Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session C53: Mechanics of Networks III |
Hide Abstracts |
Sponsoring Units: GSOFT GSNP DPOLY Chair: Corentin Coulais, Univ of Leiden Room: LACC 513 |
Monday, March 5, 2018 2:30PM - 2:42PM |
C53.00001: A full network model of complementary non-Gaussian energy explain the mechanics of biological tissue Pablo Saez, Chiara Venturini, Jose Felix Rodriguez The biophysics behind the mechanics of biology, from single molecules to the whole tissue, has been largely analyzed. The early non-Gaussian statistical mechanics has fostered fine physical models of the mechanics of DNA proteins or of the cardiovascular tissue. However, when the complexity of the physical system increases one needs to build up the assembly of a number of these elements in different configurations which usually do not reproduce the mechanical behavior obtained at the system level. A simple example can be found at the top and bottom level of the cardiovascular tissue. Collagen fibrils have been reported to be in the range 0.1-0.5GPa. However, when whole tissue is tested mechanically, the equivalent Young's modulus is found to be in the KPa range. We have developed a full network model based on a novel complementary strain energy function of non-gaussian statistical mechanics. The proposed framework is capable of reproducing the whole system response based on the actual behavior of the underlying elements. The methodology shows promising applicability in other biological systems, for instance in adhesion complexes with intricate configurations of proteins (e.g. vinculin-talin-integrin complexes). |
Monday, March 5, 2018 2:42PM - 2:54PM |
C53.00002: Complex Network Analysis of Bone for Understanding Multiscale Mechanisms of Strength Chantal Nguyen, Avik Mondal, Xiao Ma, Ahmed Elbanna, Jean Carlson Bone is a complex, heterogeneous material that displays mechanisms of fracture resistance across multiple scales. At the mesoscale, trabecular (cancellous) bone is a strong, lightweight tissue consisting of interconnected bone struts (trabeculae) that erode with age and disease, resulting in increased fracture propensity. Due to its structural resemblance to a network, we use micro-computed-tomography images to model trabecular bone as weighted networks, and we compare network metrics with mechanical response in order to investigate how its architecture gives rise to fragilities or conversely robustness to fracture. This approach also allows us to use dynamic community detection to identify pathways for force propagation. We simulate damage with finite element analysis on beam-element structures that correspond to 3-D realizations of the network models, but are less computationally intensive than continuum-element reconstructions of bone, and we validate our results against the continuum models. Our results can be integrated into a comprehensive, multiscale characterization of bone, and our approach can be applied to the analysis of other hierarchical materials. |
Monday, March 5, 2018 2:54PM - 3:06PM |
C53.00003: Crack propagation in Articular Cartilage modeled as a biopolymer double network Leo Sutter, Andrew Sindermann, Thomas Jackson, Lena Bartell, Lawrence Bonassar, Itai Cohen, Moumita Das Articular cartilage (AC) is a soft tissue that covers the ends of bones providing a smooth cushion at the joints. It has very few cells, and its extracellular matrix can be primarily thought of as a double network of stiff collagen fibers and flexible proteoglycans. As a material, AC is remarkable. It is only a few millimeters thick, yet can withstand large forces over 100-200 million loading cycles without fracturing. Here we investigate the structure-function properties underlying the fracture toughness of AC by using a framework that combines a double network model of cartilage with rigidity percolation theory. We study how the stress-strain properties and crack propagation in the double network depend on its composition and on loading conditions. Our results may help to formulate a quantitative criterion for crack propagation and fracture in soft tissues akin to the Griffith criterion for fracture of brittle materials. |
Monday, March 5, 2018 3:06PM - 3:18PM |
C53.00004: Non linear mechanics of dense dendritic actin networks Pierre Bauër, Julien Heuvingh, Joe Tavacoli, Olivia DU ROURE Actin is a protein which self-assembles into dynamic filaments organized in cells in different kind of meshworks. The combination of their mechanics and their dynamics enables the cell to achieve essential processes like migration, deformation or integration of external mechanical cues. Rheology of actin suspensions has been extensively studied at low concentrations at which the elastic response of filament is entropic, in agreement with their semi-flexible nature. Here we focus on more concentrated actin networks whose density and microscopic architecture is closer to the one found in cells. We use a cellular biochemical machinery, called Arp2/3 machinery, that assembles dense and dendritic networks; the mesh size is small compared to the actin persistence length implicating that actin filaments behave as rigid rod. We probed the elastic responses of these particular actin networks by a new technique based on magnetic particles and have shown that the mechanics is strongly non linear with a non linear modulus that decreases linearly towards low values when applied stress decreases. We attribute this behavior at low stress to the low connectivity of the networks as Arp2/3 mediates connection between three actin strands and not four as a more conventional crosslinker would do. |
