Polyacrylamide Hydrogels Produce Hydrogen Peroxide from Osmotic Swelling in Aqueous Media

This work demonstrates that hydrogen peroxide (H₂O₂) is generated in weak polyacrylamide hydrogels due to mechanochemical reactions to osmotic swelling. Hydrogels are important tools and materials for many biomedical applications, particularly for growth of stem cells. However, swollen gels are under constant tension, which makes their individual chains susceptible to mechanochemical bond breakage. In this work, an assay was developed to measure the generation of H₂O₂ as a result of hydrogel swelling. Polyacrylamide hydrogels with both weak disulfide and strong PEG-diacrylate crosslinkers were synthesized and swelled. H₂O₂ generation increased in the presence of weaker crosslinkers, up to 30 μM H₂O₂, whereas stronger crosslinkers reduced this to 5 μM H₂O₂. H₂O₂ levels decreased when swelled in the presence of dextran to reduce osmotic stress or increased if the gels were conjugated to an acrylated surface. Finally, H₂O₂ continued to form for days after the gels had reached their equilibrium sizes, independently of dissolved oxygen. The results of this work impact those working in the 3D cell culture community and demonstrate that even well-characterized systems undergo mechanochemical processes in mild environments.