Emergence of hexanematic order in a growing confluent cell monolayer.

Collective migration of epithelial layers underlies processes ranging from wound healing to cancer invasion. A defining yet challenging feature is the emergence of distinct cell morphologies within a single migrating confluent sheet, with larger, elongated cells at the active boundary and smaller, hexatically ordered cells in the bulk. Here, we develop a stochastic particle-Voronoi framework that captures this hexanematic organization without prescribing target geometries and distinct cell types. We show that boundary-driven collective motion generates an outward velocity gradient. This gradient, coupled to a density and velocity-dependent division rule, produces peripheral cells that are larger, more elongated, and more defect-prone, while bulk cells remain smaller, isotropic, and hexagonally packed. These results show how minimal, non-equilibrium mechanical interactions give rise to emergent, self-organized tissue-scale patterning during collective migration.