Advanced Wearable Devices Research Articles

Stable, Scalable, and Free-Standing Perovskite Quantum Dots Composite Reinforced by Cellulose Fibers.

Perovskite quantum dots (PQDs) have attracted emerging attention as fluorescent and light-absorbing materials for next-generation optoelectronics due to their outstanding properties and cost-efficiency. However, PQD thin film suffers significant instability due to structure and material failures, which hinders their application in flexible and reliable PQD-based advanced wearable devices. Herein, we use commercial cellulose fiber-based filter paper as a substrate to synthesize PQDs in situ and fabricate PQD-paper free-standing flexible composite film. The abundant hydroxy capping ligands of cellulose fibers and the unique dense network structure of the filter paper can facilitate confined crystallization, forming strong interactions between the PQDs and substrate, the unpackaged PQD composite film showed extraordinary stability (>30 days) in the air with high humidity (90%). Meanwhile, the strong interaction between PQDs and paper enables an ultrasimple drop-cast synthesis process with excellent process tolerance, making it customizable and easy to scale up (10 cm in diameter). Due to the uniformly dispersed PQDs on cellulose fibers of the substrate, the composite demonstrates impressive photo-responsive properties. Photodetector (PD) arrays were designed on free-standing PQD paper and flexible graphitic electrodes, and circuits were fabricated by drawing. The PD arrays can work as optical and electrical dual-mode image sensors with incredible bending robustness, enduring up to 100,000 cycles at 180°.

Multifunctional nanomaterials for smart wearable diabetic healthcare devices

Wearable diabetic healthcare devices have attracted great attention for real-time continuous glucose monitoring (CGM) using biofluids such as tears, sweat, saliva, and interstitial fluid via noninvasive ways. In response to the escalating global demand for CGM, these devices enable proactive management and intervention of diabetic patients with incorporated drug delivery systems (DDSs). In this context, multifunctional nanomaterials can trigger the development of innovative sensing and management platforms to facilitate real-time selective glucose monitoring with remarkable sensitivity, on-demand drug delivery, and wireless power and data transmission. The seamless integration into wearable devices ensures patient's compliance. This comprehensive review evaluates the multifaceted roles of these materials in wearable diabetic healthcare devices, comparing their glucose sensing capabilities with conventionally available glucometers and CGM devices, and finally outlines the merits, limitations, and prospects of these devices. This review would serve as a valuable resource, elucidating the intricate functions of nanomaterials for the successful development of advanced wearable devices in diabetes management.

Self-repairing thermoplastic polyurethane-based triboelectric nanogenerator with molybdenum disulfide charge-trapping for advanced wearable devices

In the realm of wearable electronics, the development of materials that can endure and adapt to the human experience while harvesting energy is paramount. Herein, we introduce a novel self-healable thermoplastic polyurethane (TPU) for a triboelectric nanogenerator (TENG) that harmonizes self-healing efficacy with mechanical durability. Utilizing a unique electrospinning technique, we engineered TPU fibers that not only exhibit remarkable elasticity—withstanding over 600% strain—but also possess the capability to self-repair at just 80 ºC. For the negative triboelectric layers, beside choosing fluorinated ethylene propylene (FEP) as the main electron-withdrawing surface, the introduction of molybdenmum disulfide (MoS2) as a charge-trapping layer exploits its two-dimensional structure to enhance both the stretchability and electrical output of the TENG. Our study demonstrates the TENG’s proficiency in energy generation, producing up to 1000 V from vigorous motion and maintaining a consistent output after mechanical stress and chemical exposure. Moreover, the device showcases excellent motion-sensing capabilities and can power up to 200 (light-emitting diodes) LEDs, underscoring its efficiency and adaptability. This robust TENG sets a precedent for self-healing materials in sustainable energy devices and marks a substantial advance towards their integration into everyday wearables. The culmination of these features highlights the potential mass application of TENGs, paving the way for their ubiquitous adoption in the near future.

