Living Crystals of Light-Activated Colloidal Surfers
22 Feb 2013-Science (American Association for the Advancement of Science)-Vol. 339, Iss: 6122, pp 936-940
TL;DR: A form of self-organization from nonequilibrium driving forces in a suspension of synthetic photoactivated colloidal particles is demonstrated, which leads to two-dimensional "living crystals," which form, break, explode, and re-form elsewhere.
Abstract: Spontaneous formation of colonies of bacteria or flocks of birds are examples of self-organization in active living matter. Here, we demonstrate a form of self-organization from nonequilibrium driving forces in a suspension of synthetic photoactivated colloidal particles. They lead to two-dimensional "living crystals," which form, break, explode, and re-form elsewhere. The dynamic assembly results from a competition between self-propulsion of particles and an attractive interaction induced respectively by osmotic and phoretic effects and activated by light. We measured a transition from normal to giant-number fluctuations. Our experiments are quantitatively described by simple numerical simulations. We show that the existence of the living crystals is intrinsically related to the out-of-equilibrium collisions of the self-propelled particles.
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TL;DR: This review summarizes theoretical progress in the field of active matter, placing it in the context of recent experiments, and highlights the experimental relevance of various semimicroscopic derivations of the continuum theory for describing bacterial swarms and suspensions, the cytoskeleton of living cells, and vibrated granular material.
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.
3,314 citations
TL;DR: In this article, the authors provide a guided tour through the development of artificial self-propelling microparticles and nanoparticles and their application to the study of nonequilibrium phenomena, as well as the open challenges that the field is currently facing.
Abstract: Differently from passive Brownian particles, active particles, also known as self-propelled Brownian particles or microswimmers and nanoswimmers, are capable of taking up energy from their environment and converting it into directed motion. Because of this constant flow of energy, their behavior can be explained and understood only within the framework of nonequilibrium physics. In the biological realm, many cells perform directed motion, for example, as a way to browse for nutrients or to avoid toxins. Inspired by these motile microorganisms, researchers have been developing artificial particles that feature similar swimming behaviors based on different mechanisms. These man-made micromachines and nanomachines hold a great potential as autonomous agents for health care, sustainability, and security applications. With a focus on the basic physical features of the interactions of self-propelled Brownian particles with a crowded and complex environment, this comprehensive review will provide a guided tour through its basic principles, the development of artificial self-propelling microparticles and nanoparticles, and their application to the study of nonequilibrium phenomena, as well as the open challenges that the field is currently facing.
2,188 citations
Cites background or methods from "Living Crystals of Light-Activated ..."
...This was first predicted theoretically (Fily and Marchetti, 2012; Redner et al., 2013a; Tailleur and Cates, 2008) and has recently been observed experimentally (Buttinoni et al., 2013; Palacci et al., 2013)....
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...very 5s. dynamics | to which we shall refer as rotational diusion dynamics (Fig. 5a) | is often encountered in the case of self-propelling Janus colloids (Buttinoni et al., 2012; Howse et al., 2007; Palacci et al., 2013). There are, however, other processes that generate active Brownian motion; here we will consider, in particular, the runand-tumble dynamics and the Gaussian noise dynamics (Koumakis et al., 2014). Mo...
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...5a) — is often encountered in the case of self-propelling Janus colloids (Buttinoni et al., 2012; Howse et al., 2007; Palacci et al., 2013)....
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...ve interactions. This was rst predicted theoretically (Fily and Marchetti, 2012; Redner et al., 2013a; Tailleur and Cates, 2008) and has recently been observed experimentally (Buttinoni et al., 2013; Palacci et al., 2013). A simple qualitative explanation of this phenomenon is shown in Figs. 13a-d: when two active particles collide, they block each other due to the persistence of their motion (sequence of Figs. 13a to...
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...Instead of Pt or Pd, hematite has also been used as a catalyst; this has the advantage of permitting one to control the H2O2 decomposition using light: in fact the hematite catalyzes the H2O2 decomposition only when illuminated with blue light (Palacci et al., 2013)....
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TL;DR: Active Brownian particles, also referred to as microswimmers and nanoswimmers, are biological or manmade microscopic and nanoscopic particles that can self-propel as mentioned in this paper.
