Supramolecular assemblies in active motor-filament systems: micelles, bilayers, and foams

TL;DR

This paper models active motor-filament systems, deriving continuum equations that reveal how supramolecular structures like micelles, bilayers, and foams form and transition due to instabilities driven by motor activity and filament interactions.

Contribution

It introduces a microscopic model and continuum equations for active motor-filament systems, explaining the formation and transition of complex supramolecular assemblies.

Findings

Identification of a branching instability causing structure transitions.

Discovery of a fingering instability affecting micelle shape.

Analysis of mechanisms like contractility and active splay influencing instabilities.

Abstract

Active matter systems evade the constraints of thermal equilibrium, leading to the emergence of intriguing collective behavior. A paradigmatic example is given by motor-filament mixtures, where the motion of motor proteins drives alignment and sliding interactions between filaments and their self-organization into macroscopic structures. After defining a microscopic model for these systems, we derive continuum equations, exhibiting the formation of active supramolecular assemblies such as micelles, bilayers and foams. The transition between these structures is driven by a branching instability, which destabilizes the orientational order within the micelles, leading to the growth of bilayers at high microtubule densities. Additionally, we identify a fingering instability, modulating the shape of the micelle interface at high motor densities. We study the role of various mechanisms in these two instabilities, such as contractility, active splay, and anchoring, allowing for generalization beyond the system considered here.