Bulletin of the American Physical Society
75th Annual Meeting of the Division of Fluid Dynamics
Volume 67, Number 19
Sunday–Tuesday, November 20–22, 2022; Indiana Convention Center, Indianapolis, Indiana.
Session G04: Vesicles and Micelles |
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Chair: Rodrigo Reboucas, Northwestern University Room: 131 |
Sunday, November 20, 2022 3:00PM - 3:13PM |
G04.00001: Spindle-like vesicle shapes in external fields Rodrigo B Reboucas, Michael J Miksis, Petia M Vlahovska A phospholipid bilayer is the main structural component of cells and internal cellular organelles. For the past decades, researchers have used giant unilamellar vesicles (GUVs) as a popular biomimetic model to study membrane biophysics. This work focuses on the mechanical properties and deformation of GUVs which qualitatively resemble the rich dynamics of living cells in external fields (e.g., under electric potential difference across the plasma membrane). Here, the classical Helfrich bending energy model is minimized under constraints of constant area and volume and the corresponding Euler-Lagrange equations are solved numerically to yield equilibrium shapes. We investigate the parameter space of vesicle geometric properties and environmental stimuli (e.g., osmotic pressure), and report regimes where vesicle morphologies resemble spindle-like structures observed in recent experimental results of vesicles embedded in nematic liquid crystals and vesicles suspended in electrolyte solutions under strong AC electric fields. Results show that under conditions of constant bending rigidity and low excess-area, spindle-like vesicle shapes are accessible. Allowing for a spatially varying bending rigidity to simulate the effect of an external field yields similar spindle-like configurations; the origin of this local variation is the subject of ongoing research. |
Sunday, November 20, 2022 3:13PM - 3:26PM Author not Attending |
G04.00002: Influence of Membrane Slip on Vesicle Dynamics David Salac, Afsoun Rahnama Falavarjani Vesicles are multiphase fluid systems where a lipid bilayer separates the two fluids. They form model systems for more complicated biological cells and have been proposed for various biotechnologies such as drug delivery systems. Due to the complex nature of the membrane, an understanding of how the properties of said membrane is crucial to advancing the use of vesicles in modern technologies. One less investigated property of these membranes is the ability to slide past each other due to the layers being weakly coupled. From a macroscopic point-of-view, this appears as a jump in the tangential velocity of the surrounding fluid, with the magnitude of this discontinuity depending on membrane properties. Building upon prior works in modeling vesicles with fully coupled membranes, a numerical model is presented capable of modeling vesicles with interfacial slip in general flows. After a brief discussion of the numerical methods involved, including the composition of computational stencils, the model will then be used to explore the dynamics of vesicles in various types of flows as a function of the membrane slip coefficient. |
Sunday, November 20, 2022 3:26PM - 3:39PM |
G04.00003: Viscous modes of quasi-spherical fluid bilayer membranes Petia M Vlahovska, Hammad Faizi, Rony Granek Membrane viscosity is usually assumed to only affect short-wavelength undulations of lipid bilayers [Seifert and Langer, Europhys. Lett. (1993)]. Here, we show that fluctuation dynamics about a curved shape such as a quasi-spherical vesicle is sensitive to the membrane viscosity even at long-wavelengths, if the Saffman-Debruck length is larger than the radius of curvature. The theory predicts a relaxation rate of ~1/q^4 for a spherical harmonic mode of order q, a drastic change from the classic result ~ 1/q^3. Accordingly, the stretched exponential in the Dynamic Structure Factor (DSF) becomes ~ t^{1/2} instead of the commonly used ~t^{2/3} [Zilman and Granek, Phys. Rev. Lett. (1996)]. Experimental measurements of the shape fluctuations of giant vesicles made of DPPC:Chol confirm the theoretical results and for the first time quantify the effect of membrane viscosity in the bilayer bending dynamics. The new DSF scaling implies that the data analysis in methods that utilize DSF of liposomes, e.g., neutron spin-echo, need to be reassessed. |
Sunday, November 20, 2022 3:39PM - 3:52PM |
G04.00004: Pore Dynamics of Lipid Vesicles under Photoinduced Oxidative Stress Vinit Kumar, Jie Feng Exposure of cell membrane to reactive oxygen species (ROS), can cause oxidative damage; disrupting biological functions. Oxidation of lipids alters their structural properties, compromising membrane integrity and causing cell death. Previous studies have observed degradation of lipid membranes leads to transient pores as well as total sudden catastrophic collapse of vesicles, a phenomenon recognized as vesicle explosion. However, the physical mechanism leading to explosion is unknown. Here, we discuss the mechanical response of lipid-bilayers under extreme oxidative stress. Through experiments and theoretical modeling, we demonstrate how spontaneous curvature, induced by asymmetric oxidation of the membrane, plays a key role in vesicle explosion. We propose a model of pore-opening dynamics, including oxidation, spontaneous curvature, and curling instability, which aligns with experimental observations. We characterize the dependence of explosion on the rate of ROS generation as well as lipid unsaturation. Our results could advance fundamental understandings of the stability of organelles and bio-membranes subject to oxidative insults, and provide potential insights to aide in strategizing and fine-tuning release rates for a targeted precision delivery and cell mimetic systems. |
Sunday, November 20, 2022 3:52PM - 4:05PM |
G04.00005: Hydrodynamics of a Multicomponent Vesicle Under Strong Confinement Bryan Quaife, Yuan-Nan Young, Ashley Gannon The biophysical lipid bilayer membrane (such as a vesicle) often consists of multiple species of macromolecules such as cholesterol, surface proteins, surfactants, and different lipids. The presence of the multiple components results in different mechanical responses, such as the bending stiffness, and this affects the vesicle's hydrodynamics. I will demonstrate some of these differences by considering multicomponent vesicles subjected to strong confinement. Comparisons will be made with single component vesicles. |
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