3D‐Printed Hygroscopic Matrices Based on Granular Hydrogels for Atmospheric Water Adsorption and On‐Demand Defogging

Abstract Sorption‐based atmospheric water harvesting is an emerging technology with great potential in clean water production, humidity management, and passive cooling applications. Hygroscopic salt‐embedded composites represent intriguing three‐dimensional (3D) porous sorbents across a broad humidity range. However, none of the commonly used hygroscopic materials—including inorganic powders, organic polymers, and inorganic‐organic hybrids—are inherently printable, limiting kinetics‐enhancing strategies and application‐specific use. Herein, hygroscopic 3D matrices are developed based on granular hydrogel‐mediated direct‐ink writing (DIW). Microgels cross‐linked with percolating polymer networks synergistically improve printability and shape fidelity of the inks, enabling precise printing of previously unprintable hygroscopic composites. Hygroscopic 3D matrices with well‐defined hierarchical porosity—spanning millimeter‐scale lattice channels, micrometer‐scale wrinkled surfaces, and nanometer‐scale granular hydrogel assemblies—maximize surface areas and mass transporting pathways, enhancing sorption/desorption kinetics, structural durability, and performance stability. Compared to hygroscopic aerogels, the hygroscopic matrix reduces raw material requirement by 53% and increases specific surface areas by 5.8‐fold, leading to a 1.4‐fold improvement in water uptake (2.85 g g −1 ). This work significantly broadens the applicability and versatility of hygroscopic materials through a microgel‐mediated DIW approach and shines light on 3D‐printable hygroscopic matrices tailored for reliable and user‐defined dehumidification and anti‐fogging.