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Cartographie des contraintes mécaniques in situ dans les tissus vivants

Abstract : Measuring the mechanical stresses in a living tissue is critical to link the development with the spatial and temporal distribution of forces. A quantitative study about the impact of mechanical effects on morphogenesis requires a precise knowledge of mechanical stresses, from the subcellular scale to the tissue scale.In this work, I describe an original method enabling for a direct measurement of the stress distribution within a living tissue. The technique consists in using micro-beads (30 ¹mof diameter, similar to a cell size), made of a soft elastic PDMS (Young’s modulus ' 1500 Pa, similar to a cell rigidity), embedded in the tissue, as micrometric sensors of local stresses. An efficient fluorescent labelling of the PDMS has been developed in order to image the captors in 3D in the tissues. Then, through an active contour method, the captor border is reconstructed and fitted with an ellipsoid. Knowing the mechanical properties of the elastic gel, the shear stress tensor can be directly retrieved from the captor deformations.A first calibration of the bulk gel elastic properties has been performed with a classical rheometer. Another independent calibration has been performed in situ in cell aggregates. Both calibrations have yielded similar results and enable for absolute measurements of the shear stress without requiring any mechanical model for the tissue. The captors have been used for both in vitro and in vivo studies.The in vitro study in cell aggregates has enabled to map, at successive times, the shear stress within the aggregate. These results highlighted preferential radial and orthoradial orientations of the shear stress main directions. Besides, one observed a variation of its norm along the aggregate’s radius.An exploratory study in vivo in the zebra fish embryo has also enabled to map the shear stress developed into the pre-chordal plate during epiboly.Both these results permit to conclude on the efficiency of the developed.
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  • HAL Id : tel-03377205, version 1

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Alexandre Souchaud. Cartographie des contraintes mécaniques in situ dans les tissus vivants. Biophysique [physics.bio-ph]. Université de Paris, 2020. Français. ⟨NNT : 2020UNIP7213⟩. ⟨tel-03377205⟩

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