Tunable corrugated patterns in an active gel sheet

TL;DR

This paper demonstrates that active gels can form stable, static, centimeter-sized corrugated patterns driven by active forces, with pattern characteristics controlled by motor concentration, revealing new static pattern formation mechanisms in active matter.

Contribution

It shows that active gels can spontaneously form stable, static corrugated patterns in two dimensions, controlled by motor concentration, expanding understanding of pattern formation in active matter.

Findings

Stable, static corrugated patterns form in active gels.

Pattern wavelength and stability depend on motor concentration.

At higher activity, patterns become transient and turbulence emerges.

Abstract

Active matter locally converts chemical energy into mechanical work and, for this reason, it provides new mechanisms of pattern formation. In particular, active gels made of protein motors and filaments are far-from-equilibrium systems that exhibit spontaneous flow,[Kruse2004, Voituriez2005] leading to active turbulence in two and three dimensions[Sanchez2012, Kumar2018] and coherent flow in three dimensions[Wu2017] (3D). Although these dynamic flows reveal a characteristic length scale resulting from the interplay between active forcing and passive restoring forces, the observation of static and long-range spatial patterns in active gels has remained elusive. In this work, we demonstrate that a 2D free-standing nematic active gel, formed spontaneously by depletion forces from a 3D solution of kinesin motors and microtubule filaments, actively buckles out-of-plane into a centimeter-sized periodic corrugated sheet that is stable for several days at low activity. Importantly, the corrugations are formed in the absence of flow and their wavelength and stability are controlled by the motor concentration, in agreement with a hydrodynamic theory. At higher activities these patterns are transient with the gel becoming turbulent at longer times. Our results underline the importance of both passive and active forces in shaping active gels and indicate that a static material can be sculpted through an active mechanism.