Enhanced Motility of a Microswimmer in Rigid and Elastic Confinement

Ledesma‐Aguilar, Rodrigo; Yeomans, J. M.

doi:10.1103/physrevlett.111.138101

Cited by 61 publications

(54 citation statements)

References 33 publications

(41 reference statements)

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“…We will first provide a brief summary of wall effects reported so far in the literature before discussing our results. The fact that the wall enhances motility is reported in several papers [12,[43][44][45][46][47][48]. However, we must stress, as we found, that this is not always true.…”

Section: On the Non Monotonous Behavior Of The Swimmer Velocity Ascontrasting

confidence: 52%

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Amoeboid swimming in a channel

Farutin

et al. 2016

Soft Matter

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Several micro-organisms, such as bacteria, algae, or spermatozoa, use flagellar or ciliary activity to swim in a fluid, while many other micro-organisms instead use ample shape deformation, described as amoeboid, to propel themselves by either crawling on a substrate or swimming. Many eukaryotic cells were believed to require an underlying substratum to migrate (crawl) by using membrane deformation (like blebbing or generation of lamellipodia) but there is now increasing evidence that a large variety of cells (including those of the immune system) can migrate without the assistance of focal adhesion, allowing them to swim as efficiently as they can crawl. This paper details the analysis of amoeboid swimming in a confined fluid by modeling the swimmer as an inextensible membrane deploying local active forces (with zero total force and torque). The swimmer displays a rich behavior: it may settle into a straight trajectory in the channel or navigate from one wall to the other depending on its confinement. The nature of the swimmer is also found to be affected by confinement: the swimmer can behave, on the average over one swimming cycle, as a pusher at low confinement, and becomes a puller at higher confinement, or vice versa. The swimmer's nature is thus not an intrinsic property. The scaling of the swimmer velocity V with the force amplitude A is analyzed in detail showing that at small enough A, V ∼ A 2 /η 2 (where η is the viscosity of the ambient fluid), whereas at large enough A, V is independent of the force and is determined solely by the stroke cycle frequency and swimmer size. This finding starkly contrasts with currently known results found from swimming models where motion is based on ciliary and flagellar activity, where V ∼ A/η. To conclude, two definitions of efficiency as put forward in the literature are analyzed with distinct outcomes. We find that one type of efficiency has an optimum as a function of confinement while the other does not. Future perspectives are outlined.

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Section: On the Non Monotonous Behavior Of The Swimmer Velocity Ascontrasting

confidence: 52%

“…Bilbao et al [45] analyzed a model inspired by nematode locomotion by simulation and found that walls enhance the speed. Ledesma et al [46] treated a dipolar swimmer bounded both by rigid or an elastic tube and obtained a speed enhancement due to walls.…”

Section: On the Non Monotonous Behavior Of The Swimmer Velocity Asmentioning

confidence: 99%

Amoeboid swimming in a channel

Farutin

et al. 2016

Soft Matter

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“…Second, the collective behaviour of microswimmers has been studied at moving boundaries [46,53,54] but all of which were of fixed shape. Bacteria and active particles near flexible boundaries have not yet been explored systematically and it is interesting to understand how clustering and trapping phenomena are modified for flexible boundaries [55]. Our case of a flexible polymer chain is therefore one of the simplest key examples to proceed along this important direction.…”

Section: Introductionmentioning

confidence: 99%

Unusual swelling of a polymer in a bacterial bath

Kaiser

Löwen

2014

The Journal of Chemical Physics

102

106

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The equilibrium structure and dynamics of a single polymer chain in a thermal solvent is by now well-understood in terms of scaling laws. Here we consider a polymer in a bacterial bath, i.e. in a solvent consisting of active particles which bring in nonequilibrium fluctuations. Using computer simulations of a self-avoiding polymer chain in two dimensions which is exposed to a dilute bath of active particles, we show that the Flory-scaling exponent is unaffected by the bath activity provided the chain is very long. Conversely, for shorter chains, there is a nontrivial coupling between the bacteria intruding into the chain which may stiffen and expand the chain in a nonuniversal way. As a function of the molecular weight, the swelling first scales faster than described by the Flory exponent, then an unusual plateau-like behaviour is reached and finally a crossover to the universal Flory behaviour is observed. As a function of bacterial activity, the chain end-to-end distance exhibits a pronounced non-monotonicity. Moreover, the mean-square displacement of the center of mass of the chain shows a ballistic behaviour at intermediate times as induced by the active solvent. Our predictions are verifiable in two-dimensional bacterial suspensions and for colloidal model chains exposed to artificial colloidal microswimmers.

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“…[31][32][33][34][35][36][37] An important consideration in mechanical microswimming is the way elastic forces interact with the fluid and any external forces present in determining the motion. In the literature different aspects of these forces that have been studied are the elasticity of the swimming mechanism (such as those involving flagella and cilia), [14,38] the influence of flexible surrounding walls if the motion occurs close to them, [39,40] and even the elasticity (or the viscoelasticity) of the ambient fluid. [8,[41][42][43][44][45][46][47][48][49] In addition, the advantage of having elastic bodies has been investigated for the forced motion of microbodies, such as capsules driven through constrictions.…”

Section: Introductionmentioning

confidence: 99%

Effect of body deformability on microswimming

et al. 2017

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In this work we consider the following question: given a mechanical microswimming mechanism, does increased deformability of the swimmer body hinder or promote the motility of the swimmer? To answer this we study a microswimmer model composed of deformable beads connected with springs. We determine the velocity of the swimmer analytically, starting from the forces driving the motion and assuming that the oscillations in the effective radii of the beads are known and are much smaller than the radii themselves. We find that to the lowest order, only the driving frequency mode of the surface oscillations contributes to the swimming velocity, and that this velocity may both rise and fall with the deformability of the beads depending on the spring constant. To test these results, we run immersed boundary lattice Boltzmann simulations of the swimmer, and show that they reproduce both the velocity-promoting and velocity-hindering effects of bead deformability correctly in the predicted parameter ranges. Our results mean that for a general swimmer, its elasticity determines whether passive deformations of the swimmer body, induced by the fluid flow, aid or oppose the motion.

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Enhanced Motility of a Microswimmer in Rigid and Elastic Confinement

Cited by 61 publications

References 33 publications

Amoeboid swimming in a channel

Amoeboid swimming in a channel

Unusual swelling of a polymer in a bacterial bath

Effect of body deformability on microswimming

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