The Fluid Dynamics of Swimming Microorganisms and Cells (original) (raw)
Related papers
Collective Hydrodynamics of Swimming Microorganisms: Living Fluids
Annual Review of Fluid Mechanics, 2011
Experimental observations indicate that, at sufficiently high cell densities, swimming bacteria exhibit coordinated motions on length scales (10 to 100 μm) that are large compared with the size of an individual cell but too small to yield significant gravitational or inertial effects. We discuss simulations of hydrodynamically interacting self-propelled particles as well as stability analyses and numerical solutions of averaged equations of motion for low Reynolds number swimmers. It has been found that spontaneous motions can arise in such systems from the coupling between the stresses the bacteria induce in the fluid as they swim and the rotation of the bacteria due to the resulting fluid velocity disturbances.
A model of hydrodynamic interaction between swimming bacteria
Bulletin of mathematical …, 2010
We study the dynamics and interaction of two swimming bacteria, modeled by self-propelled dumbbell-type structures. We focus on alignment dynamics of a coplanar pair of elongated swimmers, which propel themselves either by "pushing" or "pulling" both in three-and quasi-twodimensional geometries of space. We derive asymptotic expressions for the dynamics of the pair, which, complemented by numerical experiments, indicate that the tendency of bacteria to swim in or swim off depends strongly on the position of the propulsion force. In particular, we observe that positioning of the effective propulsion force inside the dumbbell results in qualitative agreement with the dynamics observed in experiments, such as mutual alignment of converging bacteria.
Collective motion in a suspension of micro-swimmers that run-and-tumble and rotary diffuse
Journal of Fluid Mechanics, 2015
Recent experiments have shown that suspensions of swimming micro-organisms are characterized by complex dynamics involving enhanced swimming speeds, large-scale correlated motions and enhanced diffusivities of embedded tracer particles. Understanding this dynamics is of fundamental interest and also has relevance to biological systems. The observed collective dynamics has been interpreted as the onset of a hydrodynamic instability, of the quiescent isotropic state of pushers, swimmers with extensile force dipoles, above a critical threshold proportional to the swimmer concentration. In this work, we develop a particle-based model to simulate a suspension of hydrodynamically interacting rod-like swimmers to estimate this threshold. Unlike earlier simulations, the velocity disturbance field due to each swimmer is specified in terms of the intrinsic swimmer stress alone, as per viscous slender-body theory. This allows for a computationally efficient kinematic simulation where the inter...
The role of hydrodynamic interaction in the locomotion of microorganisms
Biophysical Journal, 1993
A general Boundary Element Method is presented and benchmarked with existing Slender Body Theory results and reflection solutions for the motion of spheres and slender bodies near plane boundaries. This method is used to model the swimming of a microorganism with a spherical cell body, propelled by a single rotating flagellum. The swimming of such an organism near a plane boundary, midway between two plane boundaries or in the vicinity of another similar organism, is investigated. It is found that only a small increase (less than 10%) results in the mean swimming speed of an organism swimming near and parallel to another identical organism. Similarly, only a minor propulsive advantage (again, less than 10% increase in mean swimming speed) is predicted when an organism swims very close and parallel to plane boundaries (such as a microscopic plate and (or) a coverslip, for example). This is explained in terms of the flagellar propulsive advantage derived from an increase in the ratio of the normal to tangential resistance coefficients of a slender body being offset by the apparently equally significant increase in the cell body drag. For an organism swimming normal to and toward a plane boundary, however, it is predicted that (assuming it is rotating its flagellum, relative to its cell body, with a constant angular frequency) the resulting swimming speed decreases asymptotically as the organism approaches the boundary.
Flagellar swimmers oscillate between pusher- and puller-type swimming
2015
Self-propulsion of cellular microswimmers generates flow signatures, commonly classified as pusher- and puller-type, which characterize hydrodynamic interactions with other cells or boundaries. Using experimentally measured beat patterns, we compute that flagellated alga and sperm oscillate between pusher and puller. Beyond a typical distance of 100 um from the swimmer, inertia attenuates oscillatory micro-flows. We show that hydrodynamic interactions between swimmers oscillate in time and are of similar magnitude as stochastic swimming fluctuations.
