Hydrodynamics of isotropic and liquid crystalline active polymer solutions

Ahmadi, Aphrodite; Marchetti, M. Cristina; Liverpool, Tanniemola B.

doi:10.1103/physreve.74.061913

Cited by 81 publications

(117 citation statements)

References 41 publications

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“…Although steric interactions between particles play an important role in all liquids, they have so far been neglected in most models of polar filaments driven by crosslinking motors, which consider isolated filament pairs. (We note that the effects of steric interactions on filament alignment have been considered 25,29 ).…”

Section: Introductionmentioning

confidence: 99%

Microscopic origins of anisotropic active stress in motor-driven nematic liquid crystals

et al. 2016

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The cytoskeleton, despite comprising relatively few building blocks, drives an impressive variety of cellular phenomena ranging from cell division to motility. These building blocks include filaments, motor proteins, and static crosslinkers. Outside of cells, these same components can form novel materials exhibiting active flows and nonequilibrium contraction or extension. While dipolar extensile or contractile active stresses are common in nematic motor-filament systems, their microscopic origin remains unclear. Here we study a minimal physical model of filaments, crosslinking motors, and static crosslinkers to dissect the microscopic mechanisms of stress generation in a two-dimensional system of orientationally aligned rods. We demonstrate the essential role of filament steric interactions which have not previously be considered to significantly contribute to active stresses. With this insight, we are able to tune contractile or extensile behavior through control of motor-driven filament sliding and crosslinking. This work provides a roadmap for engineering stresses in active liquid crystals. The mechanisms we study may help explain why flowing nematic motor-filament mixtures are extensile while gelled systems are contractile.

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Section: Introductionmentioning

confidence: 99%

Microscopic origins of anisotropic active stress in motor-driven nematic liquid crystals

et al. 2016

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“…They show a rich variety of collective behaviour, including dynamical order-disorder transitions and pattern formation on various scales. A much studied example are collections of self-propelled objects [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] which independently translate due to internally generated motions by the objects themselves.In this article we study, a particularly simple class of self-driven particles and their interactions. These are self-rotating objects (that we call rotors) lying in a plane [16][17][18].…”

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confidence: 99%

Dynamics and interactions of active rotors

Leoni

Liverpool

2010

EPL

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Abstract. -We consider a simple model of an internally driven self-rotating object; a rotor, confined to two dimensions by a thin film of low Reynolds number fluid. We undertake a detailed study of the hydrodynamic interactions between a pair of rotors and find that their effect on the resulting dynamics is a combination of fast and slow motions. We analyse the slow dynamics using an averaging procedure to take account of the fast degrees of freedom. Analytical results are compared with numerical simulations. Hydrodynamic interactions mean that while isolated rotors do not translate, bringing together a pair of rotors leads to motion of their centres. Two rotors spinning in the same sense rotate with an approximately constant angular velocity around each other, while two rotors of opposite sense, both translate with the same constant velocity, which depends on the separation of the pair. As a result a pair of counter-rotating rotors are a promising model for controlled self-propulsion in two dimensions.Soft active systems are composed of interacting units that consume energy and generate local motion and mechanical stresses. They show a rich variety of collective behaviour, including dynamical order-disorder transitions and pattern formation on various scales. A much studied example are collections of self-propelled objects [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] which independently translate due to internally generated motions by the objects themselves.In this article we study, a particularly simple class of self-driven particles and their interactions. These are self-rotating objects (that we call rotors) lying in a plane [16][17][18]. Our motivation is two-fold. First recent developments [19][20][21][22] have shown the possibility of experimentally realising such self-driven rotors on the nanoscale. In addition recent progress in nano-scale microfabrication techniques have been able to generate synthetic chemically driven rotors that rotate fast enough so that the effects of their interactions on their dynamics can been measured experimentally [23]. Second, a collection of active rotors provide a particularly simple example of an active system as their collective behaviour can be described in terms of scalar rather than vector equations. The first step in the quest to understand their collective behaviour is to develop a detailed understanding of their interactions.Motivated by this we investigate analytically and numerically the dynamics of rotors confined in two dimensions (the x − y plane) by a viscous film, such as a membrane. We first introduce the model of a single rotor: (which when isolated rotates around its centre but does not translate). Each rotor can be described by a scalar σ, the value of the projection of its angular velocity ω on thê z direction, that we call spin. We next study the hydrodynamic interactions between a pair, in the absence of noise when the distance between their centres is large compared to their size. We find that the resulting dynamics can be described in terms ...

