Nonlocal fluctuation correlations in active gels

D. A. Head and D. Mizuno
Phys. Rev. E 81, 041910 – Published 13 April 2010

Abstract

Many active materials and biological systems are driven far from equilibrium by embedded agents that spontaneously generate forces and distort the surrounding material. Probing and characterizing these athermal fluctuations are essential to understand the properties and behaviors of such systems. Here we present a mathematical procedure to estimate the local action of force-generating agents from the observed fluctuating displacement fields. The active agents are modeled as oriented force dipoles or isotropic compression foci, and the matrix on which they act is assumed to be either a compressible elastic continuum or a coupled network-solvent system. Correlations at a single point and between points separated by an arbitrary distance are obtained, giving a total of three independent fluctuation modes that can be tested with microrheology experiments. Since oriented dipoles and isotropic compression foci give different contributions to these fluctuation modes, ratiometric analysis allows us characterize the force generators. We also predict and experimentally find a high-frequency ballistic regime, arising from individual force-generating events in the form of the slow buildup of stress followed by rapid but finite decay. Finally, we provide a quantitative statistical model to estimate the mean filament tension from these athermal fluctuations, which leads to stiffening of active networks.

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  • Received 18 February 2010

DOI:https://doi.org/10.1103/PhysRevE.81.041910

©2010 American Physical Society

Authors & Affiliations

D. A. Head1,2 and D. Mizuno3

  • 1Institute of Industrial Science, University of Tokyo, Meguro-ku, Tokyo 153-8505, Japan
  • 2Institut für Festkörperforschung, Theorie II, Forschungszentrum Jülich, Jülich 52425, Germany
  • 3Institute for Advanced Study, Kyushu University, 812-8581 Fukuoka, Japan

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Issue

Vol. 81, Iss. 4 — April 2010

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