Monday, March 5, 2018 3:18PM - 3:30PM |
C53.00005: Geometry and Elasticity Induced Bi-stability in a Cellular Structure with Star-Shaped Unit Cells Soroush Kamrava, Ashkan Vaziri We introduce a novel family of origami-based structures with reversible foldability and bi-stability which relies on both properties of material and hinge characteristics. The proposed cellular structure is consisted of star-shaped bi-stable unit cells with two zero-energy states. Transition of the unit cells between two stable (zero-energy) configurations take place through elastic deformation of sub-components and hinge rotations. In this project, we prove bi-stability of unit cells experimentally and then investigate the effect of geometrical parameters on the existence and quality of bi-stability. The resultant unit cells can be designed to form different types of stars (three-pointed star, four-pointed star, and etc.) which also make difference in force-folding response of unit cells. Tiling star-shaped unit cells in three-dimensional space under different patterns forms various cellular structures with bi-stability transferred from underlying unit cells. The other interesting feature which arises from unit cell and transfers to cellular structure is auxeticity. Cross-section of unit cells under compressive load will be decreased gradually until it ends in second zero-energy configuration with smaller cross-section compared to first stable state. |
Monday, March 5, 2018 3:30PM - 3:42PM |
C53.00006: Finding the Mechanically Stable States of Prismatic Architected Materials Agustin Iniguez-Rabago, Johannes Overvelde, Yun Li Advances in fabrication technologies are enabling the production of architected materials with unprecedented properties. While most of these materials are characterized by a fixed geometry, an intriguing avenue is to add internal mechanisms capable of reconfiguring their spatial architecture enabling tunable functionality. Previously we proposed a design strategy based on space-filling extruded polyhedra to create 3D reconfigurable materials comprising a periodic assembly of rigid plates and elastic hinges. Interestingly, when the rigidity constraint of the faces is softened, new folding pathways open up that lead to multiple mechanically stable states. By performing numerical analysis and harnessing symmetries that exits in these geometries, we systematically explore the energy landscape to find the possible stable states. The final goal is to understand and design a wealth of multistable materials that can switch between different mesostructures through applying global stimuli. |
Monday, March 5, 2018 3:42PM - 3:54PM |
C53.00007: 1D Capillary Bending of a Thin, Floating Polymer Film Timothy Twohig, Andrew Croll Interest in the application of capillary origami has been expanding to many different areas of science and technology. However, insight into the basic physics of the process behind how a thin film is pulled to cover a droplet of fluid is still lacking. For example, the role of the substrate is largely ignored, but can easily arrest the wrapping process. The process can also be stopped by the friction and jamming which occurs due to self contact. Our work seeks to further the basic understanding with a one-dimensional experiment that both avoids bot self contact and uncontrolled substrate interactions. Specifically, we create a long, flat triple line on a film which rests on a fluid bath (modeled as a Winkler foundation). The capillary force acts on the film in a one-dimensional manner, pulling perpendicular to the triple line, without creating wrinkles or folds in the floating film. The experiment allows the system to reach an equilibrium between the capillary forces, the bending of the film, and the displacement of the substrate. A model of the system allows the further characterization of the effects of each of these forces on the shape of the bend produced in the supported film. |
Monday, March 5, 2018 3:54PM - 4:06PM |
C53.00008: Using multiphase microfluidics and pore-network modeling for fabrication of tissue regeneration scaffolds Hamed Haddadi, Dino Di Carlo Packings of injectable hydrogel particles provide a porous scaffold for tissue regeneration in which the interconnected network of micro-pores enables accelerated regrowth of the tissue. In this work, we propose a framework for fabrication of porous scaffolds using microfluidic droplet generators and pore-network modeling. We utilize microfluidic droplet generators in jetting regime for high-throughput fabrication of the scaffold building blocks, i.e the spherical microgels. After packing the hydrogel particles in a three-dimensional porous scaffold, we characterize the architecture of the pore network using the Maximal-Ball modeling. The extracted features of the pore network such as the pore size distribution and the pore connectivity are then related to the regrowth rate of human bone-marrow mesenchymal stem cells. The insight gained by comparing the cell growth rate and characteristics of the pore network is used as a feedback to modulate the size of the microgel particles in the microfluidic droplet generator. |
Monday, March 5, 2018 4:06PM - 4:18PM |
C53.00009: In situ visualization and mechanical study of a transparent filled rubber Zach Gault, Zsolt Terdik, Joerg Werner, Frans Spaepen, David Weitz Filled rubbers are composite materials containing two interpenetrating phases: crosslinked elastomers, and a ‘filler’ consisting of colloidal particle aggregates. Above a critical volume fraction, the colloidal aggregates form a system-spanning subnetwork that reinforces the elastomer network and introduces a new energy loss mechanism at low strains of only 1-5%. This loss mechanism, known as the Payne Effect, is one of the mechanical hallmarks of filled rubbers and is a major contributor to rolling friction in tires. |
