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Critical Capillary Waves of Biomolecular Condensates

Shunsuke F. Shimobayashi*

Paul J. Ackerman

Tomo Kurimura

Takashi Taniguchi

Clifford P. Brangwynne

  • Center for iPS Cell Research and Application, Kyoto University, Sakyo-ku, Kyoto 606-8507, Japan

  • Department of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey 08544, USA

  • Center for iPS Cell Research and Application, Kyoto University, Sakyo-ku, Kyoto 606-8507, Japan

  • Department of Chemical Science and Engineering, Kyoto University, Kyoto 615-8510, Japan

  • *Contact author: s.shimobayashi@cira.kyoto-u.ac.jp
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PRX Life 4, 023032 – Published 25 June, 2026

DOI: https://doi.org/10.1103/8rgq-wymv

Abstract

Biomolecular condensates formed by phase separation are key players in cellular organization, yet their interfacial mechanics remain poorly understood. Here we show that both synthetic and endogenous nuclear condensates exhibit critical-like interfacial behaviors near the phase boundary, including enhanced capillary fluctuations and reduced surface tension. By combining optogenetic control with submicron-resolution fluctuation spectroscopy, we quantitatively estimate surface tension, bending rigidity, and effective viscosity. Surface tension diminishes as the system approaches the critical composition, consistent with classical theories of phase separation. Notably, bending elasticity emerges as an unexpected feature of these nuclear liquidlike structures, suggesting the formation of structured interfacial layers that progressively weaken near criticality. Among these condensates, the nucleolus displays exceptionally high viscosity, which may arise in part from viscoelastic coupling to the surrounding perinucleolar heterochromatin, effectively increasing the apparent viscosity in the long-time fluctuation regime. This noninvasive approach enables probing condensate mechanics in living cells and may provide a basis for diagnosing or modulating condensates in biomedical contexts.

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This article appears in the following collection:

Collection on Physics of Biomolecular Condensates

From the fundamentals of phase separation, dynamics and structure of condensates in biological settings, to advanced imaging methods, this special collection presented by PRX Life showcases exciting and timely work on the physics of biomolecular condensates.

This Invited Collection is coordinated by PRX Life Associate Editor Christoph Weber, in consultation with Jerelle Joseph, Simon Alberti, and Tanja Mittag. Every article published in this collection underwent a rigorous peer review process, adhering to the same high standards applied to all papers handled by the journal. The PRX Life editorial team managed the peer review and made all editorial decisions.

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PRX Life 4, 023032– Published 25 June, 2026
  • Received 1 December 2025
  • Accepted 21 May 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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