Amoeboid Swimming: A Generic Self-Propulsion of Cells in Fluids by Means of Membrane Deformations
Physical Review Letters, 2013
Microorganisms, such as bacteria, algae, or spermatozoa, are able to propel themselves forward thanks to flagella or cilia activity. By contrast, other organisms employ pronounced changes of the membrane shape to achieve propulsion, a prototypical example being the Eutreptiella gymnastica. Cells of the immune system as well as dictyostelium amoebas, traditionally believed to crawl on a substratum, can also swim in a similar way. We develop a model for these organisms: the swimmer is mimicked by a closed incompressible membrane with force density distribution (with zero total force and torque). It is shown that fast propulsion can be achieved with adequate shape adaptations. This swimming is found to consist of an entangled pusher-puller state. The autopropulsion distance over one cycle is a universal linear function of a simple geometrical dimensionless quantity A=V 2=3 (V and A are the cell volume and its membrane area). This study captures the peculiar motion of Eutreptiella gymnastica with simple force distribution.
Hydrodynamic interactions of self-propelled swimmers
Soft Matter, 2013
The hydrodynamic interactions of a suspension of self-propelled particles are studied using a direct numerical simulation method which simultaneously solves for the host fluid and the swimming particles. A modified version of the "Smoothed Profile" method (SPM) is developed to simulate microswimmers as squirmers, which are spherical particles with a specified surface-tangential slip velocity between the particles and the fluid. This simplified swimming model allows one to represent different types of propulsion (pullers and pushers) and is thus ideal to study the hydrodynamic interactions among swimmers. We use the SPM to study the diffusive behavior which arises due to the swimming motion of the particles, and show that there are two basic mechanisms responsible for this phenomena: the hydrodynamic interactions caused by the squirming motion of the particles, and the particle-particle collisions. This dual nature gives rise to two distinct time-and length-scales, and thus to two diffusion coefficients, which we obtain by a suitable analysis of the swimming motion. We show that the collisions between swimmers can be interpreted in terms of binary collisions, in which the effective collision radius is reduced due to the collision dynamics of swimming particles in viscous fluids. At short timescales , the dynamics of the swimmer is analogous to that of an inert tracer particle in a swimming suspension, in which the diffusive motion is caused by fluid-particle collisions. Our results, along with the simulation method we have introduced, will allow us to gain a better understanding of the complex hydrodynamic interactions of self-propelled swimmers.
Computational study of the emergent behavior of micro-swimmer suspensions
2016
Recently, we have shown that micro-swimmers in 3D can generate coordinate behaviours like swimming in the same direction or create giant density fluctuations induced by the emergency of a dynamic cluster that percolates in the suspension. We found that the key factor to produce these collective motions (CM) is the hydrodynamic signature of the micro-swimmers. Since the set-up of many experiments is a suspension where particles can move in a quasi-2D geometry, we developed a systematic numerical study such that experimental parameters are simulated. We present here some results of numerical simulations of interacting micro-swimmers constrained to move in a slab. The results prove that our simulations can reproduce perfectly the living clusters obtained by experimentalists for either active colloids or bacteria. We also show some results of spherical swimmers trapped in a plane but embedded in an unconstrained fluid, swimmers can move along the interface and rotate freely in all direc...
Bi-flagellate swimming dynamics
2011
The propulsion of low Reynolds number swimmers has been widely studied, from the swimming sheet models of Taylor (1951) to more recent studies by Smith (2010), where the boundary element method and the method of regularised Stokeslets are combined to observe cilia and flagella driven flow. While the majority of studies have investigated the propulsion and hydrodynamics of spermatozoa and bacteria, very little research has been undertaken in the area of bi-flagellate green algae. In this thesis we, investigate the hydrodynamics of swimming bi-flagellates via the applica-Statement This thesis is submitted in accordance with the regulations for the degree of Doctor of Philosophy at the University of Glasgow. In Chapter 1 background material and the method of regularised Stokeslets is discussed. The results in later chapters are the author's own work in collaboration with Martin Bees, with the exception of results which are explicitly referenced. The areas of Chapters 3 and 5 relating to reorientation times and the effective cell eccentricity have been submitted for publication to the Bulletin of Mathematical Biology.
Physics of Fluids
This work presents experimental and theoretical studies on the locomotion of helical artificial swimmers at low Reynolds number in both Newtonian and viscoelastic ambient liquids. We examine the effect of fluid elasticity on the propulsive force and torque on the body and speed velocity of the swimmer in terms of two physical parameters: Deborah number ( De) and Strouhal number ( Sh). For this end, some experiments with prototype microorganisms in creeping flow motion are conducted. In the experiments, a macroscopic swimmer that propels itself by mimicking helical flagella are developed and tested. Three swimming models propelled by a helical tail with different wavelengths are investigated, and their motions examined for both cases: when the ambient solvent is a pure Newtonian viscous fluid and when the base fluid is an elastic polymeric solution. In addition, we also apply the slender body theory and the method of regularized Stokeslet in order to calculate theoretically the force...