Emergence of chiral multi-armed spirals in an open system of migrating cells under continuous cell supply

Chirality organize living and active matter systems into striking collective states, yet the principles that govern chiral ordering in open systems, where elements are continuously added or removed, remain unclear. A mutant strain of Dictyostelium discoideum deficient in chemotaxis (KI cells) forms centimeter-scale, clockwise multi-armed spirals. Each arm is a traveling band produced by short-range alignment interactions and guided by a polar-ordered rotating core that encircles the cell source. A subtle clockwise bias in the single-cell migration is amplified by collective ordering into tissue-scale chirality. To uncover the minimal ingredients, we developed an open chiral Vicsek model and identified intrinsic chirality and continuous cell supply as the key factors. Our study establishes a general route by which weak microscopic chirality and sustained material flux generate macroscopic chiral order, offering new insight into chiral patterning in multicellular behaviors.