Scale-Matched Nanoscale Confinement Governs Chain Cooperativity and Fatigue Resistance in Soft Hydrogels.

Despite the presence of abundant reversible interactions in single-network hydrogels, they still frequently fail under cyclic loading. This limitation originates from the mismatch between the nanoscale anchoring distance d and the polymer correlation length ξ. As d/ξ approaches unity, nanoscale anchors cooperatively recruit previously dormant chains, suppress mesoscale heterogeneity, and enable reversible hydrogen bonding and π-π interactions to mediate efficient cyclic load transfer. Hydrogels tuned to this length-scale-matched regime exhibit an adhesion strength of 30 kPa, a fracture strain of 5000%, and an ultrahigh toughness of 5775 kJ m-3, while maintaining low hysteresis and excellent fatigue stability. These results demonstrate the existence of a measurable and transferable nanoscale control parameter for designing fatigue-resistant soft networks.