Spatial Control of Compressible Active Fluids
We study the response of compressible microtubule-based active fluids to sinusoidally varying activity patterns, using experiments and theory. Microtubules accumulate in low-activity regions and are depleted from high activity ones, with the density difference controlled by the wavelength of the activity pattern. To explain these observations the continuum model needs to account for both active stresses that are proportional to nematic order tensor and the isotropic active pressure. At short wavelengths, active vortices spanning adjacent high and low activity regions suppress density modulation. At larger wavelengths, vortical flows confined to the low or high activity region allow for the emergence of the density contrast. Our work shows that a minimal theoretical model of active compressible fluids accurately reproduces experiments, while elucidating the fundamental constraints on control protocols that seek to tame their chaotic dynamics.