Computational investigation of wall shear stress- driven in-stent restenosis Gianluca De Santis Supervisors: Verhegghe B., Verdonck P. I. INTRODUCTION When an artery occludes the insufficient blood supply to downstream districts may lead to myocardial infarction, stroke or necrosis. To reopen the artery a stent is inserted through a catheter into the stenosed location. After some weeks from the intervention the artery can re-occlude again as result of a patho-physiological remodelling process called in-stent restenosis. It is documented that restenosis rate ranges from 20 % to 30 % for bare metal stents, therefore requiring additional surgical interventions [1]. The occurrence of restenosis is partly related to alteration of the flow into the artery produced by the presence of the stent and detected by the endothelial cells. In this study we try to understand the relation between stent design, endothelial Wall Shear Stress and restenosis. Fig. 1. The axisymmetric model of stented artery. The quadrilateral mesh is refined near the wall in order to avoid underestimation of the WSS. The different regions of the boundary are shown. II. METHODS PyFormex is an open source software under development at Ghent University (http://pyFormex.berlios.de ) dedicated to pre- and post-processing both in FEA and CFD problems. An axisymmetric geometry of stented arterial lumen (a lumen with 2 strut sections) has been designed in PyFormex and meshed with quadrilateral elements (Fig.1). Other vessel/strut dimensions have been also tested by using the parametric design capabilities of the python-based PyFormex scripts. The evolution of the restenosis as local reduction of the lumen has been simulated following the scheme in Fig.2. The quadrilateral mesh (coordinates of the nodes and connectivity) was exported from PyFormex into a commercial software for CFD analysis (Fluent). A journal file set the fluid properties to approximate blood as Newtonian fluid (density 1060 kg/m 3 and viscosity 3.5 mPa•s) and defined the boundary conditions: parabolic velocity profile at the inlet (defined through a user defined function), zero pressure at the outlet and no-slip condition on arterial wall and stent surface. An axisymmetric steady state analysis was performed and WSS values at endothelium nodes were recorded and used to alter the previous lumen geometry: all the nodes experiencing a WSS <0.5 Pa where displaced towords the lumen axis. When no nodes had WSS in the atherogenic range the end of the loop was reached so that the geometry represented the lumen configuration at the end of the restenotic process [2].