(181ae) Tough Hydrogel Network Based on Calcium-Crosslinked Sulfur Salt

Current hydrogel networks display poor mechanical properties in the hydrated state with most hydrogels showing poor mechanical properties even in low water-content state. Existing research points to using crosslinking to increase the strength of these gels, particularly with the use of metal ions inserted in the matrix. Based on the bond strengths between them, this study was used to determine if incorporating a sulfur-based ligand had the potential to enhance the mechanical strength of hydrogel networks in a hydrated state, when compared to a carboxylic acid-based ligand. Hydrogel networks were synthesized using hydroxyethyl methacrylate (HEMA) and 3-Sulfopropyl methacrylate potassium salt. Calcium was chosen due to its ability to form strong crosslinks with two ligands. FTIR spectra showed the presence of characteristic hydroxyl groups from HEMA, as well as the complete consumption of monomer units when creating the network. Additionally, the intensity of the unsaturated double bonds decreased significantly after complete polymerization. Rheological analysis revealed that the storage modulus (G’) of the calcium- crosslinked sulfur hydrogels was more than a magnitude higher than the calcium-crosslinked methacrylic acid hydrogels. This elevated mechanical strength could be attributed to the bond strength between the calcium ions and sulfur units being stronger than the carboxylic acid units. This study showed that tertiary sulfur salt forms strong ionic bonds with calcium ions, forming a tough hydrogel network for diverse medical applications.