Driven shear flow in biological magneto-active fluids

TL;DR

This study investigates how magnetotactic bacteria in active fluids respond to combined chemotactic and magnetotactic cues, revealing complex flow patterns and providing a hydrodynamic model for external cue-driven dynamics.

Contribution

It introduces a magneto-active hydrodynamic model for active fluids influenced by multiple external cues, combining experimental observations with theoretical analysis.

Findings

Steady flows are well-described by the hydrodynamic model.

Time-dependent magnetic fields induce complex patterning.

External cues can be used to manipulate active fluid behavior.

Abstract

Active fluids made of powered suspended particles have unique abilities to self-generate flow and density structures. How such dynamics can be triggered and leveraged by external cues is a key question of both biological and applied relevance. Here we use magnetotactic bacteria to explore how chemotaxis and magnetotaxis -- leading, respectively, to positional and orientational responses -- combine to generate global scale flows. Such steady regime can be quantitatively captured by a magneto-active hydrodynamic model, while time-dependent magnetic driving unveils additional patterning complexity. Overall, our findings shed light on how active fluids respond to the ubiquitous situation of multiple external information, also suggesting routes for their manipulation.