Monday, March 5, 2018 4:18PM - 4:30PM |
C53.00010: Universal Geometry Controls the Mechanics of 2D and 3D Models for Dense Biological Tissues Matthias Merkel, M Manning Understanding how mechanical tissue properties emerge from cellular behavior is vital for understanding the mechanisms that guide embryonic development, cancer growth, and wound healing. To study universality of mechanical properties in dense tissues, we turn to vertex models that represent biological tissues as disordered polygonal networks (polyhedral networks in 3D). Recently, a new type of rigidity transition was discovered in a family of vertex models for 2D and 3D biological tissues, controlled by a minimal average surface (perimeter in 2D) of dense disordered cellular packings. Here, we show that not only the onset of rigidity, but also the properties of vertex models away from the transition point can be understood based on the behavior of this minimal surface. In particular, we show that universal relations exist between minimal average cell surface and the fluctuations in cell surface and volume, and these relations exactly predict the behavior of both shear and bulk moduli. Our work demonstrates how universal geometrical properties of a disordered material precisely control its mechanical behavior. |
Monday, March 5, 2018 4:30PM - 4:42PM |
C53.00011: Topology and fracture of model polymer networks Tetsuo Yamaguchi Toughening of network polymers like rubbers or gels is one of the most important problems in polymer science. While novel types of tough gels have been developed in the last decade, the toughening mechanism is not so clear: most researchers pay much attention to chain length heterogeneity, but little attention to other aspects. In this study, we focus on network topology, which is believed to be essential in complex network. We created macroscopic polymer models made of rubber strings and connecters, and performed fracture experiments of such model polymers with different topological structures. We found that periodic but systematic modifications in local coodination number with keeping the constant mean number (4, in 2D) exhibited great improvement in toughness compared with regular square lattices. In our talk, we will explain the details of our experiments and discuss the results by comparing with numerical simulations and theory. |
Monday, March 5, 2018 4:42PM - 4:54PM |
C53.00012: On the Origin of Spatial Stress Correlations in Disordered Media Robbie Rens, Edan Lerner It has been recently shown1,2 that coarse-grained stress fields in amorphous media exhibit long range spatial correlations. It has been proposed3 that these correlations stem from the nature of the dynamical processes that occur during the formation of these systems. Using numerical simulations of simple lattice-based models we show that the minimal ingredients for the emergence of stress correlations are mechanical equilibrium and some form of disorder, and therefore stress correlations are not a consequence of dynamical processes. In addition, we demonstrate that any arbitrarily small degree of disorder leads to the emergence of stress correlations, and that positional disorder is not a necessary ingredient for their emergence. Finally, we introduce a lattice model in which the functional form of the spatial decay of stress correlations can be exactly derived. |
Monday, March 5, 2018 4:54PM - 5:06PM |
C53.00013: Anomalous normal stress controlled by marginal stability in fiber networks Jordan Shivers, Jingchen Feng, Abhinav Sharma, Fred MacKintosh As first identified by Poynting, typical elastic solids exhibit axial extension under torsion. Along with related normal stress effects such as rod climbing of non-Newtonian fluids, this depends on the first normal stress difference N1, which is of fundamental importance for a variety of nonlinear deformation and flow phenomena, especially in soft matter. This stress difference is almost always positive for elastic solids and viscoelastic polymer materials. Recent work has shown that biopolymer networks can exhibit negative normal stress, but whether N1 itself can be negative in these networks has remained an open question. We demonstrate that lattice-based 2D and 3D fiber network models, as well as off-lattice 2D networks, can indeed exhibit an anomalous negative N1. We also show that this anomaly becomes most pronounced near a critical point of marginal stability, suggesting the importance of critical fluctuations in driving the change of sign in N1. Finally, we present a phase diagram indicating regimes of anomalous normal stress as a function of strain, network connectivity, and disorder. |
Monday, March 5, 2018 5:06PM - 5:18PM |
C53.00014: Jamming of soft disks within lattices of pinned particles Prairie Wentworth-Nice, Amy Graves Simulations are used to find the minimum energy configuration of soft, bidisperse disks in the presence of fixed “pins” arranged in a lattice. The presence of the lattice leads to the expected shift of the jamming threshold to lower volume fractions. Structural properties of the system both above and below the jamming threshold are calculated as a function of the pin density and lattice constant. |
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