Circular swimming motility and disordered hyperuniform state in an algae system

Abstract

Active matter comprises individually driven units that convert locally stored energy into mechanical motion. Interactions between driven units lead to a variety of nonequilibrium collective phenomena in active matter. One of such phenomena is anomalously large density fluctuations, which have been observed in both experiments and theories. Here we show that, on the contrary, density fluctuations in active matter can also be greatly suppressed. Our experiments are carried out with marine algae (Effrenium voratum), which swim in circles at the air–liquid interfaces with two different eukaryotic flagella. Cell swimming generates fluid flow that leads to effective repulsions between cells in the far field. The long-range nature of such repulsive interactions suppresses density fluctuations and generates disordered hyperuniform states under a wide range of density conditions. Emergence of hyperuniformity and associated scaling exponent are quantitatively reproduced in a numerical model whose main ingredients are effective hydrodynamic interactions and uncorrelated random cell motion. Our results demonstrate the existence of disordered hyperuniform states in active matter and suggest the possibility of using hydrodynamic flow for self-assembly in active matter.

Spontaneously rotating clusters of active droplets

“…24 Noticeably, it has been shown for swimmers with intrinsic chirality that contributions from individual swimmers can synchronise into global rotation states, both for biological systems and the respective theory models. [25][26][27][28] Rotating clusters with torques resulting from off-centre propulsion can also be engineered using binary mixtures or Janus swimmers. [29][30][31] However, as we demonstrate in this study, similar individual and collective dynamics may also emerge from systems without any pre-engineered symmetries.…”

Hyperuniform Active Chiral Fluids with Tunable Internal Structure

“…The shapes and color of the symbols correspond to different dynamic phases: vortices (blue circles), rotating flocks (green squares) and spinners (red triangles). The area fraction φ = 0.116. values of the hyperuniform scaling exponent n have been previously reported in several experimental 2D soft matter systems, such as in sheared colloidal suspensions (n = 0.25) [9], in periodically driven emulsions (n = 0.5) [6] and in algae suspensions (n = 0.6) [21].…”

“…While the global hyperuniformity in that system was observed at large length-scales, large local density fluctuations were confined within the length-scale comparable to the radius of the circular motion of the active particles. Recently, the existence of a disordered hyperuniform state in a system of marine algae performing circular motion was reported [21]. However, the large density fluctuations were fully suppressed in that system due to the lack of velocity alignment mechanisms.…”

“…The isotropic nature and defect insensitivity of the disordered hyperuniform materials make them promising candidates for applications in photonics as materials with isotropic complete photonic band gaps [3,4]. The disordered hyperuniform states have been observed in a handful of systems, including periodically driven colloidal suspensions [5][6][7][8][9], jammed packings [2,[10][11][12][13][14][15], block copolymers assemblies [16,17], amorphous 2D materials [18,19], biological systems [20,21], and simulation models [22][23][24][25][26][27].…”

Dynamic Measure of Hyperuniformity and Nonhyperuniformity in Heterogeneous Media via the Diffusion Spreadability

“…Time-dependent interphase diffusion processes in multiphase heterogeneous media arise in a wide range of physical, chemical and biological contexts, including magnetic resonance imaging [1], surface catalysis [2,3], material design [2,4,5] and cell-behavior modeling [6,7]. Heterogeneous media are ubiquitous; examples include composites, geological media, gels, foams, cell aggregates, among other natural and synthetic media [2,[8][9][10][11][12]. It is well known that the effective transport properties of heterogeneous media generally depend on an infinite set of correlation functions that characterize the microstructure [2,12,13].…”