Wearable Electronic Devices Research Articles

A robust antagonistically assembled triboelectric nanogenerator based on dead‐end closed pore through a one‐step improved phase separation

AbstractThe ongoing global energy crisis presents a significant challenge all over the world. In this study, triboelectric nanogenerator (TENG) made of recyclable thermoplastic polycarbonate has been proposed as a promising environmentally friendly solution due to its potential capability to convert low‐frequency mechanical energy sources such as human motion and ocean waves into electricity with potential applications including powering wearable electronic devices and self‐powered sensors. We introduce an antagonistically structured TENG (A‐TENG) composed of honeycomb porous polycarbonate (hc‐PC) and convex‐patterned dimethylsiloxane, employing a novel one‐stage improved phase separation method. This A‐TENG overcomes the demerits of others thanks to its high surface contact area, simplified fabrication process, enhanced energy conversion efficiency, and cost‐effectiveness, requiring minimal investment. More importantly, this work utilized hc‐PC as a framework for slippery liquid‐infused porous surface (SLIPS) based TENG owing to the special honeycomb porous structure to impregnate silicon oil within pore arrays and mechanically support the whole system. The practical application of SLIPS‐TENG was demonstrated while deployed on the house rooftop to harvest raindrop energy and act as a rain detection sensor.

Deep eutectic solvent and laser-reduced graphene oxide: Synergistic effects in ternary nanocomposite supercapacitors

In recent years, flexible supercapacitors (FSCs) have gained considerable attention as reliable power supplies for wearable and portable electronic devices. However, optimizing both energy and power densities remains a challenge and requires effective enhancement of two key components: the electrolyte and the electrode. To address this, we have developed a new and efficient approach to FSC fabrication using a ternary nanocomposite of laser-reduced graphene@polyaniline/NiFe₂O₄(LrGO@Pani-NF) as the electrode and stable polymer hydrogels as the electrolyte. Also, we constructed FSC devices using a cross-linked poly (vinyl alcohol)/deep eutectic solvent (DES) gel electrolyte (PVA/ChCl/EG) and a PVA/Polyaniline/Nickel Ferrite gel electrolyte (PVA/Pani/NF). Among these devices, the LrGO@Pani-NF//LrGO@Pani-NF demonstrated a remarkable energy density of 48.4 Wh kg⁻¹ at 401.8 W kg⁻¹ and a long cycle life of 1000 cycles with 96.9 % capacity retention at 2 mA cm⁻². Furthermore, the supercapacitors assembled with the DES gel exhibited excellent stability at higher voltages, operating within a potential window of −3.0–3.0 V. This work not only enhances FSC electrochemical performance with graphene nanocomposite electrodes but also introduces a novel method for FSC design using conductive, stable gel electrolytes, thereby improving energy storage capabilities under harsh conditions.

Strong and anti-swelling nanofibrous hydrogel composites inspired by biological tissue for amphibious motion sensors.

Conductive hydrogel-based sensors are increasingly favored for flexible electronics due to their skin-like characteristics. However, conventional hydrogels suffer from significant swelling in humid environments and poor mechanical properties which largely restrict their applications in wearable electronic devices, especially for underwater sensing. Herein, drawing inspiration from the extracellular matrix (ECM) structure, a TPU-PVAc@AgNPs/MXene nanofibrous hydrogel composite (TPAMH) with excellent mechanical robustness and anti-swelling properties is developed. The TPAMH nanofibrous hydrogel composite is created by integrating the silver nanoparticles (AgNPs) and MXene nanosheets into an interwoven network comprising of stiff TPU nanofibers as the fibril scaffold and formic acid-crosslinked PVA hydrogel fibers as the elastic matrix (PVAc). Benefiting from the unique ECM structure, the obtained nanofibrous hydrogel composites exhibit exceptional tensile strength (4.47 MPa), remarkable elongation at break (621%), excellent anti-swelling properties, and high detection sensitivity (maximum gauge factor = 105.02), which are sufficient to monitor body motions in both air and water environments effectively. They can detect large strain movements of fingers, elbows, wrists, and knees, as well as small strain physiological signals such as frown, smile, and pulse beats, with high accuracy. Particularly noteworthy is their ability to accurately identify underwater multidirectional motions and facilitate underwater smart alarms using Morse code.

