Multifunctional Wearable Electronics Research Articles

"Sweat-Driven" MXene Composites with Energy-Storage and Thermal-Management Multifunctions: A Platform for Versatile Electronic Skins.

Most exogenous electronic skins (e-skins) currently face challenges of complex structure and poor compatibility with the human body. Utilizing human secretions (e.g., sweat) to develop e-skins is an effective solution strategy. Here, a new kind of "sweat-driven" e-skin is proposed, which realizes energy-storage and thermal-management multifunctions. Through the layer-by-layer assembly of MXene-carbon nanotube (CNT) composite with paper, lightweight and versatile e-skins based on supercapacitors and actuators are fabricated. Long CNTs wrap and entangle MXene nanosheets, enhancing their long-distance conductivity. Furthermore, the CNT network overcomes the structural collapse of MXene in sweat, improving the energy-storage performance of e-skin. The "sweat-driven" all-in-one supercapacitor with a trilayer structure is patternable, which absorbs sweat as electrolyte and harnesses the ions therein to store energy, exhibiting an areal capacitance of 282.3 mF cm-2 and a high power density (2117.8 µW cm-2). The "sweat-driven" actuator with a bilayer structure can be driven by moisture (bending curvature of 0.9 cm-1) and sweat for personal thermal management. Therefore, the paper serves as a separator, actuating layer, patternable layer, sweat extractor, and reservoir. The "sweat-driven" MXene-CNT composite provides a platform for versatile e-skins, which achieve the interaction with humans and offer insights into the development of multifunctional wearable electronics.

Flexible MXene decorative nonwovens with patterned structures for integrated joule heating and strain sensing

Multifunctional textile-based wearable electronics require reliable mechanical flexibility, excellent breathability. Therefore, the manufacture of electronic products with the above characteristics is of great significance for multifunctional, physical health care, and personalized medicine. Herein, we fabricated a wearable heater by depositing MXene uniformly on the patterned thermoplastic polyurethane (TPU) fiber membrane. The unique patterned junctions of the fiber membrane not only guarantee excellent air permeability for the overall structure but also enable MXene to form more stable conductive pathways. The prepared fiber film has a stable electrothermal response and a good Joule heating effect. It can reach 44 ° C instantaneously at a 2 V voltage, and the duration was far more than the 1400 s. The temperature can reach 150 ° C at 5 V voltage, to achieve the purpose of higher temperature at low voltage and low MXene content. In addition, the fiber film also has the photothermal conversion effect, which can reach 32.4 ° C when heated by light for 100 s, and the light-off temperature can be rapidly reduced to room temperature after the 40 s. In addition, it also has the function of monitoring human movement. This study provides multifunctional wearable electronics for personal medical and health monitoring and personal thermal management, because of the uniform loading of MXene and excellent mechanical properties and air permeability provided by the patterned structure. In conclusion, we expect that this work will be beneficial to improve the Joule heating performance of smart wearable devices.

Robust salt-shelled metal halide for highly efficient photoluminescence and wearable real-time human motion perception

All-inorganic metal halide perovskites (MHPs) with the formula CsPbX3 (X = Cl-, Br-, I-) have excellent photophysical properties and low-cost fabrication, offering exciting opportunities for flexible electronics. However, the suboptimal quantum yield and inferior stability of solid-state MHPs impede their diverse wearable applications. Here, a straightforward water evaporation crystallization strategy for the preparation of salt-shelled metal halide solids is proposed. The well-designed CsPbBr3@KBr material exhibits narrow green photoluminescence (full-width at half-maximum ∼ 20 nm), high quantum yield (87.3 %), and favourable light irradiation and thermal stability. Thus, their applications in waterborne transparency inks and flexible photoluminescent films are demonstrated. Especially, they can be employed as fillers of polyvinyl alcohol (PVA) for high-performance positive friction materials in triboelectric nanogenerators (TENGs), and the output performance of the TENG is 2.3 times higher than the pristine one. As a proof-of-concept, a wearable photoluminescent sensor with a voltage response range of 0–100 kPa and a response time of 125 ms is constructed, which can potentially be served as a passive sensor-in-screen configuration to detect motions of various parts of the human body. It is believed that such metal halides will unleash the possibility of a broad variety of applications in lightweight and multifunctional wearable electronics.

