Force-induced polarization drives outward expansion in epithelial monolayers

Epithelial cell layers are an active material that play a crucial role in development, wound healing and tissue homeostasis. The spreading of epithelial layers is driven by active traction forces generated by polarized, motile cells. But how do cells polarize? Inspired by experimental findings, we propose that cells in a tissue polarize away from tension, and we formulate a continuum model that accounts for force-induced cell polarization. We show that supracellular contractile tension allows cells at the edge of a cell layer to ‘feel’ free space and polarize outwards to drive spreading. Additionally, force-induced polarization gives rise to patterns of high and low cell density regions through an instability of the uniform unpolarized state. This instability can even lead to the self-rupture of a confluent cell layer, which breaks up into cell aggregates. Our work predicts the collective behaviors arising from the feedback between cell polarity and endogenous mechanical cues.