Modeling collective cell migration on substrates with topological defects

Collective movement, arrangement and proliferation of cell monolayers are important for wound healing and tissue development, and an example of active matter physics in biology. Recent experiments have highlighted the importance of liquid crystal order and topological defects within these layers, in particular suggesting that +1 defects have a role in organizing tissue morphogenesis. In this work we perform 2D active Monte Carlo simulations to investigate cell organization, motion and proliferation on a substrate guided with ridges that induce a +1 defect. This models experiments on fibroblasts from the Serra group, who found that cells align with the ridges, and that cells are denser and more isotropic toward the center of the defect. We model different cell types as self-propelled deformable ellipses that interact via a Gay-Berne potential. We propose two potential mechanisms that can lead to increased density at the defect core: first, collective spiraling motion driven by coherent migration, and second, the regulation of proliferation by cell area and aspect ratio. By observing individual cell movements and analyzing timescales of processes in experiments we argue that the proliferation mechanism is more compatible with experiments.