Anisotropic, Flexible Wood Hydrogels and Wrinkled, Electrodeposited Film Electrodes for Highly Sensitive, Wide-Range Pressure Sensing

Abstract

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.

Development of Conductive Hydrogels for Fabricating Flexible Strain Sensors

“…Inspired by the microstructures of biological muscles, Nie and coworkers developed tough wood hydrogels for capacitive strain sensors by introducing cross‐linked PAA into the pores of delignified wood (Figure 18f). [ 208 ] The wood hydrogel was sliced in cross, radial, and tangential directions, respectively to form cross, radial, and tangential hydrogels and sandwiched between two layers of the rGO film electrode, that is, a top wrinkled rGO electrode and a bottom flat rGO electrode, forming the capacitive pressure sensor. The tangential and the radial sensors, which are made from radial and tangential hydrogels, have rather high sensitivity (58.4 and 61.5 MPa −1 , respectively in the working range of 0.1−0.125 MPa compression stress) and wide working range (0.1−1.6 MPa).…”

Recent Application of Cellulose Gel in Flexible Sensing-A Review

“…11b) can simulate the mechanical and sensing functions of muscle tissue, the sensitivity is not good. [142] The double-crosslinked hydrogels with microcrystalline and borate bonds have excellent biocompatibility and rapid resistance to strain exerted, and their sensitivity is obviously better than the former, which can detect the joint motion of human body and is suitable for human health management. Chlorinated naphthaleneabscisic acid was first prepared by periodate oxidation and reductive amination, and then mixed with MWNTs and polyvinyl alcohol.…”

Preparation and properties of a kind of high conductivity flexible wood with light switch characteristics

“…Ionic conductivity is also a commonly used conductive method. The ionic conductivity of AM based wood hydrogels at low concentration is 5 × 10 −4 S/m, 26 the ionic conductivity of the wood hydrogel prepared by complexation of acrylic acid and Al 3+ is 0.2 × 10 −1 S/m 27 …”

“…When they change the molecular arrangement from one physical state to another, they can reversibly store or release a large amount of heat energy 15,28,29 . Organic PCM, such as polyethylene glycol, fatty alcohol, paraffin and fatty acid, has been widely used in various energy‐saving materials due to its ability of reversible absorption and release of heat energy 12,20,26–34 . Because the phase transition is controlled by the crystallization and melting of the polymer chain 31 .…”