Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session F16: DSOFT Early Career and Student Awards SessionFocus Undergrad Friendly
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Sponsoring Units: DSOFT Chair: Rae Robertson-Anderson, University San Diego Room: Room 208 |
Tuesday, March 7, 2023 8:00AM - 8:36AM |
F16.00001: Early Career Award for Soft Matter Research Winner: Pierre-Thomas BrunBuilding with fluids: a lazy approach to fabricating programable soft matter Invited Speaker: Pierre-Thomas Brun We will discuss the possibility of harnessing interfacial flows as templates for the design of soft functional materials. Our idea relies on "freezing" specific fluid flows, e.g., coiling, droplets, and bubbles, using polymeric solutions that are initially liquid and then cure into soft elastic solids. The shapes and patterns we obtain are universal and transcend the traditional divisions between scientific fields or even between living and inert matter. We will show that these similarities result from mathematical analogies in the rules that govern pattern formation and offer a pathway for their directed control. In particular, we will demonstrate how to leverage these robust processes to augment our manufacturing capabilities, e.g., for the assembly and programming of soft robots. |
Tuesday, March 7, 2023 8:36AM - 8:48AM |
F16.00002: Inferring interaction potentials from particle trajectories Ella M King, Megan C Engel, Sam Schoenholz, Caroline S Martin, Vinothan N Manoharan, Michael P Brenner Interaction potentials provide rich information about systems of interacting and self-assembling particles. Measuring interaction potentials has repeatedly revealed novel physics, and extracting effective interactions in complex systems provides a path towards simulation and design in systems where the precise physics is unknown. However, measurements of interaction potentials in experiments are difficult and time-intensive. Moreover, previous methods of measuring interparticle potentials rely on highly constrained motion of small numbers of particles at equilibrium, placing limits on which interactions can be measured. We introduce a method for inferring interaction potentials directly from trajectory data. Beginning with a form for the equations of motion, we find the potential that maximizes the probability of observing a known trajectory. The method is valid both in and out of equilibrium, and is well-suited to large numbers of interacting particles. We demonstrate our method in both simulated and experimental colloidal systems. |
Tuesday, March 7, 2023 8:48AM - 9:00AM |
F16.00003: Active Chromatin Dynamics Drives Nuclear Bulge Formation Sarthak Gupta, Isabel K Oder, Yasmin Berrada, Andrew Stephens, Alison E Patteson, Edward J Banigan, J. M Schwarz The cell nucleus is an active complex environment containing long chains of DNA polymers transcribed by molecular motors. Intriguingly, we have observed that the genomic process of transcription can generate irregular nuclear protrusions called blebs, but how this morphological change occurs is not understood. We have developed a three-dimensional Brownian-dynamics-based model of a nucleus consisting of a polymeric protein shell (the lamina), a crosslinked polymer chain (chromatin), and extensive and contractile motors representing transcription and other nonequilibrium genomic processes. In simulations, we observe localized bulges on the nuclear surface, indicating the possible formation of blebs or their precursors. The number and size of these bulges grow as the number of motors and their strength increase. The model also captures mechanical properties, such as the compression-stiffening behavior of the nucleus. Nuclei respond to applied compression in a rate-dependent manner. With slow deformations, the nucleus maintains an ellipsoidal shape, whereas we observe large wrinkles, folds, and bulges with faster compression. Therefore, our model captures the cell nucleus's mechanical, morphological, and dynamical properties and demonstrates how both passive and active mechanisms can shape cellular structures. |
Tuesday, March 7, 2023 9:00AM - 9:12AM |
F16.00004: The mechanics of Fick’s Law and odd diffusion Cory M Hargus, Kranthi K Mandadapu, Ahmad K Omar Fick's Law posits a linear relationship between diffusive fluxes and density gradients. These fluxes are usually oriented down density gradients, causing matter to "spread out". Odd diffusion, however, generates fluxes orthogonal to density gradients, and is a direct consequence of broken time-reversal symmetry (TRS) at the level of individual particles. As such, it is a common feature of chiral active matter. The connection between macroscopic odd diffusion and TRS-breaking in the spontaneous fluctuations about the steady state is made quantitative through Green-Kubo relations, which hold even in systems such as active matter where the steady state is inherently out of equilibrium. In this talk we highlight a further mechanical connection between odd diffusion and the antisymmetric hydrostatic stress, which is the part of the stress arising due to microscopic (e.g. active) torques. We show that this mechanical relationship determines the exact form of the odd diffusivity for a model fluid composed of actively-torqued dumbbell particles, even when the torques are large and when the density of dumbbells is high. |
Tuesday, March 7, 2023 9:12AM - 9:24AM |
F16.00005: Slow relaxations in disordered mechanical systems - aging on the verge of instability Dor Shohat, Yaniv Friedman, Yoav Lahini Slow relaxations are a hallmark of disordered systems trapped in far-from-equilibrium conditions. After a perturbation, many of these systems exhibit logarithmically slow relaxations of one or more of their macroscopic observables. These relaxations can span many time scales, from a fraction of a second to days and even years. However, the microscopic processes underlying this behavior and the reason for its ubiquity across many different systems remain unclear. |