Structural engineering of electrodes for flexible energy storage devices.

The emergence of multifunctional wearable electronics over the past decades has triggered the exploration of flexible energy storage devices. As an important component of flexible batteries, novel electrodes with good flexibility, mechanical stability and high energy density are required to adapt to mechanical deformation while powering devices. Electrodes with sophisticated designed structures are key to achieving novel batteries and supercapacitors with extended lifetimes under long-term deformation exposures. Many different novel structures including serpentine, auxetic and biomimetic are explored to construct electrodes thanks to their excellent mechanical deformability in three dimensions. This paper considers the various design strategies established for fabricating flexible electrodes using novel structural modifications. The current state-of-the-art developments of novel structures made of two-dimensional (2D) planar and three-dimensional (3D) cellular, interconnected architectures for flexible energy storage with different functionalities, are discussed. The key tunable geometrical parameters of structures for achieving high performance are critically assessed, and the challenges and limitations of electrodes facing their practical application are revealed, to offer new insights into future prospects of this field.

Three‐in‐One Portable Electronic Sensory System Based on Low‐Impedance Laser‐Induced Graphene On‐Skin Electrode Sensors for Electrophysiological Signal Monitoring

AbstractOn‐skin sensors can precisely perceive important electrophysiological signals, including electroencephalogram (EEG), electrocardiogram (ECG), and electromyogram (EMG). Despite significant advances in the development of soft materials as electrode sensors, data acquisition (DAQ) unit—another indispensable component of on‐skin electronic sensory systems—typically exhibits bulkiness or unimodal sensing, which is detrimental to the portability of the sensory system or the comprehensiveness of the perceived information. Here, a portable and multimodal DAQ unit to tackle these challenges is designed. By assembling the DAQ unit with low‐impedance (<100 Ω) laser‐induced graphene on‐skin electrode sensors, a wireless communication module, a power supply module, and a 3D printed protective shell, the completed sensory system can realize three‐in‐one monitoring of EEG, ECG, and EMG with a light weight of 22 g and a low cost of $25. Moreover, a mobile App is developed to display the perceived electrophysiological signals in real time. Human–machine interface and embedded machine learning are demonstrated using the designed sensory system, indicating its potential applications in artificial intelligence. The success of this inexpensive three‐in‐one portable electronic sensory system sheds light on design, fabrication, and commercialization of multifunctional wearable electronics with wide applications in fitness tracking, medical diagnostics, and human–machine interface.

Bioinspired ultra-stretchable dual-carbon conductive functional polymer fiber materials for health monitoring, energy harvesting and self-powered sensing

Highly stretchable and multifunctional wearable electronics have shown a desirable attraction recently. However, most fiber-based devices are hindered by the dilemma of stretchability and sensitivity, as well as the decline of performance due to delamination. Herein, a bis-condensed inspired ultra-stretchable dual-carbon fiber (MSSS fiber) is proposed based on the synergistic interaction and tunneling effect of multi-walled carbon nanotube (MWCNTs)-superconductive carbon black (SCCB)-poly[styrene-b-isoprene-b-styrene] (SIS) conductive polymer composite (CPC) and a strong interlocked layer-by-layer structure. The MSSS fiber is developed as a strain sensor with good electric conductivity and stability, ultra-stretchability, high sensitivity (GF = 1,096 at 1,100 %), and good durability (10,000 at 1,000 %) which shows excellent sensing for various motion applications. Simultaneously, the MSSS fiber is also exploited as a single-electrode fiber-based triboelectric nanogenerator (F-TENG) by triboelectric material coating. It demonstrates a significant output power, good durability over 25,000 cycles and stable electric output performance under high-level deformation (600 %), endowing its reliability as a power source supply and self-powered sensing device. This ultra-stretchable conductive fiber further explores the development of multifunctional subtle wearable electronics. The applications of healthcare sensing and energy harvesting also give promising potential in the field of smart wearable electronics, human–computer interaction, and artificial intelligence.

Carbon Nanotube Ink Dispersed by Chitin Nanocrystals for Thermoelectric Converter for Self-Powering Multifunctional Wearable Electronics.

