Anisotropic diffusion of ellipsoidal tracers in microswimmer suspensions

Nordanger, Henrik; Morozov, Alexander; Stenhammar, Joakim

doi:10.1103/physrevfluids.7.013103

Cited by 9 publications

(8 citation statements)

References 56 publications

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“…As a first step, the current study has the potential to tackle a multitude of transport problems stemming from external or inter-particle interactions of spatially varying shapes, sizes and others for swimmers in constrained environments. For example, micro-swimmers can generate stress in the fluid, potentially causing collective motion at higher concentrations (Nordanger et al 2022). Jeffery orbits, typically associated with Newtonian fluids, undergo notable changes due to viscoelastic stresses induced by the activity (Choudhary, Nambiar & Stark 2023).…”

Section: Discussionmentioning

confidence: 99%

“…In contrast to passive particles, the rotational dynamics turns out to be crucial, especially for the time-dependent transport of self-propelling micro-swimmers, because a slight deviation of the orientation could lead to markedly distinct distributions over brief time intervals. Anisotropic diffusion of ellipsoidal tracers in suspensions of active particles could display non-Gaussian statistics and dispersive phenomena (Nordanger, Morozov & Stenhammar 2022). Rusconi, Guasto & Stocker (2014) showed that trajectories of bacteria displayed frequent loops in high-shear regions due to the hydrodynamic torque generated by the local shear, corresponding to a shear-induced trapping effect in the high-shear domains.…”

Section: Introductionmentioning

confidence: 99%

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Migration of confined micro-swimmers subject to anisotropic diffusion

Guan,

Jiang,

Tao

et al. 2024

J. Fluid Mech.

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Shear-induced migration of elongated micro-swimmers exhibiting anisotropic Brownian diffusion at a population scale is investigated analytically in this work. We analyse the steady motion of confined ellipsoidal micro-swimmers subject to coupled diffusion in a general setting within a continuum homogenisation framework, as an extension of existing studies on macro-transport processes, by allowing for the direct coupling of convection and diffusion in local and global spaces. The analytical solutions are validated successfully by comparison with numerical results from Monte Carlo simulations. Subsequently, we demonstrate from the probability perspective that symmetric actuation does not yield net vertical polarisation in a horizontal flow, unless non-spherical shapes, external fields or direct coupling effects are harnessed to generate steady locomotion. Coupled diffusivities modify remarkably the drift velocity and vertical migration of motile micro-swimmers exposed to fluid shear. The interplay between stochastic swimming and preferential alignment could explain the diverse concentration and orientation distributions, including rheological formations of depletion layers, centreline focusing and surface accumulation. Results of the analytical study shed light on unravelling peculiar self-propulsion strategies and dispersion dynamics in active-matter systems, with implications for various transport problems arising from the fluctuating shape, size and other external or inter-particle interactions of swimmers in confined environments.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Migration of confined micro-swimmers subject to anisotropic diffusion

Guan,

Jiang,

Tao

et al. 2024

J. Fluid Mech.

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“…There is one natural way to generate flows by swimming microbes such as bacteria, and they can coherent each other to create chaotic flows when they get together [21,22]. The active stress provided by the bacteria strikingly improve mixing within this bacterial suspension at low Reynolds number, and then enhance the transport of substance in the suspension [23][24][25][26][27][28][29][30][31].…”

Section: Introductionmentioning

confidence: 99%

Configurational dynamics of flexible filaments in bacterial active baths

et al. 2023

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Biopolymers with microscale length and nanoscale cross-sections subjected to active forces is a common non-equilibrium phenomenon in living creatures. It is therefore crucial to intuitively present and investigate the detailed dynamics of such flexible filaments in an active bath full of living matter. Hence, by introducing fluorescent actin filament into an active suspension of motile bacteria at different number densities in a quasi-two-dimensional chamber, we directly visualize the detailed interaction processes that bacteria deform a fluctuating filament by relative motion perpendicular to its principal axis of the filament and straighten a filament by parallel motions. We analyzed the evolution of bending energy in dilute and dense bacteria baths with gradual compact or coiled shapes. We successfully introduce a dimensionless number μ, named as active elasto-viscous number, which governs the generic deformation of filaments in the bacterial bath by comparing viscous force generated in bacterial active bath to elastic restoring force of filament.The persistence length measuring the tangential correlation of the flexible filament is found to be proportional to μ. Finally, an effective temperature of the bacterial bath is given through the relation between constant stiffness and loading forces instead of popular used Einstein relation. Our findings provide detailed information and specific scaling of flexible filaments interplay with active forces and in response to living and crowded environments.