Tuesday, March 7, 2023 9:24AM - 9:36AM |
F16.00006: Buckling instabilities in moving chains of bubbles Carmen L Lee, Kari Dalnoki-Veress When slender structures are subjected to a compressive force, they will buckle and bend as mediated by the bending modulus of the solid material or the viscosity of the liquid. Here, we explore a slender structure with no internal bending modulus by producing a chain of microscopic monodisperse bubbles in an aqueous bath. The chain rises due to the buoyancy of the bubbles. There is an attractive interaction between the bubbles and if the bubbles are produced quickly such that one bubble is produced and contacts the next, they adhere. Producing many bubbles in this fashion allows us to create a chain of sticky bubbles that are frictionless and have no bending cost. Tuning the rate of bubble production results in buckling instabilities in the rising chain as it moves through the aqueous bath due to the hydrodynamic drag. We predict the buckling onset, buckling amplitude, and speed of the chain using scaling arguments to balance buoyancy and viscous drag. |
Tuesday, March 7, 2023 9:36AM - 9:48AM |
F16.00007: Filler-polymer interactions dictate tissue-like compression stiffening in composite hydrogels Jake Song, Serra Yesilata, Gareth H McKinley Mammalian tissues such as adipose, brain, and liver exhibit stiffening in their shear moduli with increasing compressive normal strain. Though this compression stiffening property has been associated with a composite structure consisting of fibrous polymers and volume-conserving fillers, a detailed understanding of the underlying mechanisms remains missing. In this talk, we demonstrate the crucial role of filler-polymer interactions in dictating the extent of compression stiffening in composite hydrogels, and elucidate the molecular origins of this effect. Our findings suggest a significant role of cell-matrix interactions on the mechanical properties of tissues, and provide a guideline for controlling tissue-mimetic compression stiffening in engineered materials. |
Tuesday, March 7, 2023 9:48AM - 10:00AM |
F16.00008: How Life May Have Originated in Phase-separated Polymer Droplets Aman Agrawal, Syed Rizvi, Aleksandar Radakovic, Jack F Douglas, Jack W Szostak, Matthew V Tirrell, Alamgir Karim Solutions of oppositely charged polymers, upon mixing, undergo liquid-liquid phase separation. The phase-separated membraneless droplets formed by such polyelectrolyte blends, called "coacervates," find their place in the biological world not only in numerous processes inside cells but also in model early-earth scenarios for the origin of life. Modern cells with complex architectures, including lipid membranes and associated membrane proteins, must have evolved from an architecturally simple state. Coacervate droplets have recently been proposed as simple prebiotic cells (or protocells) as they provide compartmentalization to separate life from non-living surroundings, sequestration of biomolecules, and easy transportation of materials across membraneless interface. Unfortunately, the uncontrollable transport across droplet interface (t ~ sec), in addition to the droplet's inherent instability towards coalescence (merging, t ~ ms) poses a major challenge in considering these droplets as protocell models. We stabilized these "coacervate colloids" by submerging them in distilled (ion-free) water. Here, we produced droplets that showed no exchange of RNA and were stable against coalescence for more than two years. We hypothesize that the loss of counterions upon transfer to water creates a thin crosslinked layer on the droplet interface that prohibits droplet coalescence. This is a unique, minimalistic "stable" protocell model supporting Darwinian evolution and natural selection. |
Tuesday, March 7, 2023 10:00AM - 10:12AM |
F16.00009: Worm Buoys: Emergent Collective Interfacial Latching of Aquatic Worms Harry Tuazon, Emily G Kaufman, Saad Bhamla California blackworms (L. variegatus) are aquatic worms that naturally live in the benthic zones of freshwater habitats. In the absence of granular substrate such as detritus or fine sand, blackworms thigmotactically form collective worm “blobs” with each other for protection. Consequently, the resulting high density of entangled worms drives anoxia (dissolved oxygen (DO) <1 mg/L) within the blob and in its proximate regions. While blackworms can breathe through their skin, they supplement respiration by anchoring their heads in granular materials (or with conspecifics) and subsequently raising their tails upwards to access higher DO. If the water is shallow enough, blackworms position their tails on the surface, which bend at a right angle and lay parallel along the air-water interface. Due to its material property which we hypothesize to contain a pattern of hydrophobic and hydrophilic regions, portions of their tail break surface tension to access oxygen directly from air. These hydrophobic portions provide an upward force that allow worms to “latch” and hang freely using only the interface. After about 70% of the worms in a blob has latched onto the surface, the entire collective lifts off from the ground, forming a “worm buoy”. We estimate that one segment from a single worm weighing 4 mg (in water) exert enough upward force to support itself on the interface. We hypothesize this floating structure promotes collective survival and dispersal by allowing worm blobs to float (rather than climb) over obstacles. |
Tuesday, March 7, 2023 10:12AM - 10:24AM |
