Interpenetrating polymer networks (IPNs) composed of hyaluronic acid (HA) and poly(vinyl alcohol) (PVA) hydrogels were prepared and the effects of various pH conditions and an electric field on swelling hydrogels were investigated. Characterizations of IPN hydrogels were studied using Fourier transform infrared spectroscopy and differential scanning calorimetry (DSC). The swelling kinetics increased rapidly and reached equilibrium within 30 min. IPN hydrogels exhibited a relatively high swelling ratio, 325-412% at room temperature. The swelling ratio increased when the pH of the buffer was below pH 4 as a result of the dissociation of ionic bonds. The swelling ratio of IPN hydrogels depends on pH and electric-field. DSC was used to determine the amount of free water in IPN hydrogels. The amount of free water increased with increasing the HA content in HA-PVA IPN hydrogels. (C) 2003 Elsevier Science B.V. All rights reserved.