Characterization of thermosensitive chitosan gels for the sustained delivery of drugs

The aim of this study was to investigate the physical properties of a chito san/glycerophosphate (GP) thermosensitive solution which gels at 37 degrees C and evaluate the in vitro release profiles of different model compounds. The gelation rate was dependent on the temperature and on the chitosan dea cetylation degree. The solution containing 84%-deacetylated chitosan could be stored 3 months at 4 degrees C without apparent change in viscosity. The in vitro release profiles of the model compounds depended on the presence of GP in the chitosan solution, on their molecular weight and on the presen ce of lysozyme in the release media. They were not affected by the electros tatic charge of the model compound when present at low concentrations. Duri ng the first 4 h, the release was accompanied by a substantial loss of the gel weight which was mainly attributed to the leaching of water and excess GP. Scanning electron micrographs revealed that the solutions yield gels wi th a highly porous structure after 24 h of exposure to a continuous flow of phosphate buffered saline. These results indicate that the chitosan/GP the rmosensitive solutions gel rapidly at body temperature, can remain in the s ol state at 4 degrees C and can sustain the delivery of macromolecules. (C) 2000 Elsevier Science B.V. All rights reserved.