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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:20230118T083300
UID:MEC-9fe4e15b3924b1a78221734d0c063ae7@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 / HopitalSaint-Louis Paris\nMuch like traditional passive materials, active systems can beaffected by the presence of imperfections in their microscopic order,called defects, that influence their macroscopic properties. Thissuggests the possibility to steer collective patterns by introducingand controlling defects in an active system. For instance, nematicmaterials, composed of aligned, elongated building blocks, can containdefects in the local order (nematic defects) that induce long-rangedistortions and that have also been shown to play a role in a myriadof active biological systems. While this kind of defects is mostlyassociated with systems having nematic symmetry, here we show thattheir presence can also lead to the formation of active polarpatterns. By using an experimental setup in which cytoskeletalfilaments propelled by molecular motors actively glide on a fluidlipid membrane, we show that the alignment between individualfilaments resulting from these conditions leads to the formation ofcollective polar structures, despite a microscopic nematic symmetry.We also find that the transient formation of  1/2 defects plays apivotal role in sorting the filaments’ polarity [1]. We can then takeadvantage of our ability to control nematic material and their defectsto shape the morphology of patterns. First, we extend the system tofilaments gliding inside a giant vesicle [2], i.e. in a sphericalgeometry, and find that confinement enhances the global polarity,leading the formation of highly polar vortices and bands. However, atthe same time, topological constraints on the alignment of filamentsdue to the spherical geometry can affect and hinder their ability toassemble effectively, leading to “topologically jammed” states. Wefinally study the influence of passive defects on active filaments byhaving microtubules actively glide inside a passive nematic materialcomposed of actin filaments [3]. Again, we observe the formation ofpolar patterns whose emergence is now a direct effect of the presenceof spontaneously-forming passive defects, that rectify the activemotion and break the orientational symmetry, leading to globally polarflow despite a nematic environment. These results suggest strategiesto control active patterns by tuning defects in the environment, forexample by changing its topology or by controlling the position ofindividual point defects.\n[1] Sciortino, Bausch, PNAS, 2021[2] Sciortino and Hsu, et al., Nat Commun, 2022[3] Sciortino et al., Nat Mater, (in print)\n
URL:https://www.lps.u-psud.fr/events/alfredo-sciortino-from-nematic-defects-to-polar-order-polar-flow-of-gliding-filaments-steered-by-nematic-defects-2/
CATEGORIES:Séminaire Matière Molle Phys-Bio
LOCATION:Bât 510, Orsay (91)
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