Liquid Metal‐Based Organohydrogels for Wearable Flexible Electronics

Abstract

Currently, developing organohydrogel‐based wearable flexible electronics (WFEs) has aroused intensive research interest, since they possess superior environmental stabilities than hydrogel‐based WFEs, but the development of organohydrogels is still in the infant stage. Herein, an efficient strategy is developed to achieve the fast preparation of organohydrogels by exploring the high reactivity of eutectic gallium–indium alloy in inducing radical polymerization, and constructing the glycerol/water binary solvent system. The obtained organohydrogels, named liquid metal‐based ion‐conducting organohydrogels (LMIOs), possess excellent environmental adaptability over a wide temperature range (−20 to 100 °C) and high transparency. With outstanding mechanical properties and self‐healing abilities, LMIOs can act as strain sensors, showing high sensing sensitivities in broad strain range (0.1–1000%) and fast response speed (<100 ms). Therefore, LMIOs perform well in sensing strains from human motions. Besides, LMIOs can be constructed on latex gloves and prosthetic fingers, forming an LMIO skin on their surfaces. The latex gloves equipped with the LMIO skin can accurately recognize the gesture changes of users. The LMIO skin on the prosthetic finger behaves like human skin, possessing the capability to detect the finger's movements and self‐healing ability. Hence, LMIOs present great prospects in skin‐attachable devices, robotics, and prosthetics.

Materials and Structural Designs toward Motion Artifact-Free Bioelectronics

“…As shown in Figure a, the channel acts as a conductive circuit and serves as packaging to prevent leakage . Researchers have also tried to combine a liquid metal with other materials such as sponges, ,− polymers, ,, and hydrogels, ,,, as a composite as shown in Figure b–e. By mixing a liquid metal with other low-modulus polymers (Figure c) or hydrogel (Figure e), , the phenomenon of liquid flow is eliminated while maintaining fluidity at the microscopic level, resulting in a material with an electrical stability.…”

Liquid metals nanotransformer for healthcare biosensors

“…This provided a facile approach to fabricating LM circuits in miniaturized devices. Based on this principle, Zhang et al fabricated a flexible LMNPs are based on the induction of cadmium ions by a three-phase electric field; (ii) LMNPs absorb UV light; (iii) The solid-core liquid-shell structure of GaNPs senses temperature changes; (B) LMNPs-based one-dimensional circuit structures: (i) Preparation of conductive pathways from sintered nano-LMs; (ii) High conductivity of nano-LM circuits [174] ; (iii) Nano-LMs for the preparation of conductive fibres [178] ; (C) Nano-LM planar circuit structure: (i) Multiple ways of preparing plannar structures and sintering; (ii) Selfsintering of liquid metal to form planar structures; (iii) Stretchability of flat structures [184] ; (iv) Plane structures rich in other sensing properties [163] ; (D) Nanometer LM embedded elastomer structure: (i) Cross-linking network of LMEE; (ii) LMEE material with good strain sensitivity; (iii) Multiple interactions give LMEE materials self-adhesive properties [190] ; (iv) The strong self-healing capability of LMEE; (v) LMEE formed by multiple conductive fillers. CNF: Cellulose nanofiber; CNT: carbon nanotube; LMEE: LM embedded elastomer; LMNPs: LM nanoparticles; MEK: methyl ethyl ketone; PAA: poly(acrylic acid); PDMS: polydimethylsiloxane; PVDF-HFP-TFE: poly(vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene); SA: sodium alginate; UV: ultraviolet.…”

“…In recent years, hydrogels have gained increasing interest in many biomedical applications because of their ability to convert stimuli during bioassay processes into electrical signals [189,190] . Other elastomers, such as rubbers, plastic polymers [151] , etc., are also being used more and more widely.…”

“…Based on this mechanism, LMEE can be used for strain-resistance type sensors [Figure 5D ii] [154,193,194] . In addition, the good flexibility and electrical conductivity of the composite material also facilitate the detection of bioelectrical signals from the human body [192] , and the abundance of polar groups allows LMEE to form rich hydrogen and coordination bonds with human skin and thus obtain self-adhesive properties [Figure 5D iii] [190,192,195] . LMEE could also exhibit good self-healing properties by choosing appropriate substrates [196] , e.g., LMNP/poly (3,4ethylenedioxythiophene):sulfonated bacterial cellulose nanofiber (LMNP/PEDOT:BCNF) suspensions with AA can re-establish ion and electron transport channels within 0.16 s [197] [Figure 5D iv].…”

Skin‐Inspired Ultrafast Self‐Healing Wearable Patch with Hybrid Cooling for Comfortable and Durable Electromyographic Monitoring

“…Electronic skins can detect numerous physiological and physical signals, exhibiting their great potential as platforms for personal healthcare, soft robotics, behavior monitoring, and human-machine interaction. [1][2][3][4][5][6][7][8] Ideally, electronic skin should closely mimic natural skin. [9][10][11] As the body's largest organ, the skin is an integrated multisensory system with a self-healing ability that helps stabilize body temperature.…”