Designing topological edge states in bacterial active matter

TL;DR

This study demonstrates the realization of topological edge states in dense bacterial suspensions using microfabricated geometrical structures, revealing how collective bacterial flow can generate robust, localized edge transport.

Contribution

It introduces a method to create and control topological edge states in bacterial active matter through microfabricated geometries, extending topological concepts beyond chiral particles.

Findings

Edge localization of bacterial density observed in microfabricated networks

Topological origin of edge states confirmed by transport model

Design features like channel directionality and chirality are key for edge states

Abstract

Topology provides a unifying framework for understanding robust transport through protected edge states arising from nontrivial wavenumber topology. Extending these concepts to active matter, however, remains largely unexplored experimentally, with realizations limited to systems composed of chiral active particles. Here, we realize topological edge states in dense bacterial suspension, which represents a prototypical active matter system, using microfabricated geometrical structures with nontrivial wavenumber topology. Inspired by previous theoretical studies, we constructed a directional kagome network composed of ratchet-shaped channels that induce unidirectional bacterial flow. In this network, we found clear edge localization of bacterial density. A steady-state analysis based on the bacterial transport model and experimentally measured velocity field reveals how the characteristic collective flow generates edge localization. The model also uncovers the topological origin of the observed edge states. By tuning the geometry of the microfabricated networks, we identified directional channel design and network chirality as the key design features essential for the emergence of the edge state. Our results pave the way for establishing a control and design principle of topological transport in such active matter systems.