Construction of rGO-MXene@FeNi/epoxy composites with regular honeycomb structures for high-efficiency electromagnetic interference shielding

With the rapid development of 5G communication technology and wearable electronic devices, the demand for low-reflection electromagnetic interference (EMI) shielding materials is becoming increasingly urgent. In this work, reduced graphene oxide-MXene (rGMH) @FeNi/epoxy EMI shielding composites with a regular honeycomb structure were successfully prepared by the combination of surface functionalization modification, sacrificial template, and freeze-drying. The effects of magnetic FeNi alloy particle loading mode and loading amount on the EMI shielding performance of composites were investigated. The results show that rGMH@FeNi/epoxy EMI shielding composites have the highest EMI shielding effectiveness (EMI SE) and the lowest reflection shielding effectiveness when magnetic FeNi alloy particles are loaded only on the graphene skeleton. In this composite, the EMI SE value of the composite is 61 dB when the rGMH@FeNi mass fraction is 5.4 wt% (f-FeNi mass fraction is 0.9 wt%), which is 4.7 times that of the blended rGO/MXene/FeNi/ epoxy resin composite (13 dB) with the same mass fraction. At the same time, the rGMH@FeNi/epoxy composite has excellent thermal stability (heat-resistance index of 190.3 °C) and mechanical properties (energy storage modulus of 8606.7 MPa). These polymer-based EMI shielding composites with excellent EMI shielding properties and low reflection effectiveness have great potential in the protection of high-power, portable and wearable electronic devices against electromagnetic pollution.

Solid-state supercapacitors based on different electrolytes: structural characteristics and comparative performance

Abstract Solid-state supercapacitors bring huge potential for the next generation of energy storage systems and are especially significant for portable and wearable electronic devices, medical equipment, and smart textiles. This paper provides a concise overview of the device mechanism while discussing the developing status of solid-state supercapacitor electrolytes. The performance evaluation of solid-state supercapacitors is reviewed and compared based on their energy storage characteristics and electrode types (e.g., freestanding, fibre-based, and flexible), followed by an exploration of future research directions and key technical challenges in this field.

Augmenting home entertainment with digitally delivered touch.

In this narrative review, we take a critical look at the various attempts that have been made to augment home (or personal) entertainment experiences via the addition of some form of digitally controlled tactile stimulation. There has been an explosive growth in the market for home entertainment in recent years, and a majority of smartphones and other wearable electronic devices are now touch-enabled. As such, it is important to consider the challenges and potential opportunities for enhanced multisensory entertainment that may result from the introduction of tactile/haptic stimulation in the context of audiovisual digital storytelling and/or gaming. The key technological, financial (and legal), cognitive, and creative/artistic, challenges associated with the tactile augmentation of home entertainment experiences are outlined. Tactile augmentation, in the sphere of both public and personal entertainment, is more likely to succeed when it goes beyond the merely pleonastic vibrotactile reproduction of those interactions/events than can already be seen and/or heard on screen. At the same time, however, it remains uncertain under what conditions immersion in an entertainment experience will be enhanced by the addition of some form of primitive digital tactile stimulation. Ultimately, until a clear usage case can be made for the benefits of introducing a tactile element to home entertainment, it is unlikely to gain traction and switch from being merely a gimmick to more of a valuable element of multisensory storytelling.

Recent advances in self-healing hydrogel composites for flexible wearable electronic devices

Recent advances in self-healing hydrogel composites for flexible wearable electronic devices

Design, application, and recycling of zinc alginate/guar gum hydrogel-based fibers

Extreme cold events are quite common, highlighting the urgent need for flexible wearable electronic devices capable of diagnosing human health in low-temperature environments. Using a wet spinning strategy, we successfully developed sodium zinc alginate/guar gum(SZA/GG) hydrogel fibers with excellent environmental resistance, antimicrobial properties, and electrical conductivity. Building on this, we developed a flexible wearable sensing device that operates stably at low temperatures and exhibits a sensitivity of 0.585 within the range of −20 °C to −40 °C, demonstrating excellent response performance. When evaluating the physical state of outdoor athletes, the amplitude and fluctuation range of electrical resistance provide valuable information about the monitored environment and the risk of frostbite for the individual. However, like any device, it eventually reaches its usage limit. To address the issue of recycling hydrogel fiber waste, we propose recycling and carbonizing the discarded devices to use as a biomass carbon source for fabricating button-type supercapacitors. After 10,000 charge-discharge cycles, the capacitance retention rate reached 92.53 %, demonstrating the potential of these supercapacitors and offering a new approach to reducing resource waste.

