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 E05: Active Matter and Liquid Crystals in Biological and Bio-Inspired Systems IVLive
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Sponsoring Units: DSOFT DBIO DPOLY GSNP Chair: Rui Zhang, Hong Kong University of Science and Technology Room: 05 |
Tuesday, March 16, 2021 8:00AM - 8:12AM Live |
E05.00001: Global order and lane formation in Microtubule-based active matter Fereshteh Memarian, Joseph D Lopes, Linda S. Hirst Kinesin motor proteins convert chemical energy into mechanical energy, moving throughout the cell to transport cargo by “walking” on microtubules (MTs). MTs are vital components of all Eukaryotic cells. They form part of the cytoskeleton and are important for cell division, and intracellular transport. In this project, we investigated MT-kinesin-based transportation by performing experiments using kinesin motors coupled to a lipid bilayer. We take advantage of the microtubule gliding assay configuration to probe collective behavior in dense MT swarms. On a glass substrate, kinesin motors adhere and are immobile, while MTs glide on them. MT behavior with fixed motors at high MT concentration is compared with their behavior on diffusing motor proteins at similar concentrations. We used a lipid bilayer similar to that in a cell to observe the MT behavior on membrane diffusing kinesins. The MTs exhibit collective motion with orientational order on different lengthscales, sensitive to MT density. Notably, at intermediate MT densities, we were able to observe apolar lane formation and characterize the differences in local and global order parameters. |
Tuesday, March 16, 2021 8:12AM - 8:24AM Live |
E05.00002: Active self-organization in actin cytoskeleton Waleed Mirza, Marco de Corato, Alejandro Torres Sánchez, Marino Arroyo, Guillermo Vilanova Caicoya One of the architectures actin cytoskeleton exhibits is nematic, consisting of aligned actin filaments of mixed-polarity associated with actin-binding proteins. Although recent literature reports the self-assembly of nematic actin bundles with a regular wavelength, yet the mechanism of their morphogenesis is still poorly understood. In this study, we use a continuum model to explain an out-of-equilibrium self-assembly of such regularly spaced actin bundles. Our linear stability analysis predicts an unstable regime that gives rise to such patterns. Furthermore, using simulations we investigate a long time scales behavior of the self-organized actin bundles in the non-linear regime. We demonstrate that the non-linear regime is characterized by the self-organized actin bundles further maturing and interacting with each other. |
Tuesday, March 16, 2021 8:24AM - 8:36AM Live |
E05.00003: Active Matter Self-Organization Simulator (AMSOS): Combining biophysics and mechanics on HPC Wen Yan, Adam Lamson, Saad Ansari, Meredith D Betterton, Michael Shelley We have developed a simulation package to study the large-scale behavior of assemblies formed by biofilaments and crosslinkers. Each crosslinker is explicitly tracked in space and its interactions with filaments are described by a two-stage explicit kinetic Monte-Carlo model. Binding-unbinding events of a motor are modeled based on free-energy changes between unbound, singly bound, and doubly bound states, in a way that preserves detailed balance. Crosslinkers binding two filaments walk and diffuse along the filaments thus moving the filaments relative to each other. We use a new numerical method based on geometrically constrained optimization to guarantee that steric interactions and crosslinker binding forces between filaments are properly and efficiently handled. These developments are integrated into a massively parallel software package -- AMSOS -- whose application we demonstrate by a few examples, including aster formation in confinement and self-contracting bundles consisting of more than 100,000 microtubules and motor proteins. |
Tuesday, March 16, 2021 8:36AM - 8:48AM Live |
E05.00004: Collective motion of vinegar eels: metachronal waves and induced flows Anton Peshkov, Sonia McGaffigan, Esteban Wright, Alice C Quillen We experimentally study the collective motion of the free-swimming nematode Turbatrix Aceti also known as the vinegar eel. With a typical size of 1 mm these nematodes are evolving at intermediate Reynolds numbers where inertial, non-linear and time-dependent flows can play a significant role. We find that at high concentration they spontaneously aggregate at the borders and synchronize their beating motion, producing a striking collectively moving and oscillating metachronal wave. The flow produced by this collective state is sufficiently strong to visibly deform the surface of the liquid and displace objects in the bulk of the fluid. This novel biological system can become a model organism to study active matter at intermediate Reynolds numbers and show great promise for such applications as on-demand flows and controlled displacement of objects. |
Tuesday, March 16, 2021 8:48AM - 9:00AM Live |
E05.00005: Rotation and propulsion in 3D active chiral droplets Giuseppe Negro, Livio Nicola Carenza, Giuseppe Gonnella, Davide Marenduzzo Chirality is an ubiquitous feature of biological matter. |
Tuesday, March 16, 2021 9:00AM - 9:12AM Live |
E05.00006: Dynamical renormalizatin group approach to the collective behaviour of swarms Andrea Cavagna, Luca Di Carlo, Irene Giardina, Tomas Grigera, Giulia Pisegna We study the critical behavior of a model with nondissipative couplings aimed at describing the collective behavior of natural swarms, using the dynamical renormalization group under a fixed-network approximation. At one loop, we find a crossover between an unstable fixed point, characterized by a dynamical critical exponent z= d/2, and a stable fixed point with z= 2, a result we confirm through numerical simulations. The crossover is regulated by a length scale given by the ratio between the transport coefficient and the effective friction, so that in finite-size biological systems with low dissipation, dynamics is ruled by the unstable fixed point. In three dimensions this mechanism gives z= 3/2, a value significantly closer to the experimental window, 1.0≤ z≤ 1.3, than the value z≈ 2 numerically found in fully dissipative models, either at or off equilibrium. This result indicates that nondissipative dynamical couplings are necessary to develop a theory of natural swarms fully consistent with experiments. |
