2018 Maria Goeppert Mayer Award Talk: Surface tension is weird in confluent biological tissues

Many tissues in your body are composed of tightly packed, or confluent, cells. The mechanical properties and dynamical behavior of these "materials" help govern important processes such as embryonic development, wound healing, and cancer progression. Happily, models for these tissues also exhibit rich and unexpected physics. In this talk, I will focus on “tissue surface tension” which describes interfaces between two tissue types and may help govern biologically relevant patterning such as cell sorting and tissue compartmentalization. We study the properties of a simple model for confluent tissues with “heterotypic” contacts, where unlike cells alter the mechanics of their shared interface. When probed by global mechanical measurements, interfaces between two tissue types behave just as predicted from equilibrium statistical mechanics, but the interfaces are orders of magnitude sharper than expected from standard capillary wave arguments. We show that this sharpness is a special feature generated by the topological nature of the cell-cell interactions. This work has interesting implications for interactions between jamming and tissue surface tension (e.g. “biological elastocapillarity”) and boundaries in other systems, like bird flocks, that may have topological interactions.