A corn leaf based-strain sensor and triboelectric nanogenerator for running monitoring and energy harvesting

Recently, advanced wearable devices with posture sensing and energy harvesting have received widespread attention. Thus, we proposed a dual-function device (energy harvesting and running posture sensing), including carbon attached corn leaf strain sensor (CC-strain sensor) and a corn leaf-based triboelectric nanogenerator (C-TENG).According to the results, the relative resistance rate (ΔR/R0) exhibits linear characteristics in the three strain regions, and its linear coefficients are all above 0.96. Besides, at low strain rates from 0.01% to 0.1%, the CC-strain sensor can reach high sensitivity for monitoring weak signals, such as expressions in dance performances. The C-TENG device can achieve mechanical energy harvesting, providing a way to power low-power portable devices. From the results, the maximum power of C-TENG can arrive at 222 μW (resistance: 100 MΩ). This research can provide a new path to integrate strain sensors and TENG devices in running monitoring.

Large-Scale Wearable Textile-Based Sweat Sensor with High Sensitivity, Rapid Response, and Stable Electrochemical Performance.

Textile-based sweat sensors display great potential to enhance wearable comfort and health monitoring; however, their widespread application is severely hindered by the intricate manufacturing process and electrochemical characteristics. To address this challenge, we combined both impregnation coating technology and conjugated electrospinning technology to develop an electro-assisted impregnation core-spinning technology (EAICST), which enables us to simply construct a sheath-core electrochemical sensing yarn (TPFV/CPP yarn) via coating PEDOT:PSS-coated carbon fibers (CPP) with polyurethane (TPU)/polyacrylonitrile (PAN)/poloxamer (F127)/valinomycin as shell. The TPFV/CPP yarn was sewn into the fabric and integrated with a sensor to achieve a detachable feature and efficiently monitor K+ levels in sweat. By introducing EAICST, a speed of 10 m/h can be realized in the continuous preparation of the TPFV/CPP yarn, while the interconnected pores in the yarn sheath enable it to quickly capture and diffuse sweat. Besides, the sensor exhibited excellent sensitivity (54.26 mV/decade), fast response (1.7 s), anti-interference, and long-term stability (5000 s or more). Especially, it also possesses favorable washability and wear resistance properties. Taken together, this study provides a crucial technical foundation for the development of advanced wearable devices designed for sweat analysis.

Electro‐bio‐mechanical behavior of graphite nanoplatelets–silicone rubber‐based composites for wearable electronic systems

AbstractAdding graphite nanoplatelets (GNP) into silicone rubber (SR) composites have shown significant potential for wearable electronics, where electrical, mechanical, and tribological properties play a crucial role. This study investigates the effects of incorporating graphite nanoplatelets (GNP) into SR composites and their impact on these key properties. Solution mixing of SR and GNP was performed to confirm good dispersion of the GNP within the SR matrix. The results showed improved tensile strength and modulus while stabilizing the flexibility and stretchability required for wearable electronics. For example, the tensile strength of the composites was 0.86 MPa (control) and increased to 1.18 MPa (5 part per hundred rubber [phr] GNP), and 1.55 MPa (15 phr GNP). Similarly, the stretchability was 177 % (control) and increased to 190 % (5 phr GNP), and 184 % (15 phr GNP). Moreover, the electro‐mechanical tests were studied and the output voltage for the samples were 0.28 milli‐volt (mV) (5 phr GNP), and 0.31 mV (15 phr GNP). Similarly, the output voltage generation was studied through human motions. The results obtained from these biomechanical motions such as thumb pressing were 0.7 mV (5 phr GNP), and 2.7 mV (15 phr GNP). The study finds the potential of GNP‐SR composites as multifunctional materials such as wearable electronics. Overall, this research guides the development of advanced wearable devices, soft robotics, and bio‐inspired electronics with improved performance and durability.

Triggering triboelectric nanogenerator antibacterial Activities: Effect of charge polarity and host material correlation

Triboelectric nanogenerators (TENGs) offer promising motion-driven energy harvesting for human–machine interactions, particularly in wearable healthcare and biomedical devices. However, direct skin contact demands addressing aggressive bacterial growth risks. The “triangle” interaction between bacteria, electrical stimulation, and host materials has been investigated comprehensively in the present study to facilitate appropriate self-antibacterial designs for TENGs. In so doing, it was revealed that the growth of negatively charged bacterial models (Escherichia coli and Staphylococcus aureus) was inhibited by induced positively charged substrates (Al or graphene oxide (GO)), regardless of the host material's composition due to the direct electrostatic interactions. Electron capture from the bacterial respiratory chain by the substrates leads to the interruption of the bacterial energy supply. In response to negative charges, however, an appreciable host-dependent antibacterial behaviour was observed, with Al showing a negligible bactericidal effect, while GO exhibited robust antibacterial properties. This effect was assigned to reactive oxygen species (ROS) generation, triggered by shuttling the negative charges to the oxygen functional groups in GO, suppressing bacterial growth efficaciously. The observed correlation between the electrostatic charge polarity and the material composition of the substrates (hosting the bacteria) highlights the superiority of ROS induction in the antibacterial properties of TENG. These findings pave the way for developing innovative approaches to control bacterial growth effectively and enhance the applicability of TENGs as advanced wearable devices with inherent antibacterial capabilities.

