Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session M05: Active Matter in Complex Environments IVFocus Live
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Sponsoring Units: DSOFT Chair: Tapomoy Bhattacharjee, Princeton University; Sujit Datta, Princeton University Room: 05 |
Wednesday, March 17, 2021 11:30AM - 12:06PM Live |
M05.00001: Life in Complex Fluids Invited Speaker: Paulo Arratia Many microorganisms evolve in media that contain (bio)-polymers and/or solids. In this talk, I will discuss experimental and numerical results on the effects of fluid elasticity on the swimming behavior of microorganisms. Two main microorganisms are used, the green algae C. reinhardtii (a puller-type swimmer) and the bacterium E. coli (a pusher-type swimmer). For the case of pullers (C. reinhardtii), we find that fluid elasticity hinders the cell’s overall swimming speed but leads to an increase in the cell’s flagellum beating frequency. The beating kinematics and flagellum waveforms are also significantly modified by fluid elasticity. For the case of pushers (E. coli), the presence of even small amount of polymers in the medium suppresses the bacteria run-and-tumble mechanism. The bacteria spend more time in ballistic mode and swim faster as well. Single molecule experiments using fluorescently labeled DNA show that the flow fields generated by E. coli are able to stretch initially coiled polymer molecules and thus induce elastic stresses in fluid. These results demonstrate the intimate link between swimming kinematics and fluid rheology and that one can control the spreading and motility of microorganisms by tuning fluid properties. |
Wednesday, March 17, 2021 12:06PM - 12:18PM Live |
M05.00002: Local depletion of microswimmers in fluid flows due to rotational diffusion and tumbling Simon Berman, John Henry Buggeln, Tom H Solomon, Kevin A Mitchell Microswimmer trajectories in externally-driven fluid flows are constrained by one-way transport barriers, obtained from certain invariant manifolds of the microswimmer equations of motion. Here, we theoretically investigate the effect of stochastic swimmer reorientation in the presence of these one-way barriers. We consider both rotational diffusion and tumbling, i.e. sudden jumps in the swimmer orientation. In both cases, we find that noise significantly increases the probability that swimmers cross these one-way barriers. This strongly constrains their subsequent trajectories and leads to a depletion of the density of swimmers near these barriers. For the two-dimensional linear hyperbolic flow, we quantify this depletion effect by calculating the probability of stochastic swimmer trajectories crossing these one-way barriers. |
Wednesday, March 17, 2021 12:18PM - 12:30PM Live |
M05.00003: Reversible depletion-driven capture of bacterial cells on non-adhesive surfaces Wuqi Niu The adhesion of bacteria on surfaces is critical in processes such as biofouling, biofilm formation, and the infection of plants and animals. Bacteria-surface interactions involving hydrodynamics and physicochemical forces (i.e. van der Waals and electrostatic) has been well studied. However, no study has discussed the role of depletion force in bacteria adhesion to surface, even though bacteria are often found in polymer rich environments where polymer-driven depletion produces attractions. Here, we demonstrate how non-motile Escherichia coli (E. coli) are captured on polyethylene glycol (PEG) brush surfaces which are non-adhesive to E. coli on their own. The capture is reversible, and the cells are released with the removal of the polymer solution and hence the depletion force. PEG of two different molecular weights were used as depletants. We also studied the influence of depletion driven aggregation on cell capturing. The depletion driven aggregation and depletion driven surface capture are two competing mechanism in this system. |
Wednesday, March 17, 2021 12:30PM - 12:42PM Live |
M05.00004: A generalized boundary reflection rule, funnel-shaped geometries, and rectification in systems with active boundaries Vidyesh Rao Anisetti, J. M. Schwarz Confined active matter exhibits rectification in the presence of funnel-shaped geometries. This phenomenon occurs, for example, when bacteria encountering a boundary, crawl along it. Inspired by such examples, we investigate rectification in a system with funnel-shaped boundaries and with two different classes of reflection rules for randomly-moving particles colliding with the boundary; |
