几何参数对Z型覆膜支架柔顺性的影响

目的分析治疗胸主动脉瘤的常用Z型覆膜支架的几何参数对支架柔顺性能的影响及主次顺序。方法通过SolidWorks软件建立波峰数目、波峰高度、丝径及顶端圆角半径4种因素变化的覆膜支架模型,并导入ANSYS有限元软件进行仿真分析,对支架施加弯曲60°的转动变量,根据最大等效应力、节点反力、弯矩3个评价参数分析支架柔顺性。结果支架弯曲后,最大应力集中在弯曲内侧;减小支架丝径、波峰高度与波峰数目,支架的柔顺性增强;增大波峰顶端圆弧半径,支架柔顺性增强;丝径与波峰数目对支架柔顺性的影响强于顶端圆弧半径与波峰高度。结论波峰数目、波峰高度、丝径及顶端圆角半径对覆膜支架柔顺性均有显著影响。研究结果为以后临床支架的选择及优化设计提供理论依据,对减少新发破口等并发症的发生具有积极意义。     

腹主动脉瘤直型覆膜支架的生物力学分析

应用数值模拟分析方法,研究腹主动脉瘤直型覆膜支架在径向压握、自膨胀释放及植入后平衡状态3种工况下的稳定性及各项生物力学指标。建立覆膜支架、压握工具以及目标血管的有限元模型。对圆柱状压握工具沿R轴负方向施加大小为6.50 mm的位移载荷,压握覆膜支架至外径为7.00 mm;将压握工具恢复到原始尺寸,建立血管/覆膜支架接触关系;支架完全释放后平衡状态下,对其内表面均匀施加50～150 mmHg动脉压。分析支架部分在压握与平衡状态下的最大主应变(MPS)峰值及分析后形态、释放状态下变形血管以及覆膜的等效应力峰值(VMS)。在径向压握过程中,金属支架最大压握主应变峰值为5.73%;在自膨胀释放过程中,造成血管壁应力集中的峰值为0.371 MPa,覆膜应力峰值为0.388 MPa;在植入后平衡状态下,支架平均应变为0.0859%,振荡应变为0.0486%,覆膜应力峰值为2.09 MPa,安全因子为8.23。支架部分在各工况下应变处于镍钛合金屈服强度之内,在圆角弯折处应变最为集中;覆膜部分在各工况下应力值也满足e PTFE膜材料的屈服强度。该研究结果可以为覆膜支架的结构优化设计以及覆膜材料选择提供一种分析方法, 可以提高覆膜支架的生物力学性能,并给工程设计和临床操作提供参考。     

下肢动脉覆膜支架边缘狭窄的血流动力学分析

通过建立镍钛合金覆膜支架的三维模型研究治疗下肢动脉狭窄的覆膜支架植入血管后的血流动力学情况。首先,进行有限元压握仿真,模拟8 mm直径的覆膜支架植入7 mm直径的血管后受到的径向压握变形,再提取出有限元结果,建立植入血管后的模型,进行计算流体动力学仿真分析。结果显示覆膜支架近端覆膜与血管贴壁不良,血液内渗区域的低壁面切应力占总低壁面切应力区域的28.5%,血液内渗区域的低流速区域占总低流速区域的30.1%。覆膜支架边缘的贴壁不良可能是造成支架植入后边缘狭窄的主要原因。     

可降解聚合物血管支架体外力学性能测试实验研究

体外力学性能测试是评估血管支架安全性和有效性的主要手段,其性能指标具有重要的临床意义。本文对比分析了可降解聚合物血管支架径向支撑性能测试的平面压缩法、V型槽压缩法和径向压缩法,并研究了压缩速率和压缩周向位置对支撑性能测试结果的影响,采用三点弯曲法研究了压缩速率和压缩周向位置对柔顺性能测试结果的影响。选取最优测试方案,测试了本文在不同外径(1.4、1.7、2.4 mm)下设计的三种支架和生物可降解聚合物血管支架(BVS)(BVS1.1,Abbott Vascular,美国)的支撑性能和柔顺性能。结果表明,三种支撑性能测试方法得到的压缩载荷—压缩位移曲线整体趋势一致,但归一化支撑力差异较大;平面压缩法更适合对不同外径、不同结构血管支架的支撑性能进行对比测试;压缩速率对支撑性能和柔顺性能测试结果无显著影响;压缩周向位置对采用平面压缩法、V型槽压缩法测试支撑性能和采用三点弯曲法测试柔顺性能有较大影响。综合比较,本文所设计的三种支架相对BVS支架其径向支撑性能均有不同程度的提高。本研究对血管支架的力学性能测试具有一定的指导意义和参考价值。     

