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Topological structure and dynamics of three-dimensional active nematics

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Science  06 Mar 2020:
Vol. 367, Issue 6482, pp. 1120-1124
DOI: 10.1126/science.aaz4547

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Watching defects flow and grow

Orientational topological defects in liquid crystals, known as disclinations, have been visualized in polymeric materials or through mesoscale simulations of the local orientation of the molecules. Duclos et al. report the experimental visualization of the structure and dynamics of disclination loops in active, three-dimensional nematics using light-sheet microscopy to watch the motion of nematic molecules driven by the motion of microtubule bundles (see the Perspective by Bartolo). This setup makes it possible to directly watch the nucleation, deformation, recombination, and collapse of spatially extended topological defects in three dimensions.

Science, this issue p. 1120; see also p. 1075

Abstract

Topological structures are effective descriptors of the nonequilibrium dynamics of diverse many-body systems. For example, motile, point-like topological defects capture the salient features of two-dimensional active liquid crystals composed of energy-consuming anisotropic units. We dispersed force-generating microtubule bundles in a passive colloidal liquid crystal to form a three-dimensional active nematic. Light-sheet microscopy revealed the temporal evolution of the millimeter-scale structure of these active nematics with single-bundle resolution. The primary topological excitations are extended, charge-neutral disclination loops that undergo complex dynamics and recombination events. Our work suggests a framework for analyzing the nonequilibrium dynamics of bulk anisotropic systems as diverse as driven complex fluids, active metamaterials, biological tissues, and collections of robots or organisms.

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