A porous self-healing hydrogel with an island-bridge structure for strain and pressure sensors

Conductive hydrogels have attracted widespread attention in wearable electronic devices and human motion detection. However, designing self-healing hydrogels with high conductivity and excellent mechanical properties remains a challenge. In this work, polyvinyl alcohol/carbon nanotubes/graphene (PVA/CNTs/graphene) with an island-bridge hydrogel structure and self-healing properties was designed by merging PVA/CNTs hydrogel and PVA/graphene hydrogel, in which the PVA/graphene hydrogel acts as an "island" and PVA/CNTs hydrogel acts as a "bridge" to bridge the entire conductive network. Hydrogen-bonding between the borate ion and the -OH group of PVA allows the conductive hydrogel to heal without any external stimulation. The PVA/CNTs/graphene hydrogel can be used for both stretchable strain and pressure sensors. The obtained PVA/CNTs/graphene composite hydrogel exhibits excellent electrical conductivity, extreme high elastic strain (up to 900%) and strong mechanical pressure (up to 10 kPa). The strain sensor based on the PVA/CNTs/graphene hydrogel exhibits excellent tensile strain sensitivity (a gauge factor of 152.6 in the strain region of 316-600%) and wide detection working range (1-600%) with high durability and repeatability. The sensor also remains highly sensitive when being used as a pressure sensor (-0.127 kPa-1 at 0-5 kPa). Additionally, the PVA/CNTs/graphene hydrogel-based sensor can detect human motions after multiple cuts and self-healing with excellent stability and repeatability. The PVA/CNTs/graphene hydrogel provides a new idea in the development of wearable electronics, demonstrating the potential of the next generation of wearable electronics.