Soft yet robust hydrogels for flexible bio-integrated devices: from mechanics properties to applications

Soft hydrogels have emerged as key enabling materials for flexible bio-integrated devices owing to their tissue-like softness, high water content, and intrinsic biocompatibility. However, conventional hydrogels suffer from mechanical fragility, limited fatigue resistance, and poor environmental stability, which severely restrict their long-term performance under dynamic physiological conditions. Addressing this challenge has driven the development of combining compliant mechanics with high toughness, durability, and damage tolerance. This review provides a comprehensive overview of recent advances in robust soft hydrogels for flexible bio-integrated devices, with an emphasis on mechanics-guided design and manufacturing strategies. We first discussed molecular and network-level design principles, including chain architecture, dynamic crosslinking, double network structures, and sacrificial energy dissipation, that underpin enhanced toughness and fatigue resistance. We then examine mesoscale and microstructural engineering approaches, such as gradient architectures, anisotropic networks, and nanocomposite reinforcement, that enable mechanical programmability and environmental robustness. Fabrication and scalability strategies, including printing, patterning, and interface engineering, are subsequently reviewed to highlight pathways toward system-level integration. Finally, emerging applications in flexible electronics, electronic skin, soft robotics, and intelligent health monitoring are discussed, together with remaining challenges and future directions for translating robust soft hydrogels into reliable and manufacturable bio-integrated systems.