Active Solids Model: Rigid Body Motion and Shape-changing Mechanisms

TL;DR

This paper introduces a model for active solids that explains how stress can induce shape-changing and locomotion modes, providing insights into designing living and robotic materials with multiple dynamic behaviors.

Contribution

It presents a novel theoretical framework linking stress propagation to mode activation in active solids, including an adiabatic approximation and effective free energy mapping.

Findings

Stress induces spontaneous activation of soft modes.

Mode selection and collective dynamics predicted by the model.

Framework applicable to designing adaptive living and robotic materials.

Abstract

Active solids such as cell collectives, colloidal clusters, and active metamaterials exhibit diverse collective phenomena, ranging from rigid body motion to shape-changing mechanisms. The nonlinear dynamics of such active materials remains however poorly understood when they host zero-energy deformation modes and when noise is present. Here, we show that stress propagation in a model of active solids induces the spontaneous actuation of multiple soft floppy modes, even without exciting vibrational modes. By introducing an adiabatic approximation, we map the dynamics onto an effective Landau free energy, predicting mode selection and the onset of collective dynamics. These results open new ways to study and design living and robotic materials with multiple modes of locomotion and shape-change.