Hydrogels have been recognized as versatile biomaterials in biomedical applications. This article describes the synthesis and characterization of a poly(ethylene glycol) (PEG) dialdehyde derivative, the modification of gelatin with ethylenediaminetetraacetic dianhydride (EDTAD), and the conjugation of PEG dialdehyde for enhanced hydrophilicity, biocompatibility, and flexibility. Hydrogels of gelatin conjugated with various percentages of PEG dialdehyde (10-30%), 35% EDTAD-modified gelatin, and 12% PEG dialdehyde conjugated with 31% EDTAD-modified gelatin with or without 1% chlorhexidine were prepared. For all the synthesized gel formulations, the swelling kinetics and drug release in pH 7.4 and pH 4.5 buffers at 37degreesC were studied. Gels of PEG-conjugated gelatin, 35% EDTAD-modified gelatin, and 12% PEG conjugated with 31% EDTAD-modified gelatin, with or without 1% chlorhexidine, showed significantly improved swelling ratios in comparison with gelatin. The drug release was unaffected by an increase in the percentage of PEG conjugation with gelatin. Complete drug release was recorded within 48 h in the pH 4.5 buffer, whereas in the pH 7.4 buffer, the drug release was accomplished within 128 h. (C) 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1059-1067, 2004.