Applications In Wearable Devices Research Articles

Vertical organic electrochemical transistors for complementary circuits

Organic electrochemical transistors (OECTs) and OECT-based circuitry offer great potential in bioelectronics, wearable electronics and artificial neuromorphic electronics because of their exceptionally low driving voltages (<1 V), low power consumption (<1 µW), high transconductances (>10 mS) and biocompatibility1–5. However, the successful realization of critical complementary logic OECTs is currently limited by temporal and/or operational instability, slow redox processes and/or switching, incompatibility with high-density monolithic integration and inferior n-type OECT performance6–8. Here we demonstrate p- and n-type vertical OECTs with balanced and ultra-high performance by blending redox-active semiconducting polymers with a redox-inactive photocurable and/or photopatternable polymer to form an ion-permeable semiconducting channel, implemented in a simple, scalable vertical architecture that has a dense, impermeable top contact. Footprint current densities exceeding 1 kA cm−2 at less than ±0.7 V, transconductances of 0.2–0.4 S, short transient times of less than 1 ms and ultra-stable switching (>50,000 cycles) are achieved in, to our knowledge, the first vertically stacked complementary vertical OECT logic circuits. This architecture opens many possibilities for fundamental studies of organic semiconductor redox chemistry and physics in nanoscopically confined spaces, without macroscopic electrolyte contact, as well as wearable and implantable device applications.

A novel COF/MXene film electrode with fast redox kinetics for high-performance flexible supercapacitor

Covalent organic frameworks (COFs) are an emerging class of crystalline porous polymer due to their well-defined channels, highly accessible surface areas and tunable active sites, showing great application potential in the field of energy storage. However, their low inherent conductivity and poor accessibility (difficult to dissolve or melt) have largely limited their electrochemical performances and practical applications. Here, a cation-driven self-assembly process was used to prepare flexible carbonyl containing COF/MXene composite film electrode (CMFs). The uniform intercalation of porous COFs in layered MXene was realized by electrostatic attraction between negatively charged 2D MXene nanosheets and the protonated DAAQ-COFs. Porous COFs tightly contact with MXene and effectively alleviate the self-restacking of MXene nanosheets. In addition, under the synergistic effect, the ordered one-dimensional pore structure of COFs and excellent intrinsic conductivity of MXene can greatly enhances the electron transfer and ion migration rates and further improves the reaction kinetics for flexible composite electrodes. In the three-electrode system, the integrated CMFs film electrode delivers excellent electrochemical performances (the capacitance of 390 F g−1 at 0.5 A/g), excellent kinetic energy storage characteristics (capacitive contribution can be up to 96.7 % at 50 mV/s) and superb mechanical strength (repeated bending 100 times). By assembling into all-solid-state flexible supercapacitor, CMFs//CCMP asymmetric supercapacitors (ASC) achieves the maximum energy density of 27.5 Wh kg−1 (at a power density of 350 W kg−1), maximum power density of 7000 W kg−1 (at an energy density of 19.7 Wh kg−1) and the ultrahigh capacitance retention of 88.9 % after 20,000 charging-discharging long cycles, suggesting great potentials for the applications in future flexible and wearable devices.

A Flexible Pressure Sensor Based on Silicon Nanomembrane

With advances in new materials and technologies, there has been increasing research focused on flexible sensors. However, in most flexible pressure sensors made using new materials, it is challenging to achieve high detection sensitivity across a wide pressure range. Although traditional silicon-based sensors have good performance, they are not formable and, because of their rigidity and brittleness, they are not suitable for fitting with soft human skin, which limits their application in wearable devices to collect various signals. Silicon nanomembranes are ultra-thin, flexible materials with excellent piezoresistive properties, and they can be applied in various fields, such as in soft robots and flexible devices. In this study, we developed a flexible pressure sensor based on the use of silicon nanomembranes (with a thickness of only 340 nm) as piezoresistive units, which were transferred onto a flexible polydimethylsiloxane (PDMS) substrate. The flexible pressure sensor operated normally in the range of 0-200 kPa, and the sensitivity of the sensor reached 0.0185 kPa-1 in the low-pressure range of 0-5 kPa. In the high-pressure range of 5-200 kPa, the sensitivity of the sensor was maintained at 0.0023 kPa-1. The proposed sensor exhibited a fast response and excellent long-term stability and could recognize human movements, such as the bending of fingers and wrist joints, while maintaining a stable output. Thus, the developed flexible pressure sensor has promising applications in body monitoring and wearable devices.