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。     

血管收缩压作用下冠脉支架解析解推导与有限元分析

目的基于合理假设,推导冠脉支架位移及应力分布解析解;结合有限元分析结果,探究支撑筋数目对其应力的影响。方法利用弹性力学理论推导出矩形波型冠脉支架一个周期支撑筋在血管收缩压作用下的位移和应力分量解析解;利用ANSYS有限元分析软件建立支架支撑筋模型,求解得到应力数值分析结果。分析两种方法应力曲线的一致性,验证解析解正确性和适用性;再利用解析解探究支撑筋波峰数量对收缩压作用下应力的影响。结果解析解与数值解应力曲线一致性极强;波峰数为6时,横杆环向既有拉应力又有压应力。结论波峰数为6的支架在血管中支撑时,能有效避免血管中再狭窄情况的发生。推导的解析解能适用于分析矩形波型支架1个周期支撑筋的力学性能,研究结果为深入认识和研究冠脉支架的应力分布以降低介入治疗再狭窄率提供一种新思路。     

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。     

球囊扩张式冠脉支架生物力学性能研究

研究具有不同连接筋的冠状动脉支架的力学性能,为支架的设计开发以及介入治疗提供更加科学的指导.采用Solid Works建立3种不同连接筋的支架模型(根据连接筋的形状分别称为W-支架、S-支架和L-支架,压握壳以及球囊模型),使用Hypermesh软件完成模型的网格划分,应用ABAQUS软件模拟分析了径向回弹、轴向缩短,扩张不均匀性以及径向支撑刚度和柔顺性,并结合径向均匀加载和“四点弯曲”测量技术的径向支撑刚度和弯曲刚度的测试方法验证了数值模拟的合理性.结果表明:3种支架的各项力学性能都在安全范围内;相对而言,S-支架的支撑强度较大,支撑刚度为3.34 N/mm,容易造成局部血管壁的损伤;L-支架的轴向缩短率较大,为8.25％,不利于支架在血管病变部位的正确定位;S-支架和L-支架的弯曲刚度分别为:17.74 N/rad和18.00 N/rad,它们的柔顺性较差.3种支架的力学性能各有优缺点,其中W-支架的综合力学性能相对较好,这在临床上为选用支架提供良好的参考依据.     

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。     

封闭式取栓支架的生物力学研究

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.     

Computational comparison of the bending behavior of aortic stent-grafts

Secondary interventions after endovascular repair of abdominal aortic aneurysms are frequent because stent-graft (SG) related complications may occur (mainly endoleak and SG thrombosis). Complications have been related to insufficient SG flexibility, especially when devices are deployed in tortuous arteries. Little is known on the relationship between SG design and flexibility. Therefore, the aim of this study was to simulate numerically the bending of two manufactured SGs (Aorfix--Lombard Medical (A) and Zenith--Cook Medical Europe (Z)) using finite element analysis (FEA). Global SG behavior was studied by assessing stent spacing variation and cross-section deformation. Four criteria were defined to compare flexibility of SGs: maximal luminal reduction rate, torque required for bending, maximal membrane strains in graft and maximal Von Mises stress in stents. For angulation greater than 60°, values of these four criteria were lower with A-SG, compared to Z-SG. In conclusion, A-SG was more flexible than Z-SG according to FEA. A-SG may decrease the incidence of complications in the setting of tortuous aorto-iliac aneurysms. Our numerical model could be used to assess flexibility of further manufactured as well as newly designed SGs.     

