Temperature- and pH-responsive semi-interpenetrating polymer network (semi-IPN) hydrogels constructed with chitosan and polyacrylonitrile (PAN) were studied. The characterizations of semi-IPN hydrogels were investigated using Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). IPN hydrogels exhibited a relatively high swelling ratio, 23.31%-145.20% at room temperature. The swelling ratio of hydrogels depends on pH and temperature. DSC was used to determine the amount of free water in IPN hydrogels. The amount of free water increased with increasing chitosan content in the semi-IPN hydrogels. (C) 2003 Wiley Periodicals, Inc.