Moving microswimmers with tiny swirling flows

March 24, 2016, Argonne National Laboratory
A rotating particle creates a flow that pushes swimming bacteria into a spiral-shaped halo around the center. The discovery helps scientists understand the interaction of microswimmers and could help prevent films from forming in microfluidic devices such as labs-on-a-chip. Credit: Igor Aronson and Andrey Sokolov

Scientists at the U.S. Department of Energy's Argonne National Laboratory have discovered a way to use a microscopic swirling flow to rapidly clear a circle of tiny bacteria or swimming robots.

"This discovery offers a new approach for control and manipulation of microscopic swimmers," said Argonne physicist and co-author Igor Aronson, and it could be useful in tiny microfluidic ("lab-on-a-chip") devices that can quickly run chemical or biological analyses or perform tasks.

In the study, published in Nature Communications, the researchers placed a in the center of a liquid film filled with swimming bacteria.

Normally the bacteria swim randomly; but when scientists spun the particle by applying a rotating magnetic field, the swimmers shot away from the center, like a school of fish that suddenly realized there's a shark in their midst.

What's actually happening is that the particle is rotating, creating a small vortex around itself. The bacteria swim parallel to the stream lines and are quickly pushed outward—except for a few that get sucked in right next to the particle.

They're not pushed out by centrifugal force, said Argonne scientist Andrey Sokolov, who co-authored the paper; dead bacteria, which aren't swimming, are not pushed out with their living companions.

Moving microswimmers with tiny swirling flows

"Because of the curvature of the flow, some swim in and are trapped on the rotating particle, and others are forced to swim out of the curved flow," Sokolov said.

This technique could separate live from dead bacteria, or different species, bacterial strains or mutants from one another. "The shape and swimming rates of different species would mean they separate," Aronson said.

"At certain frequencies of rotation, the self-organize into a spiral-shaped halo, creating a microscopic galaxy—similar to our galaxy Milky Way, but trillions of trillions (1024) of times smaller," Sokolov said.

In addition to new understanding of the forces governing microswimmers and their environments, the vortex technique could help prevent biofilms from forming and disrupting microfluidic devices, the authors suggested.

They are particularly interested in creating systems in which microswimmers could assemble gears to build a tiny machine and then power it, Aronson said.

Explore further: Scientists combine bacteria with liquid crystals

More information: Andrey Sokolov et al. Rapid expulsion of microswimmers by a vortical flow, Nature Communications (2016). DOI: 10.1038/ncomms11114

Related Stories

Scientists combine bacteria with liquid crystals

March 6, 2014

(Phys.org) —When swimming around, bacteria aren't good with the "pool rules."  In small quantities, they'll follow the lanes, but put enough together and they'll begin to create their own flow.

Bacteria mix it up at the microscopic level

November 2, 2009

(PhysOrg.com) -- Many hands -- or many flagella -- make light work. In studies of the motion of tiny swimming bacteria, scientists at the U.S. Department of Energy's Argonne National Laboratory found that the microscopic ...

Researchers develop technique for bacteria crowd control

April 17, 2007

A surprising technique to concentrate, manipulate, and separate a wide class of swimming bacteria has been identified through a collaboration between researchers at Argonne National Laboratory, Illinois Institute of technology, ...

Recommended for you

High vinculin levels help keep aging fruit fly hearts young

July 17, 2018

Our cells tend to lose their shape as we grow older, contributing to many of the effects we experience as aging. This poses particular problems for the heart, where aging can disrupt the protein network within muscle cells ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.