Active Particles in Complex and Crowded Environments

TL;DR

This review explores the physics, behaviors, and applications of active particles that self-propel in complex environments, highlighting recent developments and ongoing challenges in the field.

Contribution

It provides a comprehensive overview of the fundamental principles, artificial micro- and nanomachines, and their applications in nonequilibrium physics and complex environments.

Findings

Active particles exhibit unique behaviors in crowded environments.

Artificial micro- and nanomachines mimic biological motility.

Open challenges include understanding interactions and control mechanisms.

Abstract

Differently from passive Brownian particles, active particles, also known as self-propelled Brownian particles or microswimmers and nanoswimmers, are capable of taking up energy from their environment and converting it into directed motion. Because of this constant flow of energy, their behavior can only be explained and understood within the framework of nonequilibrium physics. In the biological realm, many cells perform directed motion, for example, as a way to browse for nutrients or to avoid toxins. Inspired by these motile microorganisms, researchers have been developing artificial particles that feature similar swimming behaviors based on different mechanisms; these manmade micro- and nanomachines hold a great potential as autonomous agents for healthcare, sustainability, and security applications. With a focus on the basic physical features of the interactions of self-propelled Brownian particles with a crowded and complex environment, this comprehensive review will put the reader at the very forefront of the field, providing a guided tour through its basic principles, the development of artificial self-propelling micro- and nanoparticles, and their application to the study of nonequilibrium phenomena, as well as the open challenges that the field is currently facing.