Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session P31: Biological Fluid Dynamics: Vesicle and Micelles I |
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Chair: Prerna Gera, University of Wisconsin-Madison Room: 613 |
Monday, November 25, 2019 5:16PM - 5:29PM |
P31.00001: Patchy Vesicles Tremble Before a Flow Prerna Gera, David Salac, Saverio Spagnolie Biological membranes, and recently engineered synthetic vesicles, may be host to numerous components which provide spatially varying material properties such as spontaneous curvature and bending rigidity. We will discuss the dynamics of a two-dimensional vesicle with such spatially varying material properties in a shear flow. Using small amplitude asymptotics and full numerical simulations, we pay special attention to the role of variable bending stiffness. Reduced-order models are derived and used to accurately predict phenomena ranging from low wavenumber breathing modes to highly oscillatory trembling modes. [Preview Abstract] |
Monday, November 25, 2019 5:29PM - 5:42PM |
P31.00002: Non-contact Mechanical Characterization of Extracellular Vesicles with Raman Spectra Interpretations Joanna Dahl Cells exchange information by secreting micro and nanosized extracellular vesicles (EVs) ranging in size from 30nm to 5um. While it was once thought these cell-derived membranous vesicles were simply cell debris, recent efforts have determined that EVs have profound biological significance and therefore potential for clinical therapies and disease diagnostics. There is still much to understand about fundamental EV biological, physical, and chemical properties before clinical applications can be developed. The mechanical behavior of EVs---the physical implications of the lipid, protein, and nucleic acid constituents and their arrangements, all of which are linked to EV biological signature, cell of origin, and mode of biogenesis---has hardly been explored. To date, EV mechanical properties have been measured with atomic force microscopy with its problematic adhesion and hard substrate effects for small, soft EVs. We present mechanical property measurements of single microscale EVs derived from human blood plasma using a non-contact microfluidic technique. Raman spectra are used to interpret the mechanical property measurements through analysis of protein amide and phospholipid absorption bands that quantify protein and lipid composition and structures. [Preview Abstract] |
Monday, November 25, 2019 5:42PM - 5:55PM |
P31.00003: Non-equilibrium Dynamics of Initially Spherical Vesicles in Shear Flows Afsoun Rahnama Falavarjani, David Salac Many vesicles have a spherical resting shape and exposure to shear flows induces an exchange between the suboptical/thermal fluctuations and system deformation, with the total area being conserved. Here, the dynamics of such vesicles is numerically explored. Unlike other models, we do not begin with a deflated vesicle. By taking into account the membrane fluctuations, our model allows for an increase in the apparent area of the vesicle which introduces an isotropic tension force on the membrane which grows exponentially with the change in the area in low tension regime. Our results, such as the viscosity-dependence of the tank-treading, breathing/trembling, and tumbling regimes, are in good quantitative agreement with experimental observations. [Preview Abstract] |
Monday, November 25, 2019 5:55PM - 6:08PM |
P31.00004: Light-induced Non-pulsatile Bursting of Lipid Vesicles Vinit Kumar, Sangwoo Shin, Jie Feng Lipid vesicles are topologically closed compartments bounded by semi-permeable lipid shells. Upon exposure to a hypertonic bath, vesicles respond with remarkable swell-burst events, showing oscillations in vesicle size and pore formation. Such lysis has been extensively harnessed to study dynamics of biological membranes, as well as releasing encapsulated actives for targeted drug delivery. Recently, some studies show osmotic shock by light-induced reactions achieves fast release of vesicle contents via an explosion process, e.g., irreversible bursting, yet the rationale for this is missing. Here we present a fundamental and quantitative understanding of bursting dynamics through a comprehensive theoretical model. Our model accounts for the kinetics of light-triggered reactions inside vesicles while considering the stochastic nature of pore nucleation by incorporating activation energy based on the vesicle expansion rate. The model quantitatively captures features of irreversible bursting dynamics, with good agreement between experimental observations and model predictions. Our work furthers a fundamental framework for nonequilibrium vesicle dynamics under osmotic stress induced by chemical reactions, offering design guidelines for vesicle-encapsulated substance release. [Preview Abstract] |
Monday, November 25, 2019 6:08PM - 6:21PM |
