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Medical devices and stents

a. Developing Pulsatile Flow in a Deployed Coronary Stent

               Interventional techniques like balloon angioplasty with and without stent placement are used to treat arterial stenosis.  American Heart Association statistics show serious complications in 1-2% of cases following Percutaneous Transluminal Coronary Angioplasty (PTCA).  In contrast, after 6 months following procedure, 30-40% of patients develop restenosis.  Stent implantation improves the arterial blood flow by redistributing the plaque.  A major consequence of stent implantation is restenosis which occurs due to neointimal formation around the deployed stent. Recent evidence suggests that there are several factors such as geometry and size of vessel, and stent design that alters hemodynamic parameters, including local wall shear stress distributions, which influence the progression of restenosis. The present three-dimensional analysis of pulsatile flow in a deployed coronary stent (Figure 1) evaluates the effect of entrance (developing) flow (deve and compares with that of a developed flow. The study quantifies hemodynamic parameters and illustrates the changes in local wall shear stress distributions and their impact on restenosis.


Recirculation zones inside the stent

Figure 1. Mesh Plot of Coronary Artery with Deployed Palmaz Stent

Lower magnitude of wall shear stress exists between adjacent struts while negative shear stress is observed at the immediate downstream of strut intersection, showing recirculation. For developing flow, the wall shear stress near the entrance is nearly twice that of developed flow. The results indicate that the immediate downstream of each strut intersection may be prone to restenosis.

b. Drag Forces on Stent-Grafts

        Abdominal aortic aneurysm (AAA) is the abnormal enlargement of the abdominal aorta. If left untreated, an AAA continues to expand until it ruptures. The rupture of an AAA can lead to severe internal bleeding. In the past open repair was the only available treatment which results in traumatic and stressful experience. In the recent years an alternative procedure has been developed where the stent-graft is introduced, via iliac vessels into the AAA site. If placed correctly, blood will flow through the stent-graft and relieve the stress on the AAA walls, which eventually heals in the due course of time.

        In this Lab, computational fluid (blood)-structure (arterial wall) interaction technique for compliant arteries and grafts is used to investigate the pulsatile displacement forces on a stent-graft within an artery. This allows the determination of displacement forces translate into motion of the stent-graft. The velocity from the particle image velocimeter and pressure data can be used as the input boundary conditions for the blood flow-arterial wall computation. The forces from the computation are then compared with the experimental forces as recorded in-vitro model. Several different variations of stent-graft geometries are being studied. This research has being conducted in collaboration with Cleveland clinic foundation and Case Western Reserve University.

by zopeown last modified 2016-08-04 22:35