Crosslinking and depletion determine spatial instabilities in cytoskeletal active matter

TL;DR

This study reveals how ATP and depletion agent concentrations control four distinct spatial instabilities in cytoskeletal active gels, unifying their understanding through a hydrodynamic model.

Contribution

It demonstrates that all four known spatial instabilities in cytoskeletal gels can occur within a single system and are governed by ATP and depletion levels, supported by a hydrodynamic model.

Findings

All four instabilities observed in a single active gel system.

Instabilities are controlled by ATP and depletion agent concentrations.

A hydrodynamic model explains the transition and selection of instabilities.

Abstract

Active gels made of cytoskeletal proteins are valuable materials with attractive non-equilibrium properties such as spatial self-organization and self-propulsion. At least four typical routes to spatial patterning have been reported to date in different types of cytoskeletal active gels: bending and buckling instabilities in extensile systems, and global and local contraction instabilities in contractile gels. Here we report the observation of these four instabilities in a single type of active gel and we show that they are controlled by two parameters: the concentrations of ATP and depletion agent. We demonstrate that as the ATP concentration decreases, the concentration of passive motors increases until the gel undergoes a gelation transition. At this point, buckling is selected against bending, while global contraction is favored over local ones. Our observations are coherent with a hydrodynamic model of a viscoelastic active gel where the filaments are crosslinked with a characteristic time that diverges as the ATP concentration decreases. Our work thus provides a unified view of spatial instabilities in cytoskeletal active matter.