Highly stretchable, self-healing, and biocompatible betaine-based hydrogels with high water absorption and mechanical resilience

Double-physically crosslinked hydrogels are well-known for their exceptional self-healing and mechanical properties but often fall short in terms of biological functionality. Here, we introduce a novel betaine-based zwitterionic hydrogel designed to simultaneously enhance self-healing, mechanical strength, and biocompatibility. The hydrogel is synthesized via thermally initiated free-radical polymerization and utilizes dual physical crosslinking through hydrophobic monomer-based micelles and nanoscale Laponite XLG. The incorporation of betaine monomers further boosts the biological performance of the material. The resulting hydrogel exhibits excellent swelling behavior, achieving equilibrium within 48 h, with a water absorption capacity up to 5000 % and an equilibrium water content exceeding 98 %. Mechanically, the hydrogel exhibits a remarkable elongation at break of 1228 % under tensile testing. Furthermore, it shows exceptional self-healing properties, with fracture elongation recovery of 542.72 % after 2 h and 746.88 % after 24 h. Microscopic observations confirm near-complete healing within just 3 min. Cell viability assays reveal over 95 % cell survival in the presence of hydrogel extracts, confirming its excellent biocompatibility, high water retention, and mechanical resilience.