Coordination of cell movements on soft and stiff substrates. (A) Depiction of normalized cell pair separation distance measurement. Measurements were made starting 8 h after wounding (t₀). See Materials and methods for details. (B) Mean normalized cell pair separation distance over a time course (t) of 5 h for all neighboring cell pairs within 160 µm from the wound edge. (inset) Mean cell pair separation distance at the end of the 5-h observation window for different substrate stiffness. (C) Mean normalized cell pair separation distance as a function of cell position from the wound edge for different substrate stiffness. (D) Depiction of velocity correlation measurement. The migrating cell sheet was divided into bands of 160 µm starting from the wound edge. (inset) For each band, the velocities (arrows) of all cells were correlated with those of other cells falling in a ring of radius R and width ΔR and then averaged. See Materials and methods for details. (E) Velocity correlation 12 h after wounding for cells 160 µm from the wound edge for different substrate stiffness. (F) Velocity correlation as a function of cell–cell distance R, for cells in different distance bands from the wound edge and at different time points after wounding. N = number of experiments. Each plot displays means of 150–3,000 cell measurements pooled from N experiments. All nonoverlapping error bars (95% SEM) are statistically significant with P < 0.05.