Dr. Sohan Kale is currently a postdoctoral fellow at LaCàN in the ‘Mechanics of soft and living interfaces’ research team led by Prof. Marino Arroyo. He received his M.S. and Ph.D. in Mechanical Engineering at University of Illinois at Urbana-Champaign. His doctoral research revolved around understanding structure-property relations in mechanics, transport, and breakdown properties of disordered materials. His current research is broadly about epithelial tissue mechanobiology relevant in physiology, diseases, and morphogenesis. His overall research interests include modeling emergent active material properties and collective behaviors at and across the intersection of biology and engineering. He will join the Department of Mechanical Engineering at Virginia Tech as an Assistant Professor from August 2019.

Epithelial tissues are cohesive cellular sheets of adherent cells that line organs surfaces and cavities in our bodies. These bio-interfaces act as physical barriers against pathogens and regulate chemical transport while compartmentalizing the body into functional units. Epithelial mechanics is at the core of epithelial functionality. It involves maintaining mechanical integrity in a dynamic environment involving loading of varied magnitude at a wide range of loading rates and formation of functional 3D epithelial structures under the action such active or passive forces during morphogenesis. At intermediate timescales of  seconds to minutes, epithelial mechanics is governed by the architecture and dynamics of cytoskeletal structures, especially by  the active-viscoelastic rheology of the actomyosin cortex. Even in this seemingly simple regime with frozen junctional network, a rich phenomenology of epithelial behaviors governed by cortical dynamics has been discovered through several recent in vitro experiments. Yet, such a connection between cortical rheology and theoretical tissue-scale models of epithelia has been lacking. For instance, in vertex models of epithelia, a phenomenologically motivated work function governing the vertex dynamics often lacks a direct connection to the dynamic subcellular processes. We address this gap through a formulation based on Onsager’s variational principle which allows us to coarse-grain active-gel models of the cortex to tissue- scale vertex models. The tissue-scale rheology naturally emerges from the coupling between cell shapes and activity, viscoelasticity, and turnover of the cortex. This modeling approach provides a unifying framework to capture epithelial phenomenologies at different loading rates, including ’reinforcement’ and ’fluidization’ responses following sudden stretch and unstretch, solid and complex-fluid creep responses, transient flattening and stable folding of compression-induced folds in suspended epithelial sheets, pulsatile cellular oscillations, and active-superelasticity. While encapsulating these epithelial phenomenologies, the formulation also provides a common subcellular origin for seemingly disconnected tissue-scale behaviors