Topological defects in cell monolayers controlled by topography*

The organization of cells influences many key processes such as migration, cell-cell communication and morphogenesis. It is well known that some cells types have a naturally elongated shape and spontaneously align with their neighbors like nematic liquid crystals. However, cells have capabilities that liquid crystals do not have, such as the ability to divide and to change shape. This changes the types of configurations available to this active nematic system and, consequently, its response to confining boundaries. 

We induce topological defects and distortions in monolayers of fibroblasts using micro-patterned ridges with varying height, spacing and shape. This constitutes a useful platform to characterize the alignment and the organization of the fibroblasts. For example, we investigate the cell density inhomogeneities within the monolayers and their correlation with the defect locations. We hypothesize that the density difference is mainly not driven by collective cell migration, but by a different rate of cell division in the defects' proximity, and we test the hypothesis by suppressing cell migration using high ridges. Furthermore, we confine cells near defects with fractional topological charge using corners with edges and thus we characterize the cells' tendency to splay or bend near corners. Finally, we investigate the role of the cell-substrate interaction in suppressing or promoting collective cell motion.