Fig. 4: Macroscopic topological asymmetry dominating selective directional droplet transport.

a Directional droplet transport on SEMR with symmetric microstructures. b Time-sequence images showing water droplet transport on SEMR in opposite directions depending on the droplet deposit position ε. When ε = 0.39, the droplet moves to the left (negative direction), while at ε = 0.62, it moves to the right (positive direction). c Dependence of the droplet transport distance on the droplet deposit position ε. As ε increases from ~0.1 to ~0.9, the transport direction shifts from negative to positive, with the transitional position occurring at ε = 0.5. d Time-sequence images and schematic diagrams illustrating the asymmetric receding dynamics of droplets, governed by macroscopic topological asymmetry.