Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session M30: Soft Mechanics via Geometry IIFocus

Hide Abstracts 
Sponsoring Units: DSOFT DPOLY Chair: Moumita Das, Rochester Institute of Technology Room: 502 
Wednesday, March 4, 2020 11:15AM  11:51AM 
M30.00001: The topography of tuning Invited Speaker: Eleni Katifori Allosteric proteins globally adjust their conformation upon binding a ligand in order to control the activity of a distant active site. Inspired by such a system, we explore how mechanical systems achieve a specified complex function such as strain propagation in mechanical networks. We investigate computationally the maximum complexity of a tuned function that can be achieved as a function of network size. Further, we identify the structural features responsible for function in these tuned networks. We show how we can use topographical information to improve the tuning process and how the complexity of the tuned function scales with network size. Using persistent homology, we show that networks tuned to perform such functions develop characteristic features that are similar for different networks that perform the same function, regardless of differences in the local link connectivity. 
Wednesday, March 4, 2020 11:51AM  12:03PM 
M30.00002: Mechanics of soft fibrous mats with interfiber adhesion and friction Catalin Picu, Vineet Negi Many soft materials of biological and industrial interest are composed from nanofibers and take the form of quasitwodimensional mats with stochastic structure. Examples include membranes in the human and animal bodies, geotextiles, nonwovens used in consumer products and tissue scaffolds. We investigate the mechanical behavior of such structures, which is largely controlled by geometry and adhesive and frictional interactions of constituent fibers. We consider two cases: one in which the fibrous mat is stabilized by adhesion, and the other in which fibers interact only frictionally. Both systems exhibit rich nonlinear mechanics. We determine the scaling of material properties with the intensity of adhesion, and describe the interplay between frictional interactions and geometry in defining the mechanics of the mat. Stress is these systems is primarily associated with dissipation and exhibits interesting dependence on the network architecture. 
Wednesday, March 4, 2020 12:03PM  12:15PM 
M30.00003: Nonlinear Poisson effect in critical mechanical networks Jordan Shivers, Sadjad Arzash, Fred C MacKintosh Fibrous networks of stiff athermal biopolymers such as collagen, a major structural component of the extracellular matrix, have been shown to exhibit anomalously large apparent Poisson ratios, i.e. significant transverse contraction under small applied longitudinal extension. Here we show that this effect can be understood in the context of a macroscopic mechanical phase transition from a bendingdominated regime to a stretchingdominated regime at a critical applied extension controlled by the network connectivity. We measure this effect using a variety of 2D and 3D model network structures and propose a phase diagram governing the transition as a function of connectivity and strain. 
Wednesday, March 4, 2020 12:15PM  12:27PM 
M30.00004: Shear modulus discontinuity in fiber networks Sadjad Arzash, Jordan Shivers, Fred C MacKintosh Fibrous networks such as collagen are common in physiological systems. One important function of these networks is to provide mechanical stability for cells and tissues. It has been shown that athermal coarsegrained models of fibers with bending and stretching interactions can explain the experimental observations. By applying an extensional or shear deformation, subisostatic fiber networks with only central force interactions undergo a phase transition from a floppy to a rigid state. By simulating various network models, we confirm that although the network’s stiffness exhibits a discontinuity, the transition is critical in nature. We study the finitesize scaling behavior of this discontinuity in order to identify the corresponding nonmeanfield critical exponent in the thermodynamic limit. 
Wednesday, March 4, 2020 12:27PM  12:39PM 
M30.00005: Shaping curved surfaces using origami. Théo Jules, Frederic Lechenault, Mokhtar AddaBedia

Wednesday, March 4, 2020 12:39PM  12:51PM 
M30.00006: NonHookean Elastic Moduli of 2D Tissue Model Arthur Hernandez, Michael Moshe, M Cristina Marchetti, Mark J Bowick We study the peculiar mechanical response of a discrete vertex model (VM) of 2D epithelia. In the absence of T1 rearrangements, the VM exhibits a transition between a soft and a stiff solid tuned by the target shape index of the cells and associated with the onset of geometric incompatibility. By examining the response to a variety of deformations, we show that the stiff solid phase exhibits nonlinear elastic response that cannot be recast in the framework of conventional Hookean elasticity even in the limit of infinitesimal strain. The soft solid is characterized by floppy modes that can absorb strain. As a result, the linear mechanical response is not fully characterized by two independent Lamé coefficients, as in linear elasticity of a 2D isotropic solid, but depends on the specific imposed deformation. We show that this unconventional mechanical behavior is in agreement with a continuum version of the model developed recently by some of us. 
