A comparative study between three different methods of hydrogel network characterization: effect of composition on the crosslinking properties using sol–gel, rheological and mechanical analyses

Previously, different techniques were used to identify the crosslinking density of hydrogels. In this study, we aimed to compare three different methods of network structure determination: using sol–gel analyses, rheological and mechanical experiments. To do this, we synthesized a polyvinylpyrrolidone (PVP) hydrogel using gamma-ray crosslinking. The effect of dose, PVP, polyethylene glycol (PEG) and agar content on network properties and mesh size were investigated. It was found that rheological experiment gives more precise results. Determined network parameters such as molecular weight between crosslinks \(\left( {\overline{{M_{\text{c}} }} } \right)\), crosslinking density (v _e) and mesh size (ξ), were used to determine the impact of composition on physicochemical properties. It was found that increasing dose and PVP content leads to an increase in the crosslinking density and a decrease in pore size. However, increasing agar and PEG molar ratio leads to a decrease in the crosslinking density. Regarding elastic behavior, it was found that agar increases viscous modulus and acts as a crosslinking inhibitor but PEG decreases it and acts as a plasticizer. These results were confirmed by determining the state of water in hydrogel network using pulse NMR. SEM images confirmed also calculated network parameters.