摘要
镁合金具有良好的生物相容性和可降解性,已被用于作为可降解冠脉支架材料进行研究,可降解镁合金支架有望成为新一代心血管支架。然而,与不锈钢材料相比,镁合金作为支架材料,抗拉强度低、屈服强度低、断后延伸率低、塑性变形能力差,使得镁合金支架存在径向回弹率大,径向支撑力低以及应力应变不均匀(应力集中)等问题。因而本文针对镁合金材料的力学性能特点,对镁合金支架结构进行优化设计,以弥补材料本身性能的不足。本文以有限元模拟为研究方法,采用AZ31镁合金为支架材料,对课题组自行开发的镁合金支架结构进行优化研究。通过改变支架结构单元的长度、丝宽、圆弧半径等结构参数,同时利用系统分析中的敏感性分析方法,对上述不同结构参数组合下支架的径向回弹率、径向支撑力以及应力应变分布进行参数敏感性研究。结果表明,参数是决定结构性能的重要因素,不同支架性能受不同结构参数影响的敏感性不同,通过模拟分析,对于径向回弹率而言,影响其性能的主要因素按影响力大小为长度变量、丝宽变量以及半径变量以及壁厚;对于支撑力而言,影响其性能的主要因素按影响力大小依次为长度变量、丝宽变量以及壁厚变量;对于最大主应变而言影响其性能的主要因素按影响力大小依次为长度变量、丝宽变量以及半径变量。在这些因素中,以长度因素和丝宽因素为甚,分别对支架的三个性能能产生较大影响。而改变半径对径向回弹率以及最大主应变的影响较大,对支撑力的影响较小;改变壁厚能够影响支架的支撑力性能和径向回弹率性能,对最大主应变的影响较小。这些变量对各自性能的影响力大小,对支架结构设计尤其是镁合金支架结构的设计尤为重要,可以在支架结构设计中作为参考。
根据课题组支架的实际实验中发现,支架在变形过程中存在着变形不均匀性,主要是“之”字形支撑环在撑开时“V”形梁张的开角度存在差异。根据这种情况,我们对完整的支架和折叠球囊装配在一起的组合系统进行动态模拟分析,通过改变支架的结构、球囊的折翼的变化以及球囊的厚度的厚薄等变量,分别模拟支架在不同情况下的变形行为从模拟的结果看,球囊折翼的数量、支架与球囊的配合度、连接筋数量以及球囊自身厚度等情况对支架的扩张不均匀性有着重要的影响。具体来讲,支架与球囊的对称性越接近,支架的扩张越均匀,在实际可行的情况下,应采用球囊的折翼数量应与支架轴向最简单元的重复个数相同;球囊的厚度越小,支架的扩张越均匀,因此在选择球囊时,应尽量选择薄壁球囊进行扩张;同时,支架的连接筋分布越对称,连接筋越多,支架扩张越均匀,因此在支架连接筋的分布和数量选择上,应使连接筋的分布应尽量均匀,且不能过渡减少连接筋的数量,这些举措都有利于改善支架的对称不均匀性。
Magnesium alloys has recently been studied as biodegradable coronary stent material for its good biocompatibility and biodegradability. However, compared with stainless steel, magnesium alloy as the coronary stent material has lower tensile strength, yield strength, elongation and poorer plastic deformation ability, which cause magnesium alloy stent to emerge higher radial recoil rate, lower radial force and non-uniform stress and strain (stress concentration) and other poorer mechanical properties. In consideration of the premises, this paper studied about optimization design of magnesium alloy stent structure in order to cover the shortage of material property itself. The group self-developed AZ31 magnesium alloy stent has been studied to optimizing structure using the finite element method. By means of changing length, width, radial and other structure parameters of coronary stent unit, the sensitivity factor of stent radial resilience, radial force and the stress and strain distribution was researched by sensitivity analysis method.. The results show that the structure parameters is an important factor of stent properties. The different stent performance were impacted by different sensitivity to different structural parameters. Through simulation analysis, the radial recoil rate, radial force and stress and strain distribution is concerned. For the radial recoil rate, the main factors affecting its performance is variable length, wire width, radius and wall thickness, according to the order of the influence. For the radial force, the main factors affecting its performance is variable length, wire width and wall thickness. For the stress and strain distribution, the main factors affecting its performance is variable length, wire width and radius. In all of these factors, respectively, the significant impact on three performance factors are the length and wire width variable. Changing the radius of stent units can cause a great impact on both radial recoil and maximum principle strain, but less impact on the radial force; Changing the wall thickness of stent units can affect the radial force and radial recoil, but less impact on the maximum principle strain. The influence of structure parameter is important to designing the coronary stent.
