Moisture sorption and hydration dynamics in intrinsically hygroscopic hydrogels

Hygroscopic materials that capture water vapor across a wide humidity range are important for emerging applications including atmospheric water harvesting, moisture control, and thermal management. Hydrogel sorbents are attractive because they can store large amounts of water while remaining solid-like, yet common hydrophilic gels sorb little vapor at low relative humidity (RH) unless hygroscopicity is introduced by deliquescent salts. Here, we report intrinsically hygroscopic hydrogels (IHHs) assembled from inosine and Zn²⁺ through pH-controlled supramolecular coordination. The IHHs show a moisture-sorption onset near zero RH, reaching 0.17 g g^-1 at 30% RH while retaining swelling-amplified uptake at high RH (1.9 g g^-1 at 95% RH) and reversible cycling. Varying gelation pH reprograms the coordination microenvironment and network structure, reshaping early-stage sorption and shifting uptake onset. Experiments and simulations indicate that hydration-accessible Zn-centered motifs serve as important early hydration loci, while pH-dependent network structure further modulates hydration growth. These results provide a coordination-chemistry route to hygroscopic hydrogels without salt deliquescence.