Tough and fatigue-resistant anisotropic hydrogels via fiber reinforcement and magnetic field induction

Biological tissues (such as tendons and cartilages) are not only well known for their excellent strength, modulus, and toughness, but also have long-term stability which can withstand millions of high-stress cycles without fracture, and show a fatigue threshold of more than 1000 J m−2. In contrast, although synthetic hydrogels are comparable to natural soft tissues in terms of strength, modulus, toughness, and other properties, these toughened gels will still be subjected to fatigue fracture under repeated cyclic loading, exhibiting a fatigue threshold usually below 100 J m−2. Here, we report a simple strategy for the development of tough and fatigue-resistant anisotropic hydrogels with a fatigue threshold more than 100 times that of conventional hydrogels. Our two-step process mainly includes the formation of an arranged polydopamine-Fe3O4-carbon fiber structure, followed by freezing-thawing and annealing, synergistically contributing to the ultrahigh strength and toughness, excellent tribological properties, and extraordinary fatigue resistance. The tensile strength, compressive strength, and fatigue threshold of the anisotropic hydrogel were up to 11.82 ± 0.85 MPa, 5.95 ± 0.35 MPa, and 1845 J m−2, respectively, which were significantly higher than those of most biogels and synthetic hydrogels. Therefore, this research provides a feasible method for manufacturing soft materials with excellent properties and expands the application of soft materials in load-bearing materials, soft robots, flexible electronics, etc.