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Dynamics, global and local rheology of vesicles and red blood cells in microcirculation

Abstract : The rheology and dynamics of red blood cells (RBCs) under confined flows (simple shear and Poiseuille flows), are studied in the Stokes limit. We numerically investigated the rheology of a suspension of RBCs under shear flow in a confined geometry using bounday integral method. We show that the suspension can exhibit both shear-thinning and shear-thickening behavior depending on viscosity contrast between the encapsulated fluid and the suspending one. We provide an appealing interpretation of these behaviors providing a link between microdynamics and global rheology. In the second study, we found that, by increasing the internal viscosity of the suspended entity, the final position can be off-centered, a solution that may either coexist (saddle node bifurcation) or not (pitchfork bifurcation) with the centered solution. These results are somewhat surprising given the general belief that flexible particles tend to migrate away from solid boundaries in shear flow. This novel scenario strongly affects rheological properties of dilute as well as concentrated RBC suspensions.In the last part of this thesis, we focused on the local rheology of RBC suspension. A universal law is discovered: the local viscosity and the relation between stress and strain rate can be well described as a function of the local concentration only, independently of the channel's width within which the suspension flow takes place or the global concentration of the suspension.
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Abdessamad Nait Ouhra. Dynamics, global and local rheology of vesicles and red blood cells in microcirculation. Biological Physics [physics.bio-ph]. Université Grenoble Alpes, 2019. English. ⟨NNT : 2019GREAY069⟩. ⟨tel-02934497v2⟩

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