As biocompatible soft materials with stimuli-responsive characteristics, wearable strain sensors based on conductive hydrogels hold substantial promise across diverse engineering fields. However, their practical applications are often hindered by limited sensitivity and issues related to single functionality. This study presents a multifunctional composite hydrogel composed of PAA/PVA/PEDOT:PSS/Ti3C2TX designed for flexible strain sensors and synthesized through a straightforward one-pot polymerization technique. The incorporation of Ti3C2TX MXene nanosheets significantly enhances the porous architecture and mechanical properties of the hydrogel. This hydrogel features a combination of covalent and physical cross-linking networks, showcasing remarkable elastic recovery, puncture resistance, stretchability, robust interfacial adhesion, and self-healing capabilities. The hydrogel-based strain sensor demonstrates exceptional performance, including high sensitivity (GF = 21.36 in the 31-50% strain range), a low detection limit (53.0 Pa), rapid response and recovery times (42 ms/38 ms), and long-term stability (>1,600 cycles). Its practical applications in information encryption, handwriting recognition, and wireless robotic motion monitoring highlight its potential as a versatile platform for advanced flexible sensing technologies.

Although two-photon polymerization (TPP) is a flexible micro-nanoscale 3D printing technique, conventional polymeric resists contain permanently embedded organic photoinitiators that adversely affect the mechanical properties of printed structures. Here, we report a novel type of ligand-engineered nanoclusters, which serve simultaneously as the photoinitiators in the TPP resist and as mechanical reinforcement after polymerization. Uniform nanoclusters are liganded with both reactive and photosensitive molecules to achieve combined functions. An enhanced two-photon absorption of 22.45 GM (Goeppert-Mayer) suggests synergistic photoenergy conversion between the nanocluster core and photosensitive ligands. The stable dispersion of the nanoclusters enables high-fidelity 3D printing with a resolution of 141 nm. Covalently bonded interfaces between the nanoclusters and the crosslinked polymer matrix enable outstanding mechanical stiffness and strength for the printed microscale structures. In situ mechanical tests reveal that the well-incorporated nanoclusters result in a 75% enhancement in stiffness and a 105% enhancement in strength. Such a convenient ligand-engineering strategy can go beyond photoinitiation and mechanical reinforcement, enabling new potentials of the TPP technique for the fabrication of high-performance micromechanical devices with diverse applications.

Soft Li-ion batteries, based on conventional organic electrolytes, face performance degradation challenges due to moisture penetration and safety concerns due to possible leakage of toxic fluorine compounds and flammable solvents under mechanical damage. We design a water-scarce hydrogel electrolyte with fluorine-free lithium salt to achieve wide electrochemical stability window (up to 3.11 volts) in ambient air without hermetic packaging while balancing high stretchability (1348%), ion conductivity (41 millisiemens per centimeter), and self-healing capabilities for mechanically and chemically safe stretchable Li-ion batteries. Molecular synergy between hydrophilicity and lithiophilicity of zwitterionic polymer backbone is revealed by molecular dynamics simulations. The battery exhibits capacity retention under harsh mechanical stresses—enduring stretching, twisting, folding, and multiple through-punctures by a needle—while self-healing from repeated through cuts by a razor blade. Stable ambient operation for 1 month over 500 charge-discharge cycles (average coulomb efficiency, 95%) is achieved. A prototype self-healing electronic system with embedded soft batteries demonstrates practical application as a durable embodied energy source.

Dehydration has been a key limiting factor for the operation of conductive hydrogels in practical application. Here, we report self-healable ionic skins that can self-regulate their internal moisture level by capturing extenral moistures via hygroscopic ion-coordinated polymer backbones through antipolyelectrolyte effect. Results show the ionic skin can maintain its mechanical and electrical functions over 16 months in the ambient environment with high stretchability (fracture stretch similar to 2216 %) and conductivity (23.5 mS/cm). The moisture self-regulating capability is further demonstrated by repeated exposures to harsh environments such as 200 degrees C heating, freezing, and vacuum drying with recovered conductivity and stretchability. Their reversible ionic and hydrogen bonds also enable self-healing feature as a sample with the fully cut-through damage can restore its conductivity after 24 h at 40 % relative humidity. Utilizing the ionic skin as a building block, self-healing flexible piezoelecret sensors have been constructed to monitor physiological signals. Together with a facile transfer-printing process, a self-powered sensing system with a self-healable supercapacitor and humidity sensor has been successfully demonstrated. These results illustrate broad-ranging possibilities for the ionic skins in applications such as energy storage, wearable sensors, and human-machine interfaces.

