Self-organized dynamics of confined active nematics

We study the role of boundary conditions on a simplified experimental model of biological active matter composed of extensile filamentous bundles of microtubules driven by clusters of kinesin motors, to elucidate the structure and dynamics of active nematic liquid crystals. These bundles form a quasi-2D active nematic liquid crystals when sedimented onto a surfactant-stabilized oil-water interface. We further confine this system onto circular boundary conditions, imposing a total topological charge of +1. For diameters of 400 micrometer and larger, multiple +/- ½ defects continuously nucleate and annihilate at the boundary as well as in the confinement core and generate flows of either handedness. As the diameter is reduced, defects periodically nucleate at the boundary with slow dynamics and migrate toward the confinement core rendering a fast pairwise procession, referred to as doubly-periodic dynamics. Existing continuum theories fail to predict this phenomenon and we hypothesize what additional physics needs to be included to reconcile experiment and theory.