Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Y20: Active Matter and Liquid Crystals in Biological and Bio-Inspired Systems IVRecordings Available
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Sponsoring Units: DSOFT DPOLY GSNP Chair: Antonio Tavera-Vázquez, Chicago Room: McCormick Place W-185BC |
Friday, March 18, 2022 8:00AM - 8:12AM |
Y20.00001: A tale of twisting columns Sriram R Ramaswamy, S. J Kole, Ananyo Maitra, Gareth Alexander We formulate the hydrodynamics of active columnar phases, with two-dimensional translational order in the plane perpendicular to the columns and no elastic restoring force for relative sliding of the columns. Our predictions include: spontaneous chiral symmetry breaking through a helical instability of the columns; a spinning state of the helically buckled columns; and material transport along the columns through a viscous Archimedean screw mechanism if the columns are polar, i.e., up-down asymmetric. We further show that the polar phase provides a natural experimental setting to realise the odd elastic effects predicted for 2D solids. |
Friday, March 18, 2022 8:12AM - 8:24AM |
Y20.00002: Surface roughening and pulsatility of self-assembling microtubule-kinesin active foams Remi G Boros, Bezia L Lemma, Noah P Mitchell, Zvonimir Dogic Reconstituted cytoskeletal suspensions serve as quintessential model systems in the study of active materials, due in part to their tunable dynamics and mimicry of hierarchically-assembled structures within living cells. We report on the morphological dynamics and far-from-equilibrium steady-state of one such suspension composed of microtubules and microtubule-tip-adhering kinesin-4 motors. The intrinsic asymmetry of these building blocks leads to an active foam composed of bilayers, reminiscent of passive amphiphilic self-assembly. Under high microtubule concentrations, filaments are recruited via global contraction to the interface of high-density protein encapsulations before roughening into an actively rearranging foam. We describe kinetic roughening of these surfaces in terms of local curvature and dilatational flows to quantify their growth. We also explore the pulsatile nature of this suspension’s foam-like steady state. Together, these descriptions yield insights into a new class of biologically inspired active systems. |
Friday, March 18, 2022 8:24AM - 8:36AM |
Y20.00003: Probing nano-swimmer dynamics via the motion of large tracers Ashwani K Tripathi, Tsvi Tlusty Sub-micron nano-swimmers are ubiquitous in biology and nanotechnology but are extremely challenging to measure due to their small size and driving forces. A simple method is proposed for probing the elusive physical features of nano-swimmers by observing their effect on the motion of much larger, easily traceable particles. Modeling a suspension of swimmers as hydrodynamic force dipoles, we analytically compute a direct, easy-to-calibrate relation between the enhancement of tracer particles diffusion and physical features of the nano-swimmers, namely their force dipole moment and persistence time. |
Friday, March 18, 2022 8:36AM - 8:48AM |
Y20.00004: Dilute suspensions of motile microorganisms are not active liquid crystals Viktor Skultety, Cesare Nardini, Joakim Stenhammer, Davide Marenduzzo, Alexander Morozov Recent years witnessed a significant interest in physical, biological and engineering properties of self-propelled particles, such as bacteria or microtubule-kinesin mixtures, and the associated simple theoretical models that capture the main features of these systems. The most popular theory of self-propelled particles embedded in a continuum fluid is the active gel theory (AGT) that treats active agents as a liquid crystal capable of applying local force dipoles to its surroundings. |
Friday, March 18, 2022 8:48AM - 9:00AM |
Y20.00005: Rheotaxis of active droplets Prateek Dwivedi, Rahul Mangal
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Friday, March 18, 2022 9:00AM - 9:12AM |
Y20.00006: Functionally active membrane protein molecules in mesostructured silica films Bradley F Chmelka, Maxwell Berkow, Matthew Idso, Chung-Ta Han, Khanh Nguyen, Daniella Lalli, Guido Pintacuda, Songi Han Surfactant-directed mesostructured silicas are suitable abiotic host materials for the incorporation of functionally active membrane proteins in transparent and mechanically stable films. Judicious choices of conditions enable the light-responsive transmembrane protein proteorhodopsin to be stabilized in solution and subsequently co-assembled into silica−surfactant matrices with high protein loadings and retention of functional activity. Solid-state NMR yields well-resolved spectra that permit comparisons of the molecular structures and dynamics of proteorhodopsin in different host materials. Subtle variations are observed in the local protein structures and dynamics of regions that are associated with light-activated H+-ion pumping by proteorhodopsin molecules. Transient optical spectroscopy analyses yield apparent rate coefficients associated with interconversion of proteorhodopsin conformers during its photo-cycle, which are consistent with the native H+-pumping mechanism. The results establish the atomic-level structures and dynamics of functional proteorhodopsin molecules within abiotic mesostructured silica-surfactant host membranes and demonstrate the efficacy of these materials for harnessing functional membrane protein properties in robust abiological environments. |
Friday, March 18, 2022 9:12AM - 9:24AM |
Y20.00007: Instabilities of 3D dry active nematic liquid crystal Yingyou Ma, Aparna Baskaran, Michael F Hagan, Matthew Peterson Suspensions of active nematic liquid crystals exhibit a flow-induced generic instability that leads to chaotic steady states. When the flow is damped by confinement, in 2D, additional mechanisms emerge that lead to behaviors such as ordering of +1/2 defects [1-4]. The phenomenology of such damped active nematics in 3D is completely unexplored. In this talk, we combine a generalized 3D dry active nematic hydrodynamics theory, that is the 3D analog of the Toner-tu model, and numerical simulations of semiflexible active nematic polymers. With these tools, we explore the characteristics of the instability in 3D overdamped systems, the properties of defect structures, and the statistical features of the nonequilibrium steady states. |
Friday, March 18, 2022 9:24AM - 9:36AM |
