Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session A8: Biofluids: In Suspension |
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Chair: Michael Graham, University of Wisconsin-Madison Room: 3001/3003 |
Sunday, November 23, 2014 8:00AM - 8:13AM |
A8.00001: Variation of velocity profile according to blood viscosity in a microfluidic channel Eunseop Yeom, Yang Jun Kang, Sang-Joon Lee The shear-thinning effect of blood flows is known to change blood viscosity. Since blood viscosity and motion of red blood cells (RBCs) are closely related, hemorheological variations have a strong influence on hemodynamic characteristics. Therefore, understanding on the relationship between the hemorheological and hemodynamic properties is importance for getting more detailed information on blood circulation in microvessels. In this study, the blood viscosity and velocity profiles in a microfluidic channel were systematically investigated. Rat blood was delivered in the microfluidic device which can measure blood viscosity by monitoring the flow-switching phenomenon. Velocity profiles of blood flows in the microchannel were measured by using a micro-particle image velocimetry (PIV) technique. Shape of velocity profiles measured at different flow rates was quantified by using a curve-fitting equation. It was observed that the shape of velocity profiles is highly correlated with blood viscosity. The study on the relation between blood viscosity and velocity profile would be helpful to understand the roles of hemorheological and hemodynamic properties in cardiovascular diseases. [Preview Abstract] |
Sunday, November 23, 2014 8:13AM - 8:26AM |
A8.00002: Effects of viscosity on endothelial cell damage under acoustic droplet vaporization Robinson Seda, Rahul Singh, David Li, John Pitre, Andrew Putnam, J. Brian Fowlkes, Joseph Bull Acoustic droplet vaporization (ADV) is a process by which stabilized superheated microdroplets are able to undergo phase transition with the aid of focused ultrasound. Gas bubbles resulting from ADV can provide local occlusion of the blood vessels supplying diseased tissue, such as tumors. The ADV process can also induce bioeffects that increase vessel permeability, which is beneficial for localized drug delivery. Previous in vitro studies have demonstrated that vaporization at the endothelial layer will affect cell attachment and viability. Several hypotheses have been proposed to elucidate the mechanism of damage including the generation of normal and shear stresses during bubble expansion. A single 3.5 MHz ultrasound pulse consisting of 8 cycles ($\sim$ 2 .3 $\mu$s) and a 6 MPa peak rarefactional pressure was used to induce ADV on endothelial cells in media of different viscosities. Carboxylmethyl cellulose was added to the cell media to increase the viscosity up to 300 cP to and aid in the reduction of stresses during bubble expansion. The likelihood of cell damage was decreased when compared to our control ($\sim$ 1 cP), but it was still present in some cases indicating that the mechanism of damage does not depend entirely on viscous stresses associated with bubble expansion. This work was supported by NIH grant R01EB006476. [Preview Abstract] |
Sunday, November 23, 2014 8:26AM - 8:39AM |
A8.00003: Micro-PIV of Bubble Splitting in a Bifurcation Samantha Stephenson, David Li, Forian Hellmeier, John Pitre, J. Brian Fowlkes, Joseph Bull Gas embolotherapy is a proposed treatment for cancerous tumors. For this treatment, a liquid droplet solution is injected into the bloodstream and focused ultrasound is used to vaporize droplets upstream of the tumor site, resulting in bubbles that are approximately 125x larger in volume. These bubbles will then occlude the blood vessels, thereby depriving the tumor of nutrients leading to eventual tumor necrosis. However, once the bubbles are formed, they will continue to travel through the bloodstream, through bifurcations that split in to smaller daughter vessels before lodging to occlude flow. Micro-particle imaging velocimetry (PIV) was used to study the flow field surrounding the leading edge of the bubble at the bifurcation point. Consistent symmetric bubble splitting at several different flow rates was achieved. Roll angle of the bifurcation was varied to encourage uneven bubble splitting and reversal. In the absence of the bubble, Poiseuille flow was verified in the parent channel. Results were compared to a boundary elements model developed by Calderon et al. 2010. This research was funded by the NIH grant R01EB006476. [Preview Abstract] |
Sunday, November 23, 2014 8:39AM - 8:52AM |
A8.00004: Margination and demargination in confined multicomponent suspensions: a parametric study Michael Graham, Kushal Sinha, Rafael Henriquez Rivera Blood and other multicomponent suspensions display a segregation behavior in which different components are differentially distributed in the cross-stream direction during flow in a confined geometry such as an arteriole or a microfluidic device. In blood the platelets and leukocytes are strongly segregated to the near wall region and are said to be ``marginated.'' The effects of particle size, shape and rigidity on segregation behavior in confined simple shear flow of binary suspensions are computationally investigated here. The results show that in a mixture of particles with same shape and different membrane rigidity, the stiffer particles marginate while the flexible particles demarginate, moving toward the center of the channel. In a mixture of particle with same membrane rigidity and different shape, particles with smaller aspect ratio marginate while those with higher aspect ratio demarginate. These results are consistent with theoretical arguments based on wall-induced migration and pair collision dynamics. An analytical solution is presented for a model problem that reveals qualitatively different behavior in various parameter regimes. Finally, effects of viscoelasticity of the suspending phase on margination are examined. [Preview Abstract] |
Sunday, November 23, 2014 8:52AM - 9:05AM |
