Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Z08: Fluid and Elasticity in BiomechanicsFocus Recordings Available
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Sponsoring Units: GSNP DSOFT Chair: Suri Vaikuntanathan, University of Chicago Room: McCormick Place W-179B |
Friday, March 18, 2022 11:30AM - 12:06PM |
Z08.00001: Rapid Actuation in Plants: Hydraulics or Mechanics? Invited Speaker: Yoel Forterre The Venus flytrap carnivorous plant rapidly snaps in about 100 ms using a snap-buckling instability of its shell-shaped trap. While this dynamic is well understood at the macroscopic level, the internal motor used by the plant to trigger this closure and cross the instability threshold remains unknown. Here we investigate the physical origin of this "active" actuation at both the macroscopic and microscopic levels. We first unveil the active dynamics by disentangling the buckling instability in cut or clamped traps. We show that the time scale of this dynamics is too fast to result from water transport through the trap thickness, as deduced from cell pressure probe measurements and macroscopic swelling experiments. We then study the mechanical properties of the epidermal tissue before and after triggering using nanoindentation coupled with casting methods and numerical modeling. Our work shows that rapid movements in plants can occur through a rapid change in cell wall stiffness, in a tissue pre-stressed by the internal hydraulic pressure. |
Friday, March 18, 2022 12:06PM - 12:18PM |
Z08.00002: Multiscale mechanics of hydraulic actuation in plants Anja Geitmann, David Sleboda, Reza Sharif-Naeini Pulvinus organs are joint-like motor organs that power active leaf folding in many plants. To understand the underlying mechanical principles, we built a soft hydraulic actuator that mimics pulvinus structure and bending mechanics. Adding circumferential hoop reinforcements to the hydraulic "cells" made from soft silicone dramatically improved its bending performance, and we hypothesized that biological pulvinus organs may contain analogous reinforcements that guide tissue swelling during rapid turgor changes. To validate this in vivo, we used osmotic baths to swell live, isolated pulvinus organs and tissues and screened for nonuniform changes in their 3D shape. Organs displayed strongly anisotropic swelling behavior at all hierarchical scales studied, indicating that structural specializations control turgor-induced shape changes at multiple spatial scales. Specialized cell wall and epidermis morphologies revealed by electron microscopy support this interpretation. Our findings provide insight into plant motor strategies, underscore the hierarchical, emergent nature of biomechanical systems, and highlight design principles that can inform the development of biologically inspired soft actuators. |
Friday, March 18, 2022 12:18PM - 12:30PM |
Z08.00003: Insect wing deployment Simon Hadjaje, Raphael Clement, Marie-Julie Dalbe, Ignacio Andrade-Silva, Joel Marthelot During its final transformation to morph into its adult form, just after hatching from its pupal case, an insect deploys its wings within minutes. The wings unfold rapidly from a wrinkled compact structure to a plane that subsequently solidifies to generate rigidity. We study wing expansion in Drosophila melanogaster. Expansion is regulated by increasing internal pressure and injecting a viscous liquid (hemolymph) into a folded deployable structure. We perform an experimental investigation of the morphological evolution of the wing during its deployment using Micro-CT imaging and optical microscopy. We then measure the tensile properties of the wing and build a minimal mechanical model that captures the nonlinear response of the origami-like folded structure. Finally, by combining scaling analysis, numerical simulations and experiments, we build a fundamental understanding of the wing’s expansion dynamics. |
Friday, March 18, 2022 12:30PM - 12:42PM |
Z08.00004: Spore dispersal by elasticity-vortex coupling from a leaf upon raindrop impact Zixuan Wu, Saikat Basu, Francisco Javier Beron-Vera, Mark E Sorrells, Sunghwan Jung Plant pathogens such as rust spores cause significant agricultural losses in crops. Past studies have shown that liberation of rust spores from a fixed leaf surface can result from vortices induced by impacting droplets. In this present study, we find that an elastic fluttering leaf creates a periodic shedding of counter-rotating vortex tubes that enhance particle mixing and spatial transport. The dispersal trajectories of shed particles can be described by the centrifugation/expulsion from Lagrangian coherent vortices and the further expulsion of the outer conveyer belts formed by deforming vortex dipoles. We used both Lagrangian-averaged vorticity deviation (LAVD) calculations and Finite Time Lyapunov Exponents (FTLE) ridges to identify such elliptical and hyperbolic Lagrangian coherent structures (LCS) respectively, which emerge over 2D flow maps on the transverse cross-section of the leaf vibration, while investigating particle advection properties owing to such oscillatory, unsteady flow patterns. The vorticities are extracted from smoke visualization data and matched with theoretical predictions based on 2D velocity potentials commonly adopted in oscillatory airfoil theory. Dispersal statistics were collected for the dynamical process. In summary, the study visually captures vortical airflow patterns hidden in natural leaf vibrations, applies dynamics concepts to study its dry advection properties, and compares experimental data on transport with theoretical estimates. |
Friday, March 18, 2022 12:42PM - 12:54PM |
