Channeling Rather than Blocking: Balancing Chemical Cross-Linking and Entanglements for Mechanical Reliable Hydrogels with Notch Insensitivity and Puncture Resistance

Abstract Although the mechanical strength of hydrogels has been significantly improved in recent years, failure still readily occurs with defects, indicating their low fracture toughness and restricted practical applications in flexible electronics and biomedicine. To obtain both high strength and high fracture toughness, a strategy is proposed inspired by the ancient Chinese flood‑control philosophy of “channeling rather than blocking”, in which a balance between chemical cross-linking and chain entanglements is established for chemically cross-linked single‑network hydrogels with high reliability. Polyacrylic acid hydrogel with low chemical cross-linking density and moderate entanglements is used as a model system to realize excellent notch resistance and puncture resistance. This self‑regulating hydrophilic polymer network can effectively channel stress concentration within the hydrogel, thereby blunting the notch and arresting crack propagation, thus ensuring the hydrogel reliability. Such hydrogels possess outstanding ultra‑stretchability and damage resistance, including a fracture toughness of 33,000 J/m2 and a centimeter-scale fractocohesive length of over 3 cm. Furthermore, the introduction of multifunctional physical cross-linking to replace partial entanglements can also yield high strength and damage tolerance without using high monomer content. The effect of monomer side groups on hydrogel reliability was also systematically investigated followed by proposing a general design strategy that a hydrophilic polymer network with chain flexibility is equally critical. This study demonstrates that the “channeling” strategy rather than “blocking” can effectively overcome the strength-toughness trade-off, providing a facile and effective method for preparing highly reliable hydrogels.