Defect dynamics of circularly confined 2D active nematicl iquid crystals*

We study the role of boundary conditions on a simplied experimental model of biological active matter system 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 dense quasi-2D active nematic liquid crystals when sediment onto a surfactant-stabilized oil-water interface. We further confine this system ontocircular boundary conditions, imposing total topological charge. We observe unique dynamical behavior under high confinement in the order of hundred micrometers. The system produces two circulating +/- 1/2 defects, driving the material toward the edge of the circle. The circulating behavior is eventually destroyed by buckling of the nematic at the container wall which nucleates a +/- defect pair. This behavior is remarkably periodic until the energy supply of the system; ATP is drained. We study the defect-defect and defect-boundary
interactions of the nematic in the circular connement.