Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session L26: Biofluids: Complex Fluids: Locomotion and Rheology |
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Chair: Chuanbin Li, UC Davis Room: 306 |
Monday, November 23, 2015 4:05PM - 4:18PM |
L26.00001: A numerical investigation into the effects of fluid rheology and stroke kinematics on swimming alga cells in complex fluids Chuanbin Li, Robert Guy, Becca Thomases It is observed in experiments that when the fluid viscosity or elasticity is changed, \emph{Chlamydomonas reinhardtii} exhibits changes in both flagellar kinematics and the swimming speed. In order to understand the effects of rheology on both gait and swimming performance, we develop a computational model of the swimmer. We use flagellar strokes fit from experimental data to set up a constrained system, determining the forces on the swimmer and its swimming velocity. Our approach to simulating the swimming behavior demonstrates low computational costs even in three dimensions. In our simulations, stroke patterns and fluid rheologies are changed separately, so that we can dissect the contributions of stroke kinematics of the alga and the fluid environment, which can not be achieved with experiments. [Preview Abstract] |
Monday, November 23, 2015 4:18PM - 4:31PM |
L26.00002: Running and tumbling with E. coli in polymeric solutions Alison Patteson, Arvind Gopinath, Paulo Arratia Bacteria commonly utilize a run-and-tumble swimming behavior to navigate through complex environments such as mucus in the lungs or digestive system. This swimming behavior has been extensively studied in water-like fluids; yet, investigations on the role of particles or polymers in the ambient fluid on the run-and-tumble behavior are limited. Here, we experimentally investigate the swimming dynamics of E. coli in polymeric solutions. We find that small amounts of polymer drastically change the run-and-tumble behavior of E. coli cells, significantly enhancing translational diffusion and reducing rotational diffusion. The average cell velocity increases with polymer concentration (and viscosity) and the mean run times are enhanced. By varying polymer molecular weight and visualizing interactions between single E. coli and fluorescently-stained DNA-polymer molecules, we show that enhanced translation is a result of two mechanisms: (1) suppression of cell wobbling due to elasticity and (2) enhancement of run times due to viscosity. Our results show that the transport of chemotactic cells can be independently modified by viscosity and elasticity. [Preview Abstract] |
Monday, November 23, 2015 4:31PM - 4:44PM |
L26.00003: Modular microrobot for swimming in heterogeneous environments U Kei Cheang, Farshad Meshkati, Henry Fu, MinJun Kim One of the difficulties in navigating in vivo is to overcome many types of environments. This includes blood vessels of different diameters, fluids with different mechanical properties, and physical barriers. Inspired by conventional modular robotics, we demonstrate modular microrobotics using magnetic particles as the modular units to change size and shape through docking and undocking. Much like the vast variety of microorganisms navigating many different bio-environments, modular microswimmers have the ability to dynamically adapt different environments by reconfiguring the swimmers' physical characteristics. We model the docking as magnetic assembly and undocking mechanisms as deformation by hydrodynamic forces. We characterize the swimming capability of the modular microswimmer with different size and shapes. Finally, we demonstrate modular microrobotics by assembling a three-bead microswimmer into a nine-bead microswimmer, and then disassemble it into several independently swimming microswimmers.. [Preview Abstract] |
Monday, November 23, 2015 4:44PM - 4:57PM |
L26.00004: Characterization of undulatory locomotion in granular media Zhiwei Peng, On Shun Pak, Gwynn Elfring Undulatory locomotion is ubiquitous in nature, from the swimming of flagellated microorganisms in biological fluids, to the slithering of snakes on land, or the locomotion of sandfish lizards in sand. Analysis of locomotion in granular materials is relatively less developed compared with fluids partially due to a lack of validated force models but a recently proposed resistive force theory (RFT) in granular media has been shown useful in studying the locomotion of a sand-swimming lizard. Here we employ this model to investigate the swimming characteristics of an undulating slender filament of both finite and infinite length. For infinite swimmers, similar to results in viscous fluids, the sawtooth waveform is found to be optimal for propulsion speed at a given power consumption. We also compare the swimming characteristics of sinusoidal and sawtooth swimmers with swimming in viscous fluids. More complex swimming dynamics emerge when the assumption of an infinite swimmer is removed. In particular, we characterize the effects of drifting and pitching in terms of propulsion speed and efficiency for a finite sinusoidal swimmer. The results complement our understanding of undulatory locomotion and provide insights into the effective design of locomotive systems in granular media. [Preview Abstract] |