According to the actual experimental on self-developed stent, it was found that stent structure is non-uniform after the deformation process, mainly due to "V"-shaped beam opening angle is different while the support ring-shaped is unfolded. This is the case, the stent assembly with balloon was were dynamically simulated by changing the structure of the stent, balloon wings and balloon thickness under different circumstances. From the simulation results, the number of balloon wings, the compatibility of stent and balloon, the number of connected muscle and the balloon itself thickness were highly impact on non-uniformity of stent expansion.Specifically, the symmetry of Stent and balloon closer, more uniform stent expansion, in practical cases, the number of balloon wings and the number of stent easiest repeat element of the axial should be the same; more thin balloon thickness, more uniform stent expansion, and in the choice of balloon, the thin-wall balloon should be selected to expand; in the meantime, more symmetrical connected muscle structure and more the number of connected muscle, more uniform stent expansion, in the choice of reinforcement bracket, the number of connect tendons can not to reduce in excess, connect tendons should be symmetrically distributed. Therefore, these initiatives are conducive to improved stent symmetry.
引文
[1]顾东风.心血管疾病预防的现状和展望[J].中国预防医学杂志,2003,37(2):75-76.
[2]周江,丁彦.冠心病[M].长春:吉林科学出版社,2002.
[3]Gruntzig A, Schneider H. The percutaneous dilatation of chronic coronary stenoses-experiments and morphology[J]. Schweizerische medizinische Wochen schrift,1977,107:1588-1592.
[4]Forssmann W. Die Sondierung des rechten Herzens[J]. Journal of Melecular Medicine,1929,8(45):2085-2087.
[5]Cournand A. Cardiac catheterization:development of the technique, its contribu-tions to experimental medicine, and its initial applications in man[J]. Acta Medica Scandinavica. Supplementum,1975,579:3-32.
[6]Seldinger S I. Catheter replacement of the needle in percutaneous arteriography: a new technique[J]. Acta Radiologica,1953,39(5):368-376.
[7]Dotter C T, Judkins M P. Transluminal treatment of arteriosclerotic obstruction: description of a new technique and preliminary report of its application[J], Circulation,1964,30:654-670.
[8]Gruentzig A. Transluminal dilatation of coronary-artery stenosis[J]. Lancet, 1978,1:263-269.
[9]Sigwart U, Puel J, Mirkovitch V et al. Intravascular stents to prevent occlusion and restenosis after transluminal angioplasty [J]. New England Journal of Medicaine,1987,316:701-706.
[10]Fischmann D L, Leon M B, Baim D S et al. A randomized comparison of coronary stent placement and balloon angioplasty in the treatment of coronary artery disease[J]. New England Journal of Medicine,1994,331:496-501.
[11]Serruys P W, De Jagere P, Kiemenij F et al. A comparison of balloon expandable stent implantation with balloon angioplasty in patients with coronary artery disease[J]. New England Journal of Medicine,1994,331:489-495.
[12]Fishman D L, Savage M P, Penn I et al. High pressure inflation with conjunction with ticlopidine and aspirin follow coronary stent placement:Result of the STRESS 3 trial[J]. Journal of the American College of Cardiology,1997,29: 108A(abstract).
