Polyelectrolyte complex hydrogel composed of chitosan and poly(γ-glutamic acid) for biological application:: Preparation, physical properties, and cytocompatibility

Polyelectrolyte complex (PEC) hydrogels composed of chitosan as a cationic polyelectrolyte and poly (gamma-glutamic acid) (gamma-PGA) as an anionic polyelectrolyte were prepared from PEC dispersions based on a chitosan solution to which different amounts of gamma-PGA solutions were added to charge equivalency. The chemical structures of the PEC hydrogels were investigated by Fourier transform infrared spectroscopy. The physical properties, fixed charge concentration, crystallinity, mechanical properties, micromorphology, and swelling properties of the PEC hydrogels were also investigated. The total fixed charge concentration of the PEC hydrogels varied as a function of pH on the pK intervals between chitosan (pK = 6.5) and gamma-PGA (pK = 2.27). The isoelectric points (IEP) were shifted to a lower pH with a higher weight ratio of gamma-PGA to chitosan. The elastic modulus was decreased with the weight ratio increasing from 0 : 1 to 1 : 1 (gamma-PGA/chitosan) by ionic crosslinking between the amino groups of chitosan and the carboxyl groups of gamma-PGA. The results of the swelling study showed that the swelling properties of PEC hydrogels were more affected by the change in the elastic restoring force than by the change in the fixed charge concentration depending on the pH. Also, the cytotoxicity of the PEC hydrogels was investigated using normal human dermal fibroblast (NHDF) cell lines, and the results showed the PEC hydrogels were not toxic. (C) 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 386-394, 2007