Gastric fluid-induced double network hydrogel with high swelling ratio and long-term mechanical stability

Hydrogels have been widely investigated as gastric retention systems for drug delivery and bariatric intervention due to their good biocompatibility, degradability, and similarity with human tissues or organs. To realize long-term retention, hydrogels need to swell considerably on contact with gastric fluid to prevent passing through the pylorus and simultaneously maintain their mechanical stability after swelling to resist the damage of gastric pressure. However, high swelling ratio often results in the reduction of mechanical strength. Here, a swelling hydrogel with long-term mechanical stability for gastric retention is proposed. The hydrogel is designed as double networks, namely, the polyacrylamide as the first network and chitosan/sodium alginate as the second network. The hydrogel can reside in the stomach by the swelling of first network and maintain mechanical stability through the gradual formation of second network under the action of gastric fluid. The animal model test proves that the hydrogel can reside in the stomach with intact shape for 16 days, and then is biologically degraded in the gastric environment.