Strong and tough chitin hydrogel constructed by dehydration and rehydration strategy

As a renewable, biocompatible, biodegradable soft material, chitin hydrogels have better advantages in stability, antibacterial activity, antifouling, cost, immunogenicity, and so on than most polymer hydrogels. However, compared with other widely used polymer hydrogels with high strength and toughness, the practical applications of chitin-based hydrogels have been limited by their weak mechanical properties, such as cartilage repair and meniscus replacement. Here, we present the design and fabrication of chitin hydrogels with excellent mechanical strength and toughness by a dehydration and rehydration strategy. By sequential dehydration and rehydration processes, the crystalline domains in the chitin hydrogels can be properly controlled. With optimized crystallinity, the elastic modulus of the chitin hydrogels exceeds all previously reported values, and the fracture toughness is even comparable to some synthetic polymer hydrogels, while maintaining a high-water-content of about 80 wt.%. At the same water content, the mechanical properties of the chitin hydrogels are positively correlated with the hydrogel crystallinity, which proves that the change of mechanical properties of hydrogels is not simply dependent on weight concentration. The hydrogels can be further strengthened by incorporating other biopolymers that are intrinsically weak, which makes the hydrogels promising for applications in fields such as cartilage repair and meniscus replacement. Moreover, the hydrogels enable loading and release of water-soluble and poorly water-soluble drugs. This highly extendable strengthening and toughening strategy of chitin and chitin-based biopolymer hydrogels paves the way for their widely applications.