Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session L26: Mechanics of Cells and Tissues Across Scales V |
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Sponsoring Units: DBIO DSOFT GSNP DPOLY Chair: Nancy Forde, Simon Fraser University Room: 403 |
Wednesday, March 4, 2020 8:00AM - 8:12AM |
L26.00001: How does extracellular matrix rigidity affect the fluidity of an embedded spheroid? Amanda Parker, M Cristina Marchetti, M. Lisa Manning, J M Schwarz The extracellular matrix (ECM) that surrounds a tissue, such as a cancer spheroid, is known to regulate spheroid behavior, with stiffer ECM promoting invasion. Using a computational model, we explore how a simple mechanical interaction between a spheroid and its ECM promotes changes in the spheroid’s rigidity, morphology and the shapes of its constituent cells, as well as the ECM’s rigidity and structure. We model the spheroid using a vertex model and the ECM using a spring network model, with an additional term describing the interfacial tension between the spheroid and ECM. Both vertex and spring network models transition between rigid and floppy phases, depending on their respective tuning parameters (cell shape and spring rest length) and imposed strain. Therefore, we expect, and find, that by mechanically coupling the two systems, changes to the phase of one system can drive changes to the phase of the other. We identify two regimes of interest—one in which compression of the spheroid dominates and one in which stretching dominate. We find that isotropic compression promotes fluidity of tissue and preserves the relationship between cell shape and tissue phase, while stretching by the ECM results in rather different behavior. |
Wednesday, March 4, 2020 8:12AM - 8:24AM |
L26.00002: Self-organized vasculogenesis in 3D printed mixed cell populations Sarah Ellison, Thomas Angelini In the process of vasculogenesis during embryotic development, endothelial cells create blood vessel networks necessary for the survival and function of tissues. In tissue engineering, creating functional vasculature remains among the largest impediments to achieving healthy tissues. Deeper understanding of cell self-organization during vasculogensis could therefore have impacts in developmental biology and tissue engineering. To fabricate 3D multicellular systems of designed consistency, we 3D print structures made from mixtures of hepatocytes, endothelial cells, and extracellular matrix. These structures are fabricated directly in a 3D growth medium made from jammed microgels. By observing cellular spatial organization and testing biological markers, we investigate how endothelial cells and hepatocytes self-organize into co-continuous interpenetrating networks, resulting in vasculature and improved overall cellular function. Preliminary data and analysis will be presented. |
Wednesday, March 4, 2020 8:24AM - 8:36AM |
L26.00003: Interrogating collagen mechanics at the single-molecule level Nancy R. Forde Collagen is the fundamental structural protein in vertebrates, forming a variety of hierarchical material structures. In spite of its prevalence and mechanical importance in biology, its mechanics at the molecular level – where it possesses a unique triple-helical structure – are surprisingly controversial: its flexibility is unresolved, as is its response to stress. My research group has been investigating these properties through single-molecule experiments. To do so, we have developed imaging algorithms to use in atomic-force microscopy (AFM), developed a model for polymers with inherent curvature (the curved worm-like chain model - cWLC), and built an instrument for high-throughput single-molecule force spectroscopy, the mini-radio centrifuge force microscope (MR.CFM). I’ll describe what we have learned about collagen’s flexibility and stress response, how local sequence context matters, and how our work resolves some of the many contentious findings regarding collagen’s mechanics. |
Wednesday, March 4, 2020 8:36AM - 8:48AM |
L26.00004: Mechanical response of the vitreous gel in our eyes: Results from an inhomogeneous two-fluid model Pancy Lwin, Scott V Franklin, George Thurston, David Ross, Moumita Das The vitreous gel is a viscoelastic gel present between the eye lens and the retina. It is made up of a composite network of stiff collagen fibers and softer hyaluronic acid (HA) polymers, and water. Its mechanical properties are critical to proper functioning of the eye, and undergo changes with aging and disease. We study rheological properties of this gel by simulating it as a two-fluid model made of an inhomogeneous polymer network interacting with a fluid. Our results relate the time-varying mechanical response of the gel to the composition of the network, the material properties of the network and the fluid, and the strength of the coupling of between the network and the fluid. These results may provide insights into changes in mechanical-structure function properties of the vitreous gel in vitreous disorders. |
