Strain-Stiffening, Self-Healing, and Low-Hysteresis Physically Dual-Cross-Linked Hydrogels Derived from Two Mechanically Distinct Hydrogen Bonds

Herein, we propose a facile strategy to fabricate high-performance hydrogels combining strain-stiffening mechanical behavior with self-healing ability and low hysteresis, which feature a unique structure with two mechanically distinct polymeric networks. The stereocomplex micelles sc–PEG-PLA are first obtained from the mixtures of poly(ethylene glycol)-b-poly(l-lactide) (PEG–PLLA) and poly(ethylene glycol)-b-poly(d-lactide) (PEG–PDLA), then the hydrogels PAA/sc–PEG-PLA are fabricated from the one-pot free radical polymerization process of poly(acrylic acid) (PAA) with sc–PEG-PLA as a physical dynamic cross-linker. Two kinds of mechanically distinct hydrogen bonds, strong hydrogen bonding between PAA and sc–PEG-PLA and weak hydrogen bonding between PAA chains, are attributed to the creation of dual-cross-linked networks of the hydrogels. The special structure imparts the hydrogels with unique strain-stiffening behavior, self-healing capability (98.5% efficiency), and low hysteresis. When exploited as a strain sensor, the fabricated hydrogel sensor demonstrates superior sensitivity even for ultralow strains ranging from 0.5 to 10%. During mimicking practical wearable testing, the hydrogel-based sensor shows high sensitivity and reliability for the detection of diverse human motions like wrist, elbow, and knee movements. This work well elucidates the structure–property relationship of materials and further provides new insights into the development of high-performance hydrogels for broadening their applications.