Constrained motion of self-propelling eccentric disks linked by a spring

TL;DR

This study introduces an active chain model of eccentric disks linked by springs to explore how activity, elasticity, and friction induce complex non-equilibrium behaviors like self-rotation and beating, with implications for biological systems.

Contribution

The paper presents a novel experimental and simulation model of active eccentric disks linked by springs, revealing how topological constraints influence non-equilibrium dynamics.

Findings

Active chains exhibit self-rotation and beating behaviors.

Hairpin conformations emerge in free motion.

Frequency scaling with flexure number (~4/3) indicates activity-energy dissipation balance.

Abstract

It has been supposed that the interplay of elasticity and activity plays a key role in triggering the non-equilibrium behaviors in biological systems. However, the experimental model system is missing to investigate the spatiotemporally dynamical phenomena. Here, a model system of an active chain, where active eccentric-disks are linked by a spring, is designed to study the interplay of activity, elasticity, and friction. Individual active chain exhibits longitudinal and transverse motion, however, it starts to self-rotate when pinning one end, and self-beats when clamping one end. Additionally, our eccentric-disk model can qualitatively reproduce such behaviors and explain the unusual self-rotation of the first disk around its geometric center. Further, the structure and dynamics of long chains were studied via simulations without steric interactions. It was found that hairpin conformation emerges in free motion, while in the constrained motions, the rotational and beating frequencies scale with the flexure number (the ratio of self-propelling force to bending rigidity), ~4/3. Scaling analysis suggests that it results from the balance between activity and energy dissipation. Our findings show that topological constraints play a vital role in non-equilibrium synergy behavior.