Instabilities, motion and deformation of active fluid droplets

Whitfield, Carl A.; Hawkins, Rhoda J.

doi:10.1088/1367-2630/18/12/123016

Cited by 30 publications

(34 citation statements)

References 45 publications

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“…We find that for all values of contractile activity tested above a threshold value, a swimming steady state is observed with the droplet remaining circular (see Fig 3) as we predict analytically in [23]. We find it necessary to use a non-zero value of B on the interface in order to ensure numerical stability and physically reasonable results.…”

Section: Activity and Diffusion Onlysupporting

confidence: 52%

“…We consider an active liquid crystal dispersed on the interface such that the fluid particles are ordered along the tangent line of the interface. This is the 2D limit of the case of a 3D fluid droplet with an isotropically ordered liquid crystal confined to the plane of the interface (the 3D case is discussed analytically in [23]). As in the model of the actin cortex in [24] we consider that this active fluid is contractile enough to generate a negative pressure in the (1D) boundary layer for small concentrations, and that a passive pressure will become stronger at larger concentration.…”

Section: Active Isotropic Interfacementioning

confidence: 99%

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Immersed Boundary Simulations of Active Fluid Droplets

Whitfield

Hawkins

2016

PLoS ONE

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We present numerical simulations of active fluid droplets immersed in an external fluid in 2-dimensions using an Immersed Boundary method to simulate the fluid droplet interface as a Lagrangian mesh. We present results from two example systems, firstly an active isotropic fluid boundary consisting of particles that can bind and unbind from the interface and generate surface tension gradients through active contractility. Secondly, a droplet filled with an active polar fluid with homeotropic anchoring at the droplet interface. These two systems demonstrate spontaneous symmetry breaking and steady state dynamics resembling cell motility and division and show complex feedback mechanisms with minimal degrees of freedom. The simulations outlined here will be useful for quantifying the wide range of dynamics observable in these active systems and modelling the effects of confinement in a consistent and adaptable way.

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Section: Activity and Diffusion Onlysupporting

confidence: 52%

Section: Active Isotropic Interfacementioning

confidence: 99%

Immersed Boundary Simulations of Active Fluid Droplets

Whitfield

Hawkins

2016

PLoS ONE

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“…Driven by active surface flows, the sphere will therefore move relative to the laboratory frame [20], corresponding to a swimmer that exhibits spontaneous self-propulsion. For the case of vanishing surface viscosity, η b = η s = 0, this scenario is similar to swimmers driven by Marangoni flows [28,29].…”

mentioning

confidence: 72%

Minimal Model of Cellular Symmetry Breaking

et al. 2019

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The cell cortex, a thin film of active material assembled below the cell membrane, plays a key role in cellular symmetry breaking processes such as cell polarity establishment and cell division. Here, we present a minimal model of the self-organization of the cell cortex that is based on a hydrodynamic theory of curved active surfaces. Active stresses on this surface are regulated by a diffusing molecular species. We show that coupling of the active surface to a passive bulk fluid enables spontaneous polarization and the formation of a contractile ring on the surface via mechanochemical instabilities. We discuss the role of external fields in guiding such pattern formation. Our work reveals that key features of cellular symmetry breaking and cell division can emerge in a minimal model via general dynamic instabilities. arXiv:1909.12804v1 [physics.bio-ph] 26 Sep 2019 S3 2.3 Components of the Jacobian for l ≥ 2Following the general procedure outlined in Sec. 2.1, we derive in the following the components of the system's Jacobian. The Jacobian diagonalizes in the space of spherical harmonics and contributes for each mode l with J l = J l RR J l Rc J l cR J l cc

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“…The active case is like the case of a passive viscoelastic fluid 40 , for which the effective shear viscosity depends on ω, and we must solve Eq. (22) for ω as a function of k, which yields…”

Section: Instability Of An Active Fluid Filmmentioning

confidence: 99%

“…Since the characteristic equation (33) for the cylinder is of a similar form as the characteristic equation (22) for the planar surface, the growth rate is given by Eq. (25) with F replaced by −G/k and d replaced by R. (Note that in this section τ s = η/(γR).)…”

Section: Rayleigh-plateau Capillary Instabilitymentioning

confidence: 99%

Stability of the interface of an isotropic active fluid

2019

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We study the linear stability of an isotropic active fluid in three different geometries: a film of active fluid on a rigid substrate, a cylindrical thread of fluid, and a spherical fluid droplet. The active fluid is modeled by the hydrodynamic theory of an active nematic liquid crystal in the isotropic phase. In each geometry, we calculate the growth rate of sinusoidal modes of deformation of the interface. There are two distinct branches of growth rates; at long wavelength, one corresponds to the deformation of the interface, and one corresponds to the evolution of the liquid crystalline degrees of freedom. The passive cases of the film and the spherical droplet are always stable. For these geometries, a sufficiently large activity leads to instability. Activity also leads to propagating damped or growing modes. The passive cylindrical thread is unstable for perturbations with wavelength longer than the circumference. A sufficiently large activity can make any wavelength unstable, and again leads to propagating damped or growing modes.

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Instabilities, motion and deformation of active fluid droplets

Cited by 30 publications

References 45 publications

Immersed Boundary Simulations of Active Fluid Droplets

Immersed Boundary Simulations of Active Fluid Droplets

Minimal Model of Cellular Symmetry Breaking

Stability of the interface of an isotropic active fluid

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