Double-network hydrogel and its potential biomedical application: A review.

Double-network hydrogels are one of the most promising candidates as artificial soft supporting tissues owing to their excellent mechanical performance, water storage capability, and biocompatibility. A double-network hydrogel consists of two contrasting polymer networks: rigid and brittle first network and soft and ductile second network. To satisfy this double-network requirement, polyelectrolyte and neutral polymer are suitable as the first and the second networks, respectively. Combination of these two networks gives rise to extraordinarily tough double-network hydrogel as a result of substantial internal fracture of the brittle first network at large deformation, which contributes to the energy dissipation. Therefore, the first network serves as the sacrificial bonds to toughen the material. The double-network principle is universal and many kinds of double-network hydrogels composed of various chemical species have been developed. Moreover, a molecular stent technology has been developed to synthesize the double-network hydrogels using neutral polymer network as the brittle first network. The sulfonic double-network hydrogel was found to induce spontaneous hyaline cartilage regeneration in vivo.