Microhemorheology

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The long-term goal of this research program is to fulfill a role in the international efforts to develop a precise model of microscopic blood flow. It is essential to describe blood flow in both physiological and diagnostic settings. Blood is a very interesting fluid that must be better understood to serve many medical applications: understanding physiology, pathology as well as understanding how blood flows in medical devices. The blood at the microscale cannot be considered as liquid flow, but rather as a collection of particles: the red blood cells (RBCs). The RBCs represents approximately half of the volume of the blood and the rest of the volume of the blood is occupied by plasma. Blood is in the family of suspensions particularly complex: it is a dense suspension of particles that are highly deformable and interact with each other, for example, they can aggregate. We are interested in the rheology of blood because this is the foundation of its mechanics: it is the link between force and displacements. Great results are dating back to the 1970s that show that blood is a shear-thinning fluid i.e. its apparent viscosity decreases when shear rate increases. However, this overall description cannot predict the blood behavior at the microscale because in this circumstance the local viscosity depends on many other factors such as local shear, cell density or cells interaction with each other or with the walls. Besides this overall model cannot be used to understood or predict local transfers of gas, nutriment or drugs. It has been shown that the local density of red blood cells (or hematocrit) is inconstant in the flow, for example there are areas of the flow where there is almost no red blood cell including close to the walls and areas of high concentration especially in the center of the vessel or at the bifurcations. The interactions of the cells and the strong heterogeneities, although already observed in the '70s, have never been included in the rheological modeling of the blood. Recently, great progress has been made in the field of suspension rheology, which highlights the importance of the local particle density. Regarding blood, it is time to couple the rheological measurements with the characterization of local microstructures. Relying on world-class highly-specific equipment, along with original experimental procedures developed in our laboratory and benefiting of strong international collaborations, our goal is to study cellular transport in the microcirculation focusing on the characterization of blood flow in relation to microstructure. In particular, we aim to study the collective dynamics of red blood cells in confined flows and networks, for healthy and model of pathological cells.