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 Q32: Biological Fluid Dynamics: Vesicle and Micelles II |
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Chair: Daniel Tam, TU Delft Room: 614 |
Tuesday, November 26, 2019 7:45AM - 7:58AM |
Q32.00001: Transport phenomena in a fluid film with curvature elasticity Arijit Mahapatra, David Saintillan, Padmini Rangamani Lipid bilayers are fluid films that are elastic in bending. Cellular membranes are lipid bilayers that contain different proteins, including ion channels, receptors, and scaffolding proteins. These proteins are known to diffuse in the plane of the membrane and to influence bending of the membrane. Experiments have shown that lipid flow in the plane of the membrane is closely coupled with the diffusion of membrane proteins. Thus there is a need for a comprehensive framework that accounts for the coupling between these processes. Here, we present a theory for the coupled in-plane viscous flow of lipids, diffusion of membrane proteins, and curvature elastic deformation of lipid bilayers. The proteins in the membrane are modeled such that they influence membrane bending by inducing a spontaneous curvature. We formulate the free energy for the system as a Helfrich-like curvature elastic energy density function modified to account for the chemical potential energy of proteins. Then, we apply the principle of virtual work to minimize the free energy and derive conservation laws and equation of motions. Finally, we present results from dimensional analysis and numerical simulations and demonstrate that asymmetry in protein distribution plays an important role in driving lipid flows. [Preview Abstract] |
Tuesday, November 26, 2019 7:58AM - 8:11AM |
Q32.00002: Formation of vesicles in a viscous solvent: A hybrid coarse-grain/continuum approach Szu-Pei Fu, Rolf Ryham, Yuan-Nan Young In this talk a theoretical model for long-range, hydrophobic attraction between amphiphilic particles (such as lipid molecules) is developed to quantify the macroscopic assembly and mechanics of a lipid bilayer membrane in solvents. The non-local interactions between amphiphilic particles are obtained from the first domain variation of a hydrophobicity functional, giving rise to forces and torques (between particles) that dictate the motion of both particles and the fluid flow in the viscous solvent. Both the hydrophobic and hydrodynamic interactions between the coarse-grained amphiphilic particles are formulated into integral equations, which allow for accurate and efficient numerical simulations in both two- and three-dimensions. Such hybrid coarse-grained model is validated by its capability to reproduce various physical properties of a lipid bilayer membrane. Furthermore we present simulation results of vesicle formation in both a quiescent flow and a pressure driven flow (as in the microfluidic jetting experiments). Finally we also illustrate how our hybrid model can be generalized to investigate the effects of local charges on the bending rigidity of a lipid bilayer membrane. [Preview Abstract] |
Tuesday, November 26, 2019 8:11AM - 8:24AM |
Q32.00003: Hydrodynamic shear transmission across cellular membranes. Daniel Tam, Guillermo Amador, Marie-Eve Aubin-Tam A cell's interactions with the environment are mediated by its cellular membrane. This nanometer-thick, liquid crystalline structure is mostly composed of a lipid bilayer, which serves as a scaffold for embedded proteins and other macromolecules. Many crucial cellular processes, such as motion, growth, and proliferation, are dependent on external mechanical stresses; therefore, understanding how cellular membranes generate and transmit forces may shed light on cell behavior and homeostasis. In this study, we use optical tweezers to both apply and measure local forces on free-standing lipid bilayers within microfluidic channels. The planar geometry of the lipid bilayer facilitates interpretation of measurements using hydrodynamic models. This technique is the first to combine multiple optical tweezers probes with planar free-standing lipid bilayers accessible on both sides of the bilayer. The aims of these measurements are to quantify fluid slip close to and transmission of shear forces across the bilayer surface, building towards a fundamental understanding of the physical principles governing the transfer of forces by and through the membrane. [Preview Abstract] |
Tuesday, November 26, 2019 8:24AM - 8:37AM |
Q32.00004: Electric Field-driven Deformation and Translation of Vesicles in Microchannels Adnan Morshed, Prashanta Dutta Bio-mimetic vesicles like liposomes exhibit complex responses when exposed to electric pulses. Their lipid membranes bear close resemblance to biological cells. Yet the lack of internal cytoskeletons and transmembrane organelles lead to different membrane deformation characteristics. The response of these vesicles is also affected by the electrical properties of the media and vesicle size and shape. We investigated the electrodeformation and transport of bio-mimetic vesicles immersed in a fluid media under a DC electric field. The deformation characteristics of vesicle membrane was represented with a Mooney-Rivlin constitutive law. The electric field, flow field, and vesicle deformation are resolved with a hybrid immersed resolved technique. Additionally, electroosmotic flows are considered for a range of surface charge conditions. Depending on the direction and magnitude of the electroosmotic flow, tumbling, tank treading, and pure translational motions were observed. Furthermore, a logarithmic scaling is realized between translational velocity of the vesicle and shear rate under electroosmotic flows. Conductivity ratio of vesicle and the surrounding media is found as a key parameter in the translational motion as well. [Preview Abstract] |
