The effect of polymer structural parameters of ionic hydrogels on the transport of drugs and proteins has been studied for a number of anionic and cationic hydrogels. Crosslinked anionic hydrogels were composed of acrylic acid and 2-hydroxyethyl methacrylate, whereas cationic hydrogels were based on diethyl aminoethyl acrylate or diethyl aminoethyl methacrylate and a-hydroxyethyl methacrylate. The hydrogel structure was investigated using dynamic swelling studies to deduce the variation of mesh size available for solute transport as a function of environmental parameters including the pH and ionic strength. For anionic hydrogels, the mesh size increased with increasing pH due to the ionization of the network. The reverse was true for cationic hydrogels. Ionizable drugs and proteins could interact with the ionizable hydrogels during the transport process. The solute size also affected the release behavior, causing additional hindrance and decreased mobility.