Autonomous waves and global motion modes in living active solids

TL;DR

This study uncovers self-sustained elastic waves and distinct global motion modes in living active solids, revealing new spatiotemporal order and potential for adaptive materials.

Contribution

It demonstrates the existence of unique elastic waves and topologically distinct motion modes in active solids, advancing understanding of their mechanical behavior.

Findings

Discovered self-sustained elastic waves with power-law scaling.

Identified two topologically distinct global motion modes.

Observed step-like frequency jump at mode transition.

Abstract

Elastic active matter or active solid consists of self-propelled units embedded in an elastic matrix. Active solid resists deformation; the shape-preserving property and the intrinsic non-equilibrium nature make active solids a superior component for self-driven devices. Nonetheless, the mechanical properties and emergent behavior of active solids are poorly understood. Using a biofilm-based bacterial active solid, here we discovered self-sustained elastic waves with unique wave properties not seen in passive solids, such as power-law scaling of wave speed with activity. Under isotropic confinement, the active solid develops two topologically distinct global motion modes that can be selectively excited, with a surprising step-like frequency jump at mode transition. Our findings reveal novel spatiotemporal order in elastic active matter and may guide the development of solid-state adaptive or living materials.