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  • Featured in Physics
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Capillary Bundling of Microtubules by Condensates

Bernardo Gouveia1,*, J. Pedro de Souza2,*, Venecia A. Valdez3, Joshua W. Shaevitz4,5, Howard A. Stone6,†, and Sabine Petry3,‡

  • *These authors contributed equally to this work.
  • †Contact author: hastone@princeton.edu
  • ‡Contact author: spetry@princeton.edu
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PRX Life 4, 043006 – Published 27 October, 2026

DOI: https://doi.org/10.1103/5flw-5xzh

Abstract

The cytoskeleton organizes the cellular interior using cytoskeletal filaments that rely on bundling, usually executed by stable and ordered cross-linking proteins. Bundling often requires protein complexes with at least two defined microtubule binding regions, as present in many molecular motors. Here, we establish a mechanism of microtubule bundling based on capillary forces, analogous to how wet hair sticks together. We show using in vitro experiments and theory that condensates can bundle microtubules through capillary forces, wherein liquidlike capillary bridges form between microtubules and adhere them together through interfacial and wetting forces. We quantify the structure and dynamics of these capillary bundles using total internal reflection fluorescence microscopy, and directly measure the interfacial tensions of condensates on microtubules using atomic force microscopy. Lastly, we show that these capillary bridges provide viscous resistance to motor-driven microtubule sliding that is insensitive to the bulk protein concentration. Taken together, we provide a novel mechanism for how cytoskeletal filaments bundle: through condensate-mediated capillary forces.

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Physics Subject Headings (PhySH)

Focus

More Than One Way to Assemble Molecular Scaffolding

Published 27 October, 2026

Experiments show that bundling of individual strands of an important protein polymer can occur through capillary forces, not just through molecular binding.

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PRX Life 4, 043006– Published 27 October, 2026
  • Received 2 January 2026
  • Accepted 2 September 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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