Fig. 4. Factors influencing the duration of linear monolayer expansion in wound healing. (A) Duration of linear expansion varies with monolayer depth and division. All curves in this panel are derived from simulations with cells carrying 4 µm sensing and 4 µm division radii. Without division, the duration of the collective phase increases with increased monolayer depth (the distance from the wound edge to the back wall of the simulation). Monolayer depths are noted in the figure. The thin dashed curve repeats the 1200 µm simulation with cell division turned on. In this case the healing curve never becomes nonlinear. We term the transition to non-linearity `breaking'. (B) Duration of linear expansion also depends on sensing radius. Simulations employed a 600 µm monolayer without division and a 2, 4 or 9 µm sensing radius. As in panel A, the healing curves break owing to the limited capacity of the monolayer for expansion, but the duration of linear expansion increases with the increased sensing radius. Division radii are not specified for the breaking curves because division does not occur and so the value is meaningless in simulations. (C,D) Breaking occurs with division if the sensing radius is smaller than the division radius. All simulation in panels C and D include division. By either holding the sensing radius constant at 2 µm and lowering the division radius (panel C), or holding the division radius constant at 9 µm and increasing the sensing radius (panel D) we see that breaking occurs when the sensing radius is smaller than the division radius. In these cases, inhibition of division is not relieved before cells crawl out of the range over which they influence each other's movements.