A time- and cost-effective fabrication methodology via a two-mode mechanical cutting process for multilayer stretchable electronics has been developed without using the conventional photolithography-based processes. A commercially available vinyl cutter is used for defining complex patterns on designated material layers by adjusting the applied force and the depth of the cutting blade. Two distinct modes of mechanical cutting can be achieved and employed to establish the basic fabrication procedures for common features in stretchable electronics, such as the metal interconnects, contact pads, and openings by the "tunnel cut" mode, and the flexible overall structure by the "through cut" mode. Three robust and resilient stretchable systems have been demonstrated, including a water-resistant, omnidirectionally stretchable supercapacitor array, a stretchable mesh applicable in sweat extraction and sensing, and a skin-mountable human breathing monitoring patch. Results show excellent electronic performances of these devices made of multilayer functional materials after repetitive large deformations.

In this work, we report a thermoelectric energy harvester based on an ion-conductive ionogel with three distinctive features as compared with the state-of-art systems: (1) self-healable in both the material and device operations under large deformations; (2) ultrahigh Seebeck coefficient with the measured value of 7068 µV/K for the material, and 298 µV/K for a prototype energy harvester in operations; and (3) stable performances under large bending states with little changes. As such, this energy harvester could find potential applications by further packaging and design in wearable devices to convert the temperature differences between human body/skin and environment to electricity.

A variety of autonomous oscillations in nature such as heartbeats and some biochemical reactions have been widely studied and utilized for applications in the fields of bioscience and engineering. Here, we report a unique phenomenon of moisture-induced electrical potential oscillations on polymers, poly([2-(methacryloyloxy)ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide-co-acrylic acid), during the diffusion of water molecules. Chemical reactions are modeled by kinetic simulations while system dynamic equations and the stability matrix are analyzed to show the chaotic nature of the system which oscillates with hidden attractors to induce the autonomous surface potential oscillation. Using moisture in the ambient environment as the activation source, this self-excited chemoelectrical reaction could have broad influences and usages in surface-reaction based devices and systems. As a proof-of-concept demonstration, an energy harvester is constructed and achieved the continuous energy production for more than 15,000 seconds with an energy density of 16.8 mJ/cm 2 . A 2-Volts output voltage has been produced to power a liquid crystal display toward practical applications with five energy harvesters connected in series.

We present the synthesis and characterizations of jellyfish inspired biomimetic hydrogels for potential applications in transparent, self-healing, and ultra-stretchable sensors and actuators. Compared to the state-of-art, this work achieved five distinctive advancements: (1) highly transparent with ~85% transmittance within the visible light range; (2) ultra-stretchable without mechanical failure under more than 1100% applied strain; (3) excellent self-healing capability with broken pieces fully amended visually in 24 hours and piezoresistive gauge factor increased from 1.4 to 2.3; (4) highly adhesive with the self-bonding property, and (5) demonstrations of strain sensing and mechanical actuating for various potential applications.

Traditional ionic liquids are sensitive to humidity but with long response time and nonlinear response. Pure liquid-state ionic liquids are usually hard for dehydration which have ultralong response time for humidity sensing. The immobilization of ionic liquids provide a possible way for high performance humidity sensing. Hydrophobic materials and structures also promised faster response in humidity sensing, because of easier desorption of water. In this work, we prepared flexible humidity sensitive composites based on hydrophobic ionic liquid and polymer. The combination of hydrophobic ionic liquid with hydrophobic polymer realized linear response, high sensitivity with low hysteresis to humidity. By adjusting the ratio of ionic liquid, not only the impedance but also the hydrophobicity of composite could be modulated, which had a significant influence on the humidity sensing performance. The morphology and microstructure of the material also affected its interaction with water molecules. Due to the diverse processing methods of polymer, highly transparent film fabricated by spinning-coating and nanofibrous membrane fabricated by electrospinning could be prepared and exhibited different response time, which could be used for different application scenarios. Especially, the fibrous membrane made with electrospinning method showed an ultrafast response and could distinguish up to 120 Hz humidity change, due to its fibrous structure with high specific surface area. The humidity sensors with ultrafast, linear response and high sensitivity showed potential applications in human respiratory monitoring and flexible non-contact switch. To better show the multifunction of ionic liquid-polymer composite, as a proof of concept, we fabricated an integrated humidity sensitive color change device by utilizing lower ionic liquid content composite for sensing in the humidity sensing module and higher ionic liquid content composite as the electrolyte in the electrochromic module.

We report a flexible, hydrogel-based electrolyte material for microsupercapacitors with: 1) self-healing property in ambient environment, 2) high stretchability (elongation> 1000%), 3) 280 times increase in ion-conductivity as compared to that of conventional polyvinyl alcohol (PVA) based acidic electrolytes, and 4) high transparency. A transfer-printing-based patterning process was developed to allow high-resolution pattering on hydrogel. Prototype self-healable micro-supercapacitors (SHMS) have been fabricated with three key demonstrations: 1) working as a power supply for commercial LEDs, 2) retention of same performances before/after a 180-degree folding process, and 3) restoration of performances even after being cut through by a razor blade and after the self-healing process.