Recent Progress on Hydrogel-Based Piezoelectric Devices for Biomedical Applications.

Flexible electronics have great potential in the application of wearable and implantable devices. Through suitable chemical alteration, hydrogels, which are three-dimensional polymeric networks, demonstrate amazing stretchability and flexibility. Hydrogel-based electronics have been widely used in wearable sensing devices because of their biomimetic structure, biocompatibility, and stimuli-responsive electrical properties. Recently, hydrogel-based piezoelectric devices have attracted intensive attention because of the combination of their unique piezoelectric performance and conductive hydrogel configuration. This mini review is to give a summary of this exciting topic with a new insight into the design and strategy of hydrogel-based piezoelectric devices. We first briefly review the representative synthesis methods and strategies of hydrogels. Subsequently, this review provides several promising biomedical applications, such as bio-signal sensing, energy harvesting, wound healing, and ultrasonic stimulation. In the end, we also provide a personal perspective on the future strategies and address the remaining challenges on hydrogel-based piezoelectric electronics.

A highly stretchable triboelectric nanogenerator with both stretch-insensitive sensing and stretch-sensitive sensing

It is an inevitable requirement for stretchable triboelectric nanogenerators to be able to sense external mechanical forces and convert them into observable electrical signals under adverse conditions (twisting, stretching, etc.). However, the vast majority of existing stretchable triboelectric nanogenerators have an inherent limitation that they cannot obtain stable contact triboelectric response under stretching deformation. Here, we propose a highly stretchable dual-mode triboelectric nanogenerator (SDTENG) with both stretch-insensitive sensing and stretch-sensitive sensing properties. By the regional modulus modulation based on cross-linked interpenetrating network (IPN), our SDTENG shows almost the same pressure sensing property represented by the triboelectric output in the 120% stretch range, mainly because the effective contact region of the friction layer is high modulus and stretch-unperturbed. While in the low modulus region, the MXene/CNT electrode of SDTENG exhibits excellent strain sensitivity with the stretching of the device, and the gauge factor is up to 238.8. The combination of stretch-insensitive pressure sensing and stretch-sensitive strain sensing makes our SDTENG with promising potential applications in wearable devices and smart robots.

Design of LTE/Sub-6 GHz Dual-Band Transparent Antenna Using Frame-Structured Metal Mesh Conductive Film

This paper proposes a dual-band transparent antenna using frame-structured metal mesh conductive film (MMCF). The frame-structured metal mesh conductive film is based on the conductive-coated thin film and forms a narrow strip surrounding the edge of the antenna. The frame-structured metal mesh conductive film can resist considerable current leakage on the edge of the conductive strip to improve the antenna's efficiency by 51% at 2.1 GHz and 53% at 3.6 GHz. As a result, the transparent dual-band antenna has an operating bandwidth of 1.9-2.4 GHz and 3.2-4.1 GHz with a high transparency of 80%, which make it valuable to the applications of biomedical electronic components, wearable devices, and automobile vehicles.

