Super tough double network hydrogels and their application as biomaterials

The double network (DN) technique, developed by authors' group, provides an innovative and universal pass way to fabricate hydrogels with super high toughness comparable to rubbers. The excellent mechanical performances of DN hydrogels originate from the specific combination of two networks with contrasting structures. The first brittle network serves as sacrificial bonds, which breaks into small clusters to efficiently disperse the stress around the crack tip into the surrounding damage zone, while the second ductile polymer chains act as hidden length, which extends extensively to sustain large deformation. Based on the principle of DN hydrogel, the author's group recently has developed several novel systems and techniques, which has greatly expanded the practical accessibility of DN technique for practical use. The DN principle and the DN gel have already attracted much attention in the soft matter community. Inspired by the DN principle, many research groups have also designed and developed some innovative hydrogels with large enhancement in their mechanical strength and toughness. Some tough hydrogels fabricated by the DN technique also exhibit good biocompatibility and low friction resistance with promising prospective in industrial and medicine fields, especially for load-bearing artificial soft tissues such as artificial cartilage. In this feature article, we address the major concept and toughening mechanism of DN gel, then we describe some recent novel hydrogel systems based on the DN concept, and finally the applicability of DN gel as soft biomaterials is discussed.