Understanding the mechanism of the stability and decay of surface electrostatic charges in different liquid environments is critical for the reliability of devices based on electrostatic functions or preventing the damage from electrostatic charge accumulation. In this work, the influences of surface electrostatic charges in polar and protic (Ethanol and Water), polar and aprotic (Tetrahydrofuran and Chloroform), and non-polar and aprotic (Benzene and Hexane) liquids have been investigated. Results prove that ionization in liquid or polarity of the liquid molecules can determine the electrostatic charges neutralization, and adding small amount of matter (1% Vol) that can ionize in non-polar and aprotic liquids can avoid the electrostatic charges accumulation. Moreover, air-bubble-structured electret is designed to improve the water-against ability for surface electrostatic charges.

Paper-based pressure/strain sensors could have potential wide applications with wearable features in disposable products. In this study, molybdenum carbide-graphene (MCG) composites with porous and stacking micro-structures are fabricated on top of the paper substrate to act as piezo-resistivity strain/pressure sensors. As a strain sensor, this paper-based device can detect not only the amplitude and frequency of applied strain but also the direction as tensile or compressive deformation. The gauge factors are 73 and 43 for tensile and compressive strain, respectively, with demonstration example in detecting and recognizing human body motions. As a pressure sensor, this MCG-based paper device has high sensitivity to weak pressure signals such as sounds by distinguishing the seven piano notes. Our study provides a simple strategy for developing paper-based electronics with unique properties toward practical applications.

Metallic materials based sensors have shown potential applications in the detections of strain, temperature, pressure, and surface-enhanced Raman scattering (SERS). However, most metal-based sensors can only detect a single stimulus. In this work, we designed a multifunctional silver sensing platform for simultaneous strain sensing and SERS sensing. The silver nanoporous structures were facilely deposited by a pulsed laser deposition technique. The microstructure of silver layer could be readily controlled by adjusting deposition parameters, which greatly influenced the sensitivity and sensing range of strain detection. The interface of a sensor could be controlled to achieve a high sensitivity of strain sensing. Different trace substances were detected by the sensing platform through SERS. This sensing platform also had good antibacterial properties, which are advantageous in wearable electronics. (C) 2019 Elsevier B.V. All rights reserved.

Narrowing the bandgap of lead-free double-perovskite Cs2AgBiBr6 is required for using this material in future photovoltaics. Herein, we demonstrate a bandgap engineering of Cs2AgBiBr6 by introducing Sb to substitute up to 75% of Bi via a versatile solution-processed method in dimethyl sulfoxide at 180 degrees C. The resultant Cs2AgSbxBi1-xBr6 (x = 0, 0.25, 0.50, 0.75) thin films possess high crystallinity and good thermostability. Moreover, the Sb substitution enables an obvious bandgap reduction of 0.25 eV. The fabricated solar cell using the Cs2AgSbxBi1-xBr6 (x = 0.25) thin film obtained an increased performance than the reference Cs2AgBiBr6. The effective bandgap narrowing via a facile solution method might accelerate the development of Cs2AgBiBr6-based materials for photovoltaic applications.

A paper-based, disposable strain sensor by means of a direct laser printing process with high sensitivity has been developed and demonstrated. Commercially-available printing papers are first soaked with the gelatin-Mo 5+ ink and ablated by a CO 2 laser to convert molybdenum ions into conductive MoC and graphene nanocomposite flakes for disposable paper electronics. The strain sensor made of continuous MoC flakes has the capability of detecting and distinguishing both tensile and compressive strain. It is found that the stability of the sensor is preserved when there are defects in the device as well as in environments with heavy humidity for potential applications in wearable devices.

•Using NH4HCO3 as chemical foaming agent to produce porous composites.•Being able to detect both tensile and compression strains.•Observing strain-enhanced-sensitivity phenomenon in both sensors.•Applications in wearable devices, circuit control and strain gauges.

Temperature and moisture are critical factors for both the environment and living creatures. Most temperature sensors and humidity sensors are rigid. It still remains an unsolved problem to fabricate a flexible sensor that can easily detect temperature and humidity at the same time. In this work, we made a flexible multifunctional temperature and humidity sensor from graphene woven fabrics. The integrated sensor could measure temperature and humidity simultaneously. The temperature-sensing part and the humidity-sensing part were stacked in layer structure, occupying little space and showing good flexibility while exhibiting high sensitivity and very little mutual interference. The different factors that affected the sensing properties of the sensor were examined. The integrated sensor was successfully utilized in several real life application scenarios, which showed its potential for wider use in environment sensing and health monitoring.