LAUSR

DOI: 10.1002/admi.201701245 exhibit bidirectionally anisotropic sliding property to lead water droplets to slide in the longitudinal direction rather than the perpendicular direction, which gives rice more opportunities to survive in arid environments.[2] The unidirectionally anisotropic sliding behavior of butterfly wings, which means water droplets can roll off the wings freely in the radial outward direction but be pinned along the opposite direction, allows butterfly to fly and keep dry even on a rainy day.[3] Directional wettability also plays a vital role in the survival of some other natural systems, such as the leg of water strider,[4,5] spider silk,[6] cactus spine,[7] and the others.[8–10] Mimicking the intricate structures of creature surfaces, many artificial anisotropic wetting surfaces have been obtained through various technologies including duplication from a natural template,[1,9] lithography,[11,12] film deposition,[13] laser microfabrication,[14,15] and so on.[16–18] Especially, superwetting surfaces with anisotropic sliding property attract great attentions because of a wide range of applications, such as liquid-repellence, self-cleaning, lab-on-chips, antimicroorganisms, liquid manipulations, etc.[19–28] Jiang and co-workers prepared a rice-leaf-like aligned carbon nanotube film by pyrolysis and achieved superhydrophobicity with bidirectionally anisotropic sliding behavior.[2] Wu et al. prepared a rice-leaf-like surface by the cooperation of photolithography, imprint lithography, and micro/nanostructure coating and realized controllable bidirectionally anisotropic sliding.[29] Inspired by butterfly wings, Chen and co-workers obtained the same unidirectionally adhesive superhydrophobicity which was derived from a laser-induced directional pattern structure.[15] Up to now, almost all of the reported anisotropic sliding superhydrophobic surfaces solely exhibit rice-leaf-like anisotropy[29–32] or butterflywing-like anisotropy.[3,13,33] However, it is more important to prepare artificial surfaces with properties and functions beyond nature, such as switchable superhydrophobic–superhydrophilic surface,[34–36] self-repairing surface,[37] self-driven directional long-range transport surface,[38,39] and so on. Thus, a kind of tridirectionally anisotropic sliding surface (these three directions are on the same plane) is imperative for the development of microfluidic technology and the design of smart devices. To the Precisely arranged multiscale microstructures in living systems provide inspirations for the fabrication of artificial advanced materials and devices. Recently, uni-bioinspired surfaces with anisotropic wettability are built for various applications. Here, a kind of bi-bioinspired (rice leaf and butterfly wing) tridirectionally anisotropic sliding superhydrophobic surface for the first time is reported. First, a microgroove array structured polydimethylsiloxane surface is constructed by selective femtosecond laser ablation. The as-prepared surface shows bidirectional anisotropy which can be easily tuned by the width (L) and the depth of the microgrooves. A “steps” structure is further introduced into the microgrooves. Interestingly, tridirectionally anisotropic sliding superhydrophobicity that combined the rice-leaf-like and butterfly-wing-like anisotropy is achieved on such surface. The tridirectional anisotropy is demonstrated to result from the directional “steps” structures and the uneven distribution of rough structures. The bi/tridirectionally anisotropic sliding property will provide a fresh cognition of anisotropic wettability for researchers and have enormous potential applications in smart microfluidic systems.