MPIDS Colloquium: Collective dynamics in tissues and colonies

Cells typically do not live in isolation, but build tissues and colonies with a large number of their peers. These collective structures are often highly dynamic, especially during development. As the cells can move by self-propulsion and repeated growth and division cycles, the collective is in a far from equilibrium state. This state often breaks virtually all symmetries, and hence all conservation laws, of equilibrium physics. Nonetheless, the cells often form systems that can be characterized by thermodynamic-like quantities, like density and orientational order. We study the effect of the me-chanical interactions between the cells on their large-scale collective dynamics, resulting in motile-to-jamming transitions, order-to-disorder transitions, pattern formation, and the emergence of topo-logical defects. We find that even with very simple mechanical interactions, many of these effects can be captured, and used to both study developmental processes and eventually design cellular pat-terns.