Dynamics and rheology of vesicles in a shear flow under gravity and microgravity

International audienceThe behaviour of a vesicle suspension in a simple shear flow between plates (Couette flow) was investigated experimentally in parabolic flight and sounding rocket experiments by Digital Holographic Microscopy. The lift force which pushes deformable vesicles away from walls was quantitatively investigated and is found to be rather well described by a theoretical model by Olla [1]. At longer shearing times, vesicles reach a steady distribution about the center plane of the shear flow chamber, through a balance between the lift force and shear induced diffusion due to hydrodynamic interactions between vesicles. This steady distribution was investigated in the BIOMICS experiment in the MASER 11 sounding rocket. The results allow an estimation of self-diffusion coefficients in vesicle suspensions and reveal possible segregation phenomena in polydisperse suspensions

Dynamique de vésicules en écoulement

Dynamics of vesicle and red blood cell suspensions in simple shear and microfluidic flows.Dynamique de suspensions de vésicules et de globules rouges en écoulement de cisaillement simple et en microfluidique

Dynamique de vésicules en écoulement

La compréhension de la rhéologie du sang (fluide complexe composé de 50% de plasma et 40% de globules rouges en volume) est d'une grande importance. Pour atteindre cette compréhension, il est nécessaire de comprendre le comportement des globules rouges en écoulement. Nous avons étudié l'écoulement de vésicules lipidiques, qui sont des modèles simples de globules rouges, en possèdent les propriétés mécaniques de base et en reproduisent certains comportements. Notre but premier est de comprendre le comportement de l'objet isolé avant d'étudier les interactions hydrodynamiques entre objets en écoulement et la rhéologie des suspensions L'étude de ve sicules soumises à un écoulement de cisaillement, expérimentale dans un premier temps, a montré un ralentissement du régime de tumbling prédit par le modèle théorique qui fait référence. Ce ralentissement est confirmé par un modèle analytique simple de vésicule rectangulaire. ou il est montré que le ralentissement apparent de la rotation est dû au couplage entre le mouvement de rotation et la déformation de l'objet. L'étude de vésicules en écoulement confiné (ou les dimensions du canal sont comparables à celles des objets en écoulement) a montré une large gamme de forme accessible aux vésicules dont certaines sont identiques à la forme observée pour les globules rouges dans les capillaires sanguins (forme de parachutes). L'influences des différents paramètres de l'écoulement et de l'objet sur la forme adoptée est soulignée. Les tests de résistances ainsi que le matériel développé dans le cadre du projet Biomics (BlOMlmetic and Cellular Systems) sont présentés.Understanding blood rheology and flow (blood is a complex fluid composed of 50% of plasma and 40% of red blood cells, RBC) is a major issue. A first important step is the understanding of the behavior of individual RBC in flow. We studied the flow of a simple model of RBC : giant lipid-vesicles. Vesicles have RBC's basic mechanical properties and reproduce sorne oftheir behaviour in flow. Our purpose is to understand the flow of isolated object then to study hydrodynamical interactions between several flowing objects and last, the rheology of suspensions. We first experimentaly studied the dynamics ofvesicles under shear flow and notice a significant slowing down of the tumbling motion as the shear rate is increased, with respect to the analytical reference mode! which does not include deformability of objects. A simple analytical model ofrectangular vesicles, taking in to account the coupling between rotation an shape was developped. This model qualitatively show the same slowing down of the rotation and strong deformation ofvesicle during tumbling. We also studied confined flows ofvesicles (in tubes with diameters close to vesicles' sizes). We observed a variety ofequilibrium shapes, sorne ofthem similar to RBCs flowing into narrow blood capillaries (bell shape). The influence ofvesicles and flow parameter over the equilibrium shape is studied. We also present different facilities developped in the frame of the ESA Biomics project (BIOMlmetic and Cellular Systems) and results of mechanical tests on vesicles performed in that context.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Dynamique de vésicules sous cisaillement

Giant vesicles are deformable lipid membranes enclosing a fluid, with diameters of several microns. They are useful models for the study of biological flows. Their behaviour under shear flow reveals a complex dynamics involving several regimes: stationary tank-treading motion, periodic fliping or tumbling motion, and periodic vacillating-breathing motion. Our experimental study reveals that the deformability of vesicles strongly influences the dynamics. One noticeable feature is a slowing down of the tumbling motion with respect to the shear rate when the latter increases. A semi-phenomonological model including the deformability of objects helps understand the connection between the slowing down of the tumbling motion and a coupling between rotation and deformation. A new vacillating-breathing motion is also predicted and a complex phase diagram can be established

Digital holographic microscopy with reduced spatial coherence for three-dimensional study of photolipids vesicles in a shear flow under microgravity conditions

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Filter-less submicron hydrodynamic size sorting

International audienceWe propose a simple microfluidic device able to separate submicron particles (critical size ~0.1 µm) from a complex sample with no filter (minimum channel dimension being 5 µm), by hydrodynamic filtration. A model taking into account the actual velocity profile and hydrodynamic resistances enables predicting the chip sorting properties for any geometry. Two design families are studied to obtain (i) small sizes within minutes (low-aspect ratio, two-level chip) and (ii) micron-sized sorting with µL flowrate (3D architecture based on lamination). We obtain quantitative agreement of sorting performances both with experiments and with numerical solving, and determine the limits of the approach. We therefore demonstrate a passive, filter-less sub-micron size sorting with simple, robust, easy to fabricate design

Biomics experiment: Dynamics of a vesicle suspension under shear flow

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Micro-Macro Link in Rheology of Erythrocyte and Vesicle Suspensions

We report on the rheology of dilute suspensions of red blood cells (RBC) and vesicles. The viscosity of RBC suspensions reveals a previously unknown signature: it exhibits a pronounced minimum when the viscosity of the ambient medium is close to the value at which the transition from tank-treading to tumbling occurs. This bifurcation is triggered by varying the viscosity of the ambient fluid. It is found that the intrinsic viscosity of the suspension varies by about a factor of 4 in the explored parameter range. Surprisingly, this significant change of the intrinsic viscosity is revealed even at low hematocrit (5%). We suggest that this finding may be used to detect blood flow disorders linked to pathologies that affect RBC shape and mechanical properties. This opens future perspectives on setting up new diagnostic tools, with great efficiency even at very low hematocrit. Investigations are also performed on giant vesicle suspensions, and compared to RBCs