Taxis of cargo-carrying microswimmers in traveling activity waves

TL;DR

This study investigates how cargo-carrying microswimmers behave in traveling activity waves, revealing complex tactic behaviors influenced by cargo mobility and friction ratios, with potential applications in designing bio-hybrid microswimmers.

Contribution

It introduces a theoretical and numerical analysis of active-passive dimers in traveling waves, highlighting emergent tactic behaviors and the conditions for active surfing.

Findings

Low mobility cargo always drifts with the wave.

High mobility cargo can drift against the wave.

Dimer can actively surf wave maxima in slow waves.

Abstract

Many fascinating properties of biological active matter crucially depend on the capacity of constituting entities to perform directed motion, e.g., molecular motors transporting vesicles inside cells or bacteria searching for food. While much effort has been devoted to mimicking biological functions in synthetic systems, such as transporting a cargo to a targeted zone, theoretical studies have primarily focused on single active particles subject to various spatial and temporal stimuli. Here we study the behavior of a self-propelled particle carrying a passive cargo in a travelling activity wave and show that this active-passive dimer displays a rich, emergent tactic behavior. For cargoes with low mobility, the dimer always drifts in the direction of the wave propagation. For highly-mobile cargoes, instead, the dimer can also drift against the traveling wave. The transition between these two tactic behaviors is controlled by the ratio between the frictions of the cargo and the microswimmer. In slow activity waves the dimer can perform an active surfing of the wave maxima, with an average drift velocity equal to the wave speed. These analytical predictions, which we confirm by numerical simulations, might be useful for the future efficient design of bio-hybrid microswimmers.