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X-WR-CALNAME:Laboratoire de physique des Solides
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DTSTART;TZID=Europe/Paris:20230331T110000
DTEND;TZID=Europe/Paris:20230331T120000
DTSTAMP:20230118T083400
UID:MEC-18a010d2a9813e91907ce88cd9143fdf@lps.u-psud.fr
CREATED:20230118
LAST-MODIFIED:20230118
PRIORITY:5
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SUMMARY:Alfredo Sciortino – From nematic defects to polar order: polar flow of gliding filaments steered by nematic defects
DESCRIPTION:PostDoc at CytoMorphoLab, CEA Grenoble / Hopital\nSaint-Louis Paris\nMuch like traditional passive materials, active systems can be\naffected by the presence of imperfections in their microscopic order,\ncalled defects, that influence their macroscopic properties. This\nsuggests the possibility to steer collective patterns by introducing\nand controlling defects in an active system. For instance, nematic\nmaterials, composed of aligned, elongated building blocks, can contain\ndefects in the local order (nematic defects) that induce long-range\ndistortions and that have also been shown to play a role in a myriad\nof active biological systems. While this kind of defects is mostly\nassociated with systems having nematic symmetry, here we show that\ntheir presence can also lead to the formation of active polar\npatterns. By using an experimental setup in which cytoskeletal\nfilaments propelled by molecular motors actively glide on a fluid\nlipid membrane, we show that the alignment between individual\nfilaments resulting from these conditions leads to the formation of\ncollective polar structures, despite a microscopic nematic symmetry.\nWe also find that the transient formation of  1/2 defects plays a\npivotal role in sorting the filaments’ polarity [1]. We can then take\nadvantage of our ability to control nematic material and their defects\nto shape the morphology of patterns. First, we extend the system to\nfilaments gliding inside a giant vesicle [2], i.e. in a spherical\ngeometry, and find that confinement enhances the global polarity,\nleading the formation of highly polar vortices and bands. However, at\nthe same time, topological constraints on the alignment of filaments\ndue to the spherical geometry can affect and hinder their ability to\nassemble effectively, leading to “topologically jammed” states. We\nfinally study the influence of passive defects on active filaments by\nhaving microtubules actively glide inside a passive nematic material\ncomposed of actin filaments [3]. Again, we observe the formation of\npolar patterns whose emergence is now a direct effect of the presence\nof spontaneously-forming passive defects, that rectify the active\nmotion and break the orientational symmetry, leading to globally polar\nflow despite a nematic environment. These results suggest strategies\nto control active patterns by tuning defects in the environment, for\nexample by changing its topology or by controlling the position of\nindividual point defects.\n[1] Sciortino, Bausch, PNAS, 2021\n[2] Sciortino and Hsu, et al., Nat Commun, 2022\n[3] Sciortino et al., Nat Mater, (in print)\n
URL:https://www.lps.u-psud.fr/en/events/alfredo-sciortino-from-nematic-defects-to-polar-order-polar-flow-of-gliding-filaments-steered-by-nematic-defects/
CATEGORIES:Soft matter and Phys-Bio seminar
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