Recent Advances in Chitosan-Based Hydrogels for Flexible Wearable Sensors

Flexible wearable sensors show great potential for applications in wearable devices, remote health monitoring, artificial intelligence, soft robotics, and artificial skin due to their stretchability, bendability, thinness and portability, and excellent electrical properties. Hydrogels have tunable mechanical properties, excellent biocompatibility, and flexibility, making them attractive candidates for wearable flexible sensors. Among them, tremendous efforts have focused on the advancement of chitosan-based hydrogels (CS-Gels) to realize multifunctional wearable sensing by modifying hydrogel networks with additives/nanofillers/functional groups. Recently, remarkable progress has been made in flexible wearable sensors. Herein, this review summarizes recent advances in CS-Gels wearable sensors for applications such as human motion monitoring, health monitoring, human-machine interface and soft robotics. Representative synthesis methods and strategies for CS-Gels are briefly described, the problems and deficiencies of CS-Gels for wearable sensors are discussed. Finally, the possible opportunities and challenges for the future development of CS-Gels flexible wearable devices are proposed.

Flexible Ti3C2Tx MXene/polypyrrole composite films for high-performance all-solid asymmetric supercapacitors

Ti3C2Tx MXene has shown great potential as supercapacitor electrode due to its unique high conductivity and specific surface area, but achieving high capacitance, high energy density, good mechanical flexibility and cycling stability simultaneously is challenging. Herein, MXene/polypyrrole (M-PPy) composite films are fabricated by vacuum-assisted suction filtration of a mixture of MXene nanosheets and polypyrrole (PPy) nanofibers. MXene nanosheet layers are optimally arranged by the intercalation of PPy nanofiber to reduce MXene self-stacking while reducing PPy swelling. The optimal M-PPy3 (3 mL PPy) possesses high capacitance (563.8 F g−1, 0.5 A g−1) and excellent cycling performance (79.5%, 6000 times, 5 A g−1). Next, the flexible M-PPy3//MnO2 asymmetric supercapacitor (ASC) are assembled with MnO2 as the positive electrode and M-PPy3 as the negative electrode. The ASC exhibits 86.8% capacitance retention even after 6000 charge/discharge tests at 2 A g−1, and provides an energy density of 35.3 Wh kg−1 at 486.1 W kg−1, demonstrating remarkable energy storage capacity. Furthermore, a 1.8 V LED is successfully lit up by connecting two ASCs in series. This study provides a better electrode structure for the study of the electrochemical performances of MXene, and the M-PPy3 displays its application in flexible wearable devices.

Synthesizing Metal Oxide Semiconductors on Doped Si/SiO2 Flexible Fiber Substrates for Wearable Gas Sensing.

Traditional metal oxide semiconductor (MOS) gas sensors have limited applications in wearable devices owing to their inflexibility and high-power consumption by substantial heat loss. To overcome these limitations, we prepared doped Si/SiO2 flexible fibers by a thermal drawing method as substrates to fabricate MOS gas sensors. A methane (CH4) gas sensor was demonstrated by subsequently in situ synthesizing Co-doped ZnO nanorods on the fiber surface. The doped Si core acted as the heating source through Joule heating, which conducted heat to the sensing material with reduced heat loss; the SiO2 cladding was an insulating substrate. The gas sensor was integrated into a miner cloth as a wearable device, and the concentration change of CH4 was monitored in real time through different colored light-emitting diodes. Our study demonstrated the feasibility of using doped Si/SiO2 fibers as the substrates to fabricate wearable MOS gas sensors, where the sensors have substantial advantages over tradition sensors in flexibility, heat utilization, etc.

Application and Development Prospect of MXene Materials in Textile and Garment

Mxene, as a new two-dimensional (2D) nanomaterial, has attracted extensive attention in many fields due to its unique high conductivity and high electrochemical surface activity. At present, the research on MXene materials mainly focuses on the fields of composite materials, lubricants, environmental pollution control, energy storage, catalysis, sensors and so on, and there are few applications in the field of textile and garment. However, MXene materials have multi-functional properties and many advantages, and the future application prospect in the field of clothing should not be underestimated. Taking Ti3C2Tx MXene as the main research object, this paper summarizes the various characteristics of MXene that may be suitable for clothing materials, and explores its application in wearable devices, electromagnetic shielding, antibacterial and other clothing materials. The prospects and challenges of Mxene in clothing materials are analyzed.