Wednesday, March 17, 2021 12:42PM - 12:54PM Live |
M05.00005: Conserved Quantities and Structural States in Active Systems Yuval Shoham Both biological organisms such as bacteria or spermatozoa as well as lab-generated self-propelled particles can be described as microswimmers - force-free particles interacting with one another through the flow created by their motion. By solving the flow generated by a swimmer using the multipole expansion, we represent a microswimmer with a set of basic flow modes. When the swimmers are bound to a two-dimensional fluid, the leading modes are very long-ranged, decaying algebraically as $1/r$. We show that an ensemble of swimmers can be described by a geometric Hamiltonian formalism. Using Noether's theorem, we link the symmetries of the Hamiltonian to corresponding structural conservation laws, which can lead to ordering or to collective motion. |
Wednesday, March 17, 2021 12:54PM - 1:06PM Live |
M05.00006: Self-organization and mixing of microtubule-kinesin active fluid in an activity gradient Teagan Bate, Kun-Ta Wu Active fluid, composed of kinesin-driven extensile bundles of microtubules, consumes ATP locally to create a self-mixing flow. Mean speed of microtubule-kinesin active fluid was shown to be tunable by varying its components’ concentrations. Such tunability demonstrated the controllability of active fluid with uniform activity. However, how active fluid self-organizes when its activity is non-uniform remains poorly understood. Here, we characterized active fluid behavior and its associated mixing performance in an activity gradient. The activity gradient was created by imposing a temperature gradient because our previous work showed that microtubule-kinesin active fluid exhibited an Arrhenius response to temperature: Increasing temperature sped up active fluid flow, and thus, along a temperature gradient, active fluid flowed faster on one side and slower on the other, forming an activity gradient. We characterized how such a gradient influenced the mixing performance of active fluid in terms of mixing efficiency, stretching rate, and mean squared displacement, comparing with an activity-uniform sample. Our work suggests that applying an activity gradient can serve as a new in-situ method for controlling self-organization and mixing performance of microtubule-kinesin active fluid. |
Wednesday, March 17, 2021 1:06PM - 1:18PM Live |
M05.00007: Engineering motile amoeboid cells toward targeted cell-mediated transport Setareh Sharifi Panah, Robert Großmann, Oliver Nagel, Valentino Lepro, Carsten Beta The necessity of reliable bio-hybrid microsystems, especially in the field of medical science, is becoming more obvious every day. Despite the growing efforts, applications such as targeted drug delivery remain challenging. Inspired by leukocytes, we propose to exploit the potential of eukaryotic cells as microtransporters, using D. discoideum cells. Our preliminary tests demonstrated the ability of cells to displace cargo, with faster spreading agent cells, suggesting cell-particle interactions as a stimulus promoting cell motility [1]. Chemotaxis experiments showed a guided transport driven by single or collective cells also across 3D collagen matrices, highlighting reliability of our system also in complex environments. |
Wednesday, March 17, 2021 1:18PM - 1:30PM Live |
M05.00008: Active Transport Dynamics with Wave-Based Interactions Steven Tarr, Blake Castleman, Enes Aydin, Daniel I Goldman Diverse locomoting systems disturb the environment which then can in turn affect the locomotor. Inspired by the dynamics of small bouncing droplets interacting with obstacles via complex surface fluid waves, we study an 11.7 cm diameter circular robot fan boat in a 9 cm deep pool of water. We augment these dynamics with a vibration motor mounted on the boat which generates outwardly propagating waves at the boat-water interface with frequency range 10-45 Hz. We study the boat’s interaction with a triangular lattice of fixed circular obstacles of diameter ~9 cm and edge-edge separation distance ~17 cm. In most (14/16) trials without vibration, the boat is pinned indefinitely to the first or second lattice site it encounters. With vibration, the boat traverses the lattice via spontaneous reorientations and subsequent escapes at lattice sites due to complex interactions from generated and reflected waves. Higher frequency enables greater traversal; the mean number of times the boat contacts a lattice site before becoming trapped at the edge of the container was 1.2 ± 0.5 without waves and 5.1 ± 1.8, 5.8 ± 2.0 for vibration frequencies of 14.2 ± 1.1 Hz, 35.5 ± 0.6 Hz. |
