Direction-dependent adhesion of water strider's legs for water-walking

We report the direction-dependent adhesion of water strider's legs for fleetly walking on water surface. The flexibly oriented setae of legs involving the hierarchical micro/nanostructure tune effectively the solid-liquid-air three phase interfaces in two opposite directions: the direction along the setae and opposite the setae, generating different adhesion dependent on the direction. A model is proposed to elucidate the underlying mechanism of water-walking based on direction-dependent adhesion induced by the orientation of the aligned setae. This finding will improve our understandings of the interaction between the oriented structured surface and water surface, and is significant to boost biomimetic structured surface that can be applied into microfluidics and aquatic microdevices.