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“…2016; Ortlieb et al. 2019; von Rüling, Kolley & Eremin 2021), and theoretically, with microswimmers typically being modelled either as force dipoles acting on the surrounding fluid (Pushkin, Shum & Yeomans 2013; Pushkin & Yeomans 2013; Morozov & Marenduzzo 2014; Nordanger, Morozov & Stenhammar 2022), as spherical ‘squirmers’ with an imposed slip velocity along their body (Thiffeault & Childress 2010; Lin et al. 2011; Thiffeault 2015), or as needle-shaped ‘slender swimmers’ with imposed stresses along their body lengths (Saintillan & Shelley 2012; Krishnamurthy & Subramanian 2015).…”

Section: Introductionmentioning

confidence: 99%

“…When swimming through a viscous fluid, these swimmers create long-range flow fields that advect the tracers, leading to tracer dynamics that is ballistic at short times and diffusive over time scales longer than the autocorrelation time of the local flow field (Lin, Thiffeault & Childress 2011). Realisations of this system have been studied extensively both experimentally, typically in suspensions of E. coli bacteria (Wu & Libchaber 2000;Kim & Breuer 2004;Drescher et al 2011;Jepson et al 2013;Koumakis et al 2013;Miño et al 2013Miño et al , 2011Patteson et al 2016;Peng et al 2016;Semeraro, Devos & Narayanan 2018) or Chlamydomonas algae (Leptos et al 2009;Yang et al 2016;Ortlieb et al 2019;von Rüling, Kolley & Eremin 2021), and theoretically, with microswimmers typically being modelled either as force dipoles acting on the surrounding fluid (Pushkin, Shum & Yeomans 2013;Morozov & Marenduzzo 2014;Nordanger, Morozov & Stenhammar 2022), as spherical 'squirmers' with an imposed slip velocity along their body (Thiffeault & Childress 2010;Lin et al 2011;Thiffeault 2015), or as needle-shaped 'slender swimmers' with imposed stresses along their body lengths (Saintillan & Shelley 2012;Krishnamurthy & Subramanian 2015). While the details of these three microswimmer models differ, the results regarding enhanced tracer diffusion are largely generic and consistent with experimental results, which have shown the swimmer-induced, hydrodynamic diffusivity D A to scale linearly with microswimmer density n in the dilute limit where swimmer-swimmer correlations can be neglected (Thiffeault & Childress 2010;Lin et al 2011;Miño et al 2013).…”

Section: Introductionmentioning

confidence: 99%

Interplay between Brownian and hydrodynamic tracer diffusion in suspensions of swimming microorganisms

Nordanger,

Morozov,

Stenhammar

2023

J. Fluid Mech.

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The general problem of tracer diffusion in non-equilibrium baths is important in a wide range of systems, from the cellular level to geographical length scales. In this paper, we revisit the archetypical example of such a system: a collection of small passive particles immersed in a dilute suspension of non-interacting dipolar microswimmers, representing bacteria or algae. In particular, we consider the interplay between thermal (Brownian) diffusion and hydrodynamic (active) diffusion due to the persistent advection of tracers by microswimmer flow fields. Previously, it has been argued that even a moderate amount of Brownian diffusion is sufficient to significantly reduce the persistence time of tracer advection, leading to a significantly reduced value of the effective active diffusion coefficient $D_A$ compared to the non-Brownian case. Here, we show by large-scale simulations and kinetic theory that this effect is in fact practically relevant only for microswimmers that effectively remain stationary while still stirring up the surrounding fluid – so-called shakers. In contrast, for moderate and high values of the swimming speed, relevant for biological microswimmer suspensions, the effect of Brownian motion on $D_A$ is negligible, leading to the effects of advection by microswimmers and Brownian motion being additive. This conclusion contrasts with previous results from the literature, and encourages a reinterpretation of recent experimental measurements of $D_A$ for tracer particles of varying size in bacterial suspensions.

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Anisotropic diffusion of ellipsoidal tracers in microswimmer suspensions

Cited by 9 publications

References 56 publications

Migration of confined micro-swimmers subject to anisotropic diffusion

Migration of confined micro-swimmers subject to anisotropic diffusion

Configurational dynamics of flexible filaments in bacterial active baths

Interplay between Brownian and hydrodynamic tracer diffusion in suspensions of swimming microorganisms

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