Spraying Conformal Hydrogel Skins as Functional Platform

ABSTRACT Functional skins represent a transformative platform for diverse applications, yet their highly conformal deployment and maintenance remain challenging on substrates with arbitrary geometries, complex microstructures and dynamic deformation. Herein, we present a material‐form shift for functional skin fabrication, utilizing spray‐deposited polyacrylic acid/polyethyleneimine (PAA/PEI) lyophilized hydrogel powders embedded with functional components. Upon rehydration, these powders instantaneously coalesce into conformal hydrogel skins (<5 s). Their micron‐scale particle size enables high‐fidelity deposition that preserves substrate topography, including microstructural features. The resulting functional hydrogel skins exhibit exceptional mechanical properties: a magnetoactive variant demonstrates softness (Young's modulus ≈140 kPa), high toughness (≈800 J/m 2 ), and strong interfacial adhesion (≈600 J/m 2 ) to various substrates. Soft robots are constructed by conformally coating magnetic hydrogel skins onto elastomer films, maple leaves, or liquid metal balls, capable of flapping, grasping, locomotion, and therapeutic operation. The versatility of the platform is further exemplified through integrated bioinspired functionalities such as thermochromic response and fluorescence. Leveraging convenience, versatility, and broad applicability, this strategy presents an enticing pathway for engineering functional surfaces in devices and robotics.