Effect of sulfation on a tough hybrid hydrogel network

Hybrid hydrogels can mimic the exceptional stiffness of tough native tissues (e.g., articular cartilage). However, many of these tough hybrid hydrogels currently lack bioactive moieties. Therefore, our work focuses on introducing sulfated alginate into a tough poly(acrylamide-co-acrylic acid)/alginate hybrid hydrogel network. This modification introduces the potential for effective tissue interactions and allows further diversification through chemical transformations. These hydrogels are synthesized via the radical-mediated polymerization and covalent crosslinking of acrylamide and acrylic acid. The covalent network is fortified with a second ionically crosslinked sulfated alginate network. FTIR, ¹³C-NMR, and elemental analysis confirmed a degree of sulfation of 42.5%. Mechanical testing showed that hydrogels with a sulfated alginate content of 2 wt% exhibit comparable compressive stiffness (up to 230 kPa) to native articular cartilage. Cyclical mechanical testing revealed the network's resilience and remarkable toughness. These results suggest the hydrogels’ potential as cartilage mimics and support their additional investigation in vitro.