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 M09: Emerging Trends in Soft Microscale Mechanics IFocus
|
Hide Abstracts |
Sponsoring Units: DSOFT Chair: Rae Robertson-Anderson, University San Diego Room: Room 132 |
Wednesday, March 8, 2023 8:00AM - 8:36AM |
M09.00001: Cell-Matrix Elastocapillary Interactions Drive Pressure-based Wetting of Cell Aggregates Invited Speaker: Michael P Murrell Cell-matrix interfacial energies and the energies of matrix deformations may be comparable on cellular length-scales,yet how capillary effects influence tissue shape and motion are unknown.In this work, we induce wetting (spreading and migration) of cell aggregates, as models of active droplets onto adhesive substrates of varying elasticity and correlate the dynamics of wetting to the balance of interfacial tensions. Upon wetting rigid substrates,cell-substrate tension drives outward expansion of the monolayer. By contrast, upon wetting compliant substrates, cell substrate tension is attenuated and aggregate capillary forces contribute to internal pressures that drive expansion.Thus, we show by experiments, data-driven modelingand computational simulations that myosin-driven'active elasto-capillary' effects enable adaptation of wetting mechanisms to substrate rigidity and introduce a novel, pressure-based mechanism for guiding collective cell motion. |
Wednesday, March 8, 2023 8:36AM - 8:48AM |
M09.00002: Active restructuring of kinesin-driven cytoskeletal composites with hydrogel inclusions Maya Hendija
|
Wednesday, March 8, 2023 8:48AM - 9:00AM |
M09.00003: Engineered Composites of Actin Filaments, Microtubules, and Associated Motor Proteins Lauren Melcher, Michael J Rust, Jennifer L Ross, Megan T Valentine, Rae M Robertson-Anderson, Moumita Das The cytoskeleton plays a key role in cellular force generation, shape change, and movement. Characterizing the physics of this dynamic structure is critical to understanding cell mechanobiology and functions. The interactions between the two main biopolymers that constitute the cytoskeleton, actin and microtubules, and the associated molecular motors myosin and kinesin are essential to cytoskeletal properties, but the mechanisms of their interactions are not easily understood. While actin systems and microtubule systems have been studies extensively, the material properties of their composites are less well-understood. We have developed a 3D bead-chain model of actin and microtubules without and with motors. We measure collective properties such as network acceleration, contraction speeds, and spatial correlations to provide insights into the emergent structure patterns and dynamics of this composite network. Our results may provide a broader understanding of the actin-microtubule interplay and how various motor proteins and crosslinkers impact the spatial organization and response to mechanical forces. |
Wednesday, March 8, 2023 9:00AM - 9:12AM |
M09.00004: Globally ordered states in the collective motions of self-propelled, semi-flexible, penetrable filaments. Madhuvanthi Athani, Daniel A Beller Gliding assays, in which cytoskeletal filaments translate over a substrate containing motor proteins, offer an experimental model system for studying the collective motions of self-propelled, anisotropic units. A wealth of active phases has been reported, characterized by orientational order that may be local or global, polar or nematic (apolar), and involving significant bending and crossovers when filaments collide. To elucidate the connection between these macroscopic and microscopic observations, we use Brownian dynamics simulations to study the collective motions of semi-flexible filaments that self-propel with a constant force along the local tangent direction. Crossovers are modeled with a finite energetic penalty for overlap. We focus on a high-density, high-penetrability regime where global orientational order emerges. Our results suggest that a globally ordered active nematic (apolar) state is transient, and the systems' steady state is instead a globally ordered active polar state. We find that the time required to saturate the global polar order increases with increasing stiffness of the active filaments. |
Wednesday, March 8, 2023 9:12AM - 9:24AM |
