A minimal model for structure, dynamics, and tension of monolayered cell colonies

Abstract

The motion of cells in tissues is an ubiquitous phenomenon. In particular, in monolayered cell colonies in vitro, pronounced collective behavior with swirl-like motion has been observed deep within a cell colony, while at the same time, the colony remains cohesive, with not a single cell escaping at the edge. Thus, the colony displays liquid-like properties inside, in coexistence with a cell-free “vacuum” outside. We propose an active Brownian particle model with attraction, in which the interaction potential has a broad minimum to give particles enough wiggling space to be collectively in the fluid state. We demonstrate that for moderate propulsion, this model can generate the fluid-vacuum coexistence described above. In addition, the combination of the fluid nature of the colony with cohesion leads to preferred orientation of the cell polarity, pointing outward, at the edge, which in turn gives rise to a tensile stress in the colony—as observed experimentally for epithelial sheets. For stronger propulsion, collective detachment of cell clusters is predicted. Further addition of an alignment preference of cell polarity and velocity direction results in enhanced coordinated, swirl-like motion, increased tensile stress and cell-cluster detachment.

Hydrodynamics of simple active liquids: the emergence of velocity correlations

“…Besides the appearance of spontaneous density inhomogeneities, recent experimental, theoretical and numerical investigations have shown the existence of spontaneous equal-time velocity correlations in active matter systems, an emergent collective phenomenon. This new property has been experimentally observed in different contexts, such as cell monolayers [13][14][15][16] and bacterial colonies [17][18][19][20]. Spontaneous velocity correlations represent a peculiar property of active matter systems and, thus, understanding the underlying physical mechanism could be an important advancement.…”

On the origins of order

“…The notion of fluidization of a solid-like multicellular collective is not at all new. [24][25][26][27][28][29][30] More recently it has become wellestablished that certain cases of fluidization of a multicellular collective can be cast into the interpretive context of a jammedto-unjammed transition. 8,[12][13][14]21,25,31,32 Moreover, to describe the wide range of material phases that a multicellular collective might find to be attainable while remaining consistent within the laws of physics, various jamming phase diagrams have been proposed including the one addressed in greater detail below.…”

Intrinsic structure perspective for MIPS interfaces in two-dimensional systems of active Brownian particles

“…[6][7][8] Depending on the nature of inter-particle interactions and of the particles' activity, the system forms different steady-state structures. On the one side, a dilute suspension of attractive ABPs is characterised by a distribution of dynamic clusters whenever the inter-particle attraction strength is sufficient to compete with the particles' activity, [6][7][8][9] without any phase separation taking place. Clustering is due to a balance between new particles joining already-formed clusters and large clusters breaking into smaller ones.…”