Biological muscles generally possess well-aligned muscle fibers and thus excellent strength and toughness. Inspired by their microstructure, tough wood hydrogels with a preserved unique alignment of cellulose fibers, mechanical anisotropy, and desirable flexibility were developed by introducing chemically and ionically cross-linked poly(acrylic acid) (PAA) into the abundant pores of delignified wood. PAA chains well infiltrated the parallelly aligned cellulose fibers of wood and formed a layer-by-layer network structure, resulting in strong, elastic tangential, and radial wood hydrogel slices. The tangential slices had a high compressive strength of 1.73 MPa and a maximum strain at fracture of 69.4%, while those of the radial slices were 0.6 MPa and 47.0%. After sandwiching the radial and tangential hydrogel slices with reduced graphene oxide (rGO) film electrodes into capacitive pressure sensors (CPSs), the tangential CPS displayed the most desired, gradient sensitivity values in the whole stress range. Additionally, the wrinkling treatment of the rGO electrode greatly improved the capacitance responsiveness toward pressure. The real-time sensing stress values of our tangential CPS during monitoring practical human activities were calculated in the range of 0.1−1.3 MPa, demonstrating the achievement of ultrafast, highly sensitive, and wide-stress-range detection for potential applications in human−machine interfaces.
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
hydrogelpoly(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.
Taking inspiration and utilizing materials directly from nature, a simple and green strategy to fabricate biomass-based highly sensitive flexible tactile sensors was developed. The capacitive sensing devices were constructed by...
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