Formulation and characterization of chitosan-based hydrogel films having both temperature and pH sensitivity

Chitosan-based hydrogel films having both temperature and pH sensitivity were prepared by blending chitosan with temperature sensitive poly (N-isopropylacrylamide) (PNIPAAm) and polyethylene glycol (PEG, Mw 2000). PEG was added to enhance film properties, such as thermal, mechanical and swelling properties. Differential scanning calorimetry (DSC) study indicated that the physically blended films exhibited a lower critical solution temperature (LCST) identical to that of pure PNIPAAm (around 32 degrees C). FT-IR data indicated that the temperature sensitivity is due to the PNIPAAm component in the film. The thermal analysis showed that chitosan and PNIPAAm were compatible and the blended films are apt to crystallize. The X-ray diffraction study further showed that the blended films had a higher crystallinity level than chitosan or PNIPAAm alone. The newly formed crystalline domains acted as physical crosslinkers and greatly increased the crosslinking level of the blended films, which, in turn, affected the swelling behavior and mechanical property of the blended films. Scanning electron microscopy (SEM) revealed that the blended swollen films exhibited a more porous structure at 37 degrees C (>LCST) than at room temperature (