Flow evaluation of stents in a 180° curved tube

A common therapeutic procedure for treatment of cardiovascular disease is the implantation of stents, in the carotid artery, especially in patients with high risk factors. The procedure is not without risk as clots can be transported into the brain and also re-stenosis occurs in 10-20% of cases. Flow plays a very important role in the success of the implantation. Alterations to flow behavior can lead to clotting and re-stenosis. Slight changes in the flow rate can create velocity fluctuations which are physiologically abnormal. Higher velocity fluctuations and flow separation can lead to shear stresses and recirculation zones, so that platelets aggregate or adhere to the wall. Similar processes might arise just after implantation of stents. We studied flow in four types of stents (a self-X stent, a Wall stent, a covered stent and an improved covered stent) in a silicon rubber model with a 180° bend. We tested the influence of variations in stent design, the direction and mesh of the wires, the in- and outflow, the stretching, surface roughness and the position of the stent, on flow behavior. Of special interest were flow differences between the covered and uncovered stents, the flow resistance, the position of stent in the arterial model and the entrance flow angle.