Non-local fluctuation correlations in active gels

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 is essential for understanding 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 build-up 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.

12 pages, 7 figures; some clarifications and ammended figure notation.

References in corpus (9)

• Elasticity of Stiff Polymer Networks
• Non-equilibrium mechanics and dynamics of motor activated gels
• Strain localization in a shear transformation zone model for amorphous solids
• Non-equilibrium microtubule fluctuations in a model cytoskeleton
• Transient Binding and Dissipation in Semi-flexible Polymer Networks
• Generic phase diagram of active polar films
• Visualizing the strain field in semiflexible polymer networks: strain fluctuations and nonlinear rheology of F-actin gels
• Effective medium theory of semiflexible filamentous networks
• Dynamics of semi-flexible polymer solutions in the highly entangled regime

Cited by in corpus (8)

• Modeling semiflexible polymer networks
• Instabilities and Oscillations in Isotropic Active Gels
• Microscopic basis for pattern formation and anomalous transport in two-dimensional active gels
• Spindles and active vortices in a model of confined filament-motor mixtures
• Local mechanical response in semiflexible polymer networks subjected to an axisymmetric prestress
• Active gels, heavy tails, and the cytoskeleton
• The Effects of the Interplay Between Motor and Brownian Forces on the Rheology of Active Gels
• Nonlinear master relation in microscopic mechanical response of semiflexible biopolymer networks