Edges Impose Planar Alignment in Nematic Monolayers by Directing Cell Elongation and Migration

In confluent monolayers, elongated, adherent cells can exhibit hallmarks of active nematic systems. We show that edges impose planar anchoring at the periphery of nematic monolayers by changing cell shape and guiding migration. Despite being unconfined, isolated cells near edges elongate and preferentially migrate along the edge. By this mechanism, cells propagate nematic alignment into bulk monolayers. We find that adhesive boundaries continue to influence cell alignment and enhance migration even after cells have formed confluent monolayers. At corners, conflicting boundary cues drive topological defect formation in predictable patterns that depend on the local migration of cells at boundaries. By developing an understanding of how edges serve as anchoring conditions for nematic monolayers, we will gain control over the patterns that emerge in these tissues.