In vitro cytotoxicity assays: Cytotoxicity of the hydrogels with different concentrations with and without addition of GSH was investigated via a PrestoBlue™ viability assay on L929 mouse fibroblast cells. Cells (69,000 cells/well) were seeded on a 12-well plate with 2 mL of the culture medium and incubated at 37 °C overnight to grow and adhere. Transwell™ with a pore size of 0.45 µm were inserted on top of the plate's well. 200 mg hydrogels (17.5%, 12.5% and 8%) with and without the addition of 5 mM GSH were placed on inside the Transwell™.