The screen-printing process of conductive ink can realize simple and large-scale manufacture of micro/nano patterns for producing wearable electronic products. Herein, chitin nanocrystals (ChNCs) are used as a dispersant for the preparation of multiwalled carbon nanotube (MWCNT) ink with high viscosity and uniformity by ultrasound treatment. ChNCs can interact with MWCNT in noncovalent ways, including π-π and hydrophobic interactions. ChNCs/MWCNT (CCNT) ink does not aggregate even after standing for 3 months with a maximum MWCNT concentration of 33mg mL-1 and dispersion efficiency of 91.1%. Using CCNT ink, a paper-based thermoelectric generator (TEG) is manufactured by screen-printing technology. With good thermoelectric and strain sensing properties, CCNT coated paper can stably collect human energy at room temperature to realize self-powering. The CCNT coated paper-based TEG can convert thermal voltage signals into musical notes, monitor the changes in human behavior and respiratory rate, and monitor joint movements. Moreover, CCNT coated paper has no cytotoxicity by CCK-8 and live/dead staining. This work puts forward a strategy of green preparation of MWCNT-based ink by adding renewable chitin, which opens up a new way to apply MWCNT-based ink in self-powering wearable multifunctional sensors.

Highly conductive, stretchable, durable, breathable electrodes based on electrospun polyurethane mats superficially decorated with carbon nanotubes for multifunctional wearable electronics

As smart wearable electronics become commonplace, there exists an unmet need for stretchable, durable and breathable electrodes that can be easily integrated with the electronics and comfortable for the users when used for extended periods. Despite the enormous effort in the development of stretchable electronic materials and structures, limited progress has been made in terms of developing a facile, scalable fabrication process to produce mechanically and electrically robust, breathable conductive electrodes for wearable electronics. Herein, we develop a novel stretchable polymer-carbon nanotube composite electrode based on a fibrous polyurethane mat decorated with conductive carbon nanotubes superficially embedded into individual polyurethane fibers. The fibrous polyurethane mat is fabricated through a facile technique of electrospinning, followed by a scalable ultrasonic cavitation treatment in a carbon nanotubes suspension solution. During ultrasonic cavitation treatment, long carbon nanotubes are embedded into electrospun polyurethane fibers and mechanically interlocked with one other, forming a dense, structurally robust, and electrically stable conductive network surrounding each fiber. The as-fabricated electrodes exhibit several superior properties that are characterized by good stretchability (recoverable stretching rate up to 200 %), high conductivity (low sheet resistance of 30 ∼ 50 Ω/sq), excellent stability (over 20,000 bending and stretching cycles), remarkable durability (capable of ultrasonic washing for over 30 min), and efficient air permeability (22.83 mm s−1 at a pressure difference of 100 Pa). Based on the integrated superior performances, the multifunctional capability of this novel electrode for wearable electronics is demonstrated in applications including thin-film heaters, strain sensors, and wearable energy supply of stretchable supercapacitor electrodes. It is supposed that the developed fabrication process and stretchable electrodes could be a versatile platform for development of flexible and wearable electronics.

Highly Compressible Elastic Aerogel Spring-Based Piezoionic Self-Powering Pressure Sensor for Multifunctional Wearable Electronics.

To meet the rapid development of wearable flexible electronics, the multifunctional integrations into singe device are in extreme demand. In this paper, we developed novel self-powering multifunctional pressure sensors and supercapacitor-integrated device based on highly elastic silver nanowires@reduced graphene aerogel, being conductive to reduce integration difficulties and device size. Serving as an energy device, it behaves with a prominent specific capacitance of 146.6 F g−1, and excellent rate capability even at 500 mV s−1. The fabricated sensor demonstrates an excellent sensitivity of 2.54 kPa−1 and superior pressure-sensing stability up to 1000 compressive cycles. Piezoionization effect is suggested to reveal the sensing mechanism. Our research provides a new research direction in designing the integration of self-driving wearable electronics.

