Fig. 2. Hydrodynamic pillar array experiment with active polymer–like worms.

(A) Top view of the channel with hexagonal pillar array. The design is based on conventional (hydrodynamic) chromatography experiments (41). The dimensions of the channel are 51 cm by 12 cm by 1.5 cm. The diameter of the pillars is D_pillar = 6 mm, and the interpillar distance is D_int = 3 mm. (B) Schematic of the experimental setup. The worms enter the channel at coordinate x₀, travel through the pillar array due to the imposed flow (in the direction of the arrows), and are finally flushed out at x_f. The temperature T of the surrounding medium (distilled water) is regulated by a thermo-controlled reservoir. Motion of the transported worms along the whole channel is recorded using a camera placed on the top of the experiment. (C) Trajectories in the channel for the same worms at two different temperatures (top, T = 10°C and bottom, 25°C) in time (color gradient). The continuous line shows the tracked paths along the channel at the two different temperatures for the same amount of time (40 s); decreasing temperature increases the elution time.