Facile Graphene Oxide Modification Method via Hydroxyl-yne Click Reaction for Ultrasensitive and Ultrawide Monitoring Pressure Sensors.

Enhancing the durability and functionality of existing materials through sustainable pathways and appropriate structural design represents a time- and cost-effective strategy for the development of advanced wearable devices. Herein, a facile graphene oxide (GO) modification method via the hydroxyl-yne click reaction is present for the first time. By the click coupling between propiolate esters and hydroxyl groups on GO under mild conditions, various functional molecules are successfully grafted onto the GO. The modified GO is characterized by FTIR, XRD, TGA, XPS, and contact angle, proving significantly improved dispersibility in various solvents. Besides the high efficiency, high selectivity, and mild reaction conditions, this method is highly practical and accessible, avoiding the need for prefunctionalizations, metals, or toxic reagents. Subsequently, a rGO-PDMS sponge-based piezoresistive sensor developed by modified GO-P2 as the sensitive material exhibits impressive performance: high sensitivity (335 kPa-1, 0.8-150 kPa), wide linear range (>500 kPa), low detection limit (0.8 kPa), and long-lasting durability (>5000 cycles). Various practical applications have been demonstrated, including body joint movement recognition and real-time monitoring of subtle movements. These results prove the practicality of the methodology and make the rGO-PDMS sponge-based pressure sensor a real candidate for a wide array of wearable applications.

MieWC: Medical image encryption using wavelet transform and multiple chaotic maps

AbstractRecently, digital images have been widely used in several applications through advanced wearable devices and networks. Despite several benefits of digital images, such as easy distribution, storage, and reproduction, it is difficult to prevent the issue of identity theft, privacy leakage, and ownership conflicts. We present a wavelet‐based encryption technique, MieWC, to solve the above issues using multiple chaotic keys. This work uses multiple keys for the encryption process, which ensures high security and authenticity. Lorenz and logistic maps are used for chaotic key generation for diffusion and confusion processes. Further, the technique is tested for two different wavelet transforms, including integer wavelet transform (IWT) and discrete wavelet transform, with IWT giving better results. Hence, it is being used for further analysis. The proposed technique is easy to implement and provides high security with improved results. It has low time complexity and high key bit sensitivity. The result analysis further ensures resistance against crop attacks.

High ionic conductive, freezing-resistant and transparent polyurethane based on a novel metal ionic deep eutectic solvent

With the progress of society, flexible conductive ionic sensors are becoming more and more important for future advanced wearable devices, for biosensing or human–computer interaction.

A high κ, transparent, and stretchable Cu@TiO2 core@shell nanowire/poly(dimethylsiloxane) composite film for sensitive wearable touch sensor

Touch sensors are crucial for the development of advanced wearable devices and enhancement of the user experience through human-machine interaction. The properties of dielectric films, including their high dielectric constants (high-κ), low loss tangents (tan⁡δ), transparency, and stretchability are key factors that impact the accuracy, reliability, and display visibility of wearable touch sensors. Here, we present an approach for fabricating a Poly(dimethylsiloxane) (PDMS)-based dielectric film that can achieve a dielectric constant 6 times larger than that of pure PDMS film by loading a very low wt% (3%) of copper@titanium dioxide (Cu@TiO2) core-shell nanowires (NWs) to PDMS matrix. TiO2 was deposited on surfaces of Cu NWs by a hydrothermal reaction to form the covering shell, and it is experimentally and theoretically proved that the shell can suppress the scattering from metal surfaces, resulting in improving the transparency, and reducing the dielectric loss of the film (tan⁡δ=0.01–0.06). The nanocomposite film also exhibits outstanding mechanical property (standing up to a tensile strain of 200%). The demonstration of a transparent, highly sensitive and low noise multi-touch sensor using high-κ film suggests that this film has potential application in next-generation of wearable electronic devices for human-machine interaction.