Abstract: Active Brownian particles, also referred to as microswimmers and nanoswimmers, are biological or manmade microscopic and nanoscopic particles that can self-propel. Because of their activity, their behavior can only be explained and understood within the framework of nonequilibrium physics. In the biological realm, many cells perform active Brownian motion, for example, when moving away from toxins or towards nutrients. Inspired by these motile microorganisms, researchers have been developing artificial active particles that feature similar swimming behaviors based on different mechanisms; these manmade micro- and nanomachines hold a great potential as autonomous agents for healthcare, sustainability, and security applications. With a focus on the basic physical features of the interactions of active Brownian particles with a crowded and complex environment, this comprehensive review will put the reader at the very forefront of the field of active Brownian motion, providing a guided tour through its basic principles, the development of artificial self-propelling micro- and nanoparticles, and their application to the study of nonequilibrium phenomena, as well as the open challenges that the field is currently facing.
1,258 citations
TL;DR: A selective overview of the fast-developing field of MIPS, focusing on theory and effects, is given, which generally breaks down at higher order in gradients.
Abstract: Self-propelled particles include both self-phoretic synthetic colloids and various microorganisms. By continually consuming energy, they bypass the laws of equilibrium thermodynamics. These laws enforce the Boltzmann distribution in thermal equilibrium: The steady state is then independent of kinetic parameters. In contrast, self-propelled particles tend to accumulate where they move more slowly. They may also slow down at high density for either biochemical or steric reasons. This creates positive feedback, which can lead to motility-induced phase separation (MIPS) between dense and dilute fluid phases. At leading order in gradients, a mapping relates variable-speed, self-propelled particles to passive particles with attractions. This deep link to equilibrium phase separation is confirmed by simulations but generally breaks down at higher order in gradients: New effects, with no equilibrium counterpart, then emerge. We give a selective overview of the fast-developing field of MIPS, focusing on theory and...
1,228 citations
TL;DR: The physics of locomotion of biological and synthetic microswimmers, and the collective behavior of their assemblies, are reviewed and the hydrodynamic aspects of swimming are addressed.
Abstract: Locomotion and transport of microorganisms in fluids is an essential aspect of life. Search for food, orientation toward light, spreading of off-spring, and the formation of colonies are only possible due to locomotion. Swimming at the microscale occurs at low Reynolds numbers, where fluid friction and viscosity dominates over inertia. Here, evolution achieved propulsion mechanisms, which overcome and even exploit drag. Prominent propulsion mechanisms are rotating helical flagella, exploited by many bacteria, and snake-like or whip-like motion of eukaryotic flagella, utilized by sperm and algae. For artificial microswimmers, alternative concepts to convert chemical energy or heat into directed motion can be employed, which are potentially more efficient. The dynamics of microswimmers comprises many facets, which are all required to achieve locomotion. In this article, we review the physics of locomotion of biological and synthetic microswimmers, and the collective behavior of their assemblies. Starting from individual microswimmers, we describe the various propulsion mechanism of biological and synthetic systems and address the hydrodynamic aspects of swimming. This comprises synchronization and the concerted beating of flagella and cilia. In addition, the swimming behavior next to surfaces is examined. Finally, collective and cooperate phenomena of various types of isotropic and anisotropic swimmers with and without hydrodynamic interactions are discussed.
1,220 citations
Cites background or methods from "Living Crystals of Light-Activated ..."
...l diusion coecient. Hence, no alignment forces or hydrodynamic interactions are taken into account (Bialke et al., 2013, 2012; Buttinoni et al., 2013; Fily et al., 2014b; Fily and Marchetti, 2012; Palacci et al., 2013; Redner et al., 2013; Stenhammar et al., 2014; Wysocki et al., 2014). These simulations indeed yield cluster formation and phase separation solely by propulsion and excludedvolume interactions. For t...
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...as bacteria (Ben-Jacob et al., 2000; Chen et al., 2012; Gachelin et al., 2013a; Peru35 ani et al., 2012; Sokolov et al., 2007) and synthetic microswimmers (Buttinoni et al., 2013; Ibele et al., 2009; Palacci et al., 2013; Theurkau et al., 2012; Wang et al., 2013), but also in macroscopic systems such as ocks of birds and schools of sh (Cavagna et al., 2010; Vicsek and Zafeiris, 2012). Despite the very dierent propul...
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...Pairs of spheres and cubes then selfassemble into self-propelled microswimmers at a surface (Palacci et al., 2013)....
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...2O 2 solution. The decomposition reaction is catalyzed by the hematite cubes, but only under illumination. Pairs of spheres and cubes then selfassemble into self-propelled microswimmers at a surface (Palacci et al., 2013). The dynamic assembly results from a competition between self-propulsion of particles and an attractive interaction induced respectively by osmotic and phoretic eects activated by light. Thermophore...
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...any alignment rule reveal a rich structural and dynamical collective behavior (Bialke et al., 2012; Buttinoni et al., 2013, 2012; Deseigne et al., 2010; Fily et al., 2014b; Fily and Marchetti, 2012; Palacci et al., 2013; Redner et al., 2013; Stenhammar et al., 2014; Theurkau et al., 2012; Wysocki et al., 2014). Experiments using either spherical gold/platinum Janus particles (Theurkau et al., 2012) and polymer spher...