M09.00005: Nonlinear Mechanics and Stress Propagation in Out-of-Equilibrium Cytoskeleton Composites Daisy H Achiriloaie, Kit K Bennett, Mehrzad Sasanpour, Karthik Peddireddy, Michael J Rust, Moumita Das, Megan T Valentine, Janet Y Sheung, Jennifer L Ross, Ryan J McGorty, Rae M Robertson-Anderson The cytoskeleton is a system of interest to materials researchers because it is able to tune its material properties in response to its environment in a controlled way in part due to active reconfiguration of its constituents by ATP-consuming motor proteins. While methods for generating in vitro motor-driven composites of cytoskeleton polymers and measuring their dynamics have been established, advances in understanding of how motor activity affects mechanical properties of in vitro composites have been limited due to violation of the steady-state requirement of the generalized Stokes-Einstein relationship. We circumvent GSER by performing optical tweezers microrheology experiments on a set of kinesin-driven actin-microtubule composites carefully tuned to exhibit quasi-steady-state dynamics on the timescale of our measurements. We measure the nonlinear force response of active composites subject to cyclic straining to characterize how motor-driven restructuring alters the composite elasticity, stiffness, and length scale-dependent mechanics of the composites. We uncover a strain-rate dependent transition from dissipative to stiffening force response at mesoscopic lengthscales, and a non-monotonic dependence of stiffness and stress propagation on kinesin concentration. |
Wednesday, March 8, 2023 9:24AM - 9:36AM |
M09.00006: Nonlinear local straining leads to non-equilibrium deformation fields and dynamics of motor-driven cytoskeleton composites Mehrzad Sasanpour, Daisy H. Achiriloaie, Maya Hendija, Karthik R. Pedidireddy, Ryan J. McGorty, Rae M. Robertson Anderson
|
Wednesday, March 8, 2023 9:36AM - 9:48AM |
M09.00007: Structural rearrangement and slow dynamics near the onset of rigidity Jordan L Shivers, Saamiya Syed, Abhinav Sharma, Fred C MacKintosh A wide variety of amorphous soft materials, such colloidal suspensions and crosslinked biopolymer networks, consist of a bulk fluid phase containing many microscopic immersed solid components. These materials generally develop macroscopic rigidity at a critical value of some system-specific control parameter. For suspensions, the relevant control parameter is the particle volume fraction; for networks, it can be the average connectivity or the magnitude of applied strain. Close to the transition point, these systems share a tendency to display striking rheological signatures of critical slowing down. We show that this slowing is quantitatively controlled by nonaffine (heterogeneous) structural rearrangements that, like critical fluctuations in other systems, grow in magnitude and exhibit a diverging correlation length as the critical point is approached. Near the onset or loss of rigidity, dissipation-limiting rearrangements dominate the macroscopic viscoelastic response, giving rise to diverging relaxation times and power-law rheology. Here, we describe the quantitative relationship between nonaffine rearrangements and excess viscosity in fluid-immersed amorphous materials, and we verify this relationship in rheological simulations of crosslinked networks and dense suspensions. |
Wednesday, March 8, 2023 9:48AM - 10:00AM |
M09.00008: Circadian Clock Proteins Program Time-Dependent Materials Gregor Leech, Michelle Chiu, Maya Nugent, Lauren Melcher, Jennifer L Ross, Moumita Das, Michael J Rust, Rae M Robertson-Anderson Cyanobacteria rely on a circadian oscillator system of proteins, KaiA, KaiB and KaiC, to regulate a variety of cellular processes. KaiA and KaiB proteins alternately bind to KaiC, resulting in the cyclical assembly and disassembly of KaiC-KaiB complexes powered by ATP phosphorylation. By biotinylating KaiB monomers, we repurpose the KaiC-KaiB complexes to crosslink microscopic constituents of materials with unique time-dependent patterns. We incorporate these 'circadian crosslinkers' into suspensions of hydrogel microspheres and biopolymer networks to drive time-dependent structural changes mediate by the time-dependent formation and disassembly of KaiB-KaiC complexes. We use fluorescence microscopy, image analysis and biochemical assays to show that the rate, efficacy and oscillatory signature of material crosslinking can be tuned by altering the phosphorylation state of KaiC. Moreover, we demonstrate the versatility of circadian crosslinkers to confer autonomous changes in the properties of diverse material platforms from abiotic hydrogels and colloids to cytoskeletal composites. We anticipate the broad use of circadian crosslinkers for developing self-directed, programmable, and reconfigurable materials for applications from smart exosuits to self-repairing infrastructure to time-released drug delivery and filtration. |
