Tyler Shendruk

University of Edinburgh


Spontaneous Self-Constraint in Actively Kinky Situations


Fluids and Materials Seminar


25th April 2024, 2:00 pm – 3:00 pm
Fry Building, Fry 2.04


Active processes drive and guide biological dynamics across scales, from subcellular cytoskeletal remodelling, through tissue development in embryogenesis, to population-level bacterial colonies expansion. In all these situations, biological functionality requires collective flows occur simultaneous to autonomous protection of self-organized structures. However, the mechanisms by which active flows can spontaneously constrain their dynamics has not previously been explained. In this talk, I'll explore how non-linear coupling between flow and orientational fields in active nematics leads to a strong, two-way, spontaneous self-constraint. On the one hand, self-motile topological defects are tightly constrained to specific contours of coherent flow structures, while, on the other hand, the contours are driven by mesoscale defect-associated nematic deformations. Our results demonstrate that self-motile half-integer defects are only ever found on the interface of the fluid coherent structures identified as viscometric surfaces—contours where vorticity and strain-rate balance. Through a series of simple models, we explain that this spontaneous self-constraint arises from an interdependence between viscometric lines and elongated narrow kink walls in the orientation field. These results underscore the continual role of kinky walls in steady-state dynamics, showing that active nematic defects cannot be viewed as solitary points but are one component of mesoscale nematic structures. Ultimately spontaneous constraints in active materials could have far-reaching implications as a framework for understanding how biological systems employ active stresses for simultaneous dynamics and restraint.






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