Multifunctional starch-based double-network hydrogels as electronic skin

The realization of flexible pressure sensors that could mimic the perception functions of human skin (touch, temperature, and humidity) is important for development of electronic skin. However, the design and preparation of highly sensitive sensors for multifunctional sensing of pressure, temperature and humidity remains a challenge. Here, we first designed and prepared a flexible starch/polyacrylamide (PAM) double-network hydrogel, with additional introduction of Na+ and Cl- to further enhance the electrical properties. Subsequently, a multifunctional pressure sensor was fabricated by sandwiching a microstructured starch-based hydrogel into two flexible AgNWs electrodes. In the test run, the prepared sensor exhibited a high sensitivity of 48.35 kPa(-1), a fast response time of 11 ms, and remarkable mechanical stability (>3000 cycles). Given the satisfactory performance for pressure sensing, we demonstrated the ability of the sensor to monitor various human dynamics. Moreover, the starch-based hydrogel was further developed as a flexible temperature and humidity sensor for its water absorption and swelling properties. In particular, the asynchrony of pressure, temperature and humidity strains (straining to stability at 11 ms, 2 s and 10 s, respectively) resulted in the automatic separation of different electrical signals. The intuitive interpretation of the data without involving complex parameter separation calculations allowed the starch-based hydrogels to be developed as an integrated, multifunctional sensor of pressure, temperature and humidity with high sensitivity and flexibility. The above properties suggest that the prepared bio-based hydrogels may provide a new solution for the prospect of green and multifunctional electronic skin development.