Speaker
Description
In the realm of biological systems, active fluids are instantiated across scales from mixtures of cytoskeletal filaments and motor proteins to bacterial suspensions and migrating epithelial cell tissues. Local alignment interactions and anisotropic shapes of active constitutes induce large-scale structural order which is locally teared by active stress forming topological defects. Topological defects are localised sources of spontaneous flow which distort the order, and this feedback between structural distortions and spontaneous flows sustains active turbulence and large-scale properties of active fluids.
In this talk, I will present theoretical considerations on the spontaneous flow patterns and kinematics of topological defects across representative two-dimensional active fluids with discrete rotational symmetries, e.g. active nematics, active polar systems and confluent cell tissues. For the hydrodynamics of polar and/or nematic fluids, we derive the kinematics of the topological defects and show how defects can acquire self-propulsion due to activity through dipolar or polar forces as well as activity gradients. Flow incompressibility plays an important role in guiding the motion of defects. For confluent tissues, the T1 transitions, i.e local topological rearrangements of adjacent cell neighbors, are sources of local flow propagating to the tissue scale through chaining of T1 transitions.
