Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session R21: Biofluids: Locomotion XII - Microswimmers and Bacteria III |
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Chair: Jeffrey Guasto, Tufts University Room: 316 |
Tuesday, November 26, 2013 1:05PM - 1:18PM |
R21.00001: Ferromagnetic and antiferromagnetic order in bacterial vortex lattices Hugo Wioland, Francis G. Woodhouse, J\"orn Dunkel, Raymond E. Goldstein In conventional electronic materials, spins can organize into ordered phases that give rise to ferromagnetic or antiferromagnetic behavior. Here, we report similar observations in a completely different system: a suspension of swimming bacteria. When a dense \textit{Bacillus subtilis} suspension is confined to a small circular chamber, it can spontaneously form a stable vortex (``spin'') state that can persist for several minutes [Wioland et al., PRL {\bf 110}, 268102 (2013)]. By coupling up to 100 such chambers in microfluidic devices, we are able to realize bacterial spin lattices of different geometries. Depending on that geometry and the effective coupling strength between neighboring vortices, we observe the formation of stable ``antiferromagnetic'' and ``ferromagnetic'' bacterial vortex states, that appear to be controlled by the subtle competition between bacterial boundary layer flows and bulk dynamics. [Preview Abstract] |
Tuesday, November 26, 2013 1:18PM - 1:31PM |
R21.00002: Magnetic Control of Rigid Achiral Microswimmers U Cheang, Farshad Meshkati, Henry Fu, MinJun Kim We report control of rigid achiral microswimmers in low Reynolds number environments. A rotating magnetic field was used to actuate the microswimmers wirelessly by rotating the microswimmers, which produces propulsion. Previous magnetically actuated microswimmers in bulk fluids have been designed with either flexibility or chiral geometry; we show that simpler geometries with neither flexibility nor chirality can produce propulsion. The microswimmer consists of three magnetic beads conjugated using avidin-biotin linkages into an arc formation. We designed a magnetic field generator consisting of electromagnetic coils arranged in an approximate Helmholtz configuration. A highspeed camera provided realtime imaging of the microswimmers' motion in a PDMS chamber. The rigidity of the microswimmer was characterized by tracking the position of the individual beads and calculating their relative distances. As a function of field strength and rotation frequency, we observed changes in the rotational axis of the microswimmers and the corresponding effects on their velocities. The achiral microswimmers exhibited active propulsion and were controllable in both speed and direction, which demonstrates the possibility for future biomedical applications such as drug delivery. [Preview Abstract] |
Tuesday, November 26, 2013 1:31PM - 1:44PM |
R21.00003: Direct evidence of flagellar synchronization through hydrodynamic interactions Douglas Brumley, Marco Polin, Kirsty Wan, Raymond Goldstein Eukaryotic cilia and flagella exhibit striking coordination, from the synchronous beating of two flagella in {\it Chlamydomonas} to the metachronal waves and large-scale flows displayed by carpets of cilia. However, the precise mechanisms responsible for flagellar synchronization remain unclear. We perform a series of experiments involving two individual flagella in a quiescent fluid. Cells are isolated from the colonial alga {\it Volvox carteri}, held in place at a fixed distance $d$, and oriented so that their flagellar beating planes coincide. In this fashion, we are able to explicitly assess the role of hydrodynamics in achieving synchronization. For closely separated cells, the flagella are capable of exhibiting a phase-locked state for thousands of beats at a time, despite significant differences in their intrinsic frequencies. For intermediate values of $d$, synchronous periods are interrupted by brief phase slips, while for $d\gg1$ the flagellar phase difference drifts almost linearly with time. The coupling strength extracted through analysis of the synchronization statistics exhibits excellent agreement with hydrodynamic predictions. This study unambiguously reveals that flagella coupled only through hydrodynamics are capable of exhibiting robust synchrony. [Preview Abstract] |
Tuesday, November 26, 2013 1:44PM - 1:57PM |
