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 G19: Biofluids: Cellular II - Experimental Studies |
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Chair: Juan Carlos Del Alamo, University of California, San Diego Room: 310/311 |
Monday, November 25, 2013 8:00AM - 8:13AM |
G19.00001: Mechanical Response of Red Blood Cells Entering a Constriction Nancy Zeng, William Ristenpart Most work on RBC dynamic response to hydrodynamic stress has focused on linear velocity gradients. Relatively little experimental work has examined how RBCs respond to pressure driven flow in more complex geometries, such as in an abrupt contraction. Here, we establish the mechanical behaviors of RBCs undergoing a sudden increase in shear stress at the entrance of a narrow constriction. We pumped RBCs through a constriction in an ex vivo microfluidic device and used high speed video to visualize and track the flow behavior of more than 4,000 RBCs. We show that approximately 90\% of RBCs undergo one of four distinct modes of motion: stretching, twisting, tumbling, or rolling. Intriguingly, almost 40\% of the cells exhibited twisting (rotation around the major axis parallel to the flow direction), a mechanical behavior that is not typically observed in linear velocity gradients. We present detailed statistical analyses on the dynamics of each motion and demonstrate that the behavior is highly sensitive to the location of the RBC within the channel. Finally, we show that the tumbling and rolling motions can be rationalized qualitatively in terms of rigid body rotation, whereas twisting motion cannot, suggesting that twisting is a consequence of the viscoelastic nature of the RBCs. [Preview Abstract] |
Monday, November 25, 2013 8:13AM - 8:26AM |
G19.00002: Effect of Varying Fluid Shear Stress on Cancer Stem Cell Viability {\&} Protein Expression Ria Domier, Yonghyun Kim, David Dozier, Ursula Triantafillu Cancer stem cells cultured \textit{in vitro} in stirred bioreactors are exposed to shear stress. By observing the effect of shear stress on cancer stem cell viability, laboratory cell growth could be optimized. In addition, metastasized cancer stem cells \textit{in vivo} are naturally exposed to shear stress, a factor influencing stem cell differentiation, while circulating in the bloodstream. Changes in protein expression after exposure to shear stress could allow for identification and targeting of circulating cancer cells. In this study, blood flow through capillaries was simulated by using a syringe pump to inject suspensions of Kasumi-1 leukemia stem cells into model blood vessels composed of PEEK tubing 125 microns in diameter. The Hagen-Poisseuille equation was used to solve for operating flow rates based on specified amounts of shear stress. After exposure, cell counts and viabilities were observed using an optical microscope and proteins were analyzed using Western blotting. It was observed that at a one minute exposure to stress, cell viability increased as the amount of shear was increased from 10 to 60 dynes per square centimeter. Results from this research are applicable to optimization of large-scale stem cell growth in bioreactors as well as to the design of targeted cancer therapies. [Preview Abstract] |
Monday, November 25, 2013 8:26AM - 8:39AM |
G19.00003: Lower limit of shear to induce 2-D protein crystals James Young, David Posada, Amir Hirsa, Juan Lopez Proteins are an essential part of every organism. Protein functionality depends on its structure. In order to utilize the most widely used and powerful technique of X-ray crystallography, the protein must first be crystallized. Crystallization is not a trivial step and success rate is often dismal. One approach is two-dimensional protein crystallization at the air/water interface which entails the binding of protein initially in solution to a ligand that has been spread on the interface to form a monolayer. 2-D crystallization avoids some of the complications of 3-D crystallization such as gravity. It also reduces the amount of protein needed by 3 orders of magnitude. Here we quantify the level of interfacial shearing needed to enable crystals to be formed at protein surface concentrations lower than those required in a quiescent system. A phase diagram is presented delineating the required shear rate for a given surface pressure. In addition, surface shear viscosity is demonstrated to be a sensitive macroscopic probe for the in-situ detection of flow-induced crystals. [Preview Abstract] |
Monday, November 25, 2013 8:39AM - 8:52AM |
G19.00004: Are endothelial cell bioeffects from acoustic droplet vaporization proximity dependent? Robinson Seda, David Li, J. Brian Fowlkes, Joseph Bull Acoustic droplet vaporization (ADV) produces gas microbubbles that provide a means of selective occlusion in gas embolotherapy. Vaporization and subsequent occlusion occur inside blood vessels supplying the targeted tissue, such as tumors. Theoretical and computational studies showed that ADV within a vessel can impart high fluid mechanical stresses on the vessel wall. Previous in vitro studies have demonstrated that vaporization at an endothelial layer may affect cell attachment and viability. The current study is aimed at investigating the role of vaporization distance away from the endothelial layer. HUVECs were cultured in OptiCell\texttrademark chambers until reaching confluence. Dodecafluoropentane microdroplets were added, attaining a 10:1 droplet to cell ratio. A single ultrasound pulse (7.5 MHz) consisting of 16 cycles ($\sim$ 2 $\mu$s) and a 5 MPa peak rarefactional pressure was used to produce ADV while varying the vaporization distance from the endothelial layer (0 $\mu$m, 500 $\mu$m, 1000 $\mu$m). Results indicated that cell attachment and viability was significantly different if the distance was 0 $\mu$m (at the endothelial layer). Other distances were not significantly different from the control. ADV will significantly affect the endothelium if droplets are in direct contact with the cells. Droplet concentration and flow conditions inside blood vessels may play an important role. This work was supported by NIH grant R01EB006476. [Preview Abstract] |
Monday, November 25, 2013 8:52AM - 9:05AM |
