Statistical Correlations of Topological Defects in a Model Monolayer Confluent Tissue

There is a recent interest in studying confluent cells as active matter. The Active Vertex Model (AVM), which represents cells as Voronoi polygons, has been instrumental in elucidating various dynamical phenomena in confluent tissues, including solid-liquid phase transition as a function of cell motility and cell shape. On the other hand, treating confluent tissues as active nematic liquid crystals has provided valuable insights into the collective dynamics and stress distributions within tissues. However, how to reconcile the two views of point, and what role nematic order plays in Voronoi cells, remain unclear, which hinders our further understanding of such biological systems. To bridge this research gap, we employ the AVM to investigate the statistical correlations between lattice defects (cell shapes deviating from hexagons) and orientational defects. Our findings demonstrate that collective active fluctuations of cells can lead to extensile-like stresses and give rise to strong spatial and orientational correlations between lattice defects and +1/2 defects. We also examine the directional motion of individual cells to further reveal how orientational defects mediate local cell rearrangements. Taken together, we have shed light on the role of defects in confluent cells.