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 as porous aerogels and hydrogels represent intriguing 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.