A dual-module co-regulated stable pressure sensor for human activity monitoring.

Flexible pressure sensors have received significant attention for applications in wearable devices and human health monitoring in healthcare. Nevertheless, the preparation of pressure sensors with a wide operating range and high sensitivity remains a huge challenge. Herein, a piezoresistive sensor with a porous microstructure is prepared by using a sandpaper and salt dual-template method. Carbon black and carbon nanotubes are used as conductive fillers and the pressure sensor shows a high sensitivity (58.33 kPa-1) and extremely fast response and recovery times (3 and 10 ms, respectively). Furthermore, this CNT/PDMS/CB sensor shows a high detection limit of 400 kPa and excellent cycling stability of over 20 000 cycles. This high-performance pressure sensor is promising for many applications such as wearable electronics and health monitoring.

A Survey of Wearable Devices Pairing Based on Biometric Signals

With the rapid growth of wearable devices, more applications require direct communication between wearable devices. To secure the communication between wearable devices, various pairing protocols have been proposed to generate common keys for encrypting the communication. Since the wearable devices are attached to the same body, the devices can generate common keys based on the same context by utilizing onboard sensors to capture a common biometric signal such as body motion, gait, heartbeat, respiration, and EMG signals. The context-based pairing does not need prior information to generate common keys. As context-based pairing does not need any human involvement in the pairing process, the pairing also increase the usability of wearable devices. A wide range of context-based pairing approaches has been proposed with different sensors and different biometric signals. Given the increasing popularity of wearable devices and applications of wearable devices, we believe that it is necessary to have a comprehensive review and comparison on the context-based pairing approaches for future research on the pairing. In this paper, we compare context-based pairing approaches and review common techniques used in pairing based on various biometric signals.

Flexible colloidal quantum dot lasers enabled by self-assembly

Colloidal quantum dot (CQD) lasers show promising applications in flexible optoelectronic devices, due to their tunable emission wavelength, narrow spectrum bandwidth and high power intensity. However, fabricating a flexible CQD laser is challenging because of the difficulties in fabricating optical cavities on flexible substrates using traditional microfabrication technologies. Herein, we propose a one-step self-assembly approach to fabricate flexible CQD supraparticle lasers. The whole assembly approach is processed in a liquid environment without surfactants, and the formed spherical CQD supraparticles are featured with smooth surfaces, serving as high-quality-factor whispering-gallery mode cavities to support laser oscillation. A low lasing threshold of 54 µJ/cm2 is observed while exciting a CQD supraparticle with pulsed femtosecond lasers. The calculated cavity quality factor of 963 for CQD supraparticle lasers is twofold larger than that of CQD lasers assembled with surfactants. Moreover, the CQD supraparticles can serve as free-standing lasers, which allows them to be deposited on flexible substrates such as paper and cloth. Furthermore, our CQD lasers show high stability, after being continuously photoexcited above the threshold for 400 min, their lasing intensity remains at 85.7% of the initial value. As bright, free-standing and long-term stable light sources, the assembled CQD lasers proposed in this work show potential applications in wearable devices and medical diagnosis.

3D printed microstructured ultra-sensitive pressure sensors based on microgel-reinforced double network hydrogels for biomechanical applications.

