Double-Network Hierarchical-Porous Piezoresistive Nanocomposite Hydrogel Sensors Based on Compressive Cellulosic Hydrogels Deposited with Silver Nanoparticles

Hydrogels have attracted growing attention in electronics due to their soft, flexible nature and ion-rich physiological environment. Herein, we reported a strategy to not only enhance a traditional polyanion hydrogel—poly(acrylic acid) (PAAc)—but also improve its piezoresistive sensitivity by synthesizing and introducing a precompressed double-cross-linked (DC) lignocellulosic hydrogel with uniformly and regularly distributed big pores (with diameters of 0.6–3.3 μm) in the compact PAAc, producing double-network (DN), hierarchical-porous composite ionic hydrogels. The lignocellulosic hydrogel was coated with polydopamine (pDA) followed by in situ deposition of silver nanoparticles (AgNPs) via reduction under the assistance of pDA prior to compositing. The resulting composite ionic hydrogels exhibited excellent properties, including high water content (around 82%) and thus abundant hydration ions, outstanding mechanical properties (2.13–3.20 MPa with PAAc concentrations from 2.8–3.2 wt %), high softness (76.8%–94.8% maximum strains), and high piezoresistive sensitivity (up to 9.34 MPa–1). The assembled hydrogel sensors can detect a wide range of pressures quickly and accurately in both gentle and hard physical pressing modes, demonstrating great potential application in various human–machine interfaces in the fields of electronics, sports, recreation, and so on.