Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Y26: Membranes, Micelles and VesiclesRecordings Available
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Sponsoring Units: DSOFT Chair: Chris Santangelo, Syracuse University Room: McCormick Place W-187B |
Friday, March 18, 2022 8:00AM - 8:12AM |
Y26.00001: Solid Domain Patterns on Giant Lipid Vesicles: Vesicle size controls domain shape at fixed composition Hao Wan Stimulated by the requirements of industry, there is growing interest in mechanisms to control and exploit the growth of two-dimensional crystals on curved surfaces. Giant Lipid Vesicles are a versatile platform for studies and implementation of crystallization strategies because they provide controllable confinement, stress, and curvature. In this study, we investigated how solid lipid domains grow in the nanometrically-thin curved 2D bilayer membrane and how the growth pattern depends on the key variables. By carefully controlling the thermal history and the composition of the bicomponent vesicles, we can produce vesicles containing a single solid domain. We found that the domain shape has a dependence on the overall vesicle size. Compact domains are found on small vesicles; however, as the vesicle diameter increases, the solid domain pattern becomes increasingly elaborate and flower-like. Theory as well as micropipette experiments further suggests that the diverse domain morphology is caused by variation in membrane tension imposing out of plane stresses during nucleation and growth in vesicles of different sizes. |
Friday, March 18, 2022 8:12AM - 8:24AM |
Y26.00002: Adhesion and Dimerization of Sphero-Cylindrical Nanoparticles on Lipid Membranes Abash Sharma, Abash Sharma, Eric J Spangler, Mohamed Laradji We present a numerical investigation of the interaction of sphero-cylindrical nanoparticles (SCNP) with planar lipid bilayers, using molecular dynamics simulations of an implicit-solvent model. The SCNPs are generated using a bottom-up approach, where the hemispherical ends of the SCNPs are constructed as two icosahedra halves that are connected by a hexagonally tessellated cylinder. We found that at relatively low adhesion strength, the SCNP adheres such that its principal axis is parallel to the membrane (parallel mode). At relatively high adhesion strength, the SCNP adheres such that its principal axis is perpendicular to the bilayer (normal mode). The transition adhesion strength between these two modes is found to decrease with increasing the diameter of the SCNP, for a fixed aspect ratio, or increasing its aspect ratio, for a fixed diameter. We also investigated the modes of adhesion of two SCNPs on the bilayer and found that, at weak adhesion strength, the SCNPS are in the parallel mode and apart from each other. However, as the adhesion strength is increased, the SCNPs dimerize into a sequence of modes including in-plane dimers, V-shape dimers, and two tubular dimer states. |
Friday, March 18, 2022 8:24AM - 8:36AM |
Y26.00003: Interactions in Elastically- Responsive Composite Lipid Vesicles Weiyue Xin Giant unilamellar lipid vesicles are often studied because they provide insights to cellular behavior; however, when they contain solid membrane domains they also serve as models for two-dimensional colloidal suspensions. These new materials can form the basis for an innovative nanotechnological platform for targeted delivery and energy storage. Our work explores the experimental methods to produce lipid vesicles with limited numbers (1,2 or 3) of regular domains and focuses on the interaction potentials between these domains. We also probe the reversible multibody interactions and assembly of micron-scale domains in phospholipid vesicles through the manipulation of membrane curvature by osmotic adjustment or mechanical manipulations using micropipettes. The observations in inter-domain positions suggest the existence of long-range interdomain attractions and short-range interdomain repulsions resulting from the shear elasticity of the solid domain. This discovery suggests a new picture that allows tunable interactions to form sophisticated responsive patterns on 2D fluid materials. |
Friday, March 18, 2022 8:36AM - 8:48AM |
Y26.00004: Three-dimensional structures of chiral membrane with free edges Lijie Ding, Robert Pelcovits, Thomas Powers We carry out Monte Carlo simulations on membranes with orientational order and multiple edges subject to external forces and also with force-free conditions. The membrane resists bending and has an edge tension, the orientational order couples with the membrane surface normal through a cost for tilting, and there is a chiral liquid crystalline interaction. For a membrane with two edges, increasing the displacement between the opposite edges requires the external force applied on the membrane to increase rapidly at first, and then gradually once the separation is sufficiently large. When the cost of tilt is small, the alignment between directors results in two parallel lines of directors perpendicular to both the local surface normal and pulling direction for achiral coupling. Increasing the chirality leads to the twisting of these lines about each other and the directors pointing towards the pulling direction. When the membrane is force-free, increasing the chiral interaction leads to multiple pi walls connecting edges and wrapping around the membrane neck, resulting in the formation of catenoid or a trinoid, depending on the number of edges. |
