Flow around topological defects in active nematic films

Rønning, Jonas; Marchetti, Cristina; Bowick, Mark J.; Angheluta, Luiza

doi:10.1098/rspa.2021.0879

Cited by 6 publications

(17 citation statements)

References 65 publications

(135 reference statements)

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“…Indeed, recent work show that, for isolated defects, the self-advection velocity given by eq. ( 12) is valid even when considering the effect of the weak nematic order inside the core [26].…”

Section: Flow Field and Self-advection Velocity Of A +1/2 Defectmentioning

confidence: 98%

“…This result is similar to that of ref. [26]. A representation of this velocity field as well as of its amplitude as a function of r is shown in fig.…”

Section: Flow Field and Self-advection Velocity Of A +1/2 Defectmentioning

confidence: 99%

“…One key ingredient of the hydrodynamics of nematic liquid crystals is the backflow, the hydrodynamic motion induced by the rotation of the director field [24]. Analytical results on topological defects have been obtained by neglecting this backflow [25,26], while numerical studies have considered the coupling between the flow and the director fields in passive [27] as well as active [9,25] nematic defects. We provide here analytical solutions that account explicitly for these effects.…”

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confidence: 99%

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Spontaneous flow created by active topological defects

Brézin,

Risler,

Joanny

2022

Preprint

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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.

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Section: Flow Field and Self-advection Velocity Of A +1/2 Defectmentioning

confidence: 98%

“…This result is similar to that of ref. [26]. A representation of this velocity field as well as of its amplitude as a function of r is shown in fig.…”

Section: Flow Field and Self-advection Velocity Of A +1/2 Defectmentioning

confidence: 99%

mentioning

confidence: 99%

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Spontaneous flow created by active topological defects

Brézin,

Risler,

Joanny

2022

Preprint

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“…Data and relevant code for this research work are stored in GitHub: and have been archived within the Zenodo repository: [30].…”

Section: Data Accessibilitymentioning

confidence: 99%

“…Here p 0 þ is the pressure for the constant activity term α 0 [16]. Activity gradients induce, however, a vortical flow that is finite at the defect core, resulting in an angular velocity of the +1/2 defect, given by…”

Section: +1/2 Defectmentioning

confidence: 99%

Defect self-propulsion in active nematic films with spatially varying activity

Rønning

Angheluta

2023

R. Soc. open sci.

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We study the dynamics of topological defects in active nematic films with spatially varying activity and consider two set-ups: (i) a constant activity gradient and (ii) a sharp jump in activity. A constant gradient of extensile (contractile) activity endows the comet-like +1/2 defect with a finite vorticity that drives the defect to align its nose in the direction of decreasing (increasing) gradient. A constant gradient does not, however, affect the known self-propulsion of the +1/2 defect and has no effect on the −1/2 that remains a non-motile particle. A sharp jump in activity acts like a wall that traps the defects, affecting the translational and rotational motion of both charges. The +1/2 defect slows down as it approaches the interface and the net vorticity tends to reorient the defect polarization so that it becomes perpendicular to the interface. The −1/2 defect acquires a self-propulsion towards the activity interface, while the vorticity-induced active torque tends to align the defect to a preferred orientation. This effective attraction of the negative defects to the wall is consistent with the observation of an accumulation of negative topological charge at both active/passive interfaces and physical boundaries.

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Competing instabilities reveal how to rationally design and control active crosslinked gels

et al. 2022

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How active stresses generated by molecular motors set the large-scale mechanics of the cell cytoskeleton remains poorly understood. Here, we combine experiments and theory to demonstrate how the emergent properties of a biomimetic active crosslinked gel depend on the properties of its microscopic constituents. We show that an extensile nematic elastomer exhibits two distinct activity-driven instabilities, spontaneously bending in-plane or buckling out-of-plane depending on its composition. Molecular motors play a dual antagonistic role, fluidizing or stiffening the gel depending on the ATP concentration. We demonstrate how active and elastic stresses are set by each component, providing estimates for the active gel theory parameters. Finally, activity and elasticity were manipulated in situ with light-activable motor proteins, controlling the direction of the instability optically. These results highlight how cytoskeletal stresses regulate the self-organization of living matter and set the foundations for the rational design and optogenetic control of active materials.

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Flow around topological defects in active nematic films

Abstract: We study the active flow around isolated defects and the self-propulsion velocity of + 1 / 2 defects in an active nematic film with both viscous dissipation (with viscosity η ) and frictional damping Γ … Show more

Cited by 6 publications

References 65 publications

Spontaneous flow created by active topological defects

Spontaneous flow created by active topological defects

Defect self-propulsion in active nematic films with spatially varying activity

Competing instabilities reveal how to rationally design and control active crosslinked gels

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