Monday, November 23, 2015 4:57PM - 5:10PM |
L26.00005: New rheometer geometry to characterize delicate biological fluids in-situ. Kelly Connelly, Ethan Young, Jean-Pierre Hubschman, Jeff Eldredge, Pirouz Kavehpour The vitreous humor is a viscoelastic gel-like fluid that fills and maintains the structure of the eye. Changes in the structure of the network of macromolecules in vitreous occurs naturally during ageing causing pathological conditions such as retinal tears that may lead to blindness. Vitrectomy surgery is a common procedure to remove problematic vitreous from the eye, but must be carefully performed to prevent iatrogenic retinal tears. Minimizing invasiveness and surgical time depends on the viscoelastic behavior of vitreous as it flows from the eye out through a small gauge needle. Rheology has been used to correlate relevant viscoelastic fluid properties with the macromolecular structure previously using parallel plate rheometer geometries, and now with a new patented probe geometry. This improves upon plate geometries because measurements are in situ, so removal of the vitreous from the eye is not necessary. Creep rheological experiments with the probe indicate a region of elastic behavior exists at shorter timescales and steady state apparent viscosity at longer timescales. In-situ creep tests advance understanding of how macromolecular structure alters viscoelasticity, which may allow better predictions of fluid flow during vitrectomy in the future. [Preview Abstract] |
Monday, November 23, 2015 5:10PM - 5:23PM |
L26.00006: Role of elasticity on the Rheological Response of the Uterus Tissue Nariman Ashrafi Khorasani, PARASTOO PIROOZRAM N. Khorasani and P. piroozram Department of Mechanical Engineering, Payame Noor University, 19395-3697, Tehran, Iran, The effect of uterus tissue viscoelasticity on its internal pressure is explored. The tissue of the uterus is presented by a linear viscoelastic model with two major time constants. A proper user defined function is developed and incorporated in the simulation software, to represent the model. The geometry of the uterus is separately modeled. It is found that viscoelasticity of the tissue which can be controlled and altered by change the concentration can directly affect its internal pressure. It is also observed that the pressure decreases as the moisture of the tissue is increased. The study is repeated for several practical conditions and parameters pertaining to the viscoelasticity of the tissue are evaluated. [Preview Abstract] |
Monday, November 23, 2015 5:23PM - 5:36PM |
L26.00007: Two-Point Particle Tracking Microrheology of Nematic Complex Fluids Manuel Gomez-Gonzalez, Juan C. del Alamo Many biological and technological complex fluids exhibit tight microstructural alignment that confers them nematic mechanical properties. However, current microrheological methods are unable to characterize the rheological response of nematic complex fluids along different directions. In this talk, we present a novel directional two-point particle-tracking microrheology method (D2PTM) that allows to measure the viscoelasticity of nematic complex fluids. We establish the theoretical foundation for D2PTM by analyzing the motion of a probing microscopic particle embedded in a nematic complex fluid, and the mutual hydrodynamic interactions between pairs of distant particles. From this analysis, we generalize the formulation of two-point particle tracking microrheology for nematic complex fluids. We test the new D2PTM formulation by simulating the motion of groups of particles undergoing Brownian motion in a nematic complex fluid with prescribed directional shear moduli. Lastly, we illustrate the experimental application of the new technique by measuring nematic F-actin solutions. These experiments constitute the first microrheological measurement of shear moduli in an anisotropic soft material. [Preview Abstract] |
Monday, November 23, 2015 5:36PM - 5:49PM |
L26.00008: Local aggregation characteristics of microscale blood flows Efstathios Kaliviotis, Joseph M. Sherwood, Jonathan Dusting, Stavroula Balabani Erythrocyte aggregation (EA) is an important aspect of microvascular flows affecting blood flow and viscosity. Microscale blood flows have been studied extensively in recent years using computational and microfluidic based approaches. However, the relationship between the local structural characteristics of blood and the velocity field has not been quantified. We report simultaneous measurements of the local velocity, aggregation and haematocrit distributions of human erythrocytes flowing in a microchannel. EA was induced using Dextran and flows were imaged using brightfield microscopy. Local aggregation characteristics were investigated using statistical and edge-detection image processing techniques while velocity profiles were obtained using PIV algorithms. Aggregation intensity was found to strongly correlate with local variations in velocity in both the central and wall regions of the channel. The edge detection method showed that near the side wall large aggregates are associated with high local velocities and low local shear rates. In the central region large aggregates occurred in regions of low velocity and high erythrocyte concentration. The results demonstrate the combined effect of haematocrit and velocity distributions on local aggregation characteristics. [Preview Abstract] |
