Synopsis: Reluctant swimmers

The swimming motion of organisms in complex fluids is hindered by elasticity.

Microorganisms routinely live in complex fluids such as mud, intestinal fluid, and mucus. In this world of varying rheological properties, organisms propagate with a motion analogous to swimming. Think of spermatozoa propelled by undulations of flagella. Researchers have known that the properties of a fluid strongly affect how the organisms swim in it—the beat of a spermatozoon’s flagella, for example, goes from sinusoidal in an “ordinary” Newtonian fluid to asymmetric in a viscoelastic fluid, a medium that shows both solid- and fluid-like behavior—but quantitative studies have been scarce.

In a paper in Physical Review Letters, Xiaoning Shen and Paulo E. Arratia, at the Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania, report usage of video microscopy and velocimetry methods to measure body kinematics and swimming dynamics of a species of roundworm in a range of shear viscosities and viscoelasticities. They find that the fluid elasticity hinders swimming speed as well as efficiency. This result is surprising, if only because myriad biological processes occur in such fluids. Examples range from sperms in the female reproductive tract to allergens in the respiratory passage. The authors find that the roundworm’s swimming speed is reduced by up to 35% compared to that in ordinary fluids. This work provides a valuable experimental benchmark for what appears to be a ubiquitous phenomenon. – Sami Mitra


Announcements

More Announcements »

Subject Areas

Fluid DynamicsBiological Physics

Previous Synopsis

Next Synopsis

Atomic and Molecular Physics

Steps toward a new quantum fluid

Read More »

Related Articles

Synopsis: Tiny Droplets Do the Twist
Fluid Dynamics

Synopsis: Tiny Droplets Do the Twist

Liquid-crystal droplets can act like controllable artificial swimmers, twisting in two and three dimensions. Read More »

Synopsis: Forming Granular Plugs
Fluid Dynamics

Synopsis: Forming Granular Plugs

Experiments on grain-water-air mixtures flowing through a tube find that frictional forces between the grains and the tube lead to the creation of a series of plugs. Read More »

Focus: Biological Cells Form Electric Circuits
Biological Physics

Focus: Biological Cells Form Electric Circuits

Cells that are electrically active and that also produce light for easy voltage monitoring could lead to new studies of heart arrhythmias and possibly bio-computing. Read More »

More Articles