Setting the pace of microswimmers: when increasing viscosity speeds up self-propulsion

Pande, Jayant; Merchant, Laura; Harting, Jens; Smith, Ana‐Sunčana

doi:10.1088/1367-2630/aa6e3a

Cited by 32 publications

(55 citation statements)

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“…To calculate how the swimmer behaves around a stable mechanical equilibrium, we develop a perturbative approach that allows to split the equation of motion by orders of the driving force. We firstly rescale the equation of motion using the characteristic length a and the characteristic time ph = ( ) t a k 6 V [30], denoted as viscous time. The latter describes the time scale emerging from the interplay of viscous drag and the spring force acting on a bead.…”

Section: Discussionmentioning

confidence: 99%

“…Both time scales can be arbitrarily large or small compared to another one without impairing our method. However, the competition between these two time scales yields interesting phenomena, including the increase of the swimming velocity with the increase of viscosity [30] and the non-monotonous frequency response [29]. The main limitation of the perturbative scheme is related to the separation between the beads, as set by the choice of the model for the hydrodynamic interactions.…”

Section: Discussionmentioning

confidence: 99%

“…A swimmer with two beads comes with only one internal degree of freedom which is not sufficient to break the time-reversal symmetry [22]. The linear three-bead swimmer has been studied in detail in previous analytical works [28,20,30], where two similar perturbative calculations were performed. In the latter works [20,30], the results for the swimming velocity were expanded and truncated in orders of ν.…”

Section: Linear Three-bead Swimmermentioning

confidence: 99%

“…The accuracy of the results in terms of the bead separation is tuned by the choice of the mobility matrix, whereas the precision in terms of the actuation strength is controlled by the perturbation order. This is essentially different from previous calculations [28,30,21] as we split the equation of motion by orders of the driving force and systematically solve the long-term limit of each order, while the assumption of very large bead separation is not made within the perturbation scheme, but is imposed by the hydrodynamic model. Consequently, given a sufficiently precise mobility matrix, the presented method provides arbitrarily precise results for the swimming velocity.…”

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confidence: 91%

“…The full controllability of a triangular swimmer in the 2D space has recently been shown analytically [21], expanding on the use of the bead-spring model [20]. However, the perturbative calculations in [20,30,21] hold only in the limit of very large bead separations where the swimming velocity becomes extremely small. Especially since this limit is inaccessible in experiments (see [5,9]) as external disturbances become exuberant and can break the swimmer, an investigation of swimmers with smaller bead separations is required and still lacking.In this paper, we fill this gap by presenting a general perturbative framework to calculate the full behavior of arbitrarily shaped bead-spring swimmers, i.e.…”

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A general perturbative approach for bead-based microswimmers reveals rich self-propulsion phenomena

et al. 2019

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Studies of model microswimmers have significantly contributed to the understanding of the principles of self-propulsion we have today. However, only a small number of microswimmer types have been amenable to analytic modeling, and further development of such approaches is necessary to identify the key features of these active systems. Here we present a general perturbative calculation scheme for swimmers composed of beads interacting by harmonic potentials and via hydrodynamics, driven by an arbitrary force protocol. The approach can be used with mobility matrices of arbitrary accuracy, and we illustrate it with the Oseen and Rotne-Prager approximations. We validate our approach by using 3 bead assemblies and comparing the results with the numerically obtained full-solutions of the governing equations of motion, as well as with existing analytic models for the linear and the triangular swimmer geometry. While recovering the relation between the force and swimming velocity, our detailed analysis and the controlled level of approximation allow us to find qualitative differences already in the far field flow of the devices. Consequently, we are able to identify a behavior of the swimmer that is richer than predicted in previous models. Given its generality, the framework can be applied to any swimmer geometry, driving protocol and bead interactions, as well as in problems involving many swimmers.Despite its immense usefulness, this model suffers from the constriction of all internal degrees of freedom by the swimming stroke, namely the internal dynamical behavior of the swimmer cannot react to its surrounding. This was overcome by replacing the arms with springs and prescribing the forces acting on the beads rather than the stroke itself [28,20]. Importantly, the responsive elastic degree of freedom, which is typically associated with the swimmer design, but which could also be in the fluid, is responsible for several interesting phenomena. For example, it is the source of the optimal driving frequency in the overdamped regime [29] and it promotes swimming based on the minimization of drag or enhancement of hydrodynamic interactions [20]. Furthermore, it is also responsible for the existence of a viscosity maximising the swimming velocity [30] and synchronization effects of the stroke [20]. Similar findings have been reported in investigations of bead-based swimmers in a visco-elastic fluid [31,32]. Recently, an altered version of the bead-spring model has been proposed, where the swimmer was driven by periodic changes in the equilibrium lengths of the springs [33,34].The boundedness of the linear swimmer to one dimension is broken in a triangular swimmer geometry, allowing for translational as well as rotational motion [35,14,16]. This geometry has also been used to model Chlamydomonas reinhardtii and investigate in particular the synchronization between the beating of its two flagella [18,36,19]. Experimentally, a triangular swimmer with intrinsic elasticity has been realized by placing ferromagnetic beads subject...