Friday, March 18, 2022 8:48AM - 9:00AM |
Y26.00005: Phase diagram for an osmotically stressed lipids vesicle Vinit Kumar, Jie Feng Vesicles have been observed to explode when placed under sudden and extreme osmotic imbalance. This recently discovered behavior holds exciting opportunities for new directions in artificial cell systems, nanoparticle transport, and understanding the fundamental mechanisms of osmoregulation in living cells. Yet not all osmotic shocks will induce vesicle explosion, with some scenarios leading to simple engorgement and others causing cyclic swelling with transient pore formation. Under what conditions vesicles will transition to explosion and how this is situated in relation to other known behavioral regimes was previously unknown. In this talk we introduce a comprehensive model of vesicle osmotic response to construct the lipid vesicle phase diagram, accounting for vesicle explosion. We demonstrate the pivotal and previously unrecognized role of spontaneous curvature in determining vesicle outcomes. We present experimental evidence supporting the proposition that through reckoning with the role of spontaneous curvature, vesicle response across conditions can be unified into a single predictive model. Finally, we discuss crucial membrane and environmental properties that determine vesicle behavior. This work understanding the energy landscape of vesicle and the conditions that influence its form hold the potential in manufacturing vesicles to produce desired and precise behavioral qualities as well as reveal the processes that underlie the essential mechanisms of life. |
Friday, March 18, 2022 9:00AM - 9:12AM |
Y26.00006: Fragmentation of block copolymer micelles in mixed ionic liquids Supriya Gupta, Timothy P Lodge Block copolymers self-organize into a myriad of micellar nanostructures when placed in selective solvents, offering great potential as drug delivery carriers and nanoreactors. A comprehensive understanding of the dynamics of micelle formation and equilibration can be very useful to optimize structure-property relationships. Micelle fusion, fragmentation, and chain exchange present the likely relaxation mechanisms leading to micellar equilibration. The present study examines the kinetics of fragmentation of 1,2-polybutadiene-b-poly(ethylene oxide) block copolymer micelles in ionic liquids after a temperature jump. Micelles are characterized using in-situ characterization techniques such as dynamic light scattering, small-angle X-ray scattering, and transmission electron microscopy to obtain the tie evolution of average micelle size, aggregation number, and size distribution, respectively. The role of the driving force for fragmentation on the kinetics is investigated by altering the solvent quality after micelle preparation. Dilution of a selective solvent with a less selective solvent is found to influence the kinetics of fragmentation. |
Friday, March 18, 2022 9:12AM - 9:24AM |
Y26.00007: Multiscale Structural Dynamics of Unilamellar Liposomes in Polymeric Viscoelastic Medium: From Bulk to Micro Environment Selcan Karaz, Erkan Senses The dynamic interactions between membrane lipids and extracellular matrix in macromolecularly crowded mediums affect the properties of the membrane. In the present study, we used 100-nm unilamellar DMPC/DMPG liposomes, and Polyethylene Glycol (PEG) with various molecular weights, from 1.5 to 400 kDa, to explore the effects of length of the polymer chains on structural dynamics of the membranes from bulk to micro environment. Wide angle x-ray scattering analysis revealed that PEG chains are attached to bilayer surface due to the attractive interactions without causing a notable structural change. Rheology of the solutions shows that adsorbed PEG layers increase the bulk viscosity of membranes and cause a stiffening behavior with monotonically decreasing diffusion constants as Mw increases. According to the microviscosity measurements by fluorescence lifetime spectroscopy (FLS), the presence of PEG decreases the microviscosity in all molecular weights, and the bulk viscosity dominates the lipid bilayer dynamics. This study shows that the dynamics of the membranes can be effectively controlled by changing the length and size of the attached polymer, which can be useful for targeted drug delivery systems. |
Friday, March 18, 2022 9:24AM - 9:36AM |
Y26.00008: Swinging and tumbling of multicomponent vesicles in flow Saverio E Spagnolie, Prerna Gera, David Salac Biological membranes are host to proteins and molecules which may form domain-like structures resulting in spatially-varying material properties. Vesicles with such heterogeneous membranes can exhibit intricate shapes at equilibrium and rich dynamics when placed into a flow. Under the assumption of small deformations we develop a reduced order model to describe the fluid-structure interaction between a viscous background shear flow and an inextensible membrane with spatially varying bending stiffness and spontaneous curvature. Material property variations of a critical magnitude, relative to the flow rate and internal/external viscosity contrast, can set off a qualitative change in the vesicle dynamics. A membrane of nearly constant bending stiffness or spontaneous curvature undergoes a small amplitude swinging motion (which includes tangential tank-treading), while for large enough material variations the dynamics pass through a regime featuring tumbling and periodic phase-lagging of the membrane material, and ultimately for very large material variation to a rigid body tumbling behavior. Distinct differences are found for even and odd spatial modes of domain distribution. Full numerical simulations are used to probe the theoretical predictions, which appear valid even when studying substantially deformed membranes. |
