Ultrathin Ionogels and Hydrogels: Materials, Mechanisms, and Emerging Applications

ABSTRACT Ultrathin ionogels and hydrogels, as a class of soft materials with inherent flexibility, ionic conductivity, and stimulus responsiveness, have demonstrated tremendous application potential in emerging fields such as flexible electronics, biosensing, energy devices, and intelligent interfaces. Compared to conventional thick‐film or bulk counterparts, ultrathin structures offer superior mechanical compliance, faster response times, and enhanced interfacial adaptability, making them ideal candidates for next‐generation wearable electronics, soft robotics, and bioelectronic systems. This review provides a comprehensive overview of recent advances in ultrathin ionogels and hydrogels, focusing on material systems and fabrication strategies—including electrospinning, spin coating, in situ polymerization, free‐radical polymerization, and thickness‐controlled approaches. We also summarize key performance optimization strategies related to mechanical robustness, ionic conductivity, multistimulus responsiveness, interfacial adhesion, antibacterial functionality, and breathability. Furthermore, representative applications in wearable sensors, smart coatings, flexible energy devices, drug delivery platforms, and environmental‐responsive materials are highlighted. In addition, current challenges are critically discussed, such as achieving uniform large‐area fabrication, improving long‐term stability, integrating self‐powered capabilities, and enabling multifunctional system‐level integration. Finally, we outline future directions toward multimodal sensing, intelligent human–machine interfaces, and adaptive soft systems. This review aims to provide systematic insights and forward‐looking guidance for the rational design and practical application of ultrathin ionogel and hydrogel materials.