Hydrogel-based wearable flexible pressure sensors have great promise in human health and motion monitoring. However, it remains a great challenge to significantly improve the toughness, sensitivity and stability of hydrogel sensors. Here, we demonstrate the fabrication of hierarchically structured hydrogel sensors by 3D printing microgel-reinforced double network (MRDN) hydrogels to achieve both very high sensitivity and mechanical toughness. Polyelectrolyte microgels are used as building blocks, which are interpenetrated with a second network, to construct super tough hydrogels. The obtained hydrogels show a tensile strength of 1.61 MPa, and a fracture toughness of 5.08 MJ m-3 with high water content. The MRDN hydrogel precursors exhibit reversible gel-sol transitions, and serve as ideal inks for 3D printing microstructured sensor arrays with high fidelity and precision. The microstructured hydrogel sensors show an ultra-high sensitivity of 0.925 kPa-1, more than 50 times that of plain hydrogel sensors. The hydrogel sensors are assembled as an array onto a shoe-pad to monitor foot biomechanics during gaiting. Moreover, a sensor array with a well-arranged spatial distribution of sensor pixels with different microstructures and sensitivities is fabricated to track the trajectory of a crawling tortoise. Such hydrogel sensors have promising application in flexible wearable electronic devices.

Recent advances in supramolecular self-assembly derived materials for high-performance supercapacitors.

The key preponderance of supramolecular self-assembly strategy is its ability to precisely assemble various functional units at the molecular level through non-covalent bonds to form multifunctional materials. Supramolecular materials have the merits of diverse functional groups, flexible structure, and unique self-healing properties, which make them of great value in the field of energy storage. This paper reviews the latest research progress of the supramolecular self-assembly strategy for the advanced electrode materials and electrolytes for supercapacitors, including supramolecular self-assembly for the preparation of high-performance carbon materials, metal-based materials and conductive polymer materials, and its beneficial effects on the performance of supercapacitors. The preparation of high performance supramolecular polymer electrolytes and their application in flexible wearable devices and high energy density supercapacitors are also discussed in detail. In addition, at the end of this paper, the challenges of the supramolecular self-assembly strategy are summarized and the development of supramolecular-derived materials for supercapacitors is prospected.

Study of mechanical degradation of freestanding ALD Al2O3 by a hygrothermal environment and a facile protective method for environmentally stable Al2O3: toward highly reliable wearable OLEDs.

Al2O3 deposited via atomic layer deposition (ALD) has been used as an insulating and barrier film for thin-film transistors, organic electronics, and microelectromechanical systems. However, ALD Al2O3 films are easily degraded by hydrolysis under harsh hygrothermal conditions, owing to their poor environmental stability. In this study, the mechanical properties and water-vapor transmission rate (WVTR) of environmentally degraded Al2O3 films were investigated by varying the temperature and relative humidity (RH). The hygrothermal environment led to surface and pinhole-concentrated degradation based on aluminum hydroxide, which caused an increased WVTR and reduced elongation of the films in harsher environments. In particular, the elongation of the degraded Al2O3 films was reduced to 0.3%, which is one-third of that of as-deposited Al2O3, and their WVTR increased on the order of 10-1 g m-2 day-1, which is more than 1000 times that of as-deposited Al2O3. Therefore, we introduced a functional silane-based inorganic-organic hybrid layer (silamer) onto the Al2O3 films to improve their environmental stability. The silamer helped preserve the characteristics of Al2O3 films by forming a strong and continuous aluminate phase of Al-O-Si at their interface in hygrothermal environments. Furthermore, the silamer-capped Al2O3 was shown to be an environmentally stable encapsulation for application in wearable organic devices.

Recent advances in single crystal narrow band-gap semiconductor nanomembranes and their flexible optoelectronic device applications: Ge, GeSn, InGaAs, and 2D materials

Flexible optoelectronics have attracted much attention in recent years for their potential applications in healthcare and wearable devices.

Preparation and applications of flexible conductive organohydrogels with ultrahigh gas permeability

Flexible conductive organohydrogels with ultrahigh gas permeability for wearable electronic device applications.

Retracted: Wearable Devices and Intelligent Application in Women's Postpartum Repair for Smart Healthcare.

[This retracts the article DOI: 10.1155/2022/4454926.].

Retracted: Detection and Application of Wearable Devices Based on Internet of Things in Human Physical Health.

[This retracts the article DOI: 10.1155/2022/5678736.].