Irreversibility and symmetry breaking in the creation and annihilation of defects in active living matter

TL;DR

This study explores defect dynamics in active living matter, revealing symmetry breaking in defect creation and annihilation, driven by a fundamental dualism between nematic order and polar forces, with implications for understanding biological non-equilibrium systems.

Contribution

It uncovers the irreversibility and symmetry breaking in defect processes across different biological systems, challenging existing nematic theories and highlighting entropy production.

Findings

Defect creation and annihilation are spatially asymmetric.

Creation and annihilation processes are not reversible.

Active biological systems produce significant entropy through defect dynamics.

Abstract

Active living matter continuously creates and annihilates topological defects in a process that remains poorly understood. Here, we investigate these dynamics in two distinct active living systems: swarming bacteria and human bronchial epithelial cells. Despite their entirely different evolutionary origins, biological functions, and physical scales, both systems exhibit half-integer defects, consistent with the nematic phase. However, in contrast to active nematic theory, we find that defect creation and annihilation undergoes spatial symmetry breaking. We propose that these results stem from a fundamental dualism between nematic structural organization and generated polar forces, which are intrinsic to living systems. Furthermore, estimation of entropy production reveals that creation and annihilation are not reversed processes. Our findings challenge conventional nematic models and emphasize the role of defect-mediated dynamics in non-equilibrium biological systems as a major source of entropy production.