A strong, tough, and fast-recovery hydrogel is engineered by cooperative interactions between histidine-rich peptides and Zn ²⁺ .

Hydrogels are promising soft materials as tissue engineering scaffolds, stretchable sensors, and soft robotics. Yet, it remains challenging to develop synthetic hydrogels with mechanical stability and durability similar to those of the connective tissues. Many of the necessary mechanical properties, such as high strength, high toughness, rapid recovery, and high fatigue resistance, generally cannot be established together using conventional polymer networks. Here we present a type of hydrogels comprising hierarchical structures of picot fibres made of copper-bound self-assembling peptide strands with zipped flexible hidden length. The redundant hidden lengths allow the fibres to be extended to dissipate mechanical load without reducing network connectivity, making the hydrogels robust against damage. The hydrogels possess high strength, good toughness, high fatigue threshold, and rapid recovery, comparable to or even outperforming those of articular cartilage. Our study highlights the unique possibility of tailoring hydrogel network structures at the molecular level to improve their mechanical performance.

Marine mussels are able to firmly affix on various wet surfaces by the overproduction of special mussel foot proteins (mfps).

Ligaments are flexible and stiff tissues around joints to support body movements, showing superior toughness and fatigue-resistance. Such a combination of mechanical properties is rarely seen in synthetic elastomers because stretchability, stiffness, toughness, and fatigue resistance are seemingly incompatible in materials design. Here we resolve this long-standing mismatch through a hierarchical crosslinking design. The obtained elastomer can endure 30,000% stretch and exhibit a Young’s modulus of 18 MPa and toughness of 228 MJ m⁻³, outperforming all the reported synthetic elastomers. Furthermore, the fatigue threshold is as high as 2,682 J m⁻², the same order of magnitude as the ligaments (~1,000 J m⁻²). We reveal that the dynamic double-crosslinking network composed of Li⁺-O interactions and PMMA nanoaggregates allows for a hierarchical energy dissipation, enabling the elastomers as artificial ligaments in soft robotics.