A stretchable and conductive design based on multi-responsive hydrogel for self-sensing actuators

Abstract

Intelligent hydrogel materials have significant potential for soft robotic applications due to their sharply and reversibly responding to various external stimuli. However, obtaining a biomimetic hydrogel actuator with integrated self-sensing and self-actuation properties is still a great challenge. Herein, a multifunctional conductive hydrogel is fabricated by incorporating a conductive polymer polyaniline (PANI) into a double network poly(N-isopropylacrylamide-co-acrylamide)/poly(vinyl alcohol) (PNA/PVA) hydrogel. The as-prepared conductive PNA/PVA/PANI hydrogel could span a wide range of mechanical properties and phase transition temperatures by simply tuning polymer composition. When combined the active PNA/PVA/PANI layer with a passive polyacrylamide (PAAM) layer, a bilayer hydrogel actuator exhibits superior actuation ability with high bending speeds by the thermal stimulation. In addition, the introduction of PANI component endows the PNA/PVA/PANI hydrogel with excellent electrical conductivity up to 3.91 ± 0.15 S/m and ultrahigh-efficiency of photothermal conversion. Consequently, the PNA/PVA/PANI hydrogel not only exhibits piezoresistive strain/pressure sensing in motion recognition and physiological signal monitoring, but also displays a variety of precise and remotely driven photo-responsive locomotion such as contraction, bending, light tracking and weightlifting by locally near-infrared (NIR) illumination. Furthermore, this hydrogel can simultaneously detect these actuation states via real-time resistance change, achieving closed-loop monitoring and sensing feedback. The self-sensing actuation performance has been fully demonstrated by remotely controlling a hydrogel octopus’s grasping and object moving activities. The multi-responsiveness and real-time sensory feedback will inspire this material to be applied in novel soft biomimetic actuating materials and systems.