Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session M4: Multiple CellsBio Fluids: Internal
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Chair: Yaling Liui, Lehigh University Room: 404 |
Tuesday, November 21, 2017 8:00AM - 8:13AM |
M4.00001: Bistable synchronization modes in hydrodynamically coupled micro-rotors Hanliang Guo, Anup Kanale, Sebastian Fuerthauer, Eva Kanso Cilia often beat in synchrony, and they may transition between different synchronization modes in the same cell type. For example, cilia in the mammalian brain ventricles are reported to periodically change their collective beat orientation, providing a cilia-based switch for redirecting the transport of cerebrospinal fluid. Experimental and theoretical evidences suggest that phase coordinations can be achieved solely via hydrodynamical interactions. However, the exact mechanisms responsible for transitioning between various synchronization modes remain illusive. Here, we use a theoretical model where each cilium is represented by a bead moving along a closed trajectory close to a no-slip surface. We investigate the emergent synchronization modes and their stability for various cilia-inspired force profiles. We observe distinct stable synchronization modes between two rotors, including a bistable regime where both in-phase and anti-phase synchronizations are stable. We then extend this analysis to an array of rotors where we demonstrate the dynamical formations of metachronal waves. These findings may help us to understand the origin of synchrony in biological and bio-inspired systems, and the mechanisms underlying transitions between different synchronization modes. [Preview Abstract] |
Tuesday, November 21, 2017 8:13AM - 8:26AM |
M4.00002: Measuring and Simulating Cellular Flows during Spindle Positioning Ehssan Nazockdast, Haiyin Wu, Daniel Needleman, Michael Shelley A cell is a complex fluidic environment in which fundamental biological processes take place. One such process is the proper positioning and elongation of the mitotic spindle which is crucial for chromosome segregation and cell division, and involves the interaction of microtubule assemblies with motor-proteins and subcellular organelles. In a combined experimental and computational study, we use cytoplasmic flow measurements and computational fluid dynamics to argue that proper positioning is primarily achieved by the action of motor-proteins bound to the cell boundary. [Preview Abstract] |
Tuesday, November 21, 2017 8:26AM - 8:39AM |
M4.00003: Large-scale Synchronization in Carpets of Micro-rotors Anup Kanale, Hanliang Guo, Wen Yan, Eva Kanso Motile cilia are ubiquitous in nature, and have a critical role in biological locomotion and fluid transport. They often beat in an orchestrated wavelike fashion, and theoretical evidence suggests that this coordinated motion could arise from hydrodynamic interactions. Models based on bead-spring oscillators were used to examine the interaction between pairs of cilia, focusing on in-phase or anti-phase synchrony, while models of hydrodynamically-coupled elastic filaments looked at metachronal coordination in large but finite numbers of interacting cilia. The latter models reproduce metachronal wave coordination, but they are not readily amenable to analysis and parametric studies that highlight the origin of the instabilities that lead to wave propagations and wavelength selection. Here, we use a known model in which each cilium is represented by a rigid sphere moving along a circular trajectory close to a wall, hence the term rotor. The rotor is driven by a cilia-inspired force profile. We generalize this model to a doubly-periodic array of rotors, assuming small distance to the bounding wall, and employ Ewald summation techniques to solve for the flow field. Our goal is to examine the conditions that give rise to stable metachronal waves and their associated wavelength. [Preview Abstract] |
Tuesday, November 21, 2017 8:39AM - 8:52AM |
M4.00004: Swarm-scale eddies generated by collective swimmers Isabel A. Houghton, John O. Dabiri Biologically generated turbulence has been proposed as an important contributor to nutrient transport and ocean mixing. However, the relevance of such turbulence is dependent upon the ability of swimming organisms to generate mixing eddies at scales comparable to the length scales of stratification in the ocean. Despite their small size, marine zooplankton undergo diurnal vertical migration over hundreds of meters and aggregate in dense swarms ranging from 10-50 m in vertical extent, which introduces additional length scales of relevance to their interaction with the surrounding water. Here we show that representative centimeter-scale swimmers (\textit{Artemia salina}) migrating collectively perturb a stable density stratification at scales corresponding to the vertical extent of the laboratory controlled swarm, approaching 50 cm. This observed formation of swarm-scale mixing eddies is the result of coalescence of the flows in the wakes of the individual organisms and occurs even in the presence of strong density stratification. These results illustrate the potential for marine zooplankton to significantly alter the physical and biogeochemical structure of the water column at the scale of the swarm, orders of magnitude larger than the individual swimmers. [Preview Abstract] |
Tuesday, November 21, 2017 8:52AM - 9:05AM |
M4.00005: Trains of Red Blood Cells in a bi-dimensional microflows. Annie Viallat, Cecile Iss, Delphine Held, catherine badens, anne charrier, Emmanuèle Helfer In the vascular microcirculation RBC distribution is uneven in the direction normal to the blood flow, as first evidenced by the existence of a cell-free layer near the vessel wall. In addition, the most rigid cells such as white blood cells and platelets are known to segregate to the walls while flowing in wide channels. We use microfluidic bi-dimensional channels (60 µm wide, 8 µm high, 5 mm long) to explore the flow structure in RBC suspensions at several hematocrits, flow rates and RBC rigidities. We observe the dynamical formation of RBC clusters and their motion along the flow direction. We study healthy RBCs, RBCs stiffened with glutaraldehyde, mixture of healthy and stiffened RBCs and RBC from sickle cell patients. Initially dispersed healthy RBCs organize, while flowing along the channel, into series of parallel trains. The train length depends on RBC hematocrit and flow rate. Stiffened RBCs do not cluster and mainly display tumbling motion like rigid disks. They destabilize existing trains and are preferentially observed close to the walls. We compared our results to that observed in microcapillaries, where trains of RBCs entirely fill in width the microchannel (G. Tomaiuolo, L. Lanotte, G. Ghigliotti, C. Misbah, and S. Guido, Phys Fluids, 24, 051903 (2012). [Preview Abstract] |