F16.00010: Geometry-induced pattern formation Laeschkir Würthner, Andriy Goychuk, Erwin Frey Proteins play a critical role in organizing a multitude of cellular process, including cell division, cell motility, and nutrient uptake. To achieve this, proteins form spatiotemporal patterns that are governed by an interplay between transport processes and local biochemical reactions. Notably, protein patterns often emerge along the cell membrane, which is a dynamic object as cells alter their shape during various processes. This can lead to an intricate feedback loop between protein patterns and dynamic shape changes of the membrane, for which it is difficult to extract the mechanisms underlying the dynamics. We will discuss a conceptual model for cell polarity on a time-evolving geometry [1]. Utilizing tools from differential geometry, we derive the equations describing mass-conserving reaction-diffusion systems on dynamic membranes. Based on a recently developed framework for mass-conserving reaction-diffusion systems [2], we then analytically derive a criterion that links the onset of pattern formation to the phase-space structure of the reaction-diffusion system. We show that shape deformations can regionally induce, suppress, and spatially shift pre-existing patterns. Moreover, we demonstrate that the feedback loop between membrane shape and reaction-diffusion dynamics leads to traveling wave and standing wave patterns that do not occur on static membrane geometries. Our work underscores the local conformation of the geometry and the total protein mass as the relevant dynamic variables for pattern formation. |
Tuesday, March 7, 2023 10:24AM - 10:36AM |
F16.00011: Spatial organization of contaminants influences bioremediation strategies Jenna A Ott, Yaxin Duan, Fernando Temprano Coleto, Daniel Amchin, Sujit S Datta Access to clean water is at the forefront of top global challenges that engineers are equipped to tackle. A key source of drinking water for over half of the population in the United States is groundwater; unfortunately, over a third of groundwater sources are contaminated with harmful chemicals. Bioremediation is a promising approach to cleaning up groundwater contaminants that utilizes chemotactic bacteria to actively sense, find, and degrade these contaminants in situ---additionally, it is significantly cheaper than current pump-and-treat methods. However, how these chemotactic bacteria behave in the presence of multiple discrete, spatially-distributed contaminant sources at the pore scale remains poorly understood. To address this issue, we use mathematical modeling and numerical simulations to determine how physiological and environmental conditions influence how bacteria can chemotactically respond to multiple contaminant sources. We use our findings to establish a universal biophysical rule to predict how the dynamics of bacterial chemotaxis, spatial distribution of cells and diffusing contaminant, and overall efficacy of bioremediation depend on cellular properties, contaminant properties, and the spacing between contaminant sources. Our work thus provides a key step towards developing a deeper understanding bioremediation at the pore scale and establishing useful design principles to guide more effective bioremediation strategies. |
Tuesday, March 7, 2023 10:36AM - 10:48AM |
F16.00012: Enzyme kinetics in salt resistant complex coacervate emulsions Advait S Holkar, Shang Gao, Kathleen Villasenor, Samanvaya Srivastava Research in protocells has burgeoned in recent decades due to their fundamental importance in the origin of life and their latent technological potential. Complex coacervates formed by liquid-liquid phase separation of charged macromolecules can be simplistic protocellular models with a distinct interface, spontaneous biomolecular sequestration, and chemical conversions within macromolecularly crowded environments. While the bulk material properties of such coacervates are well understood, this knowledge is yet to be applied towards tailoring protocell design. A major limitation was the long-term stabilization of the liquid-liquid interface, which we previously demonstrated using comb-polyelectrolytes (cPEs). In this talk, we demonstrate that this approach is generic and works with distinct polymer characteristics and salt identities, over a wide range of concentrations. We show improved salt resistance of droplets, tunable by cPE concentration and an expansion of the two-phase window. Furthermore, enzyme mediated reactions yielding bioluminescent molecules delineating reaction kinetics within coacervates will be shown. Finally, the effect of coencapsulation of enzymes on kinetics in cascading reactions within optimized protocellular characteristics will be presented. |
Tuesday, March 7, 2023 10:48AM - 11:00AM |
F16.00013: Polymer-based, 3D printed, Syntactic Foams Maintain Modulus and Energy Dissipation Under Cyclic Loading due to Shell Buckling and Elastic Recovery Younghoon Kwon Additive manufacturing has magnified capabilities for on-demand fabrication of bio-inspired materials possessing complex architectures across broad length scales, leading to systems that are simultaneously stiff, tough, and lightweight. We recently developed a two-step digital light processing (DLP)-based 3D printing approach that involves an initial photopolymerization step followed by the thermal expansion of embedded microspheres, which allows additively manufactured closed-cell composite polymer foams with variable porosity and tunable mechanics. Here, we report thermomechanical characterization of the constituents (i.e., polymer matrix and shell of microspheres) which led to an improvement in material processing and facilitated the detailed mechanical analysis of the compressive behaviors of the composite foams. Effects of foaming on the stress-strain response, Poisson’s ratio, and energy dissipation were investigated using uniaxial compression. The foams show remarkable fatigue tolerance under cyclic loading at large deformation, maintaining superior energy dissipation capabilities and modulus. Electron microscopy of mechanically deformed materials via suggests that their resilience can be attributed to shell bucking and elastic recovery of the polymeric microsphere. |
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