From Uniform to Patterned: Spatiotemporal Control of a Compressible Isotropic Active Fluid

Living systems control cytoskeletal dynamics by patterning activity in space and time. To mimic such behaviors, we create a minimal synthetic platform by externally programming light-responsive kinesin motors in 3D microtubule–based isotropic active fluid. In response to spatially varying activity light patterns we observe building up filament density in low activity regions, which reveals finite compressibility. We identify a critical length scale below which the density remains uniform. Above this scale, the density contrast grows with wavelength and saturates, establishing a controllable range of spatial modulation. In contrast to static patterns, the response to a translating sinusoidal pattern is speed-dependent: at low speeds, the density field follows the light pattern; above a critical speed, the density variation fails to respond returning to a nearly uniform profile. These findings highlight the spatial and temporal limits of externally programmed structure in isotropic active fluids.