Active wetting of epithelial tissues

Development, regeneration, and cancer involve drastic transitions in tissue morphology. In analogy with the behavior of inert fluids, some of these transitions have been interpreted as wetting transitions. The validity and scope of this analogy are unclear, however, because the active cellular forces that drive tissue wetting have been neither measured nor theoretically accounted for. We show that the transition between two-dimensional epithelial monolayers and three-dimensional spheroidal cell aggregates can be understood as an active wetting transition whose physics differs fundamentally from that of passive wetting phenomena. By combining an active polar fluid model with measurements of physical forces as a function of tissue size, contractility, cell-cell and cell-substrate adhesion, and substrate stiffness, we show that the wetting transition results from the competition between active traction forces and contractile intercellular stresses. This competition defines a new intrinsic length scale of active polar fluids that gives rise to a critical size for the wetting transition: Tissues larger than the critical size wet the substrate whereas smaller tissues dewet — a striking feature that has no counterpart in classical wetting. Finally, we show that active fluctuations of the tissue shape are dynamically amplified during the dewetting process. Overall, we conclude that tissue spreading constitutes a prominent example of active wetting — a novel physical scenario that may explain morphological transitions during tissue morphogenesis and tumor progression.

C. Pérez-González*, R.Alert*, C. Blanch-Mercader, M. Gómez-González, T. Kolodziej, E. Bazellieres, J. Casademunt*, and X. Trepat*. Active wetting of epithelial tissues. Nat. Phys. (2018)