A multifunctional composite material with piezoresistivity and mechanoluminescence properties for a wearable sensor

Intelligent composite materials and devices are attracting a great interest owing to their potential impact on various future life applications. To meet the growing demand for multifunctional materials, the development and validation of visible sensing behavior is highly desirable, but the development of a single multifunctional wearable sensing material still remains a challenge to be achieved. To reach this goal, here we present a wearable intelligent fabric with piezoresistivity and mechanoluminescence ability based on a layer-structured graphene-based conductive cotton fabric and SrAl2O4:Eu2+, Dy3+/polyurethane foamed coating. The presence of the foamed coating structure endows the flexible composite fabric with a controllable positive/negative piezoresistivity (gauge factor from −2.5 to 17) and a bright mechanoluminescence ability that can be used in the darkness without additional batteries. Three-dimensional chromaticity diagrams have also been developed as advanced tools to quantitatively assess the luminescence, whose lightness, during the bending cycles, is highly repeatable with value in the range from ∼25 to ∼55. The multifunctional layered composite sensor provides multiple output signals which can be accurately recognized and assigned to independent triggering events, opening up new opportunities in advanced wearable devices based on commercial fabrics.

Flexible, Low-Cost, and Room Temperature Ammonia Sensor Based on Polypyrrole and Functionalized MWCNT Nanocomposites in Extreme Bending Conditions

We report a flexible and room temperature ammonia sensor based on polypyrrole/functionalized multiwalled carbon nanotubes (Ppy/f-MWCNTs). This nanocomposite has been synthesized by the in-situ chemical oxidative polymerization method and finally loaded on a transparent poly(vinylidene fluoride) (PVDF) membrane substrate. The entire flexible sensor fabrication process was cost-effective and easy to operate, making it ideal for commercial production on a wide scale. The optimized Ppy/f-MWCNT-based flexible sensor demonstrates improved sensing characteristics (26.5% for 100 ppm) with a low response time of 16 s and high response toward ammonia compared with pristine Ppy. In addition, high repeatability and long-term stability were also observed over a concentration range of 5–200 ppm. It shows high response toward ammonia among various gaseous analytes. Furthermore, the flexible sensor was mechanically robust and could produce a high response value even in extreme bending conditions. The flexible Ppy/f-MWCNT-based flexible sensors offer potential applications in advanced wearable devices to detect ammonia in the ambient environment.

Flexible wearable devices for intelligent health monitoring

AbstractProfited from the rapid development of flexible skin‐like electronic materials and artificial intelligent technology, remarkable achievements have been witnessed in wearable health monitoring devices in recent years. The wearable intelligent systems featured with tailored structures and compositions as well as enriched functions enable human beings to access to next‐generation closed‐loop platform for early disease prevention and diagnosis. In this context, this mini‐review focuses on the recent progress and applications of flexible wearable intelligent health monitoring devices. Specifically, the basic sensing mechanisms and corresponding property requirements for wearable healthcare devices are examined firstly. Secondly, the versatile applications of advanced wearable devices for detecting temperature, heart rate, blood pressure and glucose are scrutinized exclusively. Finally, a brief summary is presented accompanying with future outlook in terms of material preparation, mechanism development and integration design of monitoring systems. This manuscript is expected to provide critical guidelines to those working in skin‐like electronics, flexible sensors, wearable intelligent devices, health monitoring and other related disciplines, especially for the beginners.

Guest Editorial: Medical Data Security Solution for Healthcare Industries

Since smart healthcare systems are highly connected to advanced wearable devices, internet of things (IoT) and mobile internet, valuable patient information and other significant medical records are easily transmitted over the public network. The patient information and clinical records are also stored on the existing databases and local servers of hospitals and healthcare centres. These materials not only provide a reference for healthcare professionals to make correct decisions on the patients, but also provide a strong basis for other professionals to undertake effective treatment and develop plans for correct diagnosis. Furthermore, the databases may be used by various research communities for research, without any possibility of privacy violations. However, leaking of healthcare data is highly likely. Therefore, medical data security is becoming very important in smart healthcare.

Direct Wiring of Liquid Metal on an Ultrasoft Substrate Using a Polyvinyl Alcohol Lift-off Method.

