Press Room - CFD for intra-stent flow analysis

	CFD for intra-stent flow analysis
	N. Benard, D. Coisne, R. Perrault, Laboratoire d’Etudes Aérodynamiques, Université de Poitiers, France

	At the Université de Poitiers, we have recently carried our research on intra-stent flow in arteries. Currently, the common procedure for arterial stenosis reduction is coronary artery stenting (approximately 1,000,000 worldwide interventions yearly). An endovascular stent is a permanent implant, consisting of an expandable stainless tube available in lengths of 7 to 40 mm with an expansion range from 2 mm to 5 mm. Despite many recent advances, in-stent restenosis occurs in approximately 20 % of implantation cases. The intra-stent chronicle restenosis remains an important clinical complication, which can possibly have consequences in irreversible heart ischemia. Currently, the common procedure for arterial stenosis reduction is coronary artery stenting (approximately 1,000,000 worldwide interventions yearly). An endovascular stent is a permanent implant, consisting of an expandable stainless tube available in lengths of 7 to 40 mm with an expansion range from 2 mm to 5 mm. Despite many recent advances, in-stent restenosis occurs in approximately 20 % of implantation cases. The intra-stent chronicle restenosis remains an important clinical complication, which can possibly have consequences in irreversible heart ischemia.


	Fig 1 - Helistent©
	A permanent vascular implant will alter the blood flow hemodynamics by introducing regions of stagnation and recirculating flow, which modifies the wall shear stress distribution. Direct correlation between wall shear stress gradients and biochemical response of the thin mono-layer cell covering the lumen arteries (endothelial cells) is well established. The knowledge of wall shear stress gradients is therefore necessary for stent manufacturers in order to optimize stent design and to try to avoid harmful restenosis. We noted that intra-stent flow studies were rather scarce. The majority of them assume Newtonian behavior for blood’s rheological properties. One of our research topics was to numerically highlight the major differences between Newtonian and non-Newtonian blood properties on this particular geometry. This was carried out in order to estimate the velocity and wall shear stress modifications induced. Our numerical model was based on an entire real stent design (Helistent©, Hexacath©, Rueil-Malmaison, France). The stent diameter expansion was 3.5 mm (mean real artery diameter). The length was 7 mm for a wire height of 0.1 mm [Fig 1]. This prosthesis is placed into a coronary artery approximated in the calculation by a cylindrical domain without wall deformation. The easiest way to perform this type of 3D mesh was starting with a CAD model and generating a trimmed cell mesh using automatic import and meshing facilities available in the pro-STAR package. Local refinement tools provided high quality final mesh with improved velocity mapping near the wall artery. These tools are particularly valuable for our complex geometry, which includes small but significant details and a high scale factor. The entire STAR-CD mesh finally comprised of 2,150,000 trimmed cells [Fig 2]. The results were computed using the parallel processing STAR-HPC on 24 UNIX processors (SGI Origin 3800).