Fish Skin‐Inspired Janus Hydrogel Coating for Drag Reduction†

Comprehensive Summary In nature, fishes have evolved functional skins with effective hydrodynamic performance and anti‐fouling, facilitating predation and escaping from predators. Although a large number of fish scale‐inspired structured surfaces have been explored, the incorporation of mucus on the structured surfaces has been largely ignored. Inspired by the skin of Osteichthyes fishes, a Janus hydrogel coating (JHC) is successfully prepared by a two‐step UV light irradiation at room temperature. The bottom side of JHC (STH) achieves a shear adhesive strength of 103.3 ± 17.5 kPa and can strongly adhere to a large variety of surfaces, including metals, ceramic and polymers. The top surface of JHC (SLH) replicates the structure of cycloid scales, while the nature of hydrogel mimics the mucus on fish skin. SLH possesses prominent mechanical, anti‐swelling, anti‐fouling and drag reduction properties. The design strategy for JHC has potential applications in numerous fields, like, pipeline transportation, bioengineering, and shipping industry.