Dynamic swelling Behavior of pH-sensitive anionic hydrogels used for protein delivery

There have been many attempts to use anionic hydrogels as oral protein delivery carriers because of their pH-responsive swelling behavior. The dynamic swelling behavior of poly(methacrylic acid-co-methacryloxyethyl glucoside) and poly(methacrylic acid-g-ethylene glycol) hydrogels was investigated to determine the mechanism of water transport through these anionic hydrogels. The exponential relation M-t/M-infinity = kt(n) (where M-t is the mass of water absorbed at time t and M-infinity is the mass of water absorbed at equilibrium) was used to calculate the exponent (n) describing the Fickian or non-Fickian behavior of swelling polymer networks. The mechanism of water transport through these gels was significantly affected by the pH of the swelling medium. The mechanism of water transport became more relaxation-controlled in a swelling medium of pH 7.0, which was higher than pK(a) of the gels. The experimental results of the time-dependent swelling behaviors of the gels were analyzed with several mathematical models. (C) 2003 Wiley Periodicals, Inc.