Hydrodynamics of soft active matter

Abstract

This review summarizes theoretical progress in the field of active matter, placing it in the context of recent experiments. This approach offers a unified framework for the mechanical and statistical properties of living matter: biofilaments and molecular motors in vitro or in vivo, collections of motile microorganisms, animal flocks, and chemical or mechanical imitations. A major goal of this review is to integrate several approaches proposed in the literature, from semimicroscopic to phenomenological. In particular, first considered are ''dry'' systems, defined as those where momentum is not conserved due to friction with a substrate or an embedding porous medium. The differences and similarities between two types of orientationally ordered states, the nematic and the polar, are clarified. Next, the active hydrodynamics of suspensions or ''wet'' systems is discussed and the relation with and difference from the dry case, as well as various large-scale instabilities of these nonequilibrium states of matter, are highlighted. Further highlighted are various large-scale instabilities of these nonequilibrium states of matter. Various semimicroscopic derivations of the continuum theory are discussed and connected, highlighting the unifying and generic nature of the continuum model. Throughout the review, the experimental relevance of these theories for describing bacterial swarms and suspensions, the cytoskeleton of living cells, and vibrated granular material is discussed. Promising extensions toward greater realism in specific contexts from cell biology to animal behavior are suggested, and remarks are given on some exotic active-matter analogs. Last, the outlook for a quantitative understanding of active matter, through the interplay of detailed theory with controlled experiments on simplified systems, with living or artificial constituents, is summarized.

Exothermicity Is Not a Necessary Condition for Enhanced Diffusion of Enzymes

“…Fluctuations in fluorescence intensity from the diffusion of molecules were auto-correlated and fit by a multicomponent 3D model to determine the diffusion coefficients of individual species. The autocorrelation of the intensity signal is given by [1] …”

“…We propose a new physical paradigm, which reveals that the diffusion coefficient of a model enzyme hydrodynamically coupled to its environment increases significantly when undergoing changes in conformational fluctuations in a substrate-dependent manner, and is independent of the overall turnover rate of the underlying enzymatic reaction. Our results show that substrate-induced enhanced diffusion of enzyme molecules can be explained within an equilibrium picture, and that the exothermicity of the catalyzed reaction is not a necessary condition for the observation of this phenomenon.In a quest for understanding nonequilibrium processes encountered in biology and chemistry, the study of active matter, namely systems constituted of agents able to consume and convert energy extracted from their environment, has been a major focus of the contemporary physical sciences [1,2]. Recent progress led to the design, fabrication and characterization of synthetic micro-and nano-machines relying on different propulsion mechanisms, and able to reproduce functions inspired from molecular biology, such as cargo transport or chemical sensing [3,4].…”

“…In a quest for understanding nonequilibrium processes encountered in biology and chemistry, the study of active matter, namely systems constituted of agents able to consume and convert energy extracted from their environment, has been a major focus of the contemporary physical sciences [1,2]. Recent progress led to the design, fabrication and characterization of synthetic micro-and nano-machines relying on different propulsion mechanisms, and able to reproduce functions inspired from molecular biology, such as cargo transport or chemical sensing [3,4].…”

Transport of particles in liquid crystals

“…[2][3][4][5][6] The grand challenge is to establish how to construct different forms of SAMM. The two important elements are (i) elementary moving units, or "meta-atoms", and (ii) the surrounding medium that controls them.…”

Motility versus fluctuations in mixtures of self-motile and passive agents

“…Likewise, macroscopic active systems, such as animal colonies exhibit swarming, herding, and flocking behaviors that appear to share phenomenological similarities with their microscopic counterparts. Such phenomena include polar ordering, large-scale correlated motion, and intriguing rheological properties [1]. However, biological systems often consist of multiple species which differ in their motilities and other attributes.…”