Design rules for controlling active topological defects

• DOI: 10.1073/pnas.2400933121
• Publication Date: 2024-05-15T16:47:42Z
• Authors: Suraj Shankar; Luca V. D. Scharrer; Mark J. Bowick; M. Cristina March...
• Keywords: 0301 basic medicine; Condensed Matter - Materials Science; 500; Materials Science (cond-mat.mtrl-sci); FOS: Physical sciences; fluid dynamics; Physics - Applied Physics; Applied Physics (physics.app-ph); Condensed Matter - Soft Condensed Matter; 530; 03 medical and health sciences; liquid crystals; Physical Sciences; Soft Condensed Matter (cond-mat.soft); active matter; topological defects; control

Topological defects play a central role in the physics of many materials, including magnets, superconductors, and liquid crystals. In active fluids, defects become autonomous particles that spontaneously propel from internal active stresses and drive chaotic flows stirring the fluid. The intimate connection between defect textures and active flow suggests that properties of active materials can be engineered by controlling defects, but design principles for their spatiotemporal control remain elusive. Here, we propose a symmetry-based additive strategy for using elementary activity patterns, as active topological tweezers, to create, move, and braid such defects. By combining theory and simulations, we demonstrate how, at the collective level, spatial activity gradients act like electric fields which, when strong enough, induce an inverted topological polarization of defects, akin to a negative susceptibility dielectric. We harness this feature in a dynamic setting to collectively pattern and transport interacting active defects. Our work establishes an additive framework to sculpt flows and manipulate active defects in both space and time, paving the way to design programmable active and living materials for transport, memory, and logic.