Wednesday, March 4, 2020 8:48AM - 9:00AM |
L26.00005: Kinetics of Cell Adhesion Through Biomimetic Glycocalyx Yu Jing, Shlomi Cohen, Jessica Faubel, Jennifer Curtis Giant polysaccharides grafted to the external cell surface interfere with receptor-ligand binding and can strain molecular bonds. This is relevant in cell-matrix interactions during cell migration as well as in cell-cell interactions, such as T-cell immune response. We introduce a biomimetic glycocalyx platform to investigate the kinetics of cell adhesion in the presence of sugar-rich interfaces. With this approach, we study the mechanisms by which cells penetrate the thick polymer brush-like interface and how this process depends on initial brush thickness. |
Wednesday, March 4, 2020 9:00AM - 9:12AM |
L26.00006: Length regulation of epithelial cell junctions Michael Staddon, Kate E Cavanaugh, Edwin M Munro, Margaret Gardel, Shiladitya Banerjee
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Wednesday, March 4, 2020 9:12AM - 9:24AM |
L26.00007: Fast Confined Dynamics in Lipid Bilayers Sudipta Gupta
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Wednesday, March 4, 2020 9:24AM - 9:36AM |
L26.00008: In vitro characterization and numerical simulations of red blood cell transmigration through splenic inter-endothelial slits Antoni Garcia de Herreros, Huijie Lu, Zhangli Peng, Juan C Del Alamo During their circulation through the spleen, red blood cells (RBCs) are forced to squeeze through gaps between endothelial cells that are ~8 times narrower than its diameter. The ensuing squeezing motion causes large RBC deformations that remove old and diseased cells from the circulation. There is limited data about the deformation and stress experienced by RBCs. To study the mechanics of RBC splenic filtration, we designed |
Wednesday, March 4, 2020 9:36AM - 9:48AM |
L26.00009: Nucleation and Formation of a Primary Clot in Insect Blood Probed by Magnetic Rotational Spectroscopy Konstantin Kornev, Pavel Aprelev, Peter Adler, Artis Brasovs Blood clotting at wound sites is critical for preventing blood loss and invasion by microorganisms in multicellular animals, especially small insects vulnerable to dehydration. The mechanistic reaction of the clot is the first step in providing scaffolding for the formation of new epithelial and cuticular tissue. The clot, therefore, requires special materials properties. We have developed and used nano-rheological magnetic rotational spectroscopy with nanorods to quantitatively study nucleation of cell aggregates that occurs within fractions of a second. Using larvae of Manduca sexta, we discovered that clot nucleation is a two-step process whereby cell aggregation is the time-limiting step followed by rigidification of the aggregate. Clot nucleation and transformation of viscous blood into a visco-elastic aggregate happens in a few minutes, which is hundreds of times faster than wound plugging and scab formation. This discovery sets a time scale for insect clotting phenomena, establishing a materials metric for the kinetics of biochemical reaction cascades. |
Wednesday, March 4, 2020 9:48AM - 10:00AM |
L26.00010: Microfluidic platform for label-free viability cell sorting Fatima Ezahra Chrit, Abhishek Raj, Nick Stone, Todd Sulchek, Alexander Alexeev Cell biomechanical properties often change in predictable ways with important cell phenotypes changes, such as cell loss of viability. We propose a biophysical approach for cell viability sensing, enumeration, and purification that is label-free and continuous. Using microfluidics, we show that we can separate viable cells from nonviable cells based on the difference in their stiffness with an enrichment factor of >5 and an overall recovery of 95%. The technology consists of a microchannel with diagonal ridges that direct cells along different paths in a manner dependent on cell biomechanical properties. As a result, the sorted viable and nonviable cells are collected at different microchannel outlets. To investigate the sorting process, we use a tracking algorithm that tracks cells moving through the microchannel. Sorting outcomes are correlated with the tracking metrics such as the cell deflection per ridge and the interaction time with ridges in the channel. The approach can be used for cell characterization and purification either in-line with cell bioreactors or after cell manufacture and prior to administration to improve outcomes. |
Wednesday, March 4, 2020 10:00AM - 10:12AM |