[13]Williams D O, Holubkov R, Yeh W et al. Percutaneous Coronary Intervention in the Current Era Compared With 1985-1986:The National Heart, Lung, and Blood Institute Registries[J]. Circulation,2000,102(24):2945-2951.
[14]Post M J, deSmet B, vanderHelm Y et al. Arterial remodeling after balloon angioplasty or stenting in an atherosclerotic experimental model [J]. Circulation, 1997,96(3):996-1003.
[15]徐国辰,张宁仔,杜日映.血管支架的类别及其特性[J].心血管病学进展,1995,16(2):5-67.
[16]周永恒,廖健宏,蒙红云.血管支架分类与技术进展[J].华南师范大学学报(自然科学版),2005,2(2):136-142.
[17]KATHURIA Y P. An overview on laser micro-fabrication of biocompatible metallic stent for medical therapy[J]. Proceeding of SPIE,2004,5399:234-244.
[18]赵振心,刘道志,张一.血管支架材料及其临床研究进展[J].中国医疗器材杂志,2005,29(8):391-395.
[19]赵连城.合金的形状记忆效应与超弹性[M].北京:国防工业出版社,2002.
[20]O. Cisse, et al. Effect of surface treatment of Ni-Ti alloy on its corrosion behavior in Hanks'solution[J]. J.Biomed. Mater. Res.,2002,61:339-345.
[21]唐剑飞,范存义,曾炳芳.生物可降解性血管内支架的研究进展[J].国外医学·骨科学分册,2002,23(4):233-235.
[22]James E Moore J R, Joao S Soares, Kumbakonam R Rajagopal. Biodegradable Stents:Biomechanical Modeling Challenge and Opportunities[J], adiovascular Engineering and Technology,2010,1(1):52-65.
[23]马长生,盖鲁粤,张奎俊等.介入心脏病学[M].北京:人民卫生出版社,1998.
[24]林清安.完全精通Pro/Engineer野火4.0中文版综合教程[M].北京:电子工业出版社,2009.
[25]王汉元,李丽娟,李银萍.有限元法基础与程序设计[M].广州:华南理工大学出版社,2001.
[26]高耀东,刘学杰,周可璋.ANSYS机械工程应用精华30例[M].电子工业出版社,2009.
[27]李裕春,时党勇,赵远.ANSYS11.0/LS-DYNA基础理论与工程实践[M].中国水利水电出版社,2007.
[28]Whitcher F D. Simulation of in vivo loading conditions of nitinol vascular stent structures [J]. Computers and Structures,1997,64:1005-1011.
[29]Brauer H, Stolpmann J, Hallmann H et al. Measurement and numerical simulation of the dilatation behaviour of coronary stents[J]. Materical wissens chaft und Werkstofftechnik,1999,30(12):876-885.
[30]Dumoulin C, Cochelin B. Mechanical behaviour modeling of balloon expand-able stents[J]. Journal of Biomechanics,2000,33:1461-1470.
[31]Etave F, Finet G, Boivin M et al. Mechanical properties of coronary stents determined by using finite element analysis[J]. Journal of Biomechanics,2001, 34:1065-1075.
[32]Migliavacca F, Petrini L, Colombo M et al. Mechanical behavior of coronary stents investigated through the finite element method[J]. Journal of Bio-mechanics,2002,35:803-811.
[33]Chua S N D, MacDonald B J, Hashmi M S J. Finite element simulation if stent and balloon interaction[J]. Journal of Materials Processing Technology,2003, 143:591-597.
[34]Migliavacca F, Petrini L, Valeria M et al. A predictive study of mechanical behaviour of coronary stents by computer modeling[J]. Medical Engineering and Physics,2005,27:13-18.
[35]倪中华,王跃轩,程洁.球囊扩张式冠脉支架扩张变形机理数值模拟方法[J].机械工程学报,2008,44(1):102-108.
[36]王伟强.冠状动脉支架力学行为有限元分析及其结构优化[D].大连理工大学博士学位论文,2005-7.
