Emergence of coexisting ordered states in active matter systems

Abstract

Active systems can produce a far greater variety of ordered patterns than conventional equilibrium systems. In particular, transitions between disorder and either polar- or nematically ordered phases have been predicted and observed in two-dimensional active systems. However, coexistence between phases of different types of order has not been reported. We demonstrate the emergence of dynamic coexistence of ordered states with fluctuating nematic and polar symmetry in an actomyosin motility assay. Combining experiments with agent-based simulations, we identify sufficiently weak interactions that lack a clear alignment symmetry as a prerequisite for coexistence. Thus, the symmetry of macroscopic order becomes an emergent and dynamic property of the active system. These results provide a pathway by which living systems can express different types of order by using identical building blocks.

Cytoskeletal and Actin‐Based Polymerization Motors and Their Role in Minimal Cell Design

“…For example, actin monomers (5.4 nm in diameter) assemble into linear doublehelical polymers, which are subsequently organized by a variety of actin-binding proteins. [8] The property of active molecular machines to consist of the same building blocks but with high diversity in their final function may be very useful toward the design of a minimal cell. [4,5] Moreover, although consisting of the very same monomer, stress fibers made of antiparallel actin filaments and contractile myosins bridge adhesion sites, [6] while protrusions are created by filopodia consisting of assembled parallel actin filaments.…”

Molecular motors in materials science

“…33 This work is foundational to the study of active matter, because it demonstrates the emergence of distinct and long-lasting organizational states determined by the motor activity and also the boundary conditions. More recent work by the Bausch and Frey, 34 Dogic and Needleman, 35 Kakugo, 36 and Oiwa 37 research groups is driven by the appreciation of the interesting properties of these motor-filament systems from a materials science perspective.…”

“…The theoretical investigation of these systems thus often relies on agent-based simulations and theories describing the interaction dynamics. 34,38 Due to the rod-like shape of the filaments, the motorfilament systems resemble nematic materials, where local alignment is favored (Figure 2c). 39 However, alignment of filaments can be induced by diverse mechanisms.…”

“…39 The observed coexistence of different ordered states (nematic and polar) demonstrates that active matter has richer phase behavior than systems in thermal equilibrium (Figure 2e). 34 The system dynamics can be further enriched by time-varying boundary conditions, which can favor the emergence of specific steady states.…”

Cancer: A Turbulence Problem

“…Soft matter physics is demonstrating that the turbulent energy cascades of the Navier-Stokes equations may help explain collective cell migration and pattern formation within cells (93)(94)(95). The cytoskeletal protein microtubules and actin are being recognized as candidates for these active turbulence models, wherein the swarming and flocking behaviors of proteins can phase-transition from the stochastic Brownian motion to the turbulent regime of the Navier-Stokes equations (95,96). These findings suggest the role of the Navier-stokes equations in protein-mediated patterning within cancer cells severely lacks experimental investigation although it is surfacing in systems science.…”