Tuesday, November 21, 2017 9:05AM - 9:18AM |
M4.00006: Ferromagnetic Swimmers - Devices and Applications Joshua Hamilton, Peter Petrov, C. Peter Winlove, Andrew Gilbert, Matthew Bryan, Feodor Ogrin Microscopic swimming devices hold promise for radically new applications in lab-on-a-chip and microfluidic technology, diagnostics and drug delivery etc. We propose a new class of autonomous ferromagnetic swimming devices, actuated and controlled solely by an oscillating magnetic field. Experimentally, these devices (3.6 mm) are based on a pair of interacting ferromagnetic particles of different size and different anisotropic properties joined by an elastic link and actuated by an external time-dependent magnetic field. The net motion is generated through a combination of dipolar interparticle gradient forces, time-dependent torque and hydrodynamic coupling. We investigate the dynamic performance of a prototype (3.6 mm) of the ferromagnetic swimmer in fluids of different viscosity as a function of the external field parameters and demonstrate stable propulsion over a wide range of Reynolds numbers. Manipulation of the external magnetic field resulted in robust control over the speed and direction of propulsion. We also demonstrate our ferromagnetic swimmer working as a macroscopic prototype of a microfluidic pump. By physically tethering the swimmer, instead of swimming, the swimmer generates a directional flow of liquid around itself. [Preview Abstract] |
Tuesday, November 21, 2017 9:18AM - 9:31AM |
M4.00007: The spatiotemporal organization of cilia activity drives multiscale circular flows of mucus in reconstituted human bronchial epithelium Etienne Loiseau, Delphine Gras, Pascal Chanez, Annie Viallat Chronic respiratory diseases affect hundreds of millions of people worldwide. The bronchial epithelium is the first barrier to protect the respiratory tract via an innate mechanism called mucociliary clearance. It consists in the active transport of a sticky fluid, the mucus, via a myriad of cilia at the epithelial surface of the airways. The mucus traps inhaled pathogens and the protective role of the mucociliary clearance relies on the ability of the cilia to self-organize and coordinate their beating to transport the mucus over the full bronchial tree till its elimination through swallowing or expectoration. Despite a rich corpus of clinical studies, chronic respiratory diseases remain poorly understood and quantitative biophysical studies are still missing. Here we will present the physical mechanisms underlying the mucociliary transport. We will show how the cilia self-organize during the ciliogenesis and how the coordination of their beating direction leads to the formation of fluid flow patterns at the macroscopic scale. Finally, we will discuss the role of long range hydrodynamics interactions in this intricate coupled system. [Preview Abstract] |
Tuesday, November 21, 2017 9:31AM - 9:44AM |
M4.00008: Hydrodynamic effects on phase transition in active matter. Harinadha Gidituri, V S Akella, Mahesh Panchagnula, Srikanth Vedantam Organized motion of active (self-propelled) objects are ubiquitous in nature. The objective of this study to investigate the effect of hydrodynamics on the coherent structures in active and passive particle mixtures. We use a mesoscopic method Dissipative Particle Dynamics (DPD). The system shows three different states viz. meso-turbulent (disordered state), polar flock and vortical (ordered state) for different values of activity and volume fraction of active particles. From our numerical simulations we construct a phase diagram between activity co-efficient, volume fraction and viscosity of the passive fluid. Transition from vortical to polar is triggered by increasing the viscosity of passive fluid which causes strong short-range hydrodynamic interactions. However, as the viscosity of the fluid decreases, both vortical and meso-turbulent states transition to polar flock phase. We also calculated the diffusion co-efficients via mean square displacement (MSD) for passive and active particles. We observe ballistic and diffusive regimes in the present system.~ [Preview Abstract] |
Tuesday, November 21, 2017 9:44AM - 9:57AM |
M4.00009: Pair-correlations in swimmer suspensions Sankalp Nambiar, Ganesh Subramanian Suspensions of rear-actuated swimming microorganisms, such as E.coli, exhibit several interesting phenomena including spontaneous pattern formation above a critical concentration, novel rheological properties, shear-induced concentration banding etc. Explanations based on mean-field theory are only qualitative, since interactions between swimmers are important for typical experimental concentrations. We analytically characterize the hydrodynamic pair-interactions in a quiescent suspension of slender straight swimmers. The pair-correlation, calculated at leading order by integrating the swimmer velocity disturbances along straight trajectories, decays as 1/$r^2$ for r $\gg$ L (L being the swimmer size). This allows us to characterize both polar and nematic correlations in an interacting swimmer suspension. In the absence of correlations, the velocity covariance asymptotes from a constant for r $\ll$ L to a far-field decay of O(1/$r^2$) for r $\gg$ L, the latter being characteristic of a suspension of non-interacting point force-dipoles. On including correlations, the slow decay of the pair-orientation correlation leads to an additional contribution to the velocity covariance that diverges logarithmically with system size. [Preview Abstract] |
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