Flows within an active droplet immersed in oil are affected by the thickness of the oil layer. (a) Mechanism behind the activity of microtubule–kinesin active fluid. Microtubules are bundled by depletion (blue arrows) and bridged by kinesin motor dimers that slide pairs of antiparallel microtubules apart (red arrows). Figure adapted from Bate et al.36 (b) Schematic of fluidic device used to compress droplets. The device ceiling was curved into a dome-like shape (red), and a well was drilled (radius 1 mm, depth 0.2 mm) on top of the dome (yellow). The curved ceiling caused the active droplet to remain stationary at the dome center. (c) An active droplet (r ≈ 2.4 mm, ℎ ≈ 2 mm) confined in an oil layer whose thickness was 2.6 mm developed a circulatory flow (left). The circulatory flow was suppressed by decreasing the oil layer thickness to 1.1 mm (right). Black arrows represent time-averaged velocity flow fields normalized by the flow mean speed. The color maps represent normalized vorticity distributions, with red and blue representing clockwise and counterclockwise vorticities, respectively. Videos of the flows in both systems are available in Supplementary Video S2. (d) Evolution of circulation order parameter (COP) of flows within the active droplets in c (blue: 2.6-mm oil thickness; red: 1.1-mm oil thickness).