G19.00005: Fabrication of hydrogel substrates with stiffness step variations using controlled surface wettability Md. Mahmudur Rahman, Donghee Lee, Sangjin Ryu Living cells can respond to changes in the stiffness of the surrounding matrix. Well-known examples include the durotaxis of motile cells and the stiffness-dependent differentiation of stem cells. Such mechanobiological behaviors of living cells have been investigated on hydrogel substrates of which the compliance is either static or varying in one direction. Although various techniques have been developed to fabricate hydrogel substrates of controllable stiffness distributions, however, the fabricated substrates have only hydrogel regions of varying stiffness, lacking regions of static stiffness. Therefore, it has been difficult to compare cells' responses to static stiffness and varying stiffness under the same culture condition. Thus, we aim to fabricate polyacrylamide gel substrates consisting of alternating regions of static stiffness and stiffness gradient. For controlled positioning of gel solutions with different relative concentrations of acrylamide and the crosslinker, we generated superhydrophilic regions surrounded by hydrophobic barriers on glass and then filled the regions with the gel solutions. When sandwiched by another glass surface, the gel solutions experienced limited mixing only at interfaces, which created stiffness gradients between static stiffness regions. [Preview Abstract] |
Monday, November 25, 2013 9:05AM - 9:18AM |
G19.00006: Turbulent unmixing: how marine turbulence drives patchy distributions of motile phytoplankton William Durham, Eric Climent, Michael Barry, Filippo De Lillo, Guido Boffetta, Massimo Cencini, Roman Stocker Centimeter-scale patchiness in the distribution of phytoplankton increases the efficacy of many important ecological interactions in the marine food web. We show that turbulent fluid motion, usually synonymous with mixing, instead triggers intense small-scale patchiness in the distribution of motile phytoplankton. We use a suite of experiments, direct numerical simulations of turbulence, and analytical tools to show that turbulent shear and acceleration directs the motility of cells towards well-defined regions of flow, increasing local cell concentrations more than ten fold. This motility-driven `unmixing' offers an explanation for why motile cells are often more patchily distributed than non-motile cells and provides a mechanistic framework to understand how turbulence, whose strength varies profoundly in marine environments, impacts ocean productivity. [Preview Abstract] |
Monday, November 25, 2013 9:18AM - 9:31AM |
G19.00007: Getting into the flow: Red cells go on a roll, two-component vesicles swing Annie Viallat, Jules Dupire, Kamel Khelloufi, Al Hair Al Halifa Red blood cells are soft capsules. Under shear flow, their two known motions were ``tumbling'' and ``swinging-tank treading,'' depending on cell mechanics and flow conditions. We reveal new wobbling regimes, among which the ``rolling'' regime, where red cells move as wheels on a road. We show, by coupling two video-microscopy approaches providing multi-directional cell pictures that the orientation of cells flipping into the flow is determined by the shear rate. Rolling permits to avoid energetically costly cellular deformations and is a true signature of the cytoskeleton elasticity. We highlight two transient dynamics: an intermittent regime during the ``tank-treading-to-flipping'' transition and a Frisbee-like ``spinning'' regime during the ``rolling-to-tank-treading'' transition. We find that the biconcave red cell shape is very stable under moderate shear stresses, and we interpret this result in terms of shape memory and elastic buckling. Finally, we generate lipid vesicles with a shape memory by using two lipids with different bending rigidities. These vesicles swing in shear flow similarly to red blood cells but their non-axisymmetric stress-free shape changes the periodicity of the motion and induces specific features. [Preview Abstract] |
Monday, November 25, 2013 9:31AM - 9:44AM |
G19.00008: Platelet transport in microchannels Mathilde Reyssat, Anne Le Goff, Antoine Blin, Justine Pujos, Aur\'elie Magniez, Dominique Baruch Blood platelets are small enucleated cells responsible for the arrest of bleeding. These cells have the ability to tether and translocate on injured vascular endothelium, thanks to a specific interaction between a receptor of their membrane and a protein expressed by the cells composing the inner wall of the vessel, the von Willebrand factor (VWF). Others cells have such abilities of rolling. Leucocytes, for example, translocate on surface due to a specific interaction between selectin molecules and their respective glycoprotein ligands. These kinds of cells present two modes of transport: they can either be advected by the flux, or translocate on surfaces due to specific ligand-receptor interactions. Our work consists first in studying experimentally the transport of platelets along a microchannel and then in modeling this particular cell transport. Due to these two modes of transport along a channel, platelets adhering to the surface are not equally distributed along the channel axis. We describe the evolution of the density of platelets with time and distance. [Preview Abstract] |
Monday, November 25, 2013 9:44AM - 9:57AM |
G19.00009: Characterization of Intracellular Streaming and Traction Forces in Migrating Physarum Plasmodia Shun Zhang, Ruedi Meili, Robert D. Guy, Juan C. Lasheras, Juan C. del Alamo Physarum plasmodium is a model organism for cell migration that exhibits fast intracellular streaming. Single amoebae were seeded and allowed to move on polyacrilamide gels that contained 0.2 $\mu $m fluorescent beads. Joint time-lapse sequences of intracellular streaming and gel deformation were acquired respectively in the bright and fluorescent fields of a confocal microscope. Images were analyzed using particle image velocimetry (PIV) algorithms, and the traction stresses applied by the amoebae on the surface were computed by solving the elastostatic equation for the gel. These measurements provide, for the first time, a joint characterization of intracellular mass transport and the forces applied on the substrate of motile amoeboid cells with high resolution in both time and space, enables a through study about the locomotive mechanism and the relation between intracellular flow and traction stress, shedding light on related biomimetic research. The results reveal a pronounced auto-oscillation character in intracellular flow, contact area, centroid speed and strain energy, all with the same periodicity about 60 seconds. Adhesion sites are found to be almost stationary while a traction wave propagates from the tail to the anterior region in each cycle. [Preview Abstract] |
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