  Coordinated motion of cell monolayers during epithelial wound healing and
tissue morphogenesis involves mechanical stress generation. Here we propose a
model for the dynamics of epithelial expansion that couples mechanical
deformations in the tissue to contractile activity and polarization in the
cells. A new ingredient of our model is a feedback between local strain,
polarization and contractility that naturally yields a mechanism for
viscoelasticity and effective inertia in the cell monolayer. Using a
combination of analytical and numerical techniques, we demonstrate that our
model quantitatively reproduces many experimental findings [Nat. Phys. 8, 628
(2012)], including the build-up of intercellular stresses, and the existence of
traveling mechanical waves guiding the oscillatory monolayer expansion.
