Reversible swelling behaviour of Diels–Alder clicked chitosan hydrogels in response to pH changes

Poly(propylene oxide)–poly(ethylene oxide)–poly(propylene oxide) (PPO–PEO–PPO) based bismaleimide (BMI) was employed as cross–linking agent for the synthesis of pH–sensitive clicked hydrogels by Diels–Alder (DA) reaction with furan–grafted chitosan in aqueous solution. The effect of the surrounding pH over the microstructure and the swelling ability of the hydrogels was evaluated depending on the initial composition. The results suggested that the hydrogels maintained the characteristic responsive properties of the original biopolymer even after the cross–linking reaction. The different macromolecular networks remarkably affected the final properties, especially when referring to pH–swelling sensitiveness and hydrogel porosity. In addition, the swelling parameters revealed that the hydrogels presented large liquid absorption capacity, showing excellent recovery properties and responsiveness at different pHs. The promising features of the ensuing hydrogels made them suitable as targeted pH–sensitive drug delivery systems