A biodegradable cellulose-based flame-retardant triboelectric nanogenerator for fire warning

Triboelectric nanogenerator (TENG) is a type of disruptive high-entropy energy technology for the era of internet of things that drives the ubiquitous innovations of flexible/wearable electronics and sensor networks. However, developing a flexible TENG with a high sensitivity temperature response and fire warning capabilities is challenging. Here, we demonstrate a flexible, biodegradable, single electrode cellulose-based TENG with flame retardancy (FR-TENG) that is fabricated by biocompatible black phosphorus (BP) and phytic acid (PA) as flame retardants. The corresponding peak heat release rate and the total heat release rate values of FR-TENG are reduced by 64.6% and 47.6% compared with pure nanocellulose film, respectively, and the limiting oxygen index is increased to 39.1%. The FR-TENG exhibits an output of 116 V and 3.02 mA·m−2 at 2 Hz, indicating the application prospect of source for wearable electronics. An exciting feature of the FR-TENG is its resistance response to temperature with a high thermal index of 3779.16 K in the range of 35–150 ℃, which can be used as a temperature sensor to achieve quickly respond to temperature changes and fire warnings within 5 s. Therefore, the cellulose-based FR-TENG provides an idea to develop advanced multifunctional wearable electronics with potential applicability as sensors and fire alarms for firefighting and industrial applications.

Strain-Driven Auto-Detachable Patterning of Flexible Electrodes.

Flexible electrodes that are multilayer, multimaterial, and conformal are pivotal for multifunctional wearable electronics. Traditional electronic circuits manufacturing requires substrate-supported transfer printing, which limits their multilayer integrity and device conformability on arbitrary surfaces. Herein, a "shrinkage-assisted patterning by evaporation" (SHAPE) method is reported, by employing evaporation-induced interfacial strain mismatch, to fabricate auto-detachable, freestanding, and patternable electrodes. The SHAPE method utilizes vacuum-filtration of polyaniline/bacterial cellulose (PANI/BC) ink through a masked filtration membrane to print high-resolution, patterned, and multilayer electrodes. The strong interlayer hydrogen bonding ensures robust multilayer integrity, while the controllable evaporative shrinking property of PANI/BC induces mismatch between the strains of the electrode and filtration membrane at the interface and thus autodetachment of electrodes. Notably, a 500-layer substrateless micro-supercapacitor fabricated using the SHAPE method exhibits an energy density of 350 mWh cm-2 at a power density of 40mW cm-2 , 100 times higher than reported substrate-confined counterparts. Moreover, a digital circuit fabricated using the SHAPE method functions stably on a deformed glove, highlighting the broad wearable applications of the SHAPE method.

A highly adhesive, self-healing and perdurable PEDOT:PSS/PAA–Fe3+ gel enabled by multiple non-covalent interactions for multi-functional wearable electronics

A robust PEDOT:PSS/poly(acrylic acid) (PAA)–Fe3+ gel with good mechanical properties, adhesion, and favorable self-healing performance was successfully prepared and demonstrated potential application in wearable electronics.

Multifunctional pressure/temperature/bending sensor made of carbon fibre-multiwall carbon nanotubes for artificial electronic application

A flexible sensor with excellent pressure, temperature, and bending sensitivity is fabricated based on the conductive skeleton material with hierarchical porous structure. The conductive skeleton material is composed of carbon fibres (CFs) and multiwalled carbon nanotubes (MWCNTs), in which lay perpendicular to each other CFs are used as conductive frames, while MWCNTs are served as bridges to connect the CFs and increase the conductive network formation. Owing to the unique structure and the conductive materials, the as-prepared sensor exhibits a high-pressure sensing performance of 42.7 kPa (0–1 kPa), fast response, relaxation times of<100 ms, wide working range of 0–60 kPa, and high stability over more than 6000 cycles. Furthermore, the fabricated sensor presents a high thermal sensitivity of 2.46 °C−1 between 30 and 40 °C, excellent bending sensitivity of 95.5 % rad−1 in the working range of 0–180°, and great flexibility (over 1000 cycles), demonstrating its potential applications in multifunctional wearable electronics.

