Spontaneous flow created by active topological defects

Abstract

Topological defects are at the root of the large-scale organization of liquid crystals. In two-dimensional active nematics, two classes of topological defects of charges ±1/2 are known to play a major role due to active stresses. Despite this importance, few analytical results have been obtained on the flow-field and active-stress patterns around active topological defects. Using the generic hydrodynamic theory of active systems, we investigate the flow and stress patterns around these topological defects in unbounded, two-dimensional active nematics. Under generic assumptions, we derive analytically the spontaneous velocity and stall force of self-advected defects in the presence of both shear and rotational viscosities. Applying our formalism to the dynamics of monolayers of elongated cells at confluence, we show that the non-conservation of cell number generically increases the self-advection velocity and could provide an explanation for their observed role in cellular extrusion and multilayering. We finally investigate numerically the influence of the Ericksen stress. Our work paves the way to a generic study of the role of topological defects in active nematics, and in particular in monolayers of elongated cells.

Do active nematic self-mixing dynamics help growing bacterial colonies to maintain local genetic diversity?

“…2c,f). In line with nematic field theories [13,50] the +1/2 defect displays two regions of vorticity with opposite sign and the −1/2 defect shows a combination of six regions with alternating sign. These results for isolated defects lead us to expect that the +1/2 defect self-propulsion dynamics familiar from fixed-size active nematics will compete with the radial expansion flow in growing active nematics.…”