Y20.00008: Computational and Data Driven Active Nematics Chaitanya S Joshi, Linnea Lemma, Sattvic Ray, Link Morgan, Graham Sharp, Timothy J Atherton, Zvonimir Dogic, Aparna Baskaran, Michael F Hagan Active nematic liquid crystals are a class of non-equilibrium systems with constituents that generate motion by consuming energy at the molecular level. Active nematics are often studied using phenomenological theories that describe the time evolution of the nematic director and fluid velocity through partial differential equations. In this talk, we use computational and data-driven techniques to model active nematics. We infer key information about the model, such as the active time scale and director dynamics, directly from the experimental data of 2D active nematics. Further, we investigate the steady state behavior of some of these models under various biologically relevant scenarios. Our work provides crucial steps in the development of programmable active matter using model-dependent methods. |
Friday, March 18, 2022 9:36AM - 9:48AM |
Y20.00009: Lattice Boltzmann Simulations of Active Liquid Crystals Under Confinement Saloni Saxena, Thomas Powers, Robert Pelcovits Nonlinear systems out of equilibrium are characterised by the emergence of spatiotemporal patterns. When these systems are subjected to confining boundaries, the interplay between the nonlinearities and boundaries creates even richer behaviour. This is especially relevant in biological materials such as tissues and organoids which grow and develop under confinement. Here, we perform lattice Boltzmann simulations of an active nematic liquid crystal in a two dimensional cavity with a moving lid. By systematically varying the activity and lid velocity, we map out the possible steady states in the isotropic as well as nematic regimes. In both regimes, the flow field consists of a circular vortex in the centre of the cavity. The activity and shear induce ordering in the isotropic phase, with the extent of ordering increasing with activity. In the nematic phase, a spectrum of static and time-dependent states is observed. In particular, for high activities, a pair of circulating +1/2 defects appears in the centre of the cavity while -1/2 defects are observed to oscillate near the walls. Our results are summarised in a detailed phase diagram. |
Friday, March 18, 2022 9:48AM - 10:00AM |
Y20.00010: Hamiltonian structure of 2D fluid dynamics with broken parity Sriram Ganeshan, Gustavo M Monteiro, Alexander G Abanov Isotropic fluids in two spatial dimensions can break parity symmetry and sustain transverse stresses which do not lead to dissipation. Corresponding transport coefficients include odd viscosity, odd torque, and odd pressure. In this talk, I will discuss conditions on transport coefficients that correspond to dissipationless and separately to Hamiltonian fluid dynamics. The restriction on the transport coefficients will help identify what kind of hydrodynamics can be obtained by coarse-graining a microscopic Hamiltonian system. Interestingly, not all parity-breaking transport coefficients lead to energy conservation, and, generally, the fluid dynamics are energy conserving but not Hamiltonian. I will outline how such dynamics can be realized by imposing a nonholonomic constraint on the Hamiltonian system. |
Friday, March 18, 2022 10:00AM - 10:12AM |
Y20.00011: Modified Darcy's Law for parity odd three-dimensional fluids Dylan Reynolds Hele-Shaw flow is defined as Stokes flow between two parallel flat plates separated by an infinitesimally small gap. The governing equation of Hele-Shaw flow is Darcy's Law, which also describes ideal inviscid flow, and flow through a porous medium. In this work, we derive a modification to Darcy’s Law due to a longitudinal component of the three-dimensional parity-odd viscosity tensor, dubbed 'longitudinal odd viscosity’, and show that for incompressible fluids this is the only modification that is possible within the Hele-Shaw geometry. The modified Darcy’s Law acquires an off-diagonal contribution, similar in form to that seen in a rotating Hele-Shaw cell, or a ferrofluid in an external magnetic field. We discuss the observable effects of the modified Darcy’s law in various experiments relevant to the Hele-Shaw setup. In particular, we show that when confined to a channel, a single fluid exerts a transverse force on the walls. These results can be directly applied to active matter fluids, or other parity-odd three-dimensional fluids confined to a Hele-Shaw cell. |
Friday, March 18, 2022 10:12AM - 10:24AM |
Y20.00012: Nonreciprocal phase separation in living chiral crystal Junang Li, Nikta Fakhri Swimming starfish embryos spontaneously assemble into living crystals that span thousands of spinning organisms and persist for tens of hours. Carrying an arrow of time, the embryos spin in the counter clockwise manner and interact non-reciprocally with each other. As a result, this living chiral crystal exhibits many interesting phenomena from order-disorder transition to chiral waves. Here, we investigate the phase diagram of living chiral crystals formed by embryos from different developmental stages. We observe a number of different time dependent phases, from mixed to fully separated to coexisting phases. |
Friday, March 18, 2022 10:24AM - 10:36AM |
Y20.00013: Orientational correlations of active defects in flat and curved space Jyothishraj Nambisan, Daniel Pearce, Perry W Ellis, Luca Giomi, Alberto Fernandez-Nieves Topological defects are salient signatures of active nematics, which are partially-ordered systems intrinsically out of equilibrium. We experimentally study the dynamics of microtubule-kinesin active nematics constrained to both flat 2D space and toroidal surfaces and inquire whether the defects develop any form of order. In flat space, +1/2 defects develop short range ferromagnetic order (mediated by -1/2 defects) and antiferromagnetic order at length scales comparable to the mean defect spacing. Both these effects and the corresponding correlations were seen to persist independent of the total defect density, and without any global orientational order [1]. In contrast, on curved space, we find that defect orientations strongly couple to the surface they live in, resulting in both +1/2 and -1/2 defects developing orientational order in regions of non-zero Gaussian curvature. |
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