Topological defects mediate collective transport of confluent cells

Collective cell migration governs a range of physiological and pathological processes, from tissue morphogenesis to cancer invasion, in which topological defects arise as an inevitable consequence of frequent cellular rearrangement and migration. Here, we employ the active vertex model to investigate structural defects generated in the wake of transported cells. We find that while the drag coefficient of a cell in a perfect lattice is anisotropic, the threshold drag force required to mobilize the cell is isotropic. Remarkably, we find that dragging two neighboring cells along the direction of least resistance minimizes lattice disruption. By comparing defect-healing behaviors across different physical models, we disentangle the contributions of cell adhesion and many-body interactions. Together, our findings provide new insights into the topological organization of confluent tissues during collective migration, advancing our physical understanding of cellular transport processes such as wound healing, tissue repair, and cancer metastasis.