Fig. 2.

Cell spreading dynamics and collective migration modes are substrate rigidity-dependent. (a) Cell outlines, and (b) traction stress maps of the cell monolayer during aggregate spreading on a soft gel (E = 5, dimensionless units), at t = 50, 200, and 350 min. The pink shaded region indicates the contact area of the aggregate above the monolayer, at 90° contact angle. See Movies 1 and 2 for a time-lapse video. (c) Cell outlines, and (d) traction stress maps of cell monolayer spreading on a stiff gel (E = 30), at t = 50, 200, and 350 min. See Movies 3 and 4 for a time-lapse video. Scale bar represents 5 units of length.