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。     

保留前纵韧带的椎体间植骨术的稳定性实验研究

目的：为评价保留前纵韧带的椎体间支撑植骨治疗脊柱爆裂骨折提供的生物力学稳定能力。方法：用传感器及电测技术，采用新鲜人体胸腰段脊柱标本。结果：除旋转外，轴压、前屈、后伸、侧弯四种运动方式皆能提供满意的稳定性。结论：实验提示，该方法能明显增加损伤脊柱的力学稳定性，有利于提高脊柱的融合率，是一种治疗脊柱骨折较为理想的植骨方法     

A computational study on the biomechanical factors related to stent-graft models in the thoracic aorta

Endovascular aortic stent-graft is a new, minimally invasive procedure for treating thoracic aortic diseases, and has quickly evolved to be one of the standard treatments subject to anatomic constraints. This procedure involves the placement of a self-expanding stent-graft system in a high-flow thoracic aorta. Stent-graft deployment in the thoracic aorta, especially close to the aortic arch, normally experiences a significant drag force which might lead to the risk of stent-graft failure. A comprehensive investigation on the biomechanical factors affecting the drag force on a stent-graft in the thoracic aorta is thus in order, and the goal is to perform an in-depth study on the contributing biomechanical factors. Three factors affecting the deployed stent-graft are considered, namely, the internal diameter of the vessel, the starting position of the graft and the diameter of curvature of the aortic arch. Computational fluid dynamic techniques are applied to model the blood flow. The inlet velocity and outlet pressure are assumed to be pulsatile. The three-dimensional continuity equation and the time-dependent Navier–Stokes equations for an incompressible fluid were solved numerically. The drag force due to the change of momentum within the stent-graft and the shear stress were calculated and analyzed. The drag force on a stent-graft will depend critically on the internal diameter and the starting position of stent-graft deployment. Larger internal diameter leads to larger drag force and the stent-graft deployed at the more distal position may be associated with significantly diminished drag force. Smaller diameter of curvature of the aortic arch probably results in a decline of the drag force on the stent-graft, even though this factor merely causes only a modest difference. These findings may have important implications for the choice and design of stent-grafts in the future. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Structure, metallurgy, and mechanical properties of a porous tantalum foam

This study evaluated a porous tantalum biomaterial (Hedrocel) designed to function as a scaffold for osseous ingrowth. Samples were characterized for structure, Vickers microhardness, compressive cantilever bending, and tensile properties, as well as compressive and cantilever bending fatigue. The structure consisted of regularly arranged cells having struts with a vitreous carbon core with layers of CVI deposited crystalline tantalum. Microhardness values ranged from 240-393, compressive strength was 60 +/- 18 MPa, tensile strength was 63 +/- 6 MPa, and bending strength was 110 +/- 14 MPa. The compressive fatigue endurance limit was 23 MPa at 5 x 10(6) cycles with samples exhibiting significant plastic deformation. SEM examination showed cracking at strut junctions 45 degrees to the axis of the applied load. The cantilever bending fatigue endurance limit was 35 MPa at 5 x 10(6) cycles, and SEM examination showed failure due to cracking of the struts on the tension side of the sample. While properties were variable due to morphology, results indicate that the material provides structural support while bone ingrowth is occurring. These findings, coupled with the superior biocompatibility of tantalum, makes the material a candidate for a number of clinical applications and warrants further and continued laboratory and clinical investigation.     

Transrenal deployment of a modular stent graft to repair AAAs with short necks: experiments in dogs

