Physics Colloquium **POSTPONED**

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On small length-scales, the mechanics of soft materials may be dominated by their interfacial properties as opposed to their bulk properties.  These effects are described by equilibrium models of contact mechanics and elasto-capillarity.  In these models, interfacial energies and bulk material properties are held constant.  However, in biological materials, including living cells and tissues, these properties are not constant, but are ‘actively' regulated and driven far from thermodynamic equilibrium.  Likewise, the balance between interfacial and bulk properties in biological materials may depend upon a distance from equilibrium.  Here, we show that the growth, shape, and motion of biological tissues is determined by a regulated balance of interfacial and bulk material properties.  Further, we show that this regulation occurs at the molecular level, in the breaking of detailed balance by molecular interactions within the cell cytoskeleton which drives the system far from equilibrium.  Thus, a distance from equilibrium constrains the mechanical properties of the system, challenging widely utilized models of interfacial mechanics.  Further, these results provide basic energetic principles that govern the physical behaviors of cells and simple tissues.

Limited attendance in Feynman Lecture Hall, 201 E. Bridge to first 100 people. All attendees must show valid Caltech ID upon entry. Join via Zoom: https://caltech.zoom.us/j/89237465190. Meeting ID: 892 3746 5190