A8.00005: Fluid Mechanics of the Red Blood Cell and its Cytoskeleton by an Immersed Boundary Method with Nonuniform Viscosity and Density Thomas Fai, Charles Peskin The red blood cell cytoskeleton, which is anchored to a lipid bilayer membrane, is an elastic network that helps red cells recover from large deformations as they circulate. Although the cytoskeleton has a convoluted structure, as shown in recent tomographic images, it may be modeled simply as a graph of actin-based junctional complexes (nodes) connected by spectrin polymers (edges). We have developed a discrete cytoskeleton model that incorporates statistical properties of the cytoskeleton, such as the edge length and node degree distributions. A specialized image processing technique is used to gather these distributions directly from tomograms. The network elasticity comes from treating the spectrin polymers as entropic springs, and we show that the spring constant obtained from a well-known model of entropic springs is in reasonable agreement with the experimentally determined shear modulus. By simulating the behavior of red blood cells in shear flow using a variable viscosity and variable density immersed boundary method, we compare this discrete model with its approximately 40,000 nodes to more commonly used continuum ones. [Preview Abstract] |
Sunday, November 23, 2014 9:05AM - 9:18AM |
A8.00006: Simultaneous measurement of flow over and transmigration through a cultured endothelial cell layer Lori Lambert, Iraklis Pipinos, Timothy Baxter, Jason Mactaggart, Derek Moormeier, Kenneth Bayles, Timothy Wei The measurement and analysis of fluid forces on endothelial cells at the cellular and subcellular levels is an essential component of understanding mechanotransduction and atherogenesis. The ultimate goal of this study is to examine and model the transport and transmigration of low-density lipoproteins across a confluent endothelial layer as a function of fluid loading and time. In this study, steady flow over a cultured endothelial cell layer at shear rates up to 20 dynes/cm$^{2}$ in a 350 $\mu $m x 70 $\mu $m cross section mircrochannel was measured using $\mu $PTV measurements. By using multiple measurement planes parallel to the channel wall, wall shear stress and wall pressure were computed as well as the endothelial cell topography. The study was performed over a period of 18 hours in which the transport and transmigration of fluorescently tagged low-density lipoproteins through a cultured endothelial cell layer were examined as a function of fluid forces, cell topography, and time. [Preview Abstract] |
Sunday, November 23, 2014 9:18AM - 9:31AM |
A8.00007: Nanoparticle motion near a blood vessel wall in targeted drug delivery Helena Vitoshkin, Hsiu-Yu Yu, David M. Eckmann, Ravi Radhakrishnan, Portonovo S. Ayyaswamy A computational study of the motion of a spherical nanoparticle close to the bounding wall of a blood vessel in targeted drug delivery is presented. An arbitrary Lagrangian-Eulerian algorithm has been carried out, taking into account both the Brownian and the hydrodynamic effects. Pertinent to targeted drug delivery, we focus on the condition when the particle is in the lubrication layer. The velocity auto-correlation function (VACF) is seen to initially decay faster by a factor of particle radius divided by the fluid gap thickness compared to that in an unbounded medium. Long time decay is found to be algebraic. Focusing on hydrodynamic interaction between the particle and the wall, effects of wall curvature, particle size, and variations in density of the particle are investigated. We also study adhesive interactions of a nanoparticle with an endothelial cell located on the vessel wall by the modeling the nanoparticle tethered by a harmonic spring with varying spring constants. It is shown that the particle velocity is affected by hydrodynamic and harmonic spring forces leading to VACF oscillations which decay algebraically at long times. The results agree with those predicted by earlier theories for particle VACF near a wall. These findings have applications in medication administration and in the colloidal sciences. [Preview Abstract] |
Sunday, November 23, 2014 9:31AM - 9:44AM |
A8.00008: Motion induced between parallel plates with offset centers of radial stretching and shrinking Patrick Weidman The flow between parallel plates separated by distance $h$ is investigated where the upper and lower plates respectively stretch and shrink at the same rate $a$ and the centers of stretching and shrinking are horizontally separated by distance $2\,l$. A reduction of the Navier-Stokes equation yields two ordinary differential equations dependent on a Reynolds number $R = ah^2/\nu$. In addition a free parameter $\gamma$ appears which corresponds to a uniform pressure gradient acting along the line connecting the stretching/shrinking centers. We consider three cases: $\gamma = 0$, $\gamma = O(1)$ and $\gamma = O(R)$. The flow is described by two functions of the plate-normal coordinate $\eta = z/h$: the first $f(\eta)$ has an analytical solution while the second $g(\eta)$ must be resolved numerically. The small-$R$ solutions are found and the large-$R$ asymptotic behaviors of the wall shear stresses and the centerline velocities are obtained by matching the viscous boundary layer flows to the interior inviscid motion. [Preview Abstract] |
Sunday, November 23, 2014 9:44AM - 9:57AM |
A8.00009: Axisymmetric rotational slow viscous flows around asymmetric fused dumbbells D. Palaniappan Symmetric rotational viscous flows involving fused dumbbells are considered in the limit of low-Reynolds numbers. The boundary of the rigid dumbbell is formed by two spherical surfaces of arbitrary radii, $a$ and $b$ respectively, intersecting at a vertex angle, say $\frac{\pi}{n}$, $n$ an integer. Analytic solutions are obtained for the asymmetric configuration submerged in (i) a rotational flow, and (ii) a rotlet induced flow field. The image system in each case is found in terms of fundamental solutions of the Stokes flow equations. Exact expressions for the torque/couple acting on the dumbbell are computed directly from our singularity solutions. It is found that the radii of the spheres, the center-to-center distance, the vertex angle together with the location of the initial rotlet dictate the flow fields and the torque. Upper and lower bounds for the couple acting on the asymmetric dumbbell are determined as well. Our method is based on the successive reflection theory and avoids the use of complex toroidal and meromorphic functions. The utility of the toroidal frame for the axisymmetric rotational flow in the case of arbitrary vertex angle is also discussed. However, for the rotlet flow, there does not appear to be any technique available other than the one provided here. [Preview Abstract] |
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