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“…We ignore pressure gradients on the assumption that the film thickness adjusts to accommodate them. The crucial piece of the stress σ ij is the active contribution † σ act ij Wc 0 Q ij (x, r ⊥ , t) (2,3,8,9,11,12), where W < 0 and W > 0 respectively correspond to contractile and tensile stresses, and c 0 is the mean F-actin concentration. To leading order in gradients * If included, these terms would lead to shifts of effective Frank constants and additional possible instabilities in the effective equation of motion Eq.…”

Section: Physicsmentioning

confidence: 99%

“…Our treatment applies more generally to semiflexible polymers under tension in a wide variety of active media. We describe the medium by the active generalization of liquid-crystal hydrodynamics (2,3,(8)(9)(10)(11)(12)(13)(14). For the purposes of this paper, an active medium is one whose constituent particles possess the ability to extract energy from an ambient nutrient bath and dissipate it, executing some kind of systematic motion in the process.…”

mentioning

confidence: 99%

Buckling, stiffening, and negative dissipation in the dynamics of a biopolymer in an active medium

Kikuchi

Ehrlicher

Koch

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

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We present a generic theory for the dynamics of a stiff filament under tension, in an active medium with orientational correlations, such as a microtubule in contractile actin. In sharp contrast to the case of a passive medium, we find the filament can stiffen, and possibly oscillate or buckle, depending on both the contractile or tensile nature of the activity and the filament-medium anchoring interaction. We also demonstrate a strong violation of the fluctuation-dissipation (FD) relation in the effective dynamics of the filament, including a negative FD ratio. Our approach is also of relevance to the dynamics of axons, and our model equations bear a remarkable formal similarity to those in recent work [Martin P, Hudspeth AJ, Juelicher F (2001) Proc Natl Acad Sci USA 98:14380-14385] on auditory hair cells. Detailed tests of our predictions can be made by using a single filament in actomyosin extracts or bacterial suspensions.cytoskeleton | active hydrodynamics | microrheology | fluctuation-dissipation ratio | neuronal growth cone T he cytoskeleton (1) is a dense multicomponent meshwork of semiflexible polymers which interact sterically as well as through active (1-3) processes. Although the blending of polymers industrially requires special effort, the active environment of the living cell provides a setting in which polymers that differ substantially in their stiffness are naturally mixed and interact. Moreover, active processes, such as polymerization and the working of molecular motors, lead to the generation of stresses without the external imposition of flow fields. These two mechanisms combine to yield a rich range of novel physical phenomena. The role of activity in cytoskeletal mechanics is receiving increasing attention, as seen from many recent theoretical and experimental studies of the rheology of cells and cell extracts (4-6). It is clear in particular (7) that interactions between different species of filaments are crucial for cell motility, cell division, vesicular transport, and organelle positioning and integrity.In this paper, we make a study of the effect of these interactions by modeling the dynamics of a stiff filament, which we will call a "microtubule", immersed in an active medium ( Fig. 1) with orientational degrees of freedom, which we will call "F-actin". We emphasize here that the names microtubule and F-actin are introduced for convenience: We consider both contractile and tensile activity, although only the former applies to actomyosin. Our treatment applies more generally to semiflexible polymers under tension in a wide variety of active media. We describe the medium by the active generalization of liquid-crystal hydrodynamics (2,3,(8)(9)(10)(11)(12)(13)(14). For the purposes of this paper, an active medium is one whose constituent particles possess the ability to extract energy from an ambient nutrient bath and dissipate it, executing some kind of systematic motion in the process. This activity endows each such particle with a permanent uniaxial stress. The other central ingredie...

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Hydrodynamics of isotropic and liquid crystalline active polymer solutions

Cited by 81 publications

References 41 publications

Microscopic origins of anisotropic active stress in motor-driven nematic liquid crystals

Microscopic origins of anisotropic active stress in motor-driven nematic liquid crystals

Dynamics and interactions of active rotors

Buckling, stiffening, and negative dissipation in the dynamics of a biopolymer in an active medium

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