Low-Temperature, Solvent-Free and Closed-Loop Calendering Overcomes the Strength-Water Content Trade-Off in Hydrogels

Hydrogels, with their inherent flexibility, hydrophilicity, and biocompatibility, are promising candidates for diverse biomedical and environmental applications. However, the sustainable and scalable fabrication of mechanically robust, water-rich hydrogels remains a critical challenge, constrained by the intrinsic trade-off between mechanical strength, high water content, and environmentally benign processing. Here, we introduce a closed-loop, solvent-free, and low-temperature green calendering (LTGC) strategy to fabricate anisotropic hydrogels with tunable hierarchical architectures. By applying coupled shear and compressive forces, this topo-mechanical processing method induces multiscale alignment of poly(vinyl alcohol) (PVA) chains (ranging from molecular orientation to macroscale lamellar structures) mimicking the mechanical design principles of load-bearing biological tissues. The resulting hydrogels simultaneously achieve high tensile strength (3.20 ± 0.77 MPa) and high water content (90.2 wt %), overcoming conventional trade-offs. Importantly, the process enables closed-loop recyclability: fractured or discarded hydrogels can be reprocessed without performance degradation, facilitating circular material flows. Moreover, through the integration of photothermal carbonaceous fillers, discarded hydrogels can be functionally upgraded into composite materials for solar-driven interfacial evaporation, demonstrating potential in desalination and sustainable water harvesting. This work pioneers a green hydrogel manufacturing technique that unifies sustainable processing, structural biomimicry, and circularity.