The projects described below are being carried out in collaboration with Dr Olivier Bertrand, a cardiologist from Laval University, Dr Jean-Claude Tardif a cardiologist from the Montreal Heart Institute and Pr Michel Bertrand from the Institut de génie biomédical of École Polytechnique.
Design of a polymer coated stent to control restenosis:
A stent is a mechanical scaffolding device used to maintain the patency of vessel lumen after angioplasty (reopening of obstructed vessels using an intravascular balloon). Recent approaches attemp to use the stent as a mean to deliver drug locally (local drug delivery) to control restenosis (reobstruction of the vessel) using polymer coatings as a carrier for the different drugs. In this work, we investigate the design criteria (strut geometry and dimensionning, coating thickness, polymer properties) to optimize the treatment. More precisely, we propose a numerical model to study the diffusion of the molecule in the vascular wall and in the vessel lumen taking into account the complex geometry of the stent, the chemical and physical properties of the molecule and the blood blow in the vessel.
Development of a LVAD based on a shrouded impeller axial flow pump concept:
A LVAD (Left Ventricular Assist Device) is a mechanical device used to assist the failing hearts in its pumping action. We propose a new design based on a shrouded impeller axial flow pump concept. In this approach, a shroud is fixed to the impeller-hub structure to form a one piece shrouded rotor. This rotor is then inserted in a pump casing in a stator-rotor-stator configuration (one stage configuration). This design confers many advantages as compared to an unshrouded configuration. It eleminates the relative motion of the vanes with the pump casing, it allows to put the permanent magnets in the shroud (providing a better electromagnetic coupling) and it does not require mechanical seals (the gap between the rotor shroud and the pump casing being designed as an hydraulic seal). This LVAD is also designed to fit in the patient heart which provides for easier surgical procedures and less medical problems (bleeding, infections). Actual research are on optimising the shapes of the blood wetted parts in terms of hydraulic efficiencies and minimization of blood trauma.
Development of a numerical model for blood trauma prediction:
Many problems are observed when blood interacting devices are implanted into the cardiovascular system. The most common failure modes include hemolysis (rupture of the red blood cells), thrombosis (platelet activation and clot formation) and mechanical failure (wear, fracture, fatigue). These critical phenomena are highly dependent on the design and its influence of blood flow and material selection of the device. For example, it is now recognized that with mechanical devices hemolysis and platelet activation are mainly caused by exposure of the cells to high shear stress above certain thresholds. In that context, we are developing a new CFD predictive model for hemolysis and thrombosis using the Wurzinger's empirical relations as state equations. This model is in turn used to optimize the design of the different cardiovascular devices morphologies.
Study of the influence of blood flow and wall shear stress on arterial plaque rupture:
It is now recognized that hydromechanical factors (fluid and wall shear stress) can directly affect the evolution of an arterial plaque which may eventually lead to its rupture (an associated infarct). In this project, we are developing a numerical model to simulate the stresses resulting from the combination of the blood flow related stress (fluid mechanics) and the wall stress (solid mechanics) using in-vivo data (as described below).
Development of image processing algorithms for motion analysis and tissue characterization:
Development of image processing algorithms for motion analysis and tissue characterization: In this project, we are developping image processing algorithms to characterize the mechanical properties of vascular tissue using IVUS images (IntraVascular UltraSound). The in-vivo data are used to reconstruct the vessel wall anatomy (including the detailed geometry of the different pools in the plaque). This reconstruction is then used in a solid mechanical modeling to compute the principal stresses. The image data are also processed with an optical flow algorithm to compute an estimate of the apparent tissue displacement. These data are then used to infer on the relative mechanical properties of the vascular wall.