Chemotaxis of artificial microswimmers in active density waves

TL;DR

This paper investigates how artificial microswimmers respond to traveling active density waves, revealing they can move in various directions depending on wave properties, unlike biological microorganisms.

Contribution

It demonstrates, through analytical and numerical methods, that artificial microswimmers exhibit diverse tactic responses to active waves, including bidirectional diffusion and perpendicular movement for chiral swimmers.

Findings

Artificial swimmers can diffuse in either direction relative to the wave.

Chiral swimmers tend to diffuse perpendicular to the active wave.

Diffusion modulation explains the variety of tactic responses.

Abstract

Living microorganisms are capable of a tactic response to external stimuli by swimming towards or away from the stimulus source; they do so by adapting their tactic signal transduction pathways to the environment. Their self-motility thus allows them to swim against a traveling tactic wave, whereas a simple fore-rear asymmetry argument would suggest the opposite. Their biomimetic counterpart, the artificial microswimmers, also propel themselves by harvesting kinetic energy from an active medium, but, in contrast, lack the adaptive capacity. Here we investigate the transport of artificial swimmers subject to traveling active waves and show, by means of analytical and numerical methods, that self-propelled particles can actually diffuse in either direction with respect to the wave, depending on its speed and waveform. Moreover, chiral swimmers, which move along spiraling trajectories, may diffuse preferably in a direction perpendicular to the active wave. Such a variety of tactic responses is explained by the modulation of the swimmer's diffusion inside traveling active pulses.