Characterization and Enzymatic Degradation of PEG-Cross-Linked Chitosan Hydrogel Films

In our previous study (Kiuch et al., J Appl Polym Sci 2008, 107, 3823), poly(ethylene glycol) (PEG) cross-linked chitosan hydrogel films with various PEG to chitosan ratio and PEG molecular weight have been successfully prepared and their thermal, mechanical and swelling properties at acidic pH were studied. These films are potential biodegradable polymeric materials, because their constituents, that is, chitosan and PEG, are well known as biodegradable polymers. In this study, glass transition temperature (T-g), contact angle, swelling behavior at physiological conditions and in vitro enzymatic degradation behavior were investigated for the PEG-crosslinked chitosan hydrogel films. These properties of chitosan hydrogel were found to change significantly upon introducing the PEG-cross-links. According to differential scanning calorimeter analysis, the T-g value increased with the PEG content in the hydrogel films, indicating the densification of the film by PEG-crosslinking. The contact angle was decreased with increasing the number of crosslinks, reflecting that introduction of the cross-linked structure induced the reduction of chitosan ordered structure. The swelling behavior depended on the PEG to chitosan ratio and the cross-linked structure. The water content was changed with the number of PEG-crosslinks. The rate of lysozyme-catalyzed degradation was also influenced by the introduction of PEG-cross-linked structure. The surface morphology of the film was observed by the scanning electron microscopy. It was confirmed that the PEG-crosslinked chitosan hydrogel film was degraded by lysozyme from its surface area. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 1902-1907, 2009