Date(s) - 03/01/2013
Cell motion in tissues is heterogeneous in space and time. In developing, healthy, and diseased tissue, some cells move while other cells remain sedentary; some cells move in groups and other cells move as individuals. Cells also transition between these states throughout the life of an organism. Cell migration studies of single cells and of confluent monolayers help to elucidate the different dynamic states within tissues, but little is known about the physical properties of the cells as they transition between a sub-confluent, single-cell state, and a tightly packed, dense monolayer. In classical particulate systems, phase diagrams are constructed to explore how physical parameters change the state of a system, but there is no extant phase-diagram formalism for cell dynamics studies. Here we have studied cell dynamics over a large parameter space, including cell density, migration speed, and substrate stiffness. We have found a phase diagram comprising three different states of cell behavior: one uncondensed state, and two different condensed states. The transition between the uncondensed state to the low density condensed state shows clear changes in structure, but dynamical signatures of the transitions are weak. By contrast, in the transition between the low density condensed state and the high density condensed state, the dynamical signatures are strong but do not correlate strongly with structural changes. The cell dynamics phase diagram shares some characteristics with phase diagrams of classical particulate glass forming systems.