Tunable corrugated patterns in an active nematic sheet

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, 1,2 leading to active turbulence in two and three dimensions 3,4 and coherent flow in three dimensions 5 (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.

Wrinkling Instability in 3D Active Nematics

“…This remarkable sequence demonstrates 3D active nematic dynamics and instabilities similar to those observed in a recent study. 29 Conversely, no comparison can be made with 2D systems investigated so far 26 due to different spatial distribution of that system and its interaction with substrates. Inside the ribbon, nematically ordered filament bundles are clearly visible.…”

“…Similar results of a parallel study have been recently published. 29 However, the contraction in the mentioned system is passive and due to depletion agent, while our network actively contracts due to the motor action. A related folding phenomenon has been observed also in thin acto-myosin networks 30 whose behavior was generated by contracting forces and not by extensile ones as in the present work.…”

Gait-optimized locomotion of wave-driven soft sheets

“…47 Little is understood about the optimization of motion through complex fluids or granular media, or even over fluid-air interfaces along which some realworld snails crawl. 48 Furthermore, active sheets driven by turbulent patterns, rather than the regular driving waves studied here, have been examined experimentally for creating tunable actuating films 49 and merits detailed theoretical consideration. Finally, recent works have highlighted the importance of mechanical feedback for tuning self-deformations 50,51 -exploring how these and other feedback mechanisms could be used to achieve adaptable locomotion offers yet another interesting direction for future research.…”

Programmed mechano-chemical coupling in reaction-diffusion active matter

“…4,5 On the chemical side, in vitro out-of-equilibrium reaction networks produce spatio-temporal concentration patterns through reaction or reaction-diffusion instabilities. 6–14 On the mechanical side, active gels made of cytoskeletal motors and filaments reconstituted in vitro 4,15–24 convert chemical energy into mechanical work and generate static patterns and flows through hydrodynamic instabilities. 25 More recently, efforts have focused on coupling reaction networks with active fluids and gels, resulting in redox-controlled selfoscillating gels 26 and DNA-controlled passive 27 and active gels.…”

“…Considered independently, each subsystem reveals complex dynamics and macroscopic organizations which are subject to intense scrutiny. 14,15,17,19,21,24,35,37 When mixed-together, the coupling strength between the two subsystems is set by the magnitude of the flow generated by the active gel. As a result, this system may be useful for investigating self-organization when chemical and mechanical out-of-equilibrium processes are intertwined.…”