R21.00004: Feeding of swimming {\it Paramecium} with fore-aft asymmetry in viscous fluid Peng Zhang, Saikat Jana, Matthew Giarra, Pavlos Vlachos, Sunghwan Jung Swimming behaviours and feeding efficiencies of {\it Paramecium Multimicronucleatum} with fore-aft asymmetric body shapes are studied experimentally and numerically. Among various possible swimming ways, ciliates typically exhibit only one preferred swimming directions in favorable conditions. Ciliates, like {\it Paramecia}, with fore-aft asymmetric shapes preferably swim towards the slender anterior while feeding fluid to the oral groove located at the center of the body. Since both feeding and swimming efficiencies are influenced by fluid motions around the body, it is important to reveal the fluid mechanics around a moving object. Experimentally, $\mu$-PIV methods are employed to characterize the source-dipole streamline patterns and fluid motions around {\it Paramecium}. Numerical simulations by boundary element methods are also used to evaluate surface stresses and velocities, which give insights into the efficiencies of swimming and feeding depending on body asymmetry. It is concluded that a slender anterior and fat posterior increases the combined efficiency of swimming and feeding, which matches well with actual shapes of {\it Paramecium}. Discrepancies between experiments and simulations are also discussed. [Preview Abstract] |
Tuesday, November 26, 2013 1:57PM - 2:10PM |
R21.00005: Bacterial motility near crude oil and water interface Jomayra E. S\'anchez Rodr\'Iguez, Mehdi Molaei, Jian Sheng Study of biodegradation of crude oil by microbes requires profound understanding of their movement near oil-water interface as well as in/out of phase movement. Bacterial motilities are known to be modified by the presence of an interface through hydrodynamic interactions in addition to the chemotactic behavior towards the oil phase. Using digital holographic microscopy and phase contrast microscopy, we study locomotion of \textit{Pseudomonas} sp (P62), a well-known hydrocarbon degrader under various chemo- and mechano-environmental conditions. Baseline experiments have been performed at different nutrient levels and Ion levels to identify effects of chemical environment on cell motility. Utilizing novel microfluidics and surface functionalization, we have established a stable vertical oil-water interface between top and bottom surfaces of the microfluidics, which allow clear optical access to observe bacterial movement near the interface. Three-dimensional trajectories of bacteria, obtained by analyzing recorded by digital holography microscopy, enable us to characterize bacterial swimming and orientation near interfaces. Chemotaxis velocity and swimming induced dispersion are measured directly as well as cell concentration distributions with respect to the distance to the interface. [Preview Abstract] |
Tuesday, November 26, 2013 2:10PM - 2:23PM |
R21.00006: The phylogeny of swimming kinematics: The environment controls flagellar waveforms in sperm motility Jeffrey Guasto, Lisa Burton, Richard Zimmer, Anette Hosoi, Roman Stocker In recent years, phylogenetic and molecular analyses have dominated the study of ecology and evolution. However, physical interactions between organisms and their environment, a fundamental determinant of organism ecology and evolution, are mediated by organism form and function, highlighting the need to understand the mechanics of basic survival strategies, including locomotion. Focusing on spermatozoa, we combined high-speed video microscopy and singular value decomposition analysis to quantitatively compare the flagellar waveforms of eight species, ranging from marine invertebrates to humans. We found striking similarities in sperm swimming kinematics between genetically dissimilar organisms, which could not be uncovered by phylogenetic analysis. The emergence of dominant waveform patterns across species are suggestive of biological optimization for flagellar locomotion and point toward environmental cues as drivers of this convergence. These results reinforce the power of quantitative kinematic analysis to understand the physical drivers of evolution and as an approach to uncover new solutions for engineering applications, such as micro-robotics. [Preview Abstract] |
Tuesday, November 26, 2013 2:23PM - 2:36PM |
R21.00007: Flagellar Kinematics and Swimming Behavior of Algal Cells in Viscoelastic Fluids Paulo Arratia, Jing Yang, Jerry Gollub The motility behavior of microorganisms can be significantly affected by the rheology of their fluidic environment. In this talk, we experimentally investigate the effects of fluid elasticity on both the flagella kinematics and swimming dynamics of the microscopic alga \textit{Chlamydomonas reinhardtii}. We find that the flagellar beating frequency and wave speed are both enhanced by fluid elasticity. Interestingly, the swimming speeds during the alga power and recovery strokes are enhanced by fluid elasticity for De\textgreater 1. Despite such enhancements, however, the alga net forward speed is hindered by fluid elasticity by as much as 30{\%} compared to Newtonian fluids of similar shear viscosities. The motility enhancements could be explained by the mechanism of stress accumulation in the viscoelastic fluid. [Preview Abstract] |
