Viscoelastic properties of chitosan (CH), chitosan-poly(ethylene glycol) 400 (CH-PEG), and chitosanpoly(ethylene glycol) 400 with glyoxal as crosslinking agent (CH-PEG-Gly) systems were studied to analyze the effect of chitosan concentration (from 0.83 to 1.67%). Dynamic moduli increase as chitosan concentration increases for all systems. For CH and CH-PEG systems the loss modulus (G") is greater than the storage modulus (G') with predominance of the viscous over the elastic behavior. This corresponds to the characteristic behavior of solutions (nonstructured systems). The presence of PEG 400 induces a complementary reinforcement of the mechanical properties of the system. Except for the lowest chitosan concentration, when glyoxal was added to the CH-PEG systems, a gelled matrix was obtained. In this case, G' is greater than G", and practically independent of frequency. This behavior is typical of three-dimensional networks and indicates true gel formation, showing clear elastic behavior (tan delta < 1). In creep and recovery analysis, CH-PEG-Gly systems exhibited distinct regions that were mathematically modeled using Burger's model. This analysis shows that the CH-PEG-Gly matrices (from 1.25 to 1.67%) recover almost totally (100%). Therefore, these matrices could be useful as systems for the development of films for topical hydrophilic drug delivery, and the levels of the residual viscosity (eta(0)) or the complex viscosity (eta(*)) could be used to control drug release. (c) 2007 Wiley Periodicals, Inc.