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Linear Three-bead Swimmermentioning

confidence: 99%

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confidence: 99%

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A general perturbative approach for bead-based microswimmers reveals rich self-propulsion phenomena

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Programmable Design and Performance of Modular Magnetic Microswimmers

et al. 2021

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Synthetic biomimetic microswimmers are promising agents for in vivo healthcare and important frameworks to advance the understanding of locomotion strategies and collective motion at the microscopic scale. Nevertheless, constructing these devices with design flexibility and in large numbers remains a challenge. Here, a step toward meeting this challenge is taken by assembling such swimmers via the programmed shape and arrangement of superparamagnetic micromodules. The method's capacity for design flexibility is demonstrated through the assembly of a variety of swimmer architectures. On their actuation, strokes characterized by a balance of viscous and magnetic forces are found in all cases, but swimmers formed from a series of size‐graded triangular modules swim quicker than more traditional designs comprising a circular “head” and a slender tail. Linking performance to design, rules are extracted informing the construction of a second‐generation swimmer with a short tail and an elongated head optimized for speed. Its fast locomotion is attributed to a stroke that better breaks beating symmetry and an ability to beat fully with flex at high frequencies. Finally, production at scale is demonstrated through the assembly and swimming of a flock of the triangle‐based architectures to reveal four types of swimmer couplings.

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Colloidal Active Matter Mimics the Behavior of Biological Microorganisms—An Overview

Nsamela

Zintzun

Montenegro‐Johnson

et al. 2022

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resources from the environment into building blocks and provides energy, and the capacity to pass on some form of inheritable information to the next generation. [1] The creation of artificial life-able to replicate these behaviors-is extensively studied with droplets, vesicles, [2] and DNA nanotechnology. [3] However, these exciting approaches belong to synthetic biology and are reviewed in detail in other excellent reviews. [4] While bio-inspiration has long been a driver for game-changing developments such as airplanes, submarines, radar, and water-repelling surfaces, on the small scale we see yet relatively few such developments. [5] There are fascinating micro-organisms that have evolved over billions of years, and over the course of this process they managed to adapt in different environments. The integration of living beings into their environment is a dynamic process that requires reaction and adaptation to external conditions and stimuli; it is all the more impressive, therefore, that some bacteria have adapted to water and land, but socalled thermo-and extremophiles have even adapted to survive the harshest conditions. Potential uses for smart small scale devices are plentiful, and range from drug delivery to sensing and environmental remediation, with specific literature available on all of these. [6][7][8] The first step is often assumed to be the ability to sense certain physical or chemical changes in the surroundings, and then evaluate which condition is more favorable and adapt accordingly. Artificial micromotors mimic biological microswimmers (Figure 1) in a fully synthetic way, giving microdevices motility, previously the attribute of living systems. Due to the small scale of these devices, their sensing and signal processing capabilities are very limited; yet still, several resemblances with living microswimmers have been observed and studied, and often impressive similarities or even additional understanding can be found. The goal of this review paper is to summarize recent progress in this area, and to give insight into the physical backgrounds of such biomimetic behaviors. Comparison of Biological and Synthetic Active MatterBiological microorganisms, often referred to as "microbes," are a highly diversified collection of living entities from all three branches of the tree of life: Bacteria and Archaea, which are This article provides a review of the recent development of biomimicking behaviors in active colloids. While the behavior of biological microswimmers is undoubtedly influenced by physics, it is frequently guided and manipulated by active sensing processes. Understanding the respective influences of the surrounding environment can help to engineering the desired response also in artificial swimmers. More often than not, the achievement of biomimicking behavior requires the understanding of both biological and artificial microswimmers swimming mechanisms and the parameters inducing mechanosensory responses. The comparison of both classes of microswimmers provides with analogies in thei...

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Setting the pace of microswimmers: when increasing viscosity speeds up self-propulsion

Cited by 32 publications

References 60 publications

A general perturbative approach for bead-based microswimmers reveals rich self-propulsion phenomena

A general perturbative approach for bead-based microswimmers reveals rich self-propulsion phenomena

Programmable Design and Performance of Modular Magnetic Microswimmers

Colloidal Active Matter Mimics the Behavior of Biological Microorganisms—An Overview

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