Self-adhesive, self-healing, biocompatible and conductive polyacrylamide nanocomposite hydrogels for reliable strain and pressure sensors

To realize long-term and stable applications of wearable and flexible sensors for motion detection, health analysis and wisdom medication in harsh environments, self-healing, self-adhesive, electrically conductive and biocompatible polyacrylamide (PAM) nanocomposite hydrogels are fabricated as flexible strain or pressure sensors by in situ polymerization of acrylamide in the presence of polydopamine-modified carbon nanotubes (PDA@CNTs) for effectively detecting human motions, identifying materials and their shapes, and transmitting health information. The resultant PDA@CNT/PAM nanocomposite hydrogel exhibits a high self-healing efficiency of 97.3%, excellent biocompatibility, and strong adhesion with substrates based on hydrogen bonding and π–π stacking interactions. Based on the piezoresistive effect, the nanocomposite hydrogel-based strain sensor exhibits a high sense gauge factor of 3.93 at a strain of 400% and responds quickly with a fast response time of 76 ms when detecting human movement. Thanks to the contact electrification and the electrostatic induction, the nanocomposite hydrogel-based pressure sensor can respond to pressure linearly and generate voltage signals in the absence of an additional power supply. Furthermore, the self-powered smart ring made of the silicone rubber-coated PDA@CNT/PAM hydrogel enables efficient and concise information transmission via Morse code.