Figure 3. Stretch induces poroelastic flows and pressure beneath the cell cluster.

a, Illustration of the coupling between hydrogel stretching and swelling. Immediately after a rapid stretch or unstretch maneuver, the hydrogel volume is conserved. With time, the free energy balance in the hydrogel causes poroelastic flows that lead to progressive swelling or de-swelling of the hydrogel. b, Time evolution of PAA hydrogel thickness during and after stretch pulses of 1 s, 1 min, and 10 min (normalized to baseline levels). Stretch pulses were applied successively to each pattern, in a random order and spaced by >15 min (n=4 different patterns, error bars are SEM). c, Idealization of the gel underneath an epithelial cluster as a cylindrical region covered by a disc-like impermeable barrier (modeled epithelial clusters are 80 μm in diameter and the gel is 156 μm in thickness). This gel domain is modeled with the large deformation poroelastic theory (Supplementary Note 1). d, Axisymmetric finite element discretization of the system shown in (c). e, Solvent pressure and deformation of the gel during the stretch-unstretch maneuver in the presence of an impermeable disc-like barrier as predicted by the model. f, Solvent flow pattern near the edge of the epithelial cluster 6 s after stretch cessation. g, Solvent flow pattern near the edge of the epithelial cluster 6 s after stretch application.