Send Orders for Reprints to reprints@benthamscience.net Current Nanoscience, 2014, 10, 000-000 1 1573-4137/14 $58.00+.00 © 2014 Bentham Science Publishers Hemodynamic Behavior of Coronary Stents in Straight and Curved Arteries Hao-Ming Hsiao a* , Chien-Han Lin a , Ying-Chih Liao b , Hsien-Yeh Chen b and Tzu-Wei Wang c a Department of Mechanical Engineering, National Taiwan University, Taipei, Taiwan; b Department of Chemical Engineering, Na- tional Taiwan University, Taipei, Taiwan; c Department of Materials Science and Engineering, National Tsing-Hua University, Hsinchu, Taiwan Abstract: Stents are miniature medical devices that can be inserted into arteries and expanded during angioplasty to restore blood flow and prevent arterial collapse. They have been the primary treatment for cardiovascular diseases since the 1990s. However, after stenting, potential risks associated with restenosis may occur, and several studies have shown that stent design could be one of the critical factors in this process. Computational modeling has been widely used as an important tool to predict the clinical performance of stents and hemodynamic behavior in stented arteries. In this study, computational fluid dynamics models were developed to investigate the effects of cardiovascular stent design on the wall shear stress distribution in straight and curved coronary arteries. Results showed that the stent design pattern alone did not have a significant impact on stent hemodynamics; however, stenting in curved arteries increased the low shear stress area, the region where wall shear stress is less than 5 dynes/cm 2 , which may lead to a higher restenosis rate. The total surface area of low wall shear stress almost doubled when the angle of artery curvature increased from 0 o to 90 o . The implication is that stent im- plantation in a tortuous artery greatly increases the risk of restenosis. The proposed methodology and findings show that the presence of a stent in straight or curved arteries alters the flow field and wall shear stress distribution within arteries, providing great insight for the fu- ture design optimization and physician practice to help achieve the best possible clinical outcomes. Keywords: Computational fluid dynamics, Coronary Stent, Curved Arteries, Hemodynamics, Restenosis, Wall Shear Stress. 1. INTRODUCTION Atherosclerosis is a syndrome that affects the blood arteries. The accumulation of macrophage white blood cells and low-density lipoproteins such as cholesterol causes a chronic inflammatory response and thickens the arterial wall; therefore, the artery lumen becomes narrow or occlusive. A stent is a miniature medical device used primarily in the treatment of vascular diseases. It is deployed in a stenotic artery during angioplasty to restore blood flow and prevent arterial collapse. Over the past two decades, this field has seen numerous innovations aimed at perfecting the percutaneous management of vascular diseases [1-2]. However, after stenting, neo-intimal hyperplasia and thus restenosis (re-narrowing of the arteries) occur in some patients [3]. The implantation of stents alters the hemodynamics in arteries and also produces vascular injury. Several studies have shown that stent design could be one of the critical factors in this process [4]. Furthermore, clinical results have shown that low wall shear stress or oscillating wall shear stress corresponds to the location of the greatest neo-intimal thickening in stented arteries [5-6]. It has been suggested that shear stress of less than 5 dynes/cm 2 leads to endothelial proliferation of smooth mus- cle cells [7]. Therefore, it is important to understand the relation- ship between stent design and hemodynamic behavior so that the risk of restenosis can be reduced. Computational modeling can be an important tool for improv- ing the mechanical and hemodynamic behavior of a stent and achieve the optimum stent design [8]. Many researchers have ap- plied various computational fluid dynamics (CFD) models to pre- dict the wall shear stress distribution in stented arteries and thus the potential risk of restenosis. Most of the computational models were developed under the assumption that stented arteries were straight [9-10]; however, blood vessels in human bodies are typically curved at various degrees in clinical situations. For instance, coro- nary arteries vary in their degree of curvature in the plane of the myocardial surface. Furthermore, the geometry of coronary arteries *Address correspondence to this author at the Department of Mechanical Engineering, National Taiwan University, Taipei, Taiwan; Tel: 886-2- 33669429; Fax: 886-2-23631755; E-mail: hmhsiao@ntu.edu.tw alters with the contraction and relaxation of the myocardium. Simi- larly, the superficial femoral artery is affected by repeated knee movements involved in squatting and walking, which expose a long implanted stent to large, curved, and cyclic deformations. There- fore, it would be more realistic to develop CFD models based on stented curved arteries rather than straight ones. In order to under- stand the geometrical risk factors involved in coronary artery dis- eases, much research on the flow distribution of curved arteries has been conducted without stents [11-12]. The results of such research demonstrate the skewness of the velocity profile toward the outer wall of the curvature and the flow separation along the inner wall. Furthermore, the extent of flow disturbance is dependent upon the angle of artery curvature. Several studies have also investigated flow patterns through atherosclerotic lesions in coronary arteries [13-14]. However, studies on the induction of hemodynamic distur- bance by stents in curved arteries have been sparse so far [15-16]. Although wall shear stress plays such an important role in the development of restenosis, its relationship with the stent design or artery curvature has yet to be systematically investigated. To date, it is uncertain as to whether specific changes in stent design pattern, in either straight or curved arteries, would result in significant wall shear stress variations or not. In this paper, several CFD models were developed to investigate the effects of cardiovascular stent design on the wall shear stress distribution in both straight and curved arteries. Numerical simulations were performed on four commonly-used stent designs deployed in arteries with varying degrees of curvature (0 o , 15 o , 30 o , 45 o , 60 o , 75 o , and 90 o ) for com- parison. These findings could provide great insights into the hemo- dynamic behavior of stented arteries for coronary and peripheral indications and help optimize future stent design to reduce the risk of restenosis. 2. METHODOLOGY 2.1. Stented Artery Model Computational analysis was divided into two major parts. The first part investigated the effects of stent design pattern, and the second part investigated the effects of artery curvature on the wall