Rational design of bioinspired gradient conductivity and stiffness for tactile sensors with high sensitivity and large linear range

Recently, wearable piezoresistive tactile sensors have attracted considerable attention owing to their potential applications, ranging from electronic skin to human-machine interaction. However, it is still difficult to mitigate the trade-off between sensitivity and linearity. Inspired by the hierarchical and gradient structures in natural systems, a versatile resistive pressure-sensing platform with controllable stress transfer and contact areas was fabricated by designing gradient styrene-butadiene-styrene triblock copolymer (SBS) sponges followed by the deposition of silver nanoparticles (Ag NPs) and polypyrrole (PPy). The gradient porous structures accompanied by gradient stiffness and conductivity enabled the external force to be efficiently transferred and localized to the sensing areas. Furthermore, the structures enabled a controllable response to the external stress via the gradual activation of electron pathways. These synergistic effects enabled the bioinspired tactile sensors to possess excellent sensing performance, which is demonstrated by large sensing range (∼80%), large linear range (∼72%), high sensitivity (∼1.07), low hysteresis behavior (7.66%), fast response time (177 ms), and excellent durability (more than 1100 cycles). Important applications of tactile sensors, including wrist-pulse-signal detection, speech recognition, finger bending, and tactile interfaces, have been successfully demonstrated. This conceptually simple but powerful approach can be applied to other nanomaterial systems to develop next-generation electronics.