Wednesday, March 4, 2020 12:51PM  1:03PM 
M30.00007: Geometry and kinetics determine the packing structure on evolving surfaces Zhaoyu Xie, Christopher Burke, Badel L Mbanga, Patrick T Spicer, Tim Atherton We consider the evolution, arrest and jamming of particulate media on an evolving surface. As the shape changes, local regions of compression and rarefaction induce local solidification or melting and, consequently, rich kinetic effects. Here we resolve the relative influence of kinetics and geometry in determining the structure of a model system: the coalescence of Pickering emulsion droplets that can be arrested by the solid particles coated on the surface. By Monte Carlo simulations, we demonstrate that in the quasistatic regime, the geometry still governs the microstructure of these particles, resembling the spherical crystallography regime explored in previous literature. Conversely if the evolution of surface is fast, the kinetics can change the structure at the arrest point depending on the local surface deformation, with jamming fronts that develop from the compressed area. Other surfaces and particles are explored and we propose a new class "metric jamming" to describe the transition to rigidity under shape deformation. 
Wednesday, March 4, 2020 1:03PM  1:15PM 
M30.00008: CrumpleOrigami Transition for Twisting Cylindrical Shells LiMin Wang, SunTing Tsai, Chihyu Lee, PaiYi Hsiao, JiaWei Deng, HungChieh Fan Chiang, Yicheng Fei, TzayMing Hong Origami and crumpling are two extreme tools to shrink a 3D shell. In the shrink/expand process, the former is reversible due to its topological mechanism, while the latter is irreversible because of its randomgenerated creases. We observe a morphological transition between origami and crumple states in a twisted cylindrical shell. By studying the regularity of crease pattern, acoustic emission and energetics from experiments and simulations, we develop a model to explain this transition from frustration of geometry that causes breaking of rotational symmetry. In contrast to solving von KarmanDonnell equations numerically, our model allows derivations of analytic formula that successfully describe the origami state. When generalized to truncated cones and polygonal cylinders, we explain why multiple and/or reversed crumpleorigami transitions can occur. 
Wednesday, March 4, 2020 1:15PM  1:27PM 
M30.00009: Statistical mechanics of nanotubes Siddhartha Sarkar, Andrej Kosmrlj We investigate how thermal fluctuations affect mechanical properties of nanotubes by employing renormalization group procedure. For 2D sheets it was previously shown that thermal fluctuations effectively renormalize elastic constants beyond a characteristic thermal length scale (a few nanometers for graphene at room temperature), where the bending rigidity increases, while the inplane elastic constants reduce with universal power law exponents. However, the curvature of nanotubes produces new phenomena. Specifically, we find that in the axial direction the inplane elastic constants stop renormalizing at the elastic length scale (proportional to geometric mean of the radius and the effective thickness of the shell), while in the circumferential direction they continue to renormalize albeit with different universal exponents. On the other hand, the bending rigidity stops renormalizing in the circumferential direction at the elastic length scale. These results were verified with molecular dynamics simulations by measuring the mechanical response to axial loads and external pressure. We also comment on how these temperature dependent properties affect the critical buckling loads for nanotubes. 
