While
traditional fluids only flow when acted upon, a remarkable class of
biomaterials spontaneously flow by means of their own internal energy.
These “active fluids” comprise a wide range of biological systems that
bridge between biological and condensed matter systems. This Brown Bag
talk will focus on the example of microtubule-based extensile films
modelled through active nematohydrodynamic simulations. We’ll
beparticularly interestedin the continuous creation and annihilation of
topologicaldefects, singularities in the orientation field that lie at
the heart of many phenomena in active nematics. While these defectsplay a
pivotal role ingeneratingcomplex spatiotemporaldynamics, they typically
come in pairs of the lowest topological charge. We locally manipulate
active nematic films through hydrodynamic stresses created by
magnetically actuated rotation of disk-shaped colloids in proximity to
the films to drive the formation of higher energy topological vortices
through the merger of two lower energy defects. The directed motion of
the defects is accompanied by ordering of the vorticity and velocity of
the active flows within the film that is qualitatively unlike the
response of passive viscous films. We discuss how these ideas can be
used to sculpt flowing topological states without directly confining
active nematics and inspire future designs of hybrid bio-mechanical
devices to work in conjunction with active biological fluids.