[37]王伟强,杨大智,齐民.冠状动脉支架膨胀行为的有限元分析[J].生物医学工程学杂志,2006,23(6):1258-1262.
[38]张庆宝,王伟强,齐民,梁栋科,杨大智.冠脉支架紧缩反弹行为有限元分析[J].北京生物医学工程,2006,25(4):366-370.
[39]W. Wu, L. Peteini, D. Gasaldi, et al. Finite Element Shape Optimization for Biodegradable Magnesium Alloy Stents[J]. Annals of Biomedical Engineering, 2010,38(9):2829-2840.
[40]W. Wu, D. Z. Yang, Y. Y. Huang, M. Qi, and W. Q. Wang. Topology optimization of a novel stent platform with drug reservoirs [J]. Med. Eng, Phys. 2008,30:1177-1185.
[41]S. N. David Chua, B. J. MacDonald, M. S. J. Hashmi. Finite element simulation of slotted tube(stent) with the presence of plaque and artery by balloon expansion[J]. Journal of Materials Processing Technology,2004,155:1772-1779.
[42]S. N. David Chua, B. J. Mac Donald, M. S. J Hashmi. Finite-element simulation of stent expansion[J]. Journal of Materials Processing Technology,2002,120, 335-340.
[43]S. N. David Chua, B. J. MacDonald, M. S. J. Hashmi. Finite element simulation of stent and balloon interaction [J]. Journal of Materials Processing Technology. 2003,143-144,591-597.
[44]Matthieu De Beule, Peter Mortier, Stephane G. Carlier, Benedict Verhegghe, Rudy Van Impe, Pascal, Pascal Van Impe, Pascal Verdonck. Realistic finite element-based stent design:The impact of balloon folding[J]. Journal of Biomechanics.2008,41:383-389.
[45]Dyet JF, Watts WG, Ettles DF, et al. Mechanical properties of metallic stent:how do these properties influence the choice of stent for specific lesions?[J]. Cardiovasc Intervent Radiol,2000,23:47-54.
[46]Barragan P, Rieu R, Garitey V, et al. Elastic Recoil of coronary stents:a comparative analysis[J]. Cathet Cardiovasc Intervent,2000,50(1):112-119.
[47]Rieu R, Barragan P, Masson C et al. Radial force of coronary stents:a comparative analysis[J]. Cathet Cardiovasc Intervent,1999,46(3):380-391.
[48]Belytschlo T, Liu WK, Moran B著,庄茁译.连续体和结构的非线性有限元[M].北京:清华大学出版社,2002.
[49]陈振华.变形镁合金[M].北京:化学工业出版社,2005.
[50]Xia Z, Ju F, Sasaki K. A general finite element analysis method for balloon expandable stents based on repeated unit cell (RUC) model [J]. Finite Elements in Analysis and Design,2007,43(8):649-658.
[51]吴卫.人体血管支架有限元分析与结构优化[D].大连理工大学博士学位论文,2007-7.
[52]颜廷亭.AZ31B镁合金的生物医用表面改性研究[D].南京理工大学博士学位论文,2010-6.
[53]ANSYS基本过程手册[M]. In:Ansys online documentation. ANSYS Inc, Canonsburg, PA, USA.
[54]ANSYS elements reference[M]. In:Ansys online documentation. ANSYS Inc, Canonsburg, PA, USA.
[55]程声通.环境系统分析教程[M].北京:化学工业出版社,2006(5):130-161.
[56]张旭辉,龚晓南,徐日庆.边坡稳定影响因素敏感性的正交法计算分析[J].中国公路学报,2003,16(1):36-39.
[57]龚文慧,王平,陈锋.顺层岩质边坡稳定性的敏感性因素分析[J].岩土力学,2007,28(4):812-816.
[58]Peter Mortier. Computer Modeling of Coronary Bifurcation Stenting[D]. Ghent University PhD thesis,2010.