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References
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TL;DR: Numerical evidence is presented that this model results in a kinetic phase transition from no transport to finite net transport through spontaneous symmetry breaking of the rotational symmetry.
Abstract: A simple model with a novel type of dynamics is introduced in order to investigate the emergence of self-ordered motion in systems of particles with biologically motivated interaction. In our model particles are driven with a constant absolute velocity and at each time step assume the average direction of motion of the particles in their neighborhood with some random perturbation $(\ensuremath{\eta})$ added. We present numerical evidence that this model results in a kinetic phase transition from no transport (zero average velocity, $|{\mathbf{v}}_{a}|\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0$) to finite net transport through spontaneous symmetry breaking of the rotational symmetry. The transition is continuous, since $|{\mathbf{v}}_{a}|$ is found to scale as $({\ensuremath{\eta}}_{c}\ensuremath{-}\ensuremath{\eta}{)}^{\ensuremath{\beta}}$ with $\ensuremath{\beta}\ensuremath{\simeq}0.45$.
6,514 citations
TL;DR: In this article, a set of image processing algorithms for extracting quantitative data from digitized video microscope images of colloidal suspensions is described, which can locate submicrometer spheres to within 10 nm in the focal plane and 150 nm in depth.
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TL;DR: The motion of an artificial microscale swimmer that uses a chemical reaction catalyzed on its own surface to achieve autonomous propulsion is fully characterized experimentally and suggests strategies for designing artificial chemotactic systems.
Abstract: The motion of an artificial microscale swimmer that uses a chemical reaction catalyzed on its own surface to achieve autonomous propulsion is fully characterized experimentally. It is shown that at short times it has a substantial component of directed motion, with a velocity that depends on the concentration of fuel molecules. At longer times, the motion reverts to a random walk with a substantially enhanced diffusion coefficient. Our results suggest strategies for designing artificial chemotactic systems.
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TL;DR: By solving the convection-diffusion equation in the frame of the moving rod, it was found that the interfacial tension force scales approximately as SR(2)gamma/muDL, where S is the area-normalized oxygen evolution rate, gamma is the liquid-vapor interfacial pressure, R is the rod radius, mu is the viscosity, D is the diffusion coefficient of oxygen, and L is the length of the rod.
Abstract: Rod-shaped particles, 370 nm in diameter and consisting of 1 μm long Pt and Au segments, move autonomously in aqueous hydrogen peroxide solutions by catalyzing the formation of oxygen at the Pt end. In 2−3% hydrogen peroxide solution, these rods move predominantly along their axis in the direction of the Pt end at speeds of up to 10 body lengths per second. The dimensions of the rods and their speeds are similar to those of multiflagellar bacteria. The force along the rod axis, which is on the order of 10-14 N, is generated by the oxygen concentration gradient, which in turn produces an interfacial tension force that balances the drag force at steady state. By solving the convection-diffusion equation in the frame of the moving rod, it was found that the interfacial tension force scales approximately as SR2γ/μDL, where S is the area-normalized oxygen evolution rate, γ is the liquid−vapor interfacial tension, R is the rod radius, μ is the viscosity, D is the diffusion coefficient of oxygen, and L is the le...
1,786 citations
TL;DR: It is shown that a linear chain of colloidal magnetic particles linked by DNA and attached to a red blood cell can act as a flexible artificial flagellum, which induces a beating pattern that propels the structure, and that the external fields can be adjusted to control the velocity and the direction of motion.
Abstract: Microorganisms such as bacteria and many eukaryotic cells propel themselves with hair-like structures known as flagella, which can exhibit a variety of structures and movement patterns. For example, bacterial flagella are helically shaped and driven at their bases by a reversible rotary engine, which rotates the attached flagellum to give a motion similar to that of a corkscrew. In contrast, eukaryotic cells use flagella that resemble elastic rods and exhibit a beating motion: internally generated stresses give rise to a series of bends that propagate towards the tip. In contrast to this variety of swimming strategies encountered in nature, a controlled swimming motion of artificial micrometre-sized structures has not yet been realized. Here we show that a linear chain of colloidal magnetic particles linked by DNA and attached to a red blood cell can act as a flexible artificial flagellum. The filament aligns with an external uniform magnetic field and is readily actuated by oscillating a transverse field. We find that the actuation induces a beating pattern that propels the structure, and that the external fields can be adjusted to control the velocity and the direction of motion.
1,700 citations