Highly sensitive flexible pressure sensor based on laser ablated Ag-MWCNT /MXene for human motion detection

The complex and dynamic human environment, higher requirements are put forward for the high-performance flexible pressure sensors. The materials selection and microstructure design are crucial to achieve high sensitivity and stability. In this work, we fabricated pressure sensitive layer with multiple dimensional materials. Using laser ablation in liquid method, Ag nanoparticles were uniformly distributed in surface of multi-walled carbon nanotubes (MWCNT). Combined with the delaminated MXene, highly pressure sensitive composite could be prepared due to the reduction of contact resistance under pressure. The corresponding piezoresistive sensors showed high sensitivity (12.7 kPa−1), excellent response speed (150 ms), recovery speed (100 ms), and distinguished cycle stability (3000 cycles). Based on the performance of the sensor, it can realize the monitoring of tiny pressure on the human body, and further realize the detection of human activities and health. In addition, the sensor array has spatial recognition capability, providing a way of thinking for the development needs of future intelligent wearable electronic devices. The sensors can measure changes in resistance caused by finger bending, slight breathing, pulse, vocal cord vibration, and other movements to realize human activity and health monitoring. At the same time, the 3×3 sensor array system can recognize the layout of pressure in space. This simple preparation and low cost of the sensor can Facilitate the progress towards sophisticated wearable electronic gadgets.

Super-Elastic and Temperature-Tolerant Hydrogel Electrodes for Supercapacitors via MXene Enhanced Ice-Templating Synthesis.

Developing flexible energy storage devices with good deformation resistance under extreme operating conditions is highly desirable yet remains very challenging. Super-elastic MXene-enhanced polyvinyl alcohol/polyaniline (AMPH) hydrogel electrodes are designed and synthesized through vertical gradient ice templating-induced polymerization. This approach allows for the unidirectional growth of polyaniline (PANI) and 2D MXene layers along the elongated arrayed ice crystals in a controlled manner. The resulting 3D unidirectional AMPH hydrogel exhibits inherent stretchability and electronic conductivity, with the ability to completely recover its shape even under extreme conditions, such as 500% tensile strain, 50% compressive strain. The presence of MXene in the hydrogel electrode enhances its resilience to mechanical compression and stretching, resulting in less variation in resistance. AMPH has a specific capacitance of 130.68 and 88.02mFcm-2 at a current density of 0.2 and 2mAcm-2, respectively, and retains 90% and 70% of its original capacitance at elongation of 100% and 200%, respectively. AMPH-based supercapacitors demonstrate exceptional performance in high salinity environments and wide temperature ranges (-30-80°C). The high electrochemical activity, temperature tolerance, and mechanical robustness of AMPH-based supercapacitor endow it promising as the power supply for flexible and wearable electronic devices.

Constructing Electronic/Ionic‐Conductive Hydrogel with Soft Compliance and High Conductivity as Flexible Strain Sensor

Flexible sensors are garnering substantial interests for various promising applications, including medical electronics, environmental monitoring, and wearable devices. Developing a flexible sensor with high compliance, high sensitivity, and high reliability through the construction of a novel composite conductive hydrogel based on the synergistic enhancement effect of conductive polymers and metal ions is a remarkable achievement. Herein, an electronic/ionic‐conductive double network hydrogel (polypyrrole (PPy)/carboxymethyl cellulose (CMC)‐Al3+/polyvinyl alcohol (PVA)) with soft compliance, highly conductivity, and stability is presented. Moreover, owing to the synergistic reinforcement effect of the relatively immobilized “islands” of PPy particles and large amounts of movable “bridges” of aluminum ions (Al3+) within the double network hydrogel, the as‐optimized PPy/CMC‐Al3+/PVA composite gels exhibit excellent conductivity (σ = 3.47 ± 0.25 S m−1) and mechanical properties (E = 18.53 ± 0.67 kPa). Furthermore, it has been developed as strain sensors with relatively high linear sensitivity (gauge factor = 2.58) within a broad linearity range (0–400%). It can also be served as a monitoring devices for subtle physiological signals emanating from various parts of the human body. The robust sensor has great potential to be developed as wearable electronic devices and applied in healthcare monitoring fields.

