Formation of a Monolayer Observed in Self-Propelled Particle Simulation. A monolayer is obtained by simulating 100 proliferating cells with low cell-cell adhesion (parameter A = 0.02) and random cell polarity force with magnitude, |P| = 0.003. The simulation domain has periodic boundary conditions. Individual cells are shown in red, cells with one or more neighbors are shown in blue and contact-inhibited cells (those in a cluster with four or more neighbors) are shown in green.