Swelling-Tunable Hydrogels for Self-Transformable Underwater Flexible Electronics with Wireless Communication

Hydrogels have emerged as promising materials for flexible electronics due to their excellent biocompatibility, flexibility, and tunable physicochemical properties. However, traditional hydrogels often suffer from swelling-induced mechanical degradation, which limits their practical applications. In this study, a series of HEMA-HEA hydrogels were developed by modulating the ratio of hydroxyethyl methacrylate (HEMA) to hydroxyethyl acrylate (HEA). These hydrogels exhibited tunable antiswelling properties, optical transparency, mechanical robustness, and self-bonding capabilities. With increasing HEMA content, the hydrogels transitioned from hydrophilic to hydrophobic, significantly enhancing their mechanical performance and reducing swelling ratios. Notably, HEMA5-HEA0 demonstrated outstanding antiswelling behavior with a swelling ratio of only 0.9%, while HEMA4-HEA1 exhibited balanced mechanical properties and minimal strain hysteresis, making it an ideal candidate for flexible strain sensors. The fabricated sensors demonstrated sensitivity, excellent fatigue resistance, and stable operation underwater, enabling real-time motion sensing and wireless communication in aquatic environments. Additionally, by leveraging the self-bonding property and differential swelling behavior of HEMA-HEA hydrogels, we achieved postprogrammable transformation control, enabling the design of complex shapes and autonomous fixation of RFID chips underwater. The RFID embedded in the hydrogel could communicate normally underwater, indicating that the hydrogel had no effect on the transmission of wireless signals. This study provides new insights into the design of high-performance hydrogels and demonstrates their potential for flexible electronics and underwater applications.