The Influence of Molecular Weights on Dispersion and Thermoelectric Performance of Alkoxy Side-Chain Polythiophene/Carbon Nanotube Composite Materials.

In the development of wearable electronic devices, the composite modification of conductive polymers and single-walled carbon nanotubes (SWCNTs) has become a burgeoning research area. This study presents the synthesis of a novel polythiophene derivative, poly(3-alkoxythiophene) (P3(TEG)T), with alkoxy side chains. Different molecular weight variants of P3(TEG)T (P1-P4) were prepared and combined with SWCNTs to form composite materials. Density functional theory (DFT) calculations revealed a reduced bandgap for P3(TEG)T. Raman spectroscopy demonstrated π-π interactions between P3(TEG)T and SWCNTs, facilitating the dispersion of single-walled carbon nanotubes and the formation of a continuous conductive network. Among the composite films, P4/SWCNTs-0.9 exhibited the highest thermoelectric performance, with a power factor (PF) value of 449.50 μW m-1 K-2. The fabricated flexible thermoelectric device achieved an output power of 3976.92 nW at 50 K, with a tensile strength of 59.34 MPa for P4/SWCNTs. Our findings highlight the strong interfacial interactions between P3(TEG)T and SWCNTs in the composite material, providing an effective charge transfer pathway. Furthermore, an improvement in the tensile performance was observed with an increase in the molecular weight of the polymer used in the composite, offering a viable platform for the development of high-performance flexible organic thermoelectric materials.

Highly conductive, stretchable, and biocompatible graphene oxide biocomposite hydrogel for advanced tissue engineering

The importance of hydrogels in tissue engineering cannot be overemphasized due to their resemblance to the native extracellular matrix. However, natural hydrogels with satisfactory biocompatibility exhibit poor mechanical behavior, which hampers their application in stress-bearing soft tissue engineering. Here, we describe the fabrication of a double methacrylated gelatin bioink covalently linked to graphene oxide (GO) via a zero-length crosslinker, digitally light-processed (DLP) printable into 3D complex structures with high fidelity. The resultant natural hydrogel (GelGOMA) exhibits a conductivity of 15.0 S m-1as a result of the delocalization of theπ-orbital from the covalently linked GO. Furthermore, the hydrogel shows a compressive strength of 1.6 MPa, and a 2.0 mm thick GelGOMA can withstand a 1.0 kg ms-1momentum. The printability and mechanical strengths of GelGOMAs were demonstrated by printing a fish heart with a functional fluid pumping mechanism and tricuspid valves. Its biocompatibility, electroconductivity, and physiological relevance enhanced the proliferation and differentiation of myoblasts and neuroblasts and the contraction of human-induced pluripotent stem cell-derived cardiomyocytes. GelGOMA demonstrates the potential for the tissue engineering of functional hearts and wearable electronic devices.

Electroplating nickel patterns onto polyol-mediated reduced graphene oxide printed textile surfaces

This report explores advancements in multi-step printing/electroplating technique for creating conductive patterns on flexible substrates, which serve as potential structures in wearable electronic devices. The study introduces a novel procedure that employs a sequential process involving polyol screen printing and electroplating, enabling the development of conductive nickel-coated patterns with a conductivity value of about 1123 S/cm on textiles. A significant innovation in this study is the use of a graphene oxide/ethylene glycol (GO/EG) ink, which can be converted into reduced graphene oxide (rGO) through in-situ polyol treatment on the surface of PET fabrics. The effectiveness of this treatment is evidenced by various analytical and microscopic techniques, which confirm the successful printing of conductive rGO patterns onto PET fabric at 220 ˚C. The printed rGO patterns on the fabric surface are then subjected to electroplating as a target substrate and cathode for varying durations, ranging from 5 to 30 minutes. The study thoroughly examines the influence of electroplating time on the microstructures and electrical conductivity of the resulting patterns, with nickel deposition reaching up to 50.8 mg/cm².

