Motility and self propulsion of active droplets

TL;DR

This paper reviews the current theoretical and numerical research on active droplets, focusing on active gel theory, topology, and symmetry-breaking mechanisms that lead to self-propulsion in various geometries.

Contribution

It provides a comprehensive overview of the state of the art in active droplet research, emphasizing theoretical models and topological considerations.

Findings

Active gel theory models self-motile droplets.

Topology influences active droplet behavior.

Symmetry-breaking drives motility in 2D and 3D.

Abstract

In the last years self-motile droplets attracted the attention of scientists from different fields ranging from applied biology to theoretical physics, because of their promising technological applications and important biological implications. In this Chapter we review the state of the art of the research on active droplets with a particular focus on theoretical and numerical studies. In particular, we reviewed the active gel theory, namely a generalization of the standard Landau-de Gennes theory for liquid crystals adapted to take into account internal active injection due to the presence of self-motile constituents. When confined in finite geometries, liquid crystalline-like systems are also subject to topological constraints. Because of the relevance of topology in many different realizations of active droplets, we also reviewed some fundamental topological concepts. We review how motility arises in different realizations of active droplet both in 2d and 3d as the result of the breaking of specific symmetries, by looking in particular detail at the case of polar and nematic droplets and shells of active liquid crystals.