Friday, March 18, 2022 9:36AM - 9:48AM |
Y26.00009: Tuning shape transformations in light-responsive lipid vesicles: the role of domains in a binary lipid system Chris Oville, Arash Manafirad, Anthony D Dinsmore We investigate ways to tune the morphology and permeability of giant unilamellar vesicles (GUVs) containing a photo-isomerizing lipid, azo-PC, which has an azobenzene moiety in one of its hydrocarbon tails. UV radiation triggers a shift from the trans to cis isomer, which has a larger area per lipid. We mix the azo-PC with various fractions of either unsaturated or saturated lipids (DOPC or DPPC). In GUVs with azo-PC and gel-forming DPPC, UV irradiation can induce large membrane deformations with notable buckling and pinning. The response depends on azo-PC fraction and UV light intensity. Analysis of wide-field and confocal fluorescent micrographs points to correlations between solid domain organization and extent and character of UV-response. Comparing the azo-PC/DPPC membranes to the fully liquid azo-PC/DOPC membranes – both phase separated and single phase – we conclude that the finite yield-stress of the solid domains plays a key role in the buckling. In addition, we find a marked increase in solute permeation when the buckling response is observed but not otherwise. The results point to a new mode of response and a new route to tuning response in triggered solid membranes. |
Friday, March 18, 2022 9:48AM - 10:00AM |
Y26.00010: A multi-scale and multi-physics model of soft membranes for artificial photosynthesis Gabriele Falciani, Luca Bergamasco, Eliodoro Chiavazzo The present work is part of the Sofia project, which envisions the use of soft soap-film based membranes in applications for artificial photosynthesis [1][2]. In particular, we focus on an innovative multiscale and multiphysics model that describes and predicts the performances of a single photosynthetic soap-based membrane for the carbon dioxide (CO2) conversion into syngas components. |
Friday, March 18, 2022 10:00AM - 10:12AM |
Y26.00011: Hydrodynamics of Janus particles self-assembled as vesicles Rolf J Ryham, Bryan Quaife, Yuan-Nan Young, Szu-Pei Fu Janus particles have been widely used for self-assembly of mesoscopic structures with specific functions. Previously we constructed a model for self-assembly of Janus particles to form bilayer membranes under a hydrophobic potential (SIAM J. Multiscale Modeling, 2020). In this work we illustrate the hydrodynamics of a vesicle made of such bilayer membranes. We use boundary integral equations to examine the hydrodynamics under various conditions: a quiescent flow, a planar shear flow, a linear elongational flow, and a Poiseuille flow. From the simulation results we find strong similarities to the vesicle hydrodynamics of a permeable lipid bilayer membrane under these flowing conditions such as tank-treading motion, an asymmetric slipper, and membrane ruptures. Moreover, two Janus-particle leaflets exhibit intermonolayer slip, similar to those between two lipid monolayers, and we calculate the friction coefficients. |
Friday, March 18, 2022 10:12AM - 10:24AM |
Y26.00012: NMR and EPR studies of lipid membranes in the presence of ATP Azam Shafieenezhad, Andres T Cavazos, Bruce D Ray, Stephen R Wassall, Horia I Petrache Adenosine triphosphate (ATP) is an organic molecule with a net negative charge and is a source of metabolic energy. We investigated the effect of ATP on lipid membranes made of phospholipids with charged and neutral headgroups, using solid-state nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopy, complemented by zeta potential measurements. Order parameter profiles for lipid hydrocarbon chains were obtained from deuterium NMR spectra and interpreted in terms of a mean-field approximation of lipid-lipid interactions. We find that ATP affects the alignment field of electrically charged lipids more than that of neutral lipids, indicating an essential role of ATP-headgroup interactions. To investigate this aspect, EPR spectra were recorded with 3 different spin-labeled probes that examined the bilayer interior and interfacial regions. The EPR results quantified in terms of order parameters and rotational correlation times are in agreement with NMR results. Furthermore, zeta potential measurements show that ATP makes the membrane potential more positive consistent with both NMR and EPR results. Our results interpreted in terms of an alignment field of lipid chains can guide the development of biomaterials with useful electro-mechanical properties. |
Friday, March 18, 2022 10:24AM - 10:36AM |
Y26.00013: Clustering dynamics of chemotactic particles Federico Fadda, Daniel Alejandro Matoz-Fernandez, Rene' van Roij, Sara Jabbari-Farouji Micro-organisms in nature can perform chemotaxis when exposed to a chemical gradient in order to find advantageous substances (e.g. food and nutrients) or to escape from dangerous ones (e.g. toxins and poisons) [1]. |
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