Active contraction in biological fiber networks

Abstract : Large-scale force generation is essential for biological functionssuch as cell motility, embryonic development, wound healing and musclecontraction. In these processes, forces generated at the molecularlevel by motor proteins are transmitted by disordered fiber networks,resulting in large-scale active stresses. While fiber networks arewell characterized macroscopically, this stress generation bymicroscopic active units is not well understood. In this Thesis, Ipresent a comprehensive theoretical and numerical study of forcetransmission in elastic fiber networks. I show that the linear,small-force response of the networks is remarkably simple, as themacroscopic active stress depends only on the geometry of theforce-exerting unit. In contrast, as non-linear buckling occurs aroundthese units, local active forces are rectified towards isotropiccontraction, making the local geometry of force exertion irrelevant.This emergent contractility is amplified by non-linear forcetransmission through the network. This stress amplification isreinforced by the networks' disordered nature, but saturates for highdensities of active units. Our predictions are quantitativelyconsistent with experiments on reconstituted tissues and actomyosinnetworks, and that they shed light on the role of the networkmicrostructure in shaping active stresses in cells and tissue.
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Biological Physics [physics.bio-ph]. Université Paris-Saclay, 2016. English. 〈NNT : 2016SACLS154〉
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Pierre Ronceray. Active contraction in biological fiber networks. Biological Physics [physics.bio-ph]. Université Paris-Saclay, 2016. English. 〈NNT : 2016SACLS154〉. 〈tel-01359592〉

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