Figure 1.

Tractions do not align with local cellular motions. (a) Phase-contrast images of a confined cell monolayer. Time zero corresponds to the first image collected. (b and c) The radial components of velocity (b) and traction (c) are uncorrelated with one another. At some time points (e.g., 160 min), the Pearson’s correlation coefficient, R, is positive, and at other time points (e.g., 400 min) it is negative. (d) The kymograph shows the radial velocity as a function of position and time. Red and blue bands indicate oscillating outward and inward motion. (e) Kymograph of radial traction showing that cells at the perimeter apply tractions that point inward, whereas cells within the bulk apply tractions that oscillate between inward and outward. (f) Histogram of the angle between the velocity and traction vectors. Each gray line shows a single point in time for the cell island; the blue line shows all points in time. To see this figure in color, go online.