Modeling the dynamics of a tracer particle in an elastic active gel

TL;DR

This paper develops a theoretical model to analyze the non-equilibrium dynamics of tracer particles in active gels, revealing how activity affects their behavior and providing insights into experimental observations.

Contribution

It introduces a comprehensive theoretical framework for understanding tracer particle dynamics in active gels, including analytic and numerical analysis of non-equilibrium effects.

Findings

Breakdown of virial theorem and equipartition due to activity

Identification of elasticity-dependent effective temperatures

Prediction of non-Gaussian displacement distributions

Abstract

The internal dynamics of active gels, both in artificial (in-vitro) model systems and inside the cytoskeleton of living cells, has been extensively studied by experiments of recent years. These dynamics are probed using tracer particles embedded in the network of biopolymers together with molecular motors, and distinct non-thermal behavior is observed. We present a theoretical model of the dynamics of a trapped active particle, which allows us to quantify the deviations from equilibrium behavior, using both analytic and numerical calculations. We map the different regimes of dynamics in this system, and highlight the different manifestations of activity: breakdown of the virial theorem and equipartition, different elasticity-dependent "effective temperatures" and distinct non-Gaussian distributions. Our results shed light on puzzling observations in active gel experiments, and provide physical interpretation of existing observations, as well as predictions for future studies.