Helical propulsion in shear-thinning fluids

Gómez, Saúl; Godínez, F. A.; Lauga, Eric; Zenit, Roberto

doi:10.1017/jfm.2016.807

Cited by 58 publications

(54 citation statements)

References 42 publications

(56 reference statements)

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“…Asymptotic [8] and numerical [9][10][11] studies on undulatory swimmers as well as experiments on C. elegans [12,13] found equal or greater swimming speeds in a shear-thinning fluid than in a Newtonian fluid. A recent experiment on helical propulsion [14] also observed en-While propulsion speed is an important property of locomotion, a swimmer may also adjust its propulsion mechanism to reduce the energetic cost of moving through a medium at the expense of speed depending on the biological scenarios and environmental constraints. The concept of efficiency is often introduced in the analysis of locomotion.…”

Section: Introductionmentioning

confidence: 97%

Swimming efficiency in a shear-thinning fluid

2017

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Micro-organisms expend energy moving through complex media. While propulsion speed is an important property of locomotion, efficiency is another factor that may determine the swimming gait adopted by a micro-organism in order to locomote in an energetically favorable manner. The efficiency of swimming in a Newtonian fluid is well characterized for different biological and artificial swimmers. However, these swimmers often encounter biological fluids displaying shear-thinning viscosities. Little is known about how this nonlinear rheology influences the efficiency of locomotion. Does the shear-thinning rheology render swimming more efficient or less? How does the swimming efficiency depend on the propulsion mechanism of a swimmer and rheological properties of the surrounding shear-thinning fluid? In this work, we address these fundamental questions on the efficiency of locomotion in a shear-thinning fluid by considering the squirmer model as a general locomotion model to represent different types of swimmers. Our analysis reveals how the choice of surface velocity distribution on a squirmer may reduce or enhance the swimming efficiency. We determine optimal shear rates at which the swimming efficiency can be substantially enhanced compared with the Newtonian case. The nontrivial variations of swimming efficiency prompt questions on how micro-organisms may tune their swimming gaits to exploit the shear-thinning rheology. The findings also provide insights into how artificial swimmers should be designed to move through complex media efficiently.

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Section: Introductionmentioning

confidence: 97%

Swimming efficiency in a shear-thinning fluid

2017

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“…Intuitively, the existence of high-molecular weight macromolecules can be expected to slow down the translational motion of swimmers because of the (substantially) enhanced viscosity [8][9][10][11]. However, increased swimming speeds have been reported [4,[12][13][14][15][16][17][18][19][20], where enhancement is attribute to mechanical responses caused by fluid viscoelasticity [4,11,13,14,21], local shear thinning [15,22], and polymer depletion [20,23]. In addition, viscoelasticity affects other microswimmer properties, such as their rotational motion.…”

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confidence: 99%

Enhanced Rotational Motion of Spherical Squirmer in Polymer Solutions

Westphal

Gompper

et al. 2020

Phys. Rev. Lett.

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The rotational diffusive motion of a self-propelled, attractive spherical colloid immersed in a solution of self-avoiding polymers is studied by mesoscale hydrodynamic simulations. A drastic enhancement of the rotational diffusion by more than an order of magnitude in presence of activity is obtained. The amplification is a consequence of two effects, a decrease of the amount of adsorbed polymers by active motion, and an asymmetric encounter with polymers on the squirmer surface, which yields an additional torque and random noise for the rotational motion. Our simulations suggest a way to control the rotational dynamics of squirmer-type microswimmers by the degree of polymer adsorption and system heterogeneity.arXiv:2003.03319v1 [cond-mat.soft]

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“…Prominent examples include the extracellular matrix, mucosal barriers and polymer-aggregated marine snow [6,7]. Many explanations have been proposed to describe the increase in speed of bacteria in such polymeric fluids, including viscoelastic effects [5], local shear thinning [4], local shear-induced viscosity gradients [8], polymer depletion [9] or modelling the polymers as a gel-forming network [3,10] or a porous medium [11]. Experiments do not, however, yet have the resolution to distinguish between the different theories.…”

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confidence: 99%

“…4a. For the longer polymers shear-induced stretching of polymers near the helix locally induces shear-thinning, but this and viscoelastic effects are minor contributions to the swimming performance [8,26,27] compared to the polymer depletion, which depends on the value of viscosity in the bulk.…”

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confidence: 99%

Enhanced bacterial swimming speeds in macromolecular polymer solutions

Zöttl¹,

Yeomans²

2019

Nat. Phys.

114

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The locomotion of swimming bacteria in simple Newtonian fluids can successfully be described within the framework of low Reynolds number hydrodynamics [1]. The presence of polymers in biofluids generally increases the viscosity, which is expected to lead to slower swimming for a constant bacterial motor torque. Surprisingly, however, several experiments have shown that bacterial speeds increase in polymeric fluids [2][3][4][5], and there is no clear understanding why. Therefore we perform extensive coarse-grained simulations of a bacterium swimming in explicitly modeled solutions of macromolecular polymers of different lengths and densities. We observe an increase of up to 60% in swimming speed with polymer density and demonstrate that this is due to a depletion of polymers in the vicinity of the bacterium leading to an effective slip. However this in itself cannot predict the large increase in swimming velocity: coupling to the chirality of the bacterial flagellum is also necessary.Microorganisms typically move through complex biological environments which contain high-molecular weight polymeric material. Prominent examples include the extracellular matrix, mucosal barriers and polymer-aggregated marine snow [6,7]. Many explanations have been proposed to describe the increase in speed of bacteria in such polymeric fluids, including viscoelastic effects [5], local shear thinning [4], local shear-induced viscosity gradients [8], polymer depletion [9] or modelling the polymers as a gel-forming network [3,10] or a porous medium [11]. Experiments do not, however, yet have the resolution to distinguish between the different theories. Therefore there is a vital role for detailed numerical models that will allow us to understand motion through biologically relevant but rheologically complex, fluids. Drawing on ideas from simulations of polymer hydrodynamics [12] and of bacterial locomotion in Newtonian fluids (see for example ) we simulate a bacterium moving in suspensions of different polymer density (Figure 1 and Supplementary Movie 1). Hence we reproduce, and explain, the enhanced swimming speed.Swimming bacteria such as Pseudomponas aeruginosa, Helicobacter pylori or Eschericia coli rotate helical flagella attached to their cell body to create a thrust force which moves them forwards [1]. Inspired by the biological swimmers we employ a model bacterium consisting of an elongated cell body of length 2b and width 2a connected to a stiff helical flagellum of radius R (Fig. 1a). Our swimmer is driven by applying a constant motor torque T to the flagellum and an opposing torque −T to the body (Fig. 1b). This results in the body rotating with angular velocity Ω, and the counter-rotating flagellum with angular velocity ω (Fig. 1a) which drives the model cell to swim forwards at an average speed V .The fluid consists of a Newtonian background fluid at viscosity η 0 and temperature T modelled by multiparticle collision dynamics (MPCD, see Methods). This is coupled to an ensemble of coarse-grained polymers that are modelled as...

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Helical propulsion in shear-thinning fluids

Cited by 58 publications

References 42 publications

Swimming efficiency in a shear-thinning fluid

Swimming efficiency in a shear-thinning fluid

Enhanced Rotational Motion of Spherical Squirmer in Polymer Solutions

Enhanced bacterial swimming speeds in macromolecular polymer solutions

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