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Blood flow in biomimetics microchanels

Abstract : Endothelial cells are the cells lining the inner surface of every blood vessel. Acting as a selective barrier for circulating cells and molecules, endothelial cells are directly exposed to blood flow. Such flow generates viscous friction at their surface, which induces morphological changes and is involved in the maintaining of endothelial function. Endothelial cells are able to sense blood flow thanks to mechanosensors located at their surface. These mechanosensors have been identified recently, and have been shown to be part of a polymer coating covering the surface of the cells. This gel like matrix of polymers is called the endothelial surface layer, or glycocalyx, and is of major importance for the regulation of endothelial function. Grouped under the name of endothelial function are the passive or active response of endothelial cells that maintain vascular health. The glycocalyx mechanosensing properties allow the endothelium to regulated vascular tone, its composition allow the recruitment of immune cell in case of infection or injuries and finally its implication in permeability to fluid and small molecule has been recently brought to light. In physiological condition, the endothelium adopts a particular morphology called the atheroprotective phenotype, which is a sign of a proper endothelial function.In this work, we focus on the phenotypic modification brought by perturbations of the environment of endothelial cells. To do so, we use biomimetic microfluidic devices allowing for the culture of confined endothelial cells submitted to constant hydrodynamic shear stress. Such devices allow for the observation of living or fixed endothelial cells by conventional confocal microscopy. The system is a circuit where the cell culture medium flows through a network of microchannel thanks to a syringe pump allowing an easy control of the biochemical composition of the fluid that perfuse the circuit. We find that under a physiological level of shear stress, cells display long actin stress fibers oriented parallel to the flow direction, a signature of the atheroprotective phenotype. We observe that a decrease in shear stress induces a reorganization of the actin cytoskeleton, with stress fibers being disassembled or randomly reoriented and actin being recruited at the cells’ periphery. In a second set of experiments, we challenge shear-adapted endothelial cells with a diabete-mimicking high glucose concentration, and observe that the F-actin cytoskeleton loses its flow-oriented character. Finally our system was tested for the detection of endothelial permeability. We provide of proof-of-concept by challenging cells with bradykinin, known to induce vascular leakage, and show that we are indeed able to measure an increased permeability of the endothelium cultured under constant shear stress.In conclusion, we have developed an in vitro model system suitable for the study of endothelial function and observation of phenotypic modification via microscopic observation. Our work thus brings insights into the cell response to a loss of mechanical stimulation, and to an increase in the concentration of a metabolite or a permeabilization factor. Such a biomimetic system opens routes for future studies of the endothelial function in which the combined action of mechanical and biochemical stimuli can be deciphered.
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Submitted on : Tuesday, September 29, 2020 - 10:18:08 AM
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Mehdi Inglebert. Blood flow in biomimetics microchanels. Biomechanics [physics.med-ph]. Université Grenoble Alpes [2020-..], 2020. English. ⟨NNT : 2020GRALY009⟩. ⟨tel-02951960⟩

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