Hydrogels for oral drug delivery of peptides: synthesis and characterization

In this study hydrogels were synthesized by the copolymerization of acrylamide and itaconic acid in the presence of poly(N-vinyl-2-pyrrolidone) in an aqueous medium. The incorporation of a small amount of itaconic acid resulted in the transition of the swelling behavior from Fickian to non-Fickian. The hydrogels showed good response to the valency of the counterions and pH of the swelling media. The equilibrium water uptake increased with the pH of the external solution, thus attaining a maximum value at pH 7-8. The gels exhibited a number of deswelling-swelling cycles while maintaining mechanical strength and shape stability. The amount of itaconic acid present in the system affected the swelling behavior of the hydrogels in a rather unusual way. At pH 2.0 the equilibrium water uptake increased with the amount of acid monomer up to 15 mM, remained almost constant for a very small range of concentrations (i.e., up to 22 mM), and then finally decreased with the further increase of the acid content. However, a continuous increase was observed at the pH 7.0 of the swelling media. The hydrogels showed very poor temperature dependency and the activation energies for the samples with and without itaconic acid were 29.09 and 19.92 kJ mol(-1), respectively. Finally, the swelling and deswelling processes were explained on the basis of two different mechanisms that were followed by the gels. (C) 2002 John Wiley & Sons, Inc.