Wednesday, March 8, 2023 10:00AM - 10:12AM |
M09.00009: Rheology and shear banding behavior of soft hydrogels packings in the quasistatic flow regime Zohreh Farmani, Joshua A Dijksman, Jing Wang, Ralf Stannarius, Cindy Lübeck, Oliver Speck, Nazanin Ghods, Stefan Radl The flow of granular materials is strongly affected by boundaries and thus the overall flow geometry. Granular flow can be either concentrated in narrow zones or in broad shear bands. To understand the microscopic origin of such heterogeneous flow behaviour, it is important to use a boundary-driven flow geometry in which shear bands can be well characterized. A standard setup for steady-state slow flow experiments is the split-bottom geometry with a free surface. Shear zones in such a shear cell are wide and can be well captured by an empirical non-local flow formalism. One question is how the local pressure and particle properties affect the observed shear zones and the dissipative processes inside the shear zones. We investigate here how shear bands emerge from soft, low-frictional spherical grains whose interactions and gravitational stress gradients can be tuned. |
Wednesday, March 8, 2023 10:12AM - 10:24AM |
M09.00010: Optimum viscosity reduction by cruising in dense suspensions. Pappu Acharya Dense suspensions tend to shear jam at large packing fractions. However, it has recently been shown that various oscillation |
Wednesday, March 8, 2023 10:24AM - 10:36AM |
M09.00011: Dense suspension rheology beyond simple shear Michael R van der Naald, Heinrich M Jaeger
|
Wednesday, March 8, 2023 10:36AM - 10:48AM |
M09.00012: Uncovering distinct contributions to the stress relaxation in soft solids H. A Vinutha, Manon Marchand, Vishwas Vasisht, Marco Caggioni, Emanuela Del Gado, Veronique Trappe In yield stress fluids, such as jammed suspensions of soft particles, the rate-dependent rheology is due to microscopic processes building up stress anisotropies. To investigate these processes we perform flow cessation simulations and experiments at various points along the flow curve. We combine experimental rheological tests with the analysis of microscopic stresses, structure, and particle displacements from simulations for different solvent viscosity and sample preparation protocols. Our study reveals a sequence of stress relaxation mechanisms: the first is associated with the elastic motion of particles, which relaxes the microscopic stresses accumulated along the compressive direction under flow, and the second is associated with a more collective reorganization of the particle packing. Our results show how these mechanisms for stress relaxation can emerge from the yielding of soft solid materials. |
Wednesday, March 8, 2023 10:48AM - 11:00AM |
M09.00013: Active microrheology of lyotropic chromonic liquid crystals using optical tweezers Beatrice E Lunsford-Poe, Shuang Zhou, Rui Zhang, Zeyang Mou We investigate the rheological behavior of lyotropic chromonic liquid crystals in the nematic phase by moving a microparticle and directly measure the force acting on it using laser tweezers. Two liquid crystal materials, sunset yellow (SSY) and disodium cromoglycate (DSCG), show distinct behavior when the particle is dragged along the director field under constant velocities. In SSY, the particle motion does not distort the director, and the drag force rapidly relaxes to zero after the particle stops, similar to an isotropic medium. In contrast, in DSCG, particle motion distorts the director field in front of it, and the relaxation is 10 times slower. When the particle is moved perpendicular to the director, both liquid crystals show strong director deformation behind the particle and slow force relaxation after particle stops. By oscillating the particle at different frequencies, we measure the storage and loss moduli, G’ and G” respectively, of these materials. G’ measured along the director of SSY is nearly zero at low frequencies, consistent with the dragging experiments. G’ is non-zero and increases with the frequency in all other combinations. To shed light on the observations, continuum simulations accounting for disparate elastic constants and tumbling character of the nematic materials are compared to the experimental data. We discuss our current understanding of the unknown nematodynamic mechanism behind this odd rheological behavior. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700