Double-network self-healing hydrogels with ultra-stretchability and 3D printability

Double network hydrogels that can bear enormous mechanical loads enable advances in fields such as electronic skin, tissue engineering and soft robotics. The high toughness of these hydrogels are endowed by intertwined networks, a brittle network and a reversible network that dissipates energy under deformation. Despite improved mechanical properties, the double network hydrogels suffer from the loss of mechanical strength upon loading, poor recovery from rupture and complicated preparation steps. Achieving simultaneously high toughness, self-healing property, and printability in hydrogels remain a challenge. Here, by using a microfluidic printer-head, we achieve continuous printing of double network hydrogels with both covalent and physical crosslinks with self-healing property. The self-healing of the hydrogels is achieved simply by spraying water, and accelerated by increasing pH. The resultant hydrogels demonstrate a stretch up to 24 times of their original length, and up to 21 times after cutting and self-healing. The presented results provide new strategy that enable the development of tough, self-healing hydrogels for practical applications.