Entropic tug of war: Topological constraints spontaneously rectify the dynamics of a polymer with heterogeneous fluctuations

TL;DR

This study demonstrates that in dense active-passive copolymers with heterogeneous fluctuations, topological constraints induce spontaneous directional motion despite the absence of explicit directional forces, impacting biological and material systems.

Contribution

It reveals how topological constraints can spontaneously generate persistent motion in active-passive polymers without artificial correlations, a novel insight into active polymer dynamics.

Findings

Directional persistent motion arises spontaneously in dense active-passive copolymers.

Topological constraints break translational symmetry, leading to emergent dynamics.

Implications for chromatin behavior and active polymeric materials.

Abstract

Polymers with active segments constitute prospective future materials and are used as a model for some biological systems such as chromatin. The directions of the active forces are typically introduced with temporal or spatial correlations to establish directional motion of the chain and corresponding active dynamics. Instead, here we consider an active-passive copolymer, where the two segments differ only by the magnitude of their fluctuations and feature no artificial correlations. Here we show that although the model itself does not possess directional dynamics, if the chains are concentrated, directional persistent motion spontaneously arises as a consequence of the broken translational symmetry owing to the topological constraints. Using scaling arguments and simulations, we explain the phenomenon and describe the ensuing dynamics. Our work has thus far-reaching consequences for the mechanical properties of all dense active polymeric systems with heterogeneous fluctuations and in particular for chromatin conformation and dynamics that are crucial for biological functionality.