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 (<LCST), though their swelling ratios were reduced as temperature increased from room temperature to 37 degrees C because of the
dehydration nature of
PNIPAAm at temperatures above its LCST. The results demonstrated that physically blended temperature sensitive films could be formulated, which are capable of producing more pores upon heating. The blended films were also found to be pH sensitive due to the fact that
chitosan, one of the film components, has many pendant amino groups.