By IR and NMR spectroscopy methods, thermomechanical analysis, mechanical relaxation measurements, and computational simulation the effect of production conditions of acrylamide copolymer and N,N'-methylenebisacrylamide derived hydrogels with respect to their properties were studied. Four hydrogel samples, prepared under different production conditions (gamma-radiation dose and autoclaving), were investigated. It was found that autoclaving and gamma-radiation lead to a slight increase of the crosslinking degree in the polymeric network and formation of alkene structures in polymeric chains. Stress relaxation and creep processes under axial compression of gel cylindrical samples were studied in detail. To approximate stress relaxation and creep curves new memory functions were used, based on the analysis of entropy production in the system during the relaxation process. It was found that primary gamma-radiation of initial gels induces an increase of quasi-equilibrium rubbery elasticity modulus, and quasi-equilibrium compliance is decreased. The opposite situation is observed during further autoclaving at 120 degrees C. After autoclaving, required to sterilize the gels, their treatment by gamma-radiation again induced a noticeable increase of the modulus and compliance decrease. The mechanism of relaxation processes was found to be associated with the limiting stage of physical interaction between relaxants, representing different micro-inhomogeneities in the material. The investigation results were compared with the data obtained by histology and morphology methods. A hydrogel obtained under additional gamma-radiation treatment and autoclaving did not swell when implanted into a living organism, and the tissue reaction to implantation of such gel was minimal. (c) 2005 Wiley Periodicals, Inc.
