An interesting “water diode” film is fabricated by a facile electrospinning technique. The fibrous film is a composite of hydrophobic polyurethane (PU) and hydrophilic crosslinked poly (vinyl alcohol) (c-PVA) fibrous layers. By taking advantages of the hydrophobic–hydrophilic wettability difference, water can penetrate from the hydrophobic side, but be blocked on the hydrophilic side.

Electrospinning is a straightforward and versatile way to fabricate multilevel structured ultrafine fibers down to the micro-/nanometer scale. In this review, recent achievements in electrospun fibers with multilevel surfaces and inner structures are presented. The multilevel surface structures include branched structures, porous structures, necklace structures and non-cylinder deformed structures. The multilevel inner structures are classified as peapod structures, multiwalled tube structures, wire-in-tube structures and multichannel structures. Furthermore, the outstanding properties of multilevel structured fibrous materials are discussed and highlighted. These electrospun multilevel structured materials have wide applications in sensing, filtration and adsorption, catalysis, energy storage, bio-field, and many other fields.