Biaxially Stretchable Rare Earth–Polymer Multicolor Fluorescent Hydrogel for Human Motion Monitoring and Dynamic Information Encryption

Abstract Smart hydrogels are promising candidates for applications such as information security, flexible electronics, and biomedical devices due to their stimulus‐responsive properties. However, the poor mechanical properties and limited stimulus responsiveness of hydrogel materials hinder their applications in complex environments. Therefore, developing smart hydrogels with both mechanical adaptability and optical‐response capabilities remains a significant challenge. In this study, a lanthanide‐coordinated agarose hydrogel (4HBA‐PEI‐AGA@Ln 3+ ) is fabricated via one‐pot photopolymerization. The hydrogel demonstrates synergistic reinforcement through hydrogen bonding and coordination interactions, achieving breakthrough performance: a tensile strength of 110 kPa combined with 1530% tensile strain, high conductivity of 4.34 mS cm −1 and rapid response characteristics (GF = 3.14, response time of 100 ms). These features enable real‐time electrical sensing and precise monitoring of complex human movements. The 4HBA‐PEI‐AGA@Ln 3+ hydrogel maintains exceptional elasticity and fluorescence stability during biaxial tensile testing (8100% area strain), establishing a mechanical‐optical synergistic encryption system that overcomes the limitations of conventional static anti‐counterfeiting technologies. This rare‐earth‐polymer hydrogel with flexible sensing and dynamic encryption functions provides a dual‐effect solution for smart wearable devices and information security protection.