Tuesday, November 26, 2013 2:36PM - 2:49PM |
R21.00008: Fabrication and calibration of sensitively photoelastic biocompatible gelatin spheres Henry Fu, Ericson Ceniceros, Zephyr McCormick Photoelastic gelatin can be used to measure forces generated by organisms in complex environments. We describe manufacturing, storage, and calibration techniques for sensitive photoelastic gelatin spheres to be used in aqueous environments. Calibration yields a correlation between photoelastic signal and applied force to be used in future studies. Images for calibration were collected with a digital camera attached to a linear polariscope. The images were then processed in Matlab to determine the photoelastic response of each sphere. The effect of composition, gelatin concentration, glycerol concentration, sphere size, and temperature were all examined for their effect on signal response. The minimum detectable force and the repeatability of our calibration technique were evaluated for the same sphere, different spheres from the same fabrication batch, and spheres from different batches. The minimum force detectable is 10 $\mu$N or less depending on sphere size. Factors which significantly contribute to errors in the calibration were explored in detail and minimized. [Preview Abstract] |
Tuesday, November 26, 2013 2:49PM - 3:02PM |
R21.00009: Self-propelled Metallic Microrods by Ultrasonic Standing Waves Mauricio Hoyos, Suzanne Ahmed, Wei Wang, Thomas Mallouk Particulate materials like rigid particles, cells, bacteria, vesicles, or metallic micro rods can be manipulated in a resonator by ultrasonic standing waves. In a resonator, an acoustic force makes species to migrate either toward the nodes or antinodes depending on the acoustic properties of particles. The acoustic force depends on particles volume, acoustic energy and on the acoustic contrast factor. The latter is a function of particle and fluid acoustic impedances. Acoustic impedance is defined as the product between the density and the sound velocity of a material. The acoustic manipulation has been accomplished mostly in microfluidic devices for separating blood cells from lipids, for driving air bubbles or for generating micro-aggregates of cells. The range of frequencies used is between 0.5 and 10MHz. In this presentation we shall focus on a new phenomenon we called self-acoustophoresis consisting on generating very high speed displacements of metallic microrods (gold, ruthenium) suspended in water; we shall s show how ultrasonic standing waves can be used for generating high speed rotation ofindividual as well as micro rod aggregates.this manipulation opens new possibilities to drug delivery using micro rods as conveyers. [Preview Abstract] |
Tuesday, November 26, 2013 3:02PM - 3:15PM |
R21.00010: Active Motion Control of Tetrahymena pyriformis by Galvanotaxis and Geotaxis Jihoon Kim, Doyoung Byun, Min Jun Kim Recently, there has been increasing interest in the swimming behavior of microorganisms and biologically inspired micro-robots. These microorganisms naturally accompanied by complex motions. Therefore it is important to understand the flow characteristics as well as control mechanisms. One of eukaryotic cells, the protozoa are a diverse group of unicellular organisms, many of which are motile cilia. Motile cilia are cover on the surface of cell in large numbers and beat in oriented waves. Sequential beating motions of a single cilium form metachronal strokes, producing a propagation wave, and therefore the body is achieved propulsion force. So preliminary studies are achieved to understand the flow induced by swimming microorganisms. Based on hydrodynamic results, the follow study of a few micro-scale protozoa cell, such as the Tetrahymena pyriformis, has provided active or passive control into several external stimuli. In typical control methods, the galvanotaxis and geotaxis were adopted active and passive control, respectively. The validation of galvanotaxis is used DC and AC voltage. In terms of geotaxis, corrugated microstructures were used to control in the microchannel. [Preview Abstract] |
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