Toward high-performance multifunctional electronics: Knitted fabric-based composite with electrically conductive anisotropy and self-healing capacity

Textile-based electronics characterizing easy integration into textile garments and good wearability have received considerable attentions. However, it is still a huge challenge to integrate multiple functions into single electronic device, especially for those having different even opposite requirements in electrical properties. In this work, an anisotropic electrically conductive composite was prepared by encapsulating conductive knitted fabric (CKF) into polyurethane (PU). Based on anisotropic electrical conductivity, i.e., extremely low and stable resistivity in the coursewise direction and significant variation of resistivity in the walewise direction during tensile strains, the composite could efficiently integrate the electro-heating and strain-sensing functions that required opposite electrical properties. When applied for electro-heating applications in the coursewise direction, the CKF/PU composite exhibited fast thermal response, ultrahigh electric-thermal conversion (140 °C at 4 V), and stable electrothermal performance under a large strain (40%) or after long-term use (>1000 stretching cycles). When applied for strain-sensing applications in the walewise direction, the composite showed good sensing performances, including high sensitivity (GF of −8.1 at a 5% strain), low hysteresis, good reproducibility and stability (>1000 cycles), which enabled the device as a wearable sensor to accurately detect human joint movements and subtle motions. Furthermore, the self-healing function was exploited for the CKF/PU electronic device, by which the abnormal sensing property could be fully repaired at human body temperature. This work may shed new light on the future development of high-performance multifunctional wearable electronics with the anisotropic conducting feature.

"Green" Flexible Electronics: Biodegradable and Mechanically Strong Soy Protein-Based Nanocomposite Films for Human Motion Monitoring.

Soy protein isolate (SPI) is envisioned as a promising alternative to fabricate "green" flexible electronics, showing great potential in the field of flexible wearable electronics. However, it is challenging to simultaneously achieve conductive film-based human motion-monitoring strain sensors with reliable fatigue resistance, robust mechanical property, environmental degradability, and sensing capability of human motions. Herein, we prepared a series of SPI-based nanocomposite films by embedding a surface-hydroxylated high-dielectric constant inorganic filler, BaTiO3, (HBT) as interspersed nanoparticles into a biodegradable SPI substrate. In particular, the fabricated film comprising 0.5 wt % HBT and glycerin (GL), namely, SPI-HBT0.5-GL0.5, presents multifunctional properties, including a combination of excellent toughness, tensile strength, conductivity, translucence, recyclability, and excellent thermal stability. Meanwhile, this multifunctional film could be simply degraded in phosphate buffered saline solution and does not cause any pollution to the environment. Attractively, wearable sensors prepared with this particular material (SPI-HBT0.5-GL0.5) displayed excellent biocompatibility, prevented the occurrence of an immune response, and could accurately monitor various types of human joint motions and successfully remain operable after 10,000 cycles. These properties make the developed SPI-based film a great candidate in formulating biobased and multifunctional wearable electronics.

All-yarn triboelectric nanogenerator and supercapacitor based self-charging power cloth for wearable applications

Despite rapid developments, multifunctional wearable electronics are still not significant in practical applications as compared to portable and stretchable power devices. In this paper, we present the flexible and easy large-scale production of single-electrode mode triboelectric nanogenerator (TENG) and supercapacitor yarn-based self-charging power fabric, for simultaneously converting and storing biomechanical energy. Fabricated using traditional knitting technologies, the self-charging power fabric can adapt to complex mechanical deformations owing to its high flexibility and stretchability. Additionally, the output characteristics of the TENG fabric were systematically investigated with the purpose of energy generation. The TENG fabric can generate a maximum peak power density of ∼90 mW·m−2 using nylon as the contact material, with an operating frequency of 4 Hz. The as-prepared yarn-based supercapacitor exhibited high capacitance, good cycling stability, and flexibility, making it an appropriate wearable energy-storage device. Moreover, the proposed design uses energy harvested from biomechanical motions to sustainably power portable electronic devices. The results of this study indicate that the proposed design is a promising sustainable power source for wearable electronic devices.

Knittable and Sewable Spandex Yarn with Nacre-Mimetic Composite Coating for Wearable Health Monitoring and Thermo- and Antibacterial Therapies.