Monday, November 23, 2015 5:49PM - 6:02PM |
L26.00009: Spatially and temporally resolved quantification of endothelial cell modification in response to shear stress Lori Lambert, Iraklis Pipinos, Timothy Baxter, Richard Leighton, Timothy Wei This talk contains a resport on \textit{in vivo} measurements made over a confluent layer of bovine endothelial cells in a microchannel. The ultimate goal of the experiments is to understand and model cellular response to fluid stresses and the ensuing transport across the endothelial layer. High resolution $\mu$ PTV measurements were made to quantify the cellular response to steady shear rates of 5, 10 and 20 dynes/cm$^{2}$. Surface topography, shear and pressure distributions were calculated from sets of velocity fields made in planes parallel to the wall. For each experiment, measurements were made in three-hour intervals for eighteen hours. To validate the methodology, the pH of the medium was varied so that the health of the cells would vary. Clear differences in topography and cell orientation were found. Implications for future experiments and research will be discussed. [Preview Abstract] |
Monday, November 23, 2015 6:02PM - 6:15PM |
L26.00010: The Effects of Hemodynamic Shear Stress on~Stemness~of Acute~Myelogenous~Leukemia (AML) Andrew Raddatz, Ursula Triantafillu, Yonghyun (John) Kim Cancer stem cells (CSCs) have recently been identified as the root cause of tumors generated from cancer cell populations. This is because these CSCs are drug-resistant and have the ability to self-renew and differentiate. Current methods of culturing CSCs require much time and money, so cancer cell culture protocols, which maximize yield of CSCs are needed. It was hypothesized that the quantity of Acute myelogenous leukemia stem cells (LSCs) would increase after applying shear stress to the leukemia cells based on previous studies with breast cancer in bioreactors. The shear stress was applied by pumping the cells through narrow tubing to mimic the in vivo bloodstream environment. In support of the hypothesis, shear stress was found to increase the amount of LSCs in a given leukemia population. [Preview Abstract] |
Monday, November 23, 2015 6:15PM - 6:28PM |
L26.00011: Non-Newtonian fluid flow over a heterogeneously slippery surface A. Sander Haase, Jeffery A. Wood, Lisette M.J. Sprakel, Rob G.H. Lammertink The no-slip boundary condition does not always hold. In the past, we have investigated the influence of effective wall slip on interfacial transport for a bubble mattress -- a superhydrophobic surface consisting of an array of transverse gas-filled grooves. We proved experimentally that the amount of effective wall slip depends on the bubble protrusion angle and the surface porosity (Karatay et al., PNAS 110, 2013), and predicted that mass transport can be enhanced significantly (Haase et al., Soft Matter 9, 2013). Both studies involve the flow of water. In practise, however, many liquids encountered are non-Newtonian, like blood and polymer solutions. This raises some interesting questions. How does interfacial transport depend on the rheological properties of the liquid? Does the time-scale of the experiment matter? A bubble mattress is a suitable platform to investigate this, due to local variations in shear rate. We predict that for shear-thinning liquids, compared to water, the amount of wall slip can be enhanced considerably, although this depends on the applied flow rate. Experiments are performed to proof this behaviour. Simulations are used to assess what will happen when the characteristic time-scale of the system matches the relaxation time of the visco-elastic liquid. [Preview Abstract] |
Monday, November 23, 2015 6:28PM - 6:41PM |
L26.00012: A new look on blood shear thinning Manouk Abkarian, Luca Lanotte, Jean-Marc Fromental, Simon Mendez, Dmitry Fedosov, Gerhard Gompper, Johannes Mauer, Viviana Claveria Blood is a shear-thinning fluid. At shear rates $\dot{\gamma}<1 s^{-1}$, its drop of viscosity has been related primarily to the breaking-up of networks of ``rouleaux'' formed by stacked red blood cells (RBCs). For higher $\dot{\gamma}$ in the range $10-1000 s^{-1}$, where RBCs flow as single elements, studies demonstrated that RBCs suspended in a viscous fluid mimicking the viscosity of whole blood, deformed into ellipsoids aligned steadily in the direction of the flow, while their membrane rotated about their center of mass like a tank-tread. Such drop-like behavior seemed to explain shear-thinning. Here, using rheometers, microfluidics and simulations, we show that the dynamics of single RBCs in plasma-like fluids display a different sequence of deformation for increasing shear rates going from discocytes to successively, stomatocytes, folded stomatocytes, trilobes and tetralobes, but never ellipsoids. This result is also identical for physiological hematocrits. We correlate this shape diagram to the different regimes in blood rheology for high shear rates and propose a new-look on the interpretation of blood shear-thinning behavior. [Preview Abstract] |
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