Wednesday, March 4, 2020 1:27PM  1:39PM 
M30.00010: Braided biopolymer filament bundles produce topologically protected kinks Valentin Slepukhin, Maximilian Grill, Qingda Hu, Elliot Botvinick, Wolfgang Wall, Alex Levine Bundles of stiff filaments are ubiquitous in the living world, found both in the cytoskeleton and in the extracellular medium. These bundles are typically held together by smaller crosslinking molecules. We demonstrate analytically, numerically and experimentally that such bundles can be kinked, i.e., have localized regions of high curvature that appear to be at least longlived 
Wednesday, March 4, 2020 1:39PM  1:51PM 
M30.00011: Fabrication of supported lipid bilayers of designed shape with microprinting and replicamolding Melissa Rinaldin, Luca Giomi, Daniela Jutta Kraft Membrane curvature is a fundamental part of the cellular machinery. In cells, membrane curvature can be generated by different mechanisms, including cytoskeletal scaffolding and lipid and protein sorting. In proteinfree systems in vitro, membrane curvature can be artificially obtained by, for example, membrane micromanipulation, phase separation, and supported lipid bilayers fabrication. However, until now, these methods allowed for studying a restricted range of shapes only. Here, we present a general and facile method to obtain membranes of designed curvature with high precision. By combining 3D microprinting and replicamolding lithography, we fabricate scaffolds of designed shape and size suitable for lipid coating. We show that the resulting supported lipid bilayers are homogeneous and fluid. We demonstrate their potential by using them for fluorescence after photobleaching and phase separation experiments on curved surfaces. We anticipate that our method will open new possibilities to investigate curvature sensing proteins and, more generally, the role of membrane curvature in biology. 
Wednesday, March 4, 2020 1:51PM  2:03PM 
M30.00012: Curvaturedriven propulsion of floating films: Part 1 Monica Ripp, Zachariah Schrecengost, Elizabeth LawsonKeister, Joseph Paulsen Water striders can propel themselves up a curved liquid meniscus by repositioning their feet to match the curvature of their destination, providing one example of propulsion along an interface due to a mismatch in geometry [1]. How does a highlyflexible elastic solid respond when it is placed on a liquid surface with a curvature different than its own? We find that flat films spontaneously flee highlycurved menisci towards flatter regions, whereas curved shells are attracted to regions with finite curvature. These findings are borne out of experiments where polymer films are released from different initial positions in overfilled petri dishes. Focusing on flat films that are ~1 cm wide and ~100 nm thick, we examine the effects of film thickness, liquid viscosity, and meniscus curvature on the velocity of this motion. Our data across a wide range of parameters are in agreement with a theoretical picture in which the sheet is propelled by its ability to cover progressively more liquid surface area in the regions where it is attracted [2]. We develop this model and its consequences in the next talk. (This is part 1 of a 2talk series.) 
Wednesday, March 4, 2020 2:03PM  2:15PM 
M30.00013: Curvaturedriven propulsion of floating films: Part 2 Zachariah Schrecengost, Monica Ripp, Jordan V Barrett, Vincent Démery, Joseph Paulsen The remaining pieces of breakfast cereal spontaneously clump together in a cereal bowl due to the interactions of the menisci around each particle. A highlybendable elastic sheet participates in a very different interaction with the liquid around it. In the previous talk, experimental results were given where a polymer film spontaneously propels itself to a region that more closely matches its intrinsic curvature. These results were interpreted as falling within a geometric framework, where the sheet bends and wrinkles in such a way as to minimize the exposed liquid surface area [1]. Implementing this model is a nontrivial optimization problem, due to the wide variety of configurations available to the sheet and interface. We use Surface Evolver simulations and analytic calculations to study the energetic cost of placing an ultrathin elastic disc on a local topography of arbitrary curvature. We establish scaling laws that relate the total energy to the principal radii of curvature. By estimating the fluid drag forces, we develop theoretical predictions for sheet velocity, which we compare with our experiments. (This is part 2 of a 2talk series). 
Follow Us 
Engage
Become an APS Member 
My APS
Renew Membership 
Information for 
About APSThe American Physical Society (APS) is a nonprofit membership organization working to advance the knowledge of physics. 
© 2022 American Physical Society
 All rights reserved  Terms of Use
 Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 207403844
(301) 2093200
Editorial Office
1 Research Road, Ridge, NY 119612701
(631) 5914000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 200452001
(202) 6628700