Universal Chiral Dynamics and Non-Reciprocity of Topological Defects in Active Living Matter

Active living matter—bacterial swarms and bronchial epithelial cells—self-organizes into ordered phases where topological defects continuously form and annihilate. Despite vast differences in scale and function, both systems not only exhibit active nematic order, but their defect dynamics follow universal patterns that challenge standard nematic theory.
 

We observe spontaneous breaking of mirror symmetry: defect creation and annihilation follow distinct clockwise or counterclockwise spiraling paths. We attribute this behavior to a fundamental duality in living systems: nematic alignment coexists with directed motion from self-propulsion. The resulting rotational forces act asymmetrically on defect cores, driving the spiraling motion.
 

Furthermore, entropy production measurements confirm defect creation and annihilation are fundamentally different processes, breaking time-reversal symmetry. This irreversibility establishes defect events as major dissipation sources, comparable to bulk motion in cell layers. These findings require incorporating the intrinsic polar dynamics and resulting chiral, irreversible behavior into active matter models.

 

Reference: Beer, A., Neimand, E. D., Corbett, D., Pearce, D. J., Ariel, G., & Yashunsky, V. (2025). Irreversibility and symmetry breaking in the creation and annihilation of defects in active living matter. arXiv preprint arXiv:2508.15622.