| dc.description.abstract | Cell monolayer plays a crucial role in many biological processes including embryogenesis, tumorigenesis, and wound healing. It is a model coupled many-body active systems exhibiting collective motions through the interaction between the self-propelling and mutual couplings. Different from cobblestone-like epithelial cells which exhibit isotropic migrating directions, spindle-shaped fibroblasts migrate along their long axis and align with their neighbors, resulting in the formation of nematic domains and topological defects in cell monolayers. While the dynamics and structures of confluent cell monolayer are well studied, the collapsing processes of the cell-free areas (voids) in the densification of fibroblast monolayer before reaching the confluent state remain obscure.
In this work, we experimentally investigate the dynamical evolutions of the densifying spindle-shaped fibroblast monolayer before reaching the confluent state. It is found that, after cells form a connected network, voids are spontaneously formed with multiscale sizes, whose boundaries can be classified into convex and cusp-shaped concave boundaries. With increasing time, voids collapse due to the increasing cell density through cell proliferation. For large voids, cells at the cusp shaped concave boundary form extending bridges to split a large void into smaller voids. In smaller voids, the crowding induced by increasing cell density shortens cell lengths. It decreases the nematic cell alignment effect and allows cell topological rearrangements nearby the convex void boundaries, which in turn reduces the number of cells surrounding the void boundary and is the key for the final void closure. | en_US |