Z08.00005: Deployable structures with core-shell balloons Trevor J Jones, Etienne Jambon-Puillet, Joel Marthelot, Pierre-Thomas Brun Nature is abound with structures undergoing extreme mechanics to accomplish complex physical tasks. When a larva undergoes metamorphosis and emerges, its wings expand tremendously to allow for adult insect flight. Inspired by the wing vein network, we build a model system consisting of core-shell tubes made from rubber inner tubes and wrinkled shells. We first study the mechanical response of a single core-shell balloon under increasing pressure. We characterize the in-plane expansion of the structure and study its correlation to the network geometry. Finally, we explore how to control global transformations by locally changing the stiffness via differential pressure applied in the system. |
Friday, March 18, 2022 12:54PM - 1:06PM |
Z08.00006: Liquid lassos: The defensive spitting of a termite soldier Elio J Challita, Prateek Sehgal, Saad Bhamla
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Friday, March 18, 2022 1:06PM - 1:18PM |
Z08.00007: Rapid Power and Energy Release from Elastic Network Polymers Halie Kim, Carolyn Du, Lucien Tsai, Martin Gonzalez, Andrew Chen, Mark Ilton Elastic biological springs are used by animals in their locomotion primarily for either power amplification or energy conservation. Power amplification, for motions like a frog jump or a mantis shrimp punch, is achieved with asymmetrical loading rates, where energy is slowly loaded into a biological spring and rapidly released. In contrast, energy-conserving movements such as running typically show symmetric loading/unloading patterns and involve a cyclic flow of energy to/from the spring. In this work, we use numerical simulations and experimental measurements to explore the roles of mechanical properties and loading rates in both of these elastically-driven movements. We focus on two metrics relevant to elastic movements in biology: maximum power output and resilience (the fraction of total stored elastic energy that is released as useful mechanical work). We find trade-offs between resilience and maximum power output/loading rate symmetry; energy loss increases with higher maximum power and asymmetry between the rates. These results suggest that spring material properties might contribute to biologically relevant trade-offs in animal locomotion. |
Friday, March 18, 2022 1:18PM - 1:30PM |
Z08.00008: Shape transformation of thin membrane induced by flow-controlled differential expansion Yongtian Luo, Eleni Katifori A thin, planar material irrigated by a flow network can be swollen locally by fluid transport in the network and subsequent fluid absorption, resulting in spatial variation of material properties and large-scale deformation like out-of-plane buckling. This flow-controlled mechanism of shape change is proposed for plant motions such as flower blooming and petal expansion. Facilitated by the xylem vascular system, petal segments are hydrated at different rates and swell unequally due to the uneven distribution of dynamically and spatially varying water content. Inspired by the process, we develop a network model that couples fluid movement (hydrodynamics) with membrane shape (mechanics) to computationally study the hydraulically induced differential swelling and buckling. We simulate the fluid dynamics using a spatially explicit model with local fluid-storage capacitance, and the mechanical network using a spring system on discretized surface, where bonds are adjusted quasi-statically by fluid distribution. We investigate the effects of network size, spatial hierarchical organization of major/minor veins, and hydraulic resistance/capacitance on shape transformation, which includes saddle shapes with negative Gaussian curvature. |
Friday, March 18, 2022 1:30PM - 1:42PM |
Z08.00009: Uniaxial Optical Mechano-Sensing with Upconversion Nanoparticles Shuang F Lim, Kory Green, Kai Huang, Gang Han, Hans D Hallen Cells respond to forces, and their quantification can potentially inform on the role of mechanics in cell development, differentiation, tissue repair and homeostasis. Other force sensitive processes include cancer cell metastasis, heart development in embryos driven by fluid forces, and individual cell response to tension by enhancing microtubule growth and connections. Development of current mechano-sensing approaches has not yielded many options, especially in directional force measurement. We present a sharpened fiber-based approach for uniaxial forces. An upconversion nanoparticle (UCNP) is mounted on the tip of the fiber and optically accessed through the fiber, which is manipulated as a probe. In UCNPs, the modification of the crystal field via mechanical forces result in changes in emission intensity, spectral shifts, upconversion luminescence (UCL) lifetime and ratiometric UCL response. We report on a discernably large peak shift of between 5-10 nm, and an apparent phase transition, with increasing amount of applied force in the micro Newton regime, in a single direction. Moreover, the peak shift is linear to the applied compression force. We investigate the influence of the UCNP force sensing process using Raman spectroscopy. |
Friday, March 18, 2022 1:42PM - 1:54PM |
