Tissue-like Fracture Toughness and Stress–Relaxation Ability in PVA-Agar-Based Hydrogels for Biomedical Applications

This study developed fully physically crosslinked polyvinyl alcohol (PVA)–agar double-network (DN) hydrogels with tissue-like mechanical and viscoelastic properties for soft tissue engineering. Hydrogels were fabricated via thermal gelation and freeze–thaw cycles, eliminating toxic crosslinkers. Increasing agar content (0–6 wt%) enhanced elastic modulus (50→225 kPa), fracture toughness (1.06→1.76 kJ/m²), and stress–relaxation (~170% improvement) while maintaining >200% strain‑to‑failure. The hydrogels exhibited significant stress dissipation and fracture resistance comparable to articular cartilage and showed high cell viability, confirming suitability for load‑bearing applications such as cartilage repair.