Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Z14: Rheology of Biological TissueInvited Live Streamed
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Sponsoring Units: DBIO Chair: Evelyn Tang, Rice University Room: McCormick Place W-183B |
Friday, March 18, 2022 11:30AM - 12:06PM |
Z14.00001: Shear-driven solidification and nonlinear elasticity in epithelial tissues Invited Speaker: Dapeng Bi Biological processes, from morphogenesis to tumor invasion, spontaneously generate shear stresses inside living tissue. The mechanisms that govern the transmission of mechanical forces in epithelia and the collective response of the tissue to bulk shear deformations remain, however, poorly understood. Using a minimal cell-based computational model, we investigate the constitutive relation of confluent tissues under simple shear deformation. We show that an initially undeformed fluid-like tissue acquires finite rigidity above a critical applied strain. This is akin to the shear-driven rigidity observed in other soft matter systems. Interestingly, shear-driven rigidity can be understood by a critical scaling analysis in the vicinity of the second order critical point that governs the liquid-solid transition of the undeformed system. We further show that a solid-like tissue responds linearly only to small strains and but then switches to a nonlinear response at larger stains, with substantial stiffening. Finally, we propose a mean-field formulation for cells under shear that offers a simple physical explanation of shear-driven rigidity and nonlinear response in a tissue. |
Friday, March 18, 2022 12:06PM - 12:42PM |
Z14.00002: Active T1 Transitions in Dynamic Tissues Invited Speaker: Frank Julicher A fundamental question in Biology is to understand the collective organisation of many cells during morphogenesis. Morphogenesis often results from the dynamic remodeling of tissues, which involves cell rearrangements, cell divisions and cell flows. Tissues are amorphous solids, where neighbour exchanges can relax local stresses and allow the material to flow. Such neighbor exchanges are associated with T1 transitions of the polygonal network that describes cell shapes. We use a vertex model for tissue mechanics and dynamics to study T1 rearrangements in anisotropic cellular networks. We consider two different physical realizations of the active anisotropic stresses: (i) anisotropic cell bond tension and (ii) anisotropic cell body stress. Interestingly, the two types of active stress lead to patterns of oriented T1 transitions that are different. We describe and explain these findings using cell based arguments and through the lens of a continuum description of the tissue as an anisotropic active material. We furthermore discuss the energetics of the tissue and express the energy balance in terms of tissue elastic energy, mechanical work, chemical work dur to active processes and heat. This allows us to define active T1 transitions that can perform mechanical work while consuming chemical energy. We apply these concepts to fly morphogenesis: the developing pupal wing and germ band extension in the embryo and show that in these systems different types of active T1 processes are at work. |
Friday, March 18, 2022 12:42PM - 1:18PM |
Z14.00003: Rigidity phase transitions in embryo development: from identification to function Invited Speaker: Nicoletta Petridou The interchange between fluid-like and solid-like tissue states is key for multicellular morphogenesis. Recent biophysical models have quantitatively predicted and experimentally verified tissue material phase transitions, setting tissue rigidity as a bona fide example of a cell collective. The next step is to understand the function of cell collectives in context, and specifically how they respond to- and feedback on- mechanical and biochemical stimuli. In this talk, I will present how rigidity percolation theory can identify in vivo rigidity phase transitions with high spatiotemporal precision during zebrafish morphogenesis. I will further discuss how we can expand this framework to explore the role of phase transitions in key embryogenic processes, such as cell fate acquisition and germ layer formation. |
Friday, March 18, 2022 1:18PM - 1:54PM |
Z14.00004: Simple animals stretch our physical understanding of cilia, sticky cells and tissue rheology Invited Speaker: Vivek Nagendra Prakash In animals, epithelial tissues mainly provide a barrier function, but these tissues are also subjected to extreme strains during daily activities such as locomotion. The mechanics of tissues and their adaptive response in these dynamic force landscapes is an area of active research. We complement this research by carrying out a multi-modal study of the locomotion in a simple yet highly dynamic marine animal, Trichoplax adhaerens, that lacks both muscles and neurons. We report the discovery of abrupt, bulk epithelial tissue fractures and healing induced by the organism’s own motility that cause dramatic shape changes and physiological asexual division. By developing a suite of quantitative experimental and numerical techniques, we demonstrate a force-driven ‘ductile-to-brittle’ transition in these tissues. |
Friday, March 18, 2022 1:54PM - 2:30PM |
Z14.00005: Collective Mechanical Signaling Through Cell-Cell Contacts Invited Speaker: Liam P Dow The coordinated movement of epithelial cells known as collective migration is a key feature of epithelia development and repair. Mechanical linker proteins between cells such as those interacting with the cadherins complex are critical in regulating collective migration, as intercellular forces on these proteins activate downstream signals influencing cell function. Unfortunately, the way in which local mechanical signals propagate through epithelia to influence collective cellular migration is not well understood. Therefore, our lab has developed a series of microfabricated tools and quantitative approaches to both apply and measure different modes of mechanical strain on epithelial cell-cell contacts to determine their impact on epithelial behavior. In vitro, we have recently demonstrated local mid-plane epithelia shear perturbation to induce specific modes of collective, global epithelial migration dependent on intact intercellular cadherin and actomyosin signaling. In our work we have conducted a single-cell level spatiotemporal analysis of how local mechanical shear propagates change in cell morphology throughout an epithelium. These results provide the framework for biophysical models of global epithelial migration patterns. Furthermore, we have combined micromanipulation tools with a linear micropatterned epithelial model to dissect the role of single cell level intercellular cues on cell migration. Ultimately, our work combines experimental and quantitative analytical approaches to uncover the intercellular mechanics governing epithelial cell migration. |
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