Green algae scatter off sharp viscosity gradients

Coppola, Simone; Kantsler, Vasily

doi:10.1038/s41598-020-79887-7

Cited by 24 publications

(44 citation statements)

References 24 publications

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“…There is little experimental data with any bearing on our Snell's law; experiments for a few cell types show some form refraction or reflection when a swimmer encounters a drag discontinuity [18][19][20]. In once case [20], puller-type algal swimmers are observed to only reflect off of a boundary of low to high viscosity, which is the opposite of what our theory and simulation predicts. It is likely that this difference is a result of hydrodynamic interactions, which are not included in our theory.…”

Section: Discussionmentioning

confidence: 59%

“…However, there are few known mechanisms for controlling the trajectories of swimmers. Recently, there has been evidence that swimmers refract and scatter at drag discontinuities [18][19][20]. While there is theory that studies the movement of spherical swimmers down viscosity gradients [21] and theory that predicts that nonuniaxial swimmers can swim up viscosity gradients [22], there is no theory for swimmers encountering drag discontinuities.…”

Section: Introductionmentioning

confidence: 99%

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Snell's Law for Gliders

Ross,

Osmanović,

Brady

et al. 2021

Preprint

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Snell's law, which encompasses both refraction and total internal reflection, provides the foundation for ray optics and all lens-based instruments, from microscopes to telescopes. Refraction results when light crosses the interface between media of different refractive index, the dimensionless number that captures how much a medium retards the propagation of light. In this work, we show that the motion of self-propelled particles moving across a drag discontinuity is governed by an analogous Snell's law, allowing for swimmer ray optics. We derive a variant of Snell's law for swimmers moving across media of different viscosities. Just as the ratio of refractive indexes sets the path of a light ray, the ratio of viscosities is shown to determine the trajectories of swimmers. We find that the magnitude of refraction depends on the swimmer's shape, specifically the aspect ratio, as analogous to the wavelength of light. This enables the demixing of a polymorphic, many-shaped, beam of swimmers into distinct monomorphic, single-shaped, beams through a viscosity prism. In turn, beams of monomorphic swimmers can be focused by spherical and gradient viscosity lenses. Completing the analogy, we show that the shape-dependence of the total internal reflection critical angle can be used to create swimmer traps. Such analogies to ray optics suggest a universe of new devices for sorting, concentrating, and analyzing microscopic swimmers is possible.

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Section: Discussionmentioning

confidence: 59%

Section: Introductionmentioning

confidence: 99%

Snell's Law for Gliders

Ross,

Osmanović,

Brady

et al. 2021

Preprint

View full text Add to dashboard Cite

show abstract

“…For other microscopic biological swimmers, such as bi‐flagellated algae Chlamydomonas reinhardtii , fluid elasticity and viscosity strongly influence the beating pattern and swimming speed [17–19] . The swimming of Caenorhabditis elegans improves in wet granular systems [20,21] .…”

Section: Introductionmentioning

confidence: 99%

Effect of Viscosity on Microswimmers: A Comparative Study

et al. 2021

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Although many biological fluids like blood and mucus exhibit high viscosities, there are still many open questions concerning the swimming behavior of microswimmers in highly viscous media, limiting research to idealized laboratory conditions instead of application‐oriented scenarios. Here, we analyze the effect of viscosity on the swimming speed and motion pattern of four kinds of microswimmers of different sizes which move by contrasting propulsion mechanisms: two biological swimmers (bovine sperm cells and Bacillus subtilis bacteria) which move by different bending patterns of their flagella and two artificial swimmers with catalytic propulsion mechanisms (alginate microtubes and Janus Pt@SiO2 spherical microparticles). Experiments consider two different media (glycerol and methylcellulose) with increasing viscosity, but also the impact of surface tension, catalyst activity and diffusion coefficients are discussed and evaluated.

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“…Green microalgae, Chlamydomonas reinhardtii, display complex dynamics in the presence of spatial variations in viscosity. If viscosity gradients are weak, they tend to accumulate in the high viscosity regions due to slower speeds, but in the presence of strong viscosity gradients, they reorient towards the low viscosity regions, displaying negative viscotaxis [16,17]. Helicobacter pylori, a bacterium commonly found in our guts, also swims through viscosity gradients as it propels by locally lowering the viscosity of the surrounding mucus layer [18,19].…”

Section: Introductionmentioning

confidence: 99%

On the hydrodynamics of active particles in viscosity gradients

Shaik¹,

Elfring²

2021

Preprint

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In this work, we analyze the motion of an active particle, modeled as a spherical squirmer, in linearly varying viscosity fields. In general, the presence of a particle will disturb a background viscosity field and the disturbance generated depends on the boundary conditions imposed by the particle on the viscosity field. We find that, irrespective of the details of the disturbance, active squirmer-type particle tend to align down viscosity gradients (negative viscotaxis). However, the rate of rotation and the swimming speed along the gradient do depend on the details of the interaction of the particle and the background viscosity field. In addition, we explore the relative importance on the dynamics of the local viscosity changes on the surface of active particles versus the (nonlocal) changes in the flow field due to spatially varying viscosity (from that of a homogeneous fluid). We show that the relative importance of local versus nonlocal effects depends crucially on the boundary conditions imposed by the particle on the field. This work demonstrates the dangers in neglecting the disturbance of the background viscosity caused by the particle as well as in using the local effects alone to capture the particle motion.

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Green algae scatter off sharp viscosity gradients

Cited by 24 publications

References 24 publications

Snell's Law for Gliders

Snell's Law for Gliders

Effect of Viscosity on Microswimmers: A Comparative Study

On the hydrodynamics of active particles in viscosity gradients

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