P31.00005: Hydrodynamic stability of moderately-deflated, giant unilamellar vesicles in general linear flows Vivek Narsimhan, Charlie Lin In this talk, we perform boundary element simulations to describe the shape and stability of osmotically deflated vesicles in a wide range of flows. The first half of this talk recaps vesicle dynamics in purely extensional flows, which are commonly found in contractions/expansions and/or suction flows. Above a critical flowrate, we find that moderately deflated vesicles undergo an asymmetric shape instability that looks fundamentally different than droplet breakup. The physical origins of such vesicle shapes are discussed in detail and compared with microfluidic experiments. In the second half of the talk, we discuss vesicle stability in a general linear flow that contains both vorticity and extension. We find that the critical capillary number for vesicle instability diverges as one moves from pure extension to pure shear, which suggests that vesicles are incredibly hard to break in pure shear flow. We also find that the vesicle's interior viscosity plays little role in its stability, which is quite different than what is observed for droplets. We provide physical explanations for these observations by examining membrane tension profiles and using geometric scaling arguments. We will conclude by showing preliminary data of vesicle shapes in oscillatory flows. [Preview Abstract] |
Monday, November 25, 2019 6:21PM - 6:34PM |
P31.00006: Break-up of synthetic capsule in shear flow Seyeong Jeong, Daegyoum Kim A capsule, a thin elastic membrane enclosing inner material such as colloid, has been used in diverse fields including drug delivery, cell encapsulation and cosmetics. The structural robustness of the capsule comes to an important issue for drug delivery because hydrodynamic shear stress acting on the membrane surface of the capsule in microcirculation environment may cause severe deformation and burst of the capsule. Previously, many studies have focused on the rheological behavior of the capsule immersed in simple flows such as shear flow, extensional flow or Poiseuille flow in small and moderate ranges of shear rate. However, little is known for the deformation of a capsule in high shear rate and furthermore its break-up phenomenon. For the break-up of a capsule in simple shear flow, experiment is performed with a flow rheoscope, and a capsule based on Human Serum Albumin is prepared. The capsule is modelled as a 2D thin shell by adopting the concept of hyperelasticity. The deformation and fracture of a capsule and the resultant stress distribution on the capsule surface are investigated by changing the mechanical properties of the capsule and the shear rate of the flow. [Preview Abstract] |
Monday, November 25, 2019 6:34PM - 6:47PM |
P31.00007: ABSTRACT WITHDRAWN |
Monday, November 25, 2019 6:47PM - 7:00PM |
P31.00008: Dynamics of highly deformed non-spherical vesicles in steady and time-dependent flow Dinesh Kumar, Channing M. Richter, Charles M. Schroeder In this work, we study the non-equilibrium dynamics of vesicles in precisely-defined steady and time-dependent extensional flow. Using Stokes trap, we directly observe non-equilibrium vesicle shapes as a function of reduced volume $\nu $, viscosity contrast $\lambda $, and Capillary number \textit{Ca} using fluorescence microscopy. Vesicles are found to deform through a wide-range of interesting shapes in flow, including asymmetric and symmetric dumbbells, in addition to pearling, wrinkling, and buckling instabilities depending on membrane properties. Using this approach, we determine the flow phase diagram for vesicles in $\nu $\textit{-Ca} space. Our results show that the steady-state deformation of vesicles exhibits power-law behavior as a function of reduced Capillary number. We identify two distinct relaxation processes for vesicles stretched to high deformation, revealing two characteristic time scales: a short time scale corresponding to bending relaxation and a long-time scale dictated by the relaxation of membrane tension. We further discuss the dynamics of single vesicles in sinusoidal oscillatory extensional flow as a function of \textit{Ca} and Deborah number. [Preview Abstract] |
Monday, November 25, 2019 7:00PM - 7:13PM |
P31.00009: Collision of two deformable torque swimmers Hitomu Matsui, Toshihiro Omori, Takuji Ishikawa Understanding the property of a micro-organism suspension is important in bio-engineering. When the suspension is non-dilute, micro-organism interacts with each other and these interactions are governed by the hydrodynamical and biological features. Former studies focusing on cell-cell interaction have unveiled the hydrodynamical effect, however, contribution of cell's deforming during the interaction is still unknown. Moreover, biological reaction, for example avoiding and escape reactions of a ciliate, may affect the suspension property. These biological reactions are considered to be initiated by mechanical stimuli imposing over cell membrane. Thus, analyzing membrane tension should help to understand the mechanism of ciliate biological responses. In this study, to investigate the contribution of deformation and membrane condition while two swimmers interact, we numerically simulate cell-cell interaction by applying a deformable ciliate model. We modeled a ciliate body as a deformable capsule and thrust forces generated by the ciliary beat as torque distribution. Owing to the tiny cell size of ciliate, fluid is regarded as Stokes flow. We computed a variety of collisions with different geometry and cell's deformability, and then analyzed the trajectory and membrane tension. We found deformability affects the trajectory and clarified membrane tensions differ among the geometries. These results allow us to discuss the sensing ability of ciliate in the suspension. [Preview Abstract] |
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