Steric hindrance-driven confined crystallization for fabricating supramolecular macroporous hydrogels toward efficient food freshness monitoring

A confined-crystallization strategy was developed to construct hierarchical porous PVA hydrogels without templates. • Steric hindrance-guided crystallization and hydrogen-bond-mediated network toughening drive multiscale pore formation. • The PAR hydrogel exhibited >4-fold faster NH 3 response than dense films, with dual-mode colorimetric and fluorometric output. • The sensor enables real-time visual monitoring of meat freshness with excellent stability and batch reproducibility. Escalating food loss and waste from spoilage and premature disposal of perishable products along the supply chain underscore the urgent need for rapid and efficient freshness-monitoring technologies. However, most existing freshness indicators rely on dense polymer films, in which the slow diffusion of spoilage biomarkers leads to sluggish response and limited sensitivity. Herein, a hierarchically macroporous polyvinyl alcohol hydrogel doped with acid fuchsin (AF) as pore regulator and riboflavin (RFN) as structure stabilizer was proposed for real-time dual-mode monitoring of meat freshness. Molecular dynamics simulations and experimental characterizations jointly revealed that steric hindrance-guided confined crystallization and hydrogen-bond-enhanced toughening effect collectively enabled the formation of multi-level macroporous structures. Benefiting from confined crystallization-induced homogeneous macroporous architecture, the PAR supramolecular hydrogel facilitates rapid diffusion of ammonia (NH 3 , a key spoilage biomarker) and exhibits over 4-fold improvement in sensing efficiency compared with conventional dense-film materials. The sensor exhibits high sensitivity in both colorimetric and fluorometric modes, achieving detection limit as low as 1.14 μL L −1 . The improved mass transport efficiency within PAR hydrogel enables timely assessment of meat freshness, as demonstrated by monitoring chicken breast stored under ambient and refrigerated conditions. This work establishes a confined-crystallization strategy for designing hierarchically porous hydrogels that balance fast mass transport and structural stability, paving the way for scalable, high-performance gas sensors in intelligent food packaging.