Polyacrylamide hydrogels prepared by varying water content during polymerization: Material characterization, reswelling ability, and aging resistance

Abstract As easily fabricated, polyacrylamide (PAAm) hydrogels are widely used, especially in medicine. Material properties of these crosslinked polymers are usually tuned by varying monomer/crosslinker ratio during polymerization. However, the properties of resulting hydrogels are affected by an all‐in composition of the reaction mixture. As the influence of water/monomer ratio has not been systematically studied yet, the objective of this study is to provide a comprehensive investigation of this way of hydrogel preparation together with a careful examination of resulting materials. The samples of PAAm hydrogels prepared with controlled contents of water in the reaction mixture vary in achieved swelling ratios (from 5 to 25) and rigidities (Young's modulus from 300 to 5 kPa). These material properties remain practically the same even if the hydrogels are dried and reswelled again. Performed long‐time testing suggests that the PAAm hydrogels can be stored either in wet or dry state, however, to avoid possible degradation by polymer hydrolysis, they should be placed in darkness and stored at no more than room temperature. The prepared hydrogels swell more in NaCl solutions than in water. As this swelling/shrinking behavior is reversible and independent of hydrogel history, it could be applied for remote control of hydrogel properties.