Flexible all-solid-state asymmetric supercapacitor based on Ti3C2Tx MXene/graphene/carbon nanotubes

As the emerging 2D materials, MXenes have been regarded as promising electrode materials in supercapacitor as power supply for wearable and portable electronic devices due to their metallic conductivity, hydrophilic feature, abundant functional groups, and large theoretical specific surface area etc. The capacity and rate capability of MXene-based electrodes is limited by the sheet restacking, hindering their further development. Herein, Ti3C2Tx MXene/graphene/carbon nanotubes (MXene/graphene/CNTs) flexible film was successfully fabricated by vacuum assisted filtration. Intercalation and confinement of graphene and carbon nanotubes between the Ti3C2Tx MXene nanosheets could increase the spacing and specific surface area, alleviate the stacking of MXene nanosheets, thus enhancing the electrochemical properties. The prepared MXene/graphene/CNTs film possesses increased specific surface area, average pore size, pore volume (112.259 m2g−1, 9.982 nm, 0.276 cm3g−1), compared to MXene (93.088 m2g−1, 3.786 nm, 0.088 cm3g−1). Consequently, MXene/graphene/CNTs delivers high area specific capacitance of 1862.5 mF cm−2 at 1 mA cm−2 and excellent rate capability (1525 mF cm−2, 81.88 % at 20 mA cm−2). Flexible asymmetric supercapacitor constructed with MXene/graphene/CNTs film and active carbon as positive and negative electrodes, and PVA/H2SO4 gel as solid electrolyte, achieves an energy density of 133.75 μWh cm−2 at the power density of 750 μW cm−2. In addition, there is still 94.9 % of the initial performance after cycling 8000 charge/discharge cycles at 10 mA cm−2, corresponding to a single-turn decay rate down to 0.00019 %. Besides, this flexible supercapacitor manifests outstanding electrochemical stability at different bending times. These advantages make the flexible supercapacitor device very promising for wearable electronics applications.

Advanced hydrogel electrolyte with enhanced interfacial adhesion and low-temperature resistant for flexible zinc-ion batteries

Flexible zinc-ion batteries (ZIBs) have great potential in wearable devices due to their excellent mechanical properties, safety and high energy density. However, the poor adhesion of the electrodes in bending, folding and low-temperature environments remains a challenge. In this study, we developed a dual-network hydrogel electrolyte (C-PAM@TA) by incorporating tannic acid (TA) into a cross-linked polyacrylamide (PAM) network. The C-PAM@TA hydrogel electrolyte exhibits strong interfacial adhesion, high ion conductivity, and low-temperature frost resistance. Through experimental and theoretical analyses, we demonstrate that TA helps regulate anion/cation transport channels, weakens the solvation of zinc ions and enables stable and uniform plating/stripping behavior of the zinc metal anode. As a result, the Zn//Zn symmetric cell employing the C-PAM@TA hydrogel electrolyte exhibits outstanding cycling stability (2000 h) at 0.5 mA cm−2. Furthermore, the assembled Zn//C-PAM@TA//fcc@PANI flexible ZIBs can undergo 7000 cycle stability tests, withstand 4500 bending tests and operate normally in a low-temperature environment of −18 ℃. This study successfully develops high-performance, low-temperature resistant flexible ZIBs, providing valuable insights for the design of multifunctional flexible energy storage and wearable electronic devices.

Multifunctional ultraelastic helical conductive yarn for motion detection and human-machine interaction

Featured with intrinsic lightweight, great flexibility, and easy integration into functional textiles or devices, the stretchable conductive fiber has attracted much attention in the realm of wearable electronics. However, the conductive fibers encounter a troublesome “trade-off” between high conductivity and large elasticity under large deformation, which restricts their widespread applications. Herein, we designed a multifunctional highly elastic helical conductive yarn (HCY) by electrospinning polyurethane (PU) nanofibers, polydopamine (PDA)-assisted silver nanoparticles (AgNPs) deposition and over-twisting. The introduction of a PDA mediated layer fosters strong bond between the conductive AgNPs and the elastic PU nanofibers matrix, showcasing robust structural stability and electrical performance. The hierarchically interlocked conductive structure confers high electrical conductivity to the stretchable HCY, enabling it to withstand large mechanical deformation, which achieves good recoverability within a range of 700 %, great durability (40000 times at deformation of 200 %) and maximum conductive tensile elongation up to 1200 %. Furthermore, the HCY also features excellent Joule-heating ability, great antibacterial performance, and functions as a rapid-response strain sensor (GFmax = 9.82), which is ideal for detecting human motion and enhancing human–machine interactions. This work provides a new path for developing advanced stretchable conductive materials, which is of great significance for versatile ultraelastic wearable electronic devices.

