1. Physics of Living Systems
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Strong confinement of active microalgae leads to inversion of vortex flow and enhanced mixing

  1. Debasmita Mondal
  2. Ameya G Prabhune
  3. Sriram Ramaswamy
  4. Prerna Sharma  Is a corresponding author
  1. Indian Institute of Science, India
Research Article
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Cite this article as: eLife 2021;10:e67663 doi: 10.7554/eLife.67663


Microorganisms swimming through viscous fluids imprint their propulsion mechanisms in the flow fields they generate. Extreme confinement of these swimmers between rigid boundaries often arises in natural and technological contexts, yet measurements of their mechanics in this regime are absent. Here, we show that strongly confining the microalga Chlamydomonas between two parallel plates not only inhibits its motility through contact friction with the walls but also leads, for purely mechanical reasons, to inversion of the surrounding vortex flows. Insights from the experiment lead to a simplified theoretical description of flow fields based on a quasi-2D Brinkman approximation to the Stokes equation rather than the usual method of images. We argue that this vortex flow inversion provides the advantage of enhanced fluid mixing despite higher friction. Overall, our results offer a comprehensive framework for analyzing the collective flows of strongly confined swimmers.

Data availability

All data generated or analyzed during this study are included in the manuscript and supporting files. Separate source data files containing source data for each subfigure have been provided. A source code file containing the custom-written MATLAB codes has also been provided.

Article and author information

Author details

  1. Debasmita Mondal

    Department of Physics, Indian Institute of Science, Bangalore, India
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-8265-6876
  2. Ameya G Prabhune

    Department of Physics, Indian Institute of Science, Bangalore, India
    Competing interests
    The authors declare that no competing interests exist.
  3. Sriram Ramaswamy

    Centre for Condensed Matter Theory, Deptartment of Physics, Indian Institute of Science, BENGALURU, India
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0001-7726-8556
  4. Prerna Sharma

    Department of Physics, Indian Institute of Science, Bangalore, India
    For correspondence
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0003-4988-9560


The Wellcome Trust DBT India Alliance (IA/I/16/1/502356)

  • Prerna Sharma

Science and Engineering Research Board (J C Bose Fellowship)

  • Sriram Ramaswamy

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Reviewing Editor

  1. Raymond E Goldstein, University of Cambridge, United Kingdom

Publication history

  1. Received: February 18, 2021
  2. Accepted: November 16, 2021
  3. Accepted Manuscript published: November 22, 2021 (version 1)


© 2021, Mondal et al.

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.


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