Paul Gunnar Dommersnes - Polar ordering in solid living matter

Recent experiments have shown that epithelial monolayers can behave as self-propelled solid elastic membranes, and that global directed motion (polar order) emerges through the hierarchical annihilation of contractile elastic vortices and their anti-vortices[1]. Polar ordering dynamics in fluid cell layers is often modelled by neighbour alignment (Vicsek or Vicsek like models), another model is collective flow-alignment (move in the direction of flow). Here I will discuss the differences and similarities of these two mechanisms in solids. Both can give rise to interacting elastic vortices , but one model is essentially linear, while the other is non-linear and exhibit a rich dynamics which likely is relevant to many types of biological cell layers in the solid state. [1] E. Lång, A. Lång, P. Blicher, T. Rognes, P.G. Dommersnes, S. O. Bøe, Topology-guided polar ordering of collective cell migration, Sci. Adv. (2024)