High-Performance Flexible Sensor with Sensitive Strain/Magnetic Dual-Mode Sensing Characteristics Based on Sodium Alginate and Carboxymethyl Cellulose.

Flexible sensors can measure various stimuli owing to their exceptional flexibility, stretchability, and electrical properties. However, the integration of multiple stimuli into a single sensor for measurement is challenging. To address this issue, the sensor developed in this study utilizes the natural biopolymers sodium alginate and carboxymethyl cellulose to construct a dual interpenetrating network, This results in a flexible porous sponge that exhibits a dual-modal response to strain and magnetic stimulation. The dual-mode flexible sensor achieved a maximum tensile strength of 429 kPa and elongation at break of 24.7%. It also exhibited rapid response times and reliable stability under both strain and magnetic stimuli. The porous foam sensor is intended for use as a wearable electronic device for monitoring joint movements of the body. It provides a swift and stable sensing response to mechanical stimuli arising from joint activities, such as stretching, compression, and bending. Furthermore, the sensor generates opposing response signals to strain and magnetic stimulation, enabling real-time decoupling of different stimuli. This study employed a simple and environmentally friendly manufacturing method for the dual-modal flexible sensor. Because of its remarkable performance, it has significant potential for application in smart wearable electronics and artificial electroskins.

Nacre-like Anisotropic Multifunctional Aramid Nanofiber Composites for Electromagnetic Interference Shielding, Thermal Management, and Strain Sensing.

Developing multifunctional flexible composites with high-performance electromagnetic interference (EMI) shielding, thermal management, and sensing capacity is urgently required but challenging for next-generation smart electronic devices. Herein, novel nacre-like aramid nanofibers (ANFs)-based composite films with an anisotropic layered microstructure were prepared via vacuum-assisted filtration and hot-pressing. The formed 3D conductive skeleton enabled fast electron and phonon transport pathways in the composite films. As a result, the composite films showed a high electrical conductivity of 71.53 S/cm and an outstanding thermal conductivity of 6.4 W/m·K when the mass ratio of ANFs to MXene/AgNWs was 10:8. The excellent electrical properties and multi-layered structure endowed the composite films with superior EMI shielding performance and remarkable Joule heating performance, with a surface temperature of 78.3 °C at a voltage of 2.5 V. Additionally, it was found that the composite films also exhibited excellent mechanical properties and outstanding flame resistance. Moreover, the composite films could be further designed as strain sensors, which show great promise in monitoring real-time signals for human motion. These satisfactory results may open up a new opportunity for EMI shielding, thermal management, and sensing applications in wearable electronic devices.

Improving optical and electrical stabilities of fluorine-doped tin oxide films in sweat solutions with O2 addition in plasma

Abstract Recently, the use of wearable smart devices has significantly increased; however, sweat can corrode the outer-layer films, thereby decreasing their transmittance, conductivity, and overall functionality. In this study, fluorine-doped tin oxide (FTO) films for wearable smart devices were prepared via magnetron sputtering. The effects and mechanism of O2 gas flow in plasma on the properties of the fabricated films were investigated. Minor changes were observed in the film morphologies, with the preferred orientations shifting from polar (101) to nonpolar (110) and standard positions. As the O2 flow rate increased from 0 to 2 sccm, the transmittance of the film within the visible spectrum increased from 83% to 89%, with sheet resistance values in the order of 102–106 Ω·sq–1. Following immersion in an acidic sweat solution, the film without O2 peeled off, whereas several corrosion pits were observed in the films with 1 or 2 sccm O2. Conversely, following immersion in an alkaline sweat solution, several pits were observed in the films without O2, while the other films exhibited excellent corrosion resistance. The transmittance of the films immersed in different solutions did not significantly differ. Notably, the sheet resistances of the films treated with 1 sccm O2 met the industrial requirement of 3000 Ω. Moreover, the coexistence of polar and nonpolar planes provided transparency and conductive stability to the FTO films treated with 1 sccm O2. Our study aimed to not only enhance the transmittance and sweat-corrosion resistance but maintain the conductivity of the outer screen layer of a wearable smart electronic device.