Full-Integer Topological Defects in Polar Active Matter: From Collective Migration to Tissue Patterning

Polar active matter—including animal herds, aggregates of motile cells, and active colloids—often forms coordinated migration patterns, such as flocking. This orderly motion can be disrupted by full-integer topological defects representing localized disturbances in which directional alignment is lost. Such polar defects can serve as key organizing centers across scales, sustaining collective behavior such as swirling motion and other large-scale coherent states. Although significant progress has been made in understanding active matter principles in recent years, a quantitative understanding of how topological defects influence active polar matter is still needed. We present a brief overview of recent experimental observations in synthetic active colloids and various biological systems. We describe how polar defects mediate dynamical transitions and contribute to the spontaneous emergence of large-scale coherent states. We also discuss theoretical advances in the physical modeling of coupled processes involving polar defects and collective behavior in active polar matter.