Severely angulated (> 60 degrees ) or short (< 15 mm) proximal necks remain significant anatomical limitations for endovascular stent-graft repairs for abdominal aortic aneurysms. Ensuring proper proximal fixation of the stent-graft to the host artery without the short-or long-term risks of endoleak or migration represents a particular technical challenge for these anatomical circumstances. An innovative balloon expandable stent combined with a weft-knitted prosthesis was specifically designed for these situations by modelling the stent to the neck anatomy without overdistension or potential barotrauma allowing better incorporation of the device. The Latecba stent-graft consists of a 2 parts modular design. The first one, Module A, is deployed at the transrenal level and consists of a Palmaz type stent whose first half is bare and second half is sutured to a crimped weft-knitted polyester graft whose distal end holds a constriction. The second Module B is a non-crimped weft-knitted graft attached to 2 stainless steel stents. The first stent is entirely contained in the proximal textile tube, allowing fixation to module A. The second stent, which is left uncovered over the distal third, ensures proper fixation of the stent-graft distally. Following the creation of a prosthetic aneurysm in the infrarenal aorta in 32 dogs, 29 received the Latecba stent-graft for scheduled durations of 10 days, 1 month, 3 months and 6 months. Proper deployment of the stent-grafts was achieved without difficulty. All 29 animals survived and the devices were all patent at sacrifice. No device defects or migrations were observed and the stent-grafts proved to be efficient in this setting to exclude the aneurysm. Analyses of the explanted devices (gross observations, RX, CT scan, IVUS, angioscopy) confirmed the stability of this modular stent-graft. Further on-going clinical investigations are warranted to validate this concept before this stent-graft becomes commercially available without any restriction.     

Effects of Stent Structure on Stent Flexibility Measurements

Adequate delivery and placement of intracoronary artery stents is dependent on various properties of the stent itself, including flexibility and high-radial strength. Although these properties can be assessed via determination of the bending stiffness and radial stiffness of a stent, the mesh structure of the stent does not lend easily to such measurements. The goal of the present study was to determine an optimal method for determining stent bending stiffness. The four-points bending test was used to evaluate stent flexibility, and the finite element method (FEM) was employed to assess the effect of stent structure on flexibility in stents with differing link structures. The four-points bending test yielded the following bending stiffness values: 85.28 N mm² for the stent with an S-shaped link; 41.67 N mm² for the stent with an N-shaped link; 78.79 N mm² for the stent with a modified W-shaped link; and 188.67 N mm² for the stent with a W-shaped link. The stent with the point symmetric link configuration (S-, N- and modified W-shaped link) had high flexibility. FEM analysis revealed that low flexibility resulted from interference between the struts at the compressive side. Further, the flexibility predicted from FEM analysis correlated with bending stiffness of the stents. We conclude that use of the four-points bending test yields information that is critical for the design of flexible stents.     

三叉形股骨膨胀式空心加压螺钉的研制及生物力学分析*

背景：传统治疗股骨颈骨折的内固定器械在骨-螺钉界面握持力不足或术后承载负荷过大时,可造成螺钉的松动或拔出,内固定失效率较高。 目的：研制三叉形股骨膨胀式空心加压螺钉,并分析其生物力学性能。 方法：根据股骨颈骨折的特殊生物力学特性研制的三叉形股骨膨胀式空心加压螺钉,由中空主钉和可拧入主钉内孔道的内栓部分组成,通过内栓旋入后对主钉前部的挤压产生膨胀加压作用。以传统AO空心加压螺钉作为对照组进行生物力学实验,分别进行轴向压缩实验、三点弯曲实验、最大轴向拔出力实验。 结果与结论：在300 N的轴向外力作用或弯曲外力下,实验组轴向压缩刚度、弯曲刚度高于对照组(P < 0.05),纵向位移及桡度低于对照组(P < 0.05)。实验组最大轴向拔出力高于对照组(P < 0.05)。表明三叉形膨胀式空心加压螺钉固定牢靠,生物力学性能明显优于普通AO空心螺钉,具有较好的抗轴向压缩能力及抗弯曲、抗旋转能力,在抗拔出性方面更具有普通AO空心螺钉所不具备的优势。     

股骨头松质骨力学性质实验研究

目的 研究股骨头松质骨力学性质，为临床提供生物力学参数。方法 对正常国人新鲜尸体股骨头松质骨的拉伸、压缩、扭转、剪切、弯曲、冲击力学性能进行实验研究。结果 得出了股骨头松质骨的拉伸、压缩破坏载荷、强度极限、弹性模量，扭转破坏扭矩、扭转剪切强度极限，弯曲破坏载荷、弯曲强度极限、剪切破坏载荷、剪切强度极限，冲击功、冲击韧性等测试指标的实验结果。结论 股骨头松质骨抗压强度大于抗拉强度，压缩弹性模量大于拉伸弹性模量，扭转强度大于剪切强度，抗弯强度与抗压强度接近。