Tuesday, March 16, 2021 9:12AM - 9:24AM Live |
E05.00007: Linear stability analysis for asymmetric contraction of the cytokinetic ring Arkya Chatterjee, Mainak Chatterjee, Amitabha Nandi, Anirban Sain The contraction of the cytokinetic ring is a crucial part of the cell-division cycle. In a previous work [1], using a continuum gel theory framework in a weak flow coupling regime, we obtained exact analytical solutions for the quasi-static dynamics of the radially symmetric ring contraction. Here, we study the stability of this process under angular perturbations. Linear stability analysis of the angular modes shows that, in the experimentally relevant regime of the parameter space, the lowest order breathing mode and most of the higher-order modes are stable, leaving a window of unstable modes in between. Furthermore as the ring shrinks in radius, this window gradually disappears, turning all modes stable. This is consistent with the experimental observation [2] that the ring, most often, is not circular at the beginning, but becomes increasingly circular as it contracts. |
Tuesday, March 16, 2021 9:24AM - 9:36AM Live |
E05.00008: Finite wave number instability interrupts motility-induced phase separation ZHAN MA, Ran Ni Motility-induced phase separation (MIPS) is one of the intriguing findings in active colloidal systems, which has been widely studied in the content of active Brownian particles (ABPs) model. However, ABPs fails describing the effect of the intrinsic curvature and chirality properties of many active units, such as some bacteria, and self-propelled particles with asymmetric shape. Therefore, self-propulsion torque is introduced in the circle-ABPs (cABPs) model. In this work, we formulate a continuum theory for cABPs, and the fluctuation dispersion relation reveals two types of instabilities, i.e. at low torque intensity, type I instability refers to the zero wave number starting unstable mode inducing the MIPS; for large enough torque, type II instability refers to the finite wave number starting unstable modes, which results in the dynamical clustering state and interrupts the conventional MIPS. Besides, by measuring the self intermediate scattering function, we qualitatively verifies the dispersion relation derived and identify the dynamic properties of the dynamical clustering state. The main conclusion of this work is that the finite-wave number instability results in a dynamical clustering state and interrupts MIPS. |
Tuesday, March 16, 2021 9:36AM - 9:48AM Live |
E05.00009: Active cholesterics and smectics are hydrodynamically distinct Swapnil Kole, Gareth Alexander, Sriram Ramaswamy, Ananyo Maitra The cholesteric is the archetypal chiral liquid crystal, in which the molecular orientation displays a spontaneous, static, periodic twist about a pitch axis. At thermal equilibrium, this chirality is undetectable in the long-wavelength elasticity and hydrodynamics of a cholesteric, which are identical to that of a smectic. We show theoretically that active cholesterics, by contrast, display striking signatures of chirality, and are thus qualitatively distinct from smectics, even in their asymptotic long-wavelength dynamics. Our predictions include arrays of alternating vortical flow in the layers when active stresses create an undulational instability; an on-off switch for such flow using imposed uniaxial stress; and a disruption of the layers in 2D chiral striped phases. We elucidate the relation and crucial differences between these effects and "odd elasticity". We discuss possible experimental realizations. |
Tuesday, March 16, 2021 9:48AM - 10:00AM Not Participating |
E05.00010: Emergent task-driven cooperation in ant collectives Ganga Prasath S, Souvik Mandal, Fabio Giardina, Venkatesh Murthy, L. Mahadevan Ant colonies are characterized by the presence of castes that are often correlated with morphological, physiological and behavioral distinctions. However, the completion of tasks with a potential benefit to the colony are impervious to these distinctions. But how interaction amongst individuals and with the environment affects collective actions remains poorly studied. Here, we probe a paradigm of collective task execution, tunneling through a barrier, using Camponotus Pennsylvanicus, carpenter ants, to address this question. We find that ant collectives that have multiple castes are more efficient than those made of a single caste - and show how the task creates an emergent dynamic division of labor determined by the interaction with the environment that cuts across morphological and physiological distinctions. |
Tuesday, March 16, 2021 10:00AM - 10:12AM Live |
E05.00011: Sparse Identification of Continuum Theories of 2D Active Nematics Chaitanya Joshi, Linnea Lemma, Zvonimir Dogic, Aparna Baskaran, Michael F Hagan
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Tuesday, March 16, 2021 10:12AM - 10:24AM Live |
E05.00012: Strategies for Collective Adaptive Workload Distribution in Varying Work Conditions Kehinde Aina, Hui-Shun Kuan, Daniel I Goldman, Meredith Betterton Social insects such as ants robustly dig during collective nest construction. Individuals quickly adapt to changing work conditions, despite the complexity of cooperative digging and environmental constraints. In this work, we model how behavior changes if individual ants optimize an objective in a changing environment. The theory predicts that collective excavation and worker density change with tunnel length if individuals optimize their excavation behavior. To test the predictions, we studied the dynamics of confined ant excavation behavior in laboratory experiments and a collective robophysical model consisting of cohesive granular-media-excavating robots. We developed adaptive rules for robots to optimize successful pellet retrieval by modulating individual behavior. Our theory suggests a strategy by which individual behavior can drive adaptation of a group in changing work conditions through optimization of individual behavior. This may lead to insights into how social insects adapt to their environments; and how to develop similar robust and scalable strategies for task-oriented and constrained physical swarm systems. |
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