L26.00011: Simultaneous Measurement of Electrical and Mechanical Properties of Biological Cells Using a Tuning Fork-Coupled Conductive Probe Mark Schiller, Alexandra M Ivanov, Megi Maci, Eva K Pontrelli, Juan Merlo, Timothy Connolly, Michael Naughton AFM-style probes have commonly been used to measure mechanical properties of materials such as their Young’s Modulus. This technique has also been implemented to further explore biological cells1. Differentiation, pluripotency, and other attributes have been linked to certain mechanical properties of cells as well their membrane potential2,3,4. Simultaneous measurements of these quantities can help determine their inter-relation and inform on their relationship(s) with other properties. We have devised a conductive tip tuning fork probe, which is intended to simultaneously measure mechanical properties and membrane potential of a cell. We discuss fabrication and preliminary experimental results using conductive tip tuning forks to probe HeLa cells. |
Wednesday, March 4, 2020 10:12AM - 10:24AM |
L26.00012: Brain Mechanics Drive Cavitation and Fracture Response Carey Dougan, Sualyneth Galarza, Christopher Barney, yue zheng, Shengqiang Cai, Alfred J Crosby, Shelly Peyton Roughly 1.7 million cases of Traumatic Brain Injury occur in the U.S. every year. It has been suggested that impact injuries and non-impact injuries due to explosive blasts result in “cavitation-related damage.” This cavitation event is the formation of bubbles in the brain that can lead to fracture upon collapse. Therefore, it is essential to understand how brain mechanics contributes to the propagation of cavitation and fracture related damage in vivo. Needle-induced cavitation (NIC) is a useful technique to study localized deformation within brain tissue and how modulus and strain rate contribute to fracture. Utilizing the techniques of NIC and indentation we observe a significant correlation between modulus and strain rate. This strain rate dependency for NIC can result in visible fracture of specific brain regions of varying moduli at large strains. With the help of modeling, we use the NIC measurements to understand the fracture properties of brain tissue. By understanding the strain rate deformation of specific areas of the brain, we aim to gain further insight into how cavitation-related events lead to irreversible damage. |
Wednesday, March 4, 2020 10:24AM - 10:36AM |
L26.00013: Rheological properties of cellular aggregates formed by pilus mediated interactions Hui-Shun Kuan, Frank Julicher, Vasily Zaburdaev Aggregates of living cells are an example of active materials with unconventional material properties. The rheological properties of cellular aggregates can, therefore, be markedly different from those exhibited by passive soft systems. Motivated by colonies of Neisseria gonorrhoeae bacteria, we develop a continuum theory to study cellular aggregates formed by attractive pulis mediated intercellular interactions. We find that the formation of cellular aggregates is an active phase separation process and we discuss the activity-induced viscoelastic properties of such aggregates. By studying the behaviour of aggregates under oscillatory shear, we can link the loss and storage moduli of the aggregates to the dynamics of the active intercellular forces. Due to the turnover of pili, the aggregates show a liquid-like behaviour at large times and strong shear-thinning effect under the large amplitude oscillatory shear. Our theory provides an important insight on how pilus mediated intercellular forces in cellular aggregates govern their material properties which in the future could be tested experimentally. |
Wednesday, March 4, 2020 10:36AM - 10:48AM |
L26.00014: Optical tweezer application with Autofocusing Airy-Bessel beams Yi Liang, Yinxiao Xiang, Fan Shi We proposed a new autofocusing beams named autofocusing Airy-Bessel beams (AABB). Compared with traditional circular autofocusing beams (CAB), autofocusing Airy-Bessel beams exhibited a shorter autofocusing propagation distance and two times stronger peak intensity at the focusing point. We adopted this new kind of autofocusing beams as an optical tweezer to trap particles and red blood cells. This kind of optical tweezer presented a larger trapping stiffness, which corresponded a stronger trapping force as compared with conventional autofocusing beams. In other words, it could reduce the photodamage on sample especially some biological sample such as different kind of cells at realizing a same trapping. Generally, the trapping ability of this kind of optical tweezer was found to be proportion to the laser power. This new type of tweezer may find new applications in optical manipulation and biomedical research. |
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