Wednesday, March 17, 2021 1:30PM - 1:42PM Live |
M05.00009: Surfing and crawling macroscopic active particles under strong confinement Marco Leoni, Matteo Paoluzzi, Sarah Eldeen, Anthony Estrada, Wylie Ahmed We study two types of active (self-propelled) macroscopic particles under confinement: camphor surfers and hexbug crawlers, using a combined experimental, theoretical, and numerical approach. Unlike widely studied microscopic active particles and swimmers, where thermal forces are often important and inertia is negligible, our macroscopic particles exhibit complex dynamics due expressly to active non-thermal noise combined with inertial effects. Strong confinement induces accumulation at a finite distance within the boundary and gives rise to three distinguishable dynamical states; both depending on activity and inertia. These surprisingly complex dynamics arise already at the single particle level -- highlighting the importance of inertia in macroscopic active matter. |
Wednesday, March 17, 2021 1:42PM - 1:54PM Live |
M05.00010: Phenotyping photokinetic and excitable behaviours of single microswimmers in confinement Samuel Bentley, Vasileios Anagnostidis, Hannah Laeverenz-Schlogelhofer, Fabrice Gielen, Kirsty Wan All living organisms are environmentally intelligent. This is the fundamental distinction between life, and other forms of matter. Even unicellular organisms are capable of complex behaviours. Here, we study the detailed motor actions of flagellated algal microswimmers, using motility as a dynamic read-out of whole-organism behaviour. Previous studies have focussed on locomotor transients over short timescales ranging from seconds to minutes. Here we present a novel microfluidic platform which can allow us to monitor single cells over unprecedented timescales. Two representative species of microswimmers were trapped and confined inside circular arenas: a biflagellate which exhibits a form of run-and-tumble, and an octoflagellate which exhibits a distinctive, tripartite behavioural repertoire termed run-stop-shock. Stochastic transitions in swimming gait are projected onto a low-dimensional behavioural state space. Single-cell motility signatures were analysed to reveal species-specific photokinetic and excitable behaviours. Finally, we conducted on-demand pharmacological perturbations within these microenvironments, to shed new light on the physiological basis of excitable flagellar dynamics. |
Wednesday, March 17, 2021 1:54PM - 2:06PM Live |
M05.00011: The Influence of Flow on Capture and Growth of Rod-like E. coli on Cationic and Hydrophobic Surfaces Zhou Xu, Wuqi Niu, Sylvia Rivera, Sloan Siegrist, Mark Thomas Tuominen, Maria Santore Living organisms usually utilize chemical or biomolecular signals that often transmit slowly. However, bacterial cells can respond very quickly, yielding interesting opportunities for interfacing with bacteria. In this work, we study the bacterial sense of surfaces to establish the new research area of sensory-based bacterial communication. The focus is on how E. coli react to different surfaces such as cationic surface, hydrophobic surface, and bare glass. Propidium iodide and HCC-amino-D-alanine is used to check the viability and growth of E. coli on surfaces. Employing high resolution microscopy with a flow cell system, we investigate the adsorption rate, vertical orientation, and horizontal angular distribution of E. coli on three surfaces. We find orientation changes of the bacteria in the high shear flow and the significant differences were found between different type of surfaces. |
Wednesday, March 17, 2021 2:06PM - 2:18PM Live |
M05.00012: Trapped active toy robots: theory and experiment Cecilio Tapia-Ignacio, Luis L. Gutierrez-Martinez, Mario Sandoval
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