Muscle-inspired capacitive tactile sensors with superior sensitivity in an ultra-wide stress range

Taking inspiration from skeletal muscle with highly oriented myofibers, we developed a tough wood aerogel/poly(ionic liquid) (WA/PIL) hydrogel directly from wood via delignification, impregnation and gelation for the formation of a tactile sensor of electric double-layer capacitive configuration. The WA/PIL hydrogels integrated the representative properties of both wood and ionic liquids, being a promising candidate for both polyelectrolyte and separator materials. The influences of the wood texture and cross-linker (Bis) content on the mechanical and sensing performances of the hydrogels were investigated. The results showed that the tangential hydrogel slice with a 1.0 mol% Bis content (tan 1.0) displayed the most significant improvement in compressive stress (1.65 MPa) and deformation (73.3%) at fracture, suggesting the best compressibility. Electrodes also played a significant role in the sensitivity and stability of the sensor devices. While tan 1.0 with reduced graphene oxide (rGO) electrodes displayed the largest sensitivities (1.13-19.70 MPa-1), tan 1.0 with Ni foams possessed much more stable ionic signals within the whole stress range with sensitivities of 0.33-9.67 MPa-1. Due to the wide-stress-range responsiveness of our hydrogel sensor from gentle finger contact to vigorous hitting modes, it will find promising applications in various human-machine interfaces in the fields of electronics, recreation, sports, etc.