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

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.