归纳出一类条件泛函极值问题。文中还探索出了求解这类问题的一种有效的数值方法。采用本文方法对一类机械零件的仿形和性能分析均收到显著效果。还能很方便地用于光滑程度不同的曲线拟合。