Topological defects in active and living matter

Nematic order, where elongated entities preferentially align along a common orientation, has been ubiquitously observed in biology, from epithelia to entire organisms. Nematic order is generally interrupted by topological defects, strong distortion of alignment, analogous to swirls in a fluid. In active systems, which are driven out of equilibrium by internally generated local forces, defects can become motile entities and drive self-sustained flows in fluids or focus mechanical stresses in solids. Defects have been shown to play an important role in biology as center of cell extrusion and death in biological tissue and in animal morphogenesis. In this talk I will describe how the interplay or mechanical forces and orientational order can provide new mechanisms for defect motion and control in active solids. Our work provides a natural framework for understanding the restructuring of the nematic order observed in the freshwater polyp Hydra when the organism regenerates itself from an excised fragment. 

---

Note the first seminar given by Cristina Marchetti on Active Phase Separation and Liquid-Liquid Interfaces  on 13/05/2025 at 11:30 am at Amphithéatre Marie Curie