Z08.00010: Creating bio-inspired tissue mimics of African elephant trunks' wrinkled and folded skin Andrew Schulz, Michael S Dimitriyev, Krishma Singal, Sophia Sordilla, Alexander Sahin, Colin Boyle, Claire Higgins, Elisabetta A Matsumoto, David L Hu Elephant trunks have been seen bulldozing trees, throwing lions several meters into the air, and picking up a tortilla chip without breaking. The skin on an elephant’s trunk is adapted to different functions on the dorsal and ventral side of the trunk much like a human hand. We seek to understand how elephants can utilize this skin to accomplish such a wide range of tasks all while maintaining strength and flexibility. In this study, we examined the morphology and compositional differences at both the micro and macro levels of the skin down to the individual collagen fiber in the dermis. Based on the observed collagen orientation, we were able to construct knitted mimics made of yarn, an important step to creating bio-inspired and programmable tissue mimics. We use an elasticity model describing deformations of skin creases to compare the mechanical differences from the tip to the root of the trunk. Comparing the model, mimics, and elephant skin enables us to improve bio-inspired mimic designs encompassing both the morphology and composition needed for materials to be strong and flexible. This research can potentially pave the groundwork for creating programmable tissue mimics that could be used for skin graphs and other types of tissue repair engineering. |
Friday, March 18, 2022 1:54PM - 2:06PM |
Z08.00011: Bacteria-inspired Bi-flagellated Soft Robot with Bundling and Tumbling Behavior Mohammad Khalid Jawed, Zhuonan Hao, Sangmin Lim Inspired by bacteria, we present a soft macroscopic robot with two flexible helical flagella that can control its swimming speed and direction at low Reynolds number with two scalar control inputs. A physics-based computational tool, inspired by algorithms used in animation by the computer graphics community, is developed to simulate the robot's motion. Since the discovery of bacterial locomotion, the motility of bacterial flagella has inspired robotic developments under viscous fluid. Our framework introduces a silicone-based design and fabrication strategy using off-the-shelf materials and a feedback control scheme for a constant speed actuation. We investigate two modes of locomotion: bundling and tumbling, which grant the bacteria directional stability and changeable orientation. This work uses the discrete differential geometry-based Discrete Elastic Rod (DER) method to model the flagella as Kirchhoff's elastic rods. DER is coupled with the Regularized Stokeslet Segments method for the hydrodynamics and a contact model due to Spillman and Teschner for a physically accurate simulation of the bi-flagellated soft robot. We present the emergent bundling and tumbling on our macroscopic bacterial robot and compare them with simulation results. As an advance in helical flagella, we propose a simple way of achieving non-reciprocal motion to overcome the constraint set by Scallop's theorem. We expect our framework to encourage more study on the mobility of microscopic flagella robots for the in-vivo operation such as drug delivery. |
Friday, March 18, 2022 2:06PM - 2:18PM |
Z08.00012: Resistive Force Theory vs. Slender Body Theory as Hydrodynamic Models in Simulation of Bacterial Flagella Mohammad Khalid Jawed, Sangmin Lim, Saptarshi Joshi, Charbel Habchi We present a comparative study on two hydrodynamic theories in the context of bacterial flagella at low Reynolds numbers. We combine the hydrodynamic models with Discrete Differential Geometry based high fidelity simulation, Discrete Elastic Rods, and explore large deformation, including buckling of uni-flagellated bacteria. The hydrodynamics models being compared are a resistive force theory (RFT) by Gray and Hancock and Regularized Stokeslet Segments (RSS), a type of slender body theory (SBT). RFTs are computationally efficient yet inaccurate; SBTs are accurate, but require a large dimension matrix inversion. We first compare the results obtained from RFT and RSS with experimental data available in the open literature. Furthermore, exploiting the advantages of both theories, we introduce a new RFT that is deduced from RSS. This work can lead to simulations that are fast (like RFT) and physically accurate (like RSS) for slender structures under low Reynolds flows. Consequently, we expect the application of our fast simulation to contribute to further understanding the propulsive mechanism under low Reynolds number flows for the development and control of biomimetic microbots. |
Friday, March 18, 2022 2:18PM - 2:30PM |
Z08.00013: Collagen remodeling in side-to-side bowel anastomoses Nhung Nguyen, Brian Fleischer, John Alverdy, Luka Pocivavsek Side-to-side anastomosis is a surgically constructed connection often performed after a diseased portion of bowel is removed. This operation causes a highly non-linear and non-native bowel geometry. Though the correlation between this geometry, internal pressure, and bowel tissue's mechanics is critical to prevent leakage, it is currently poorly understood. Here, we integrate finite element modeling (FEM) and experiments to study the remodeling process of collagens in the strength bearing layer, the submucosa, of bowels with side-to-side construction. The bowel is modeled as a composite structure of two muscular layers, and a cross-ply submucosa layer with two symmetric, aligned collagen families. A remodeling process developed due to the stress states in the bowel tissue is used to study changes in collagen's distribution. Simulations show that under internal pressure, the anastomosis opens and leads to remote stress-focusing locations. The stress state here resembles a biaxial state that causes collagens to remodel towards a more random distribution. This is consistent with experimental measurements of collagen fiber dispersions from anastomotic geometries which indicate that active remodeling process might occur to alleviate high stress induced by surgical operations. |
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