Chiral stresses in nematic cell monolayers

Abstract

Recent experiments on monolayers of spindle-like cells plated on adhesive stripe-shaped domains have provided a convincing demonstration that certain types of collective phenomena in epithelia are well described by active nematic hydrodynamics. While recovering some of the hallmark predictions of this framework, however, these experiments have also revealed a number of unexpected features that could be ascribed to the existence of chirality over length scales larger than the typical size of a cell. In this article we elaborate on the microscopic origin of chiral stresses in nematic cell monolayers and investigate how chirality affects the motion of topological defects, as well as the collective motion in stripe-shaped domains. We find that chirality introduces a characteristic asymmetry in the collective cellular flow, from which the ratio between chiral and non-chiral active stresses can be inferred by particle-image-velocimetry measurements. Furthermore, we find that chirality changes the nature of the spontaneous flow transition under confinement and that, for specific anchoring conditions, the latter has the structure of an imperfect pitchfork bifurcation. arXiv:1909.05856v1 [cond-mat.soft]

Pressure-driven changes to spontaneous flow in active nematic liquid crystals

“…The former is added to the stress tensor, whereas the latter enters the governing equation for the polar director field. More recently, Duclos et al [40] and Hoffmann et al [41] consider spontaneously induced flows due to an active stress term unique to active cholesteric liquid crystals.…”

“…The specific active stress contribution we consider, denoted by σ a , is the most common form of activity term. First introduced by Simha and Ramaswamy [42], it has also been considered in many subsequent papers, for instance [39][40][41]. It can be obtained by considering each individual active agent as a permanent force dipole, leading to local active stresses proportional to the second moment of the molecular orientation.…”

Layered Chiral Active Matter: Beyond Odd Elasticity

“…This microscale drive manifests itself macroscopically as nonequilibrium currents and forces [10][11][12][13][14][15][16][17][18][19]. Continuum hydrodynamic theories of fluid [20], liquid-crystalline and crystalline phases [7,8,14,16,[21][22][23] of active matter have been constructed including extensions with chiral asymmetry [9,[24][25][26][27][28][29][30][31][32]. In this paper, we construct theories of layered active chiral systems.…”

Integer topological defects of cell monolayers -- mechanics and flows

“…Several theoretical studies suggest that in active systems, well-defined mechanical patterns and flows can emerge around topological defects [20][21][22][23][24]. Based on this idea, one can qualitatively understand the structure of collective flows of active systems, such as purified cytoskeletal motor-filament suspensions, by considering the dynamics of topological defect assemblies [14,[25][26][27][28].…”