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Déformation et agrégation sous écoulement de globules rouges et vésicules en microcanaux

Abstract : The investigation of red blood cells (RBCs) dynamics in blood circulation is one of the most innovative and intriguing challenge of science nowadays since erythrocytes are involved in fundamental physiological functions of human body. In particular, RBCs play a key role in microcirculation where narrow dimensions of vessels (comparable to cell size) promote a close contact between cells and capillary walls and, as a consequence, the exchange of oxygen between blood and tissues. It is well established in scientific literature that disorders in RBCs properties and damages of endothelium are the main causes of common vascular diseases, such as thrombosis, diabetes and atherosclerosis. Thus, the full understanding of mechanical and rheological properties of RBCs would allow not only to shed light on the mechanisms leading blood circulation, but also to develop increasingly reliable diagnostic devices. In this thesis, the attention is mainly focused on two topics: RBCs aggregation in microcapillaries and the role of glycocalyx in microcirculation. As regards the first theme, despite the considerable scientific importance, a quantitative analysis of RBCs aggregates formation (clustering) in microvessels is still lacking. In a first phase of the project, experimental investigations in vitro have been performed on RBCs suspensions with hematocrit almost equal to 10% to observe their tendency to aggregate during the flow in glass microtubes (diameter equal to 10 µm). RBCs aggregation has been evaluated as a function of the fixed pressure drop (Δp) and the residence time in microchannels by measuring clusters length and their statistical composition. The main aim of the experiments was to clarify the nature of the force acting on consecutive cells in a cluster: is it a pure hydrodynamic interaction or are other kinds of forces involved too? The experimental results presented in this thesis clearly show that the driving force of the phenomenon is the imposed Δp in the microtubes. The outcomes of these investigations suggest that microfluidics can represent an efficient means to develop clinical and diagnostic tests on healthy and pathological blood.In the second part of the thesis, an experimental campaign was performed on glass capillaries lined with polymer brushes to mimic in vivo conditions in microvascularity. Several scientific papers show that the lumen of vascular vessels is coated by a layer of glycopolymers linked to the endothelial cells. The full understanding of the hydrodynamic role of glycocalyx is essential to elucidate the link between its dysfunctions and vascular diseases. Moreover, it would be helpful to develop innovative clinical tests by microfluidics that could take in account the interactions between “hairy” walls and blood components. Nanometric brushes of poly-hydroxyethylmethacrylate (p-HEMA) have been produced by a grafting-from technique and, after characterization, they have been used to line internal surfaces of silica capillaries with 10 µm diameter. Here, we present the experimental results obtained by measuring velocity profiles in glass channels bearing polymer brushes of different thickness. An increasing flow resistance is observed in hairy channels as a function of brush thickness. The measured velocity decrease is significantly higher than expected from a simply geometrical reduction of the available capillary lumen. Furthermore, the observation of RBCs flow in such brush-coated channels reveals that cells velocity and deformation are closely depending on the presence of the bio-layer on the internal walls of the capillaries.
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Luca Lanotte. Déformation et agrégation sous écoulement de globules rouges et vésicules en microcanaux. Hématologie. Université de Grenoble, 2013. Français. ⟨NNT : 2013GRENY072⟩. ⟨tel-01469764⟩



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