Abstract

Co-Authors: Zihui Zhao, He Li, Yison Yao, Yonfeng Zhao, Francesca Serra, Recently, collective motions and morphogenesis of cell monolayers around topological defects have attracted much attention in statistical physics, soft matter, and biophysics. However, validity and universality of the governing equations for those systems are still in debate. Neural Progenitor Cells (NPCs) have an elongated shape and reciprocate along their elongated axes, forming nematic orientational order. We induced integer topological defects with different director angles by using microfabrication on the substrate. Integer topological defects are usually difficult to appear spontaneously except in rosette structures composed of polarized cells. We found that all types of +1 topological defects, including aster (radial), spiral, and circular patterns, attract cells toward the centers of the defects.  This phenomenon cannot be explained by the well-known models of dry active nematics. The analysis of the flow and orientation fields consistently show deviations from the minimum model. However, we have successfully reproduced this phenomenon by constructing a model of nematically interacting active particles. We also found that the new equations obtained from the hydrodynamic representation of the particle model correctly reproduce this phenomenon. These results provide a new perspective on the characterization of cell monolayer dynamics.