The emerging personal healthcare has significantly propelled the development of advanced wearable electronics with novel functions of providing diagnostic information and point-of-care therapies for specific diseases. However, it is still challenging to simultaneously achieve high sensitivity for health biomonitoring and multifunction integration for point-of-care therapies in a one single flexible, lightweight yet robust fiber-based device. Here, a knittable and sewable spandex yarn with conductive nacre-mimetic composite coating has been developed through an alternant dip-coating method employing MXene nanosheets as the "brick" and polydopamine (PDA)/Ni2+ as the "mortar". The resultant spandex yarn coating with MXene/PDA/Ni2+ (MPNi@Spandex) can be assembled as a strain sensor with high sensitivity (up to 5.7 × 104 for the gauge factor), wide sensing range (∼61.2%), and low detection limit (0.11%) to monitor the biological activities of the human body. Furthermore, MPNi@Spandex displays great potential to give on-demand thermotherapy by virtue of the fast response to near-infrared irradiation, controllable surface temperature, and applicability even under sewing conditions. In addition, MPNi@Spandex knitted textiles demonstrate a strong antibacterial effect due to the sharp edges, anionic, and hydrophilic nature of MXene nanosheets. Remarkably, near-infrared irradiation further improves the bacteria-killing efficiency of an MPNi@Spandex knitted textile to more than 99.9%. This work paves the way for the design of multifunctional wearable electronics with an all-in-one theranostic platform for personal healthcare.

Vapor phase polymerized conducting polymer/MXene textiles for wearable electronics.

Multifunctional electronic textiles hold great potential applications in the wearable electronics field. However, it remains challenging to seamlessly integrate the multiple functions on the textile substrates without sacrificing their intrinsic properties. Herein, we report a novel and facile vapor phase polymerization (VPP) and spray-coating strategy towards the construction of a laminated film containing a PEDOT film and Ti3C2Tx MXene sheets on the fiber surface. The fabricated PEDOT/MXene decorated cotton fabrics are integrated with excellent electrochemical performance, joule heating performance, good electromagnetic interference (EMI) shielding, and strain sensing performance. The resultant multifunctional textiles have a low sheet resistance of 3.6 Ω sq-1, and the assembled all-solid-state fabric supercapacitors exhibit an ultrahigh specific capacitance of 1000.2 mF cm-2, which exceeds the state-of-the-art MXene-based fabric supercapacitors. In addition, the PEDOT/MXene modified fabrics exhibit an exceptional joule heating performance of 193.1 °C at the applied voltage of 12 V, high EMI shielding effectiveness of 36.62 dB, and high sensitivity as strain sensors for human motion detection. This work provides a novel strategy for the structure design of multifunctional textiles and will lay the foundation for the development of multifunctional wearable electronics.

Ultra-stretchable and multifunctional wearable electronics for superior electromagnetic interference shielding, electrical therapy and biomotion monitoring

TAMF exhibits outstanding electromagnetic shielding, excellent Joule heating, high breathability and favorable mechanosensation performances.

Multifunctional RGO/Ti3C2Tx MXene fabrics for electrochemical energy storage, electromagnetic interference shielding, electrothermal and human motion detection

With the rapid development of information technology and electronics, the traditional textiles hardly fulfill the requirements of wearable electronics. Multifunctional textile-based electronics integrated with energy storage, joule heating, electromagnetic interference (EMI) shielding and sensing has become a favorable solution. Herein, a scalable spray-coating and dip-coating strategy is developed to fabricate the multifunctional reduced graphene oxide/Ti3C2Tx MXenes decorated cotton fabrics. The RGO/MXene modified fabrics show hydrophilic surface, high electrical conductivity, good flexibility and breathability. In addition, the RGO/MXene modified fabrics demonstrate excellent electrochemical performance, and the assembled all-solid-state supercapacitors show one of the highest specific capacitances of 383.3 F g−1 (258 mF cm−2). More importantly, the RGO/MXene fabrics show distinctive negative resistance variation and high sensitivity when they are applied as the strain sensors to detect the human motions including the bending of finger, elbow, knee and swallowing process. Moreover, the RGO/MXene fabrics show good joule heating and EMI shielding performance. This work may shed light on cost-effective but high-performance textile-based strain sensors, EMI shielding and electrochemical energy storage devices, and paves the way for the development of multifunctional wearable electronics.