Spatial Control of Active Flows through Patterns of Activity on Filaments

Active nematic liquid crystals are known to produce self-sustained chaotic flows. Recent advances in optogenetics allow the control of activity in space and time using light, offering the opportunity to generate tunable active flows. Motivated by experiments on microtubule-kinesin bundles, we study a dry, particle-based 2D model of active nematic filaments over a broad range of activity and filament stiffness. We explore new dynamical states induced by a sinusoidal activity profile. In the isotropic regime, filaments accumulate in the dark (low activity) regions while vortical flows arise in the bright (high activity) regions – consistent with experimental findings. In the nematic regime – currently unexplored experimentally – the filaments exhibit a transition as a function of polymer stiffness. At low stiffness, filaments prefer to orient vertically in all bright regions but form no permanent aligned bands. Between the low and high stiffness transition, filaments display no orientational preference. Above a threshold stiffness, and when the wavelength of the activity pattern is near the filament persistence length, one finds fewer (but permanent) vertical bands separated by splay walls. This work is an important step towards designing active patterns and tunable active flows.