Tuesday, November 26, 2019 8:37AM - 8:50AM |
Q32.00005: Active particle penetration through a planar elastic membrane Abdallah Daddi-Moussa-Ider, Benno Liebchen, Andreas M. Menzel, Hartmut Loewen Active penetration of nanoparticles through cell membranes is a fascinating phenomenon that may have important implications in various biomedical and clinical applications. Using particle-based computer simulations and theory, the penetration mechanism of an active particle through a planar elastic membrane is studied. The membrane is modeled as a self-assembled sheet of particles embedded in a Newtonian viscous fluid. A coarse-grained model is introduced to describe the mutual interactions between the membrane particles. Three distinct scenarios are identified, including trapping of the active particle, penetration through the membrane with subsequent self-healing, in addition to penetration with permanent disruption of the membrane. The latter scenario may be accompanied by a partial fragmentation of the membrane into bunches of isolated or clustered particles. Our approach might be helpful for the prediction of the transition threshold between the trapping and penetration in real-space experiments involving motile swimming bacteria or artificial active particles. Reference: A. Daddi-Moussa-Ider, B. Liebchen, A. M. Menzel, and H. Löwen, Theory of active particle penetration through a planar elastic membrane, New J. Phys. in press (2019). [Preview Abstract] |
Tuesday, November 26, 2019 8:50AM - 9:03AM |
Q32.00006: Viscoelasticity of a bacterial extracellular polymeric substance (EPS) streamer filament using micro-rheology and microfluidics Andrew White, Maryam Jalali, Jian Sheng Using \textit{Ecology-on-a-chip} (eChip), we have demonstrated that polymeric aggregates can be formed around a rising oil micro-droplet by \textit{Pseudomonas}. The EPS aggregate is initiated by forming trailing streamers with one end anchoring at the droplet surface and the other floating in the flow, which alters ``wake'' pressure field and consequently causes substantial drag on the drop. Experiments using \textit{Alcarnivorex} and \textit{Marinobacter} further reveal that although the formation of ``streamers'' is universal, its rheological characteristics vary significantly due to the EPS composition including polysaccharides, proteins, lipids and nucleic acids. To understand complex interactions of streamers and their surrounding shear flows, viscoelastic behavior of streamers must be understood. Here, we apply micro-rheology technique to quantify real-time viscoelasticity of streamers developed in a pinned oil droplet in \textit{eChip}. Using high speed microscopy, filament strain is determined by tracking trapped bacteria in real-time and concurrently viscous stresses are measured using PIV-assisted PTV of freely suspended bacteria. Stress-strain shows hysteresis of viscoelastic materials. Funded by GoMRI, ARO [Preview Abstract] |
Tuesday, November 26, 2019 9:03AM - 9:16AM |
Q32.00007: Species and orientation differences in copepod behavior in a Burgers vortex D. Elmi, S. Soumya, D.R. Webster, D.M. Fields We use a Burgers vortex experimental model to study the interaction of two marine copepod species (\textit{Temora longicornis} and \textit{Acartia tonsa}) with a single turbulent-like eddy structure. Tomographic-PIV experiments were performed at small-scale to quantify the velocity field of turbulent vortices modeling those that copepods encounter in their oceanic habitat. Turbulence intensities are discretized into four levels corresponding to dissipation rates of 0.002 to 0.25 cm$^{\mathrm{2}}$/s$^{\mathrm{3}}$. Three-dimensional swimming trajectories are retrieved from two orthogonal camera perspectives and overlaid on the Burgers vortex velocity structure to identify individual swimming kinematics and behavioral differences. We use apparatuses with the vortex axis aligned in horizontal and vertical directions to argue that the copepods are sensitive to the directionality of the hydrodynamic signals. By comparing the behavioral changes in four turbulence intensity treatments and a control treatment, we provide a framework to identify trends in behavioral responses. Both species of copepods increase their relative velocity as the strength of the Burgers vortex increases and the trend appears stronger in the vertically-aligned vortex. Further, the number of circular-shaped trajectories around the vortex core increases with increasing strength of the Burgers vortex for both species, and the trend is stronger for \textit{A. tonsa}. These trends, together with the statistical analysis, suggest that changes in oceanic turbulence intensity as a result of climate change would affect the distribution of copepods. [Preview Abstract] |
Tuesday, November 26, 2019 9:16AM - 9:29AM |
Q32.00008: An experimental implementation of a two-sphere swimmer at low Reynolds numbers Oliver Silverberg, Brent Hosoume, Nikhil Trivedi, Connor Tisch, Daniel Plascencia, Matthew Holmes, On Shun Pak, Emre Araci Locomotion at low Reynolds numbers encounters stringent constraints due to the dominance of viscous over inertial forces. Various elegant designs have been proposed to escape from the constraints of the scallop theorem and generate self-propulsion. In this talk, we present a macroscopic experimental implementation of the “Pushmepullyou” swimmer (J. E. Avron, O. Kenneth, D. H. Oaknin, New J. Phys., 7, 234, 2005), which consists of a pair of expandable spheres connected by an extensible link. We characterized the propulsion performance of the swimmer in the low Reynolds number regime with the use of highly viscous silicone oil and compared the results with theoretical predictions. [Preview Abstract] |
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