Figure 1: The design and principle of the MRS.

(a) Schematic illustration of the assembly of an MRS, which consists of a superhydrophobic mesh and an array of hydrophilic microfibres. (b) Optical micrographs showing the structure of a four-fibre MRS; a water droplet (stained blue) is locked onto the MRS. Scale bar, 300 μm. Scanning electron microscopy images of (c) a hydrophilic microfibre wrapped in a protective jacket, scale bar, 300 μm; (d) a superhydrophobic mesh coated with graphene nanoplatelets, scale bar, 30 μm; and (e) a typical magnified region in (d), scale bar, 500 nm. (f) A side-view schematic illustration of the mechanism of the MRS: the hydrophilic array (green) advances towards the superhydrophobic mesh (orange) (Capturing) until the array protrudes from the pores of the mesh, at which time the water droplet is pinned (Pinned); when the array is retracted through the mesh (Releasing), the surface returns to its non-wettable state, allowing the water droplet to roll (Released). (g) Schematic illustrations and optical micrographs showing the rolling and pinned states, respectively, of a water droplet on an MRS. Scale bar, 1 mm.