In recent years, wiring and system construction on ultrasoft materials such as biological tissues and hydrogels have been proposed for advanced wearable devices, implantable devices, and soft robotics. Among the soft conductive materials, Ga-based liquid metals (LMs) are both biocompatible and ultrasoft, making them a good match for electrodes on the ultrasoft substrates. However, gels and tissues are softer and less wettable to the LMs than conventional soft substrates such as Ecoflex and polydimethylsiloxane. In this study, we demonstrated the transfer of LM paste composed of Ga-based LM and Ni nanoparticles onto ultrasoft substrates such as biological tissue and gels using sacrificial polyvinyl alcohol (PVA) films. The LM paste pattern fabricated on the PVA film adhered to the ultrasoft substrate along surface irregularities and was transferred without being destroyed by the PVA film before the PVA's dissolution in water. The minimum line width that could be wired was approximately 165 μm. Three-dimensional wiring, such as the helical structure on the gel fiber surface, is also possible. Application of this transfer method to tissues using LM paste wiring allowed the successful stimulation of the vagus nerve in rats. In addition, we succeeded in transferring a temperature measurement system fabricated on a PVA film onto the gel. The connection between the solid-state electrical element and the LM paste was stable and maintained the functionality of the temperature-sensing system. This fundamental study of wiring fabrication and system integration can contribute to the development of advanced electric devices based on ultrasoft substrates.

Network-Aware 5G Edge Computing for Object Detection: Augmenting Wearables to “See” More, Farther and Faster

Advanced wearable devices are increasingly incorporating high-resolution multi-camera systems. As state-of-the-art neural networks for processing the resulting image data are computationally demanding, there has been a growing interest in leveraging fifth generation (5G) wireless connectivity and mobile edge computing for offloading this processing closer to end-users. To assess this possibility, this paper presents a detailed simulation and evaluation of 5G wireless offloading for object detection in the case of a powerful, new smart wearable called VIS <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> ION, for the Blind-and-Visually Impaired (BVI). The current VIS <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> ION system is an instrumented book-bag with high-resolution cameras, vision processing, and haptic and audio feedback. The paper considers uploading the camera data to a mobile edge server to perform real-time object detection and transmitting the detection results back to the wearable. To determine the video requirements, the paper evaluates the impact of video bit rate and resolution on object detection accuracy and range. A new street scene dataset with labeled objects relevant to BVI navigation is leveraged for analysis. The vision evaluation is combined with a full-stack wireless network simulation to determine the distribution of throughputs and delays with real navigation paths and ray-tracing from new high-resolution 3D models in an urban environment. For comparison, the wireless simulation considers both a standard 4G-Long Term Evolution (LTE) sub-6-GHz carrier and high-rate 5G millimeter-wave (mmWave) carrier. The work thus provides a thorough and detailed assessment of edge computing for object detection with mmWave and sub-6-GHz connectivity in an application with both high bandwidth and low latency requirements.

Do Consumers Care About Aesthetics and Compatibility? The Intention to Use Wearable Devices in Health Care

This study examined the influencing factors on consumers’ intention to use wearable devices in health care (WDH). Although the importance of the WDH market is increasing, existing empirical study results on WDH have been selectively investigated based on the technology acceptance model (TAM). To address this issue, we endeavored to contribute by integrating the theory of planned behavior (TPB) and innovation diffusion theory (IDT) on top of TAM to explain the psychological mechanism underlying consumer behaviors, especially when adopting advanced wearable devices in the health care domain. We surveyed 303 people in Pangyo IT Valley, South Korea, and attempted a path analysis using PLS-SEM estimation. The findings suggest that individual innovativeness (IIN) directly affects consumers’ intention to use (IU) WDH, while self-efficacy (SE), aesthetics (AES), and compatibility (COM) have indirectly influenced their usage intentions. Detailed results are described in the article.

Design, Analysis, and Experimental Evaluation of a New Secure Rejoin Mechanism for LoRaWAN Using Elliptic-Curve Cryptography

LoRaWAN (Long Range Wide Area Network) is a Low-Power Wide Area Networks (LPWAN) technology with very rapid uptake during the previous years, developed by the LoRa (Long Range) Alliance as an open standard operating over the unlicensed band. Current LoRaWAN architecture foresees specific techniques for bootstrapping end-to-end encryption during network initialization. In particular, this work focuses on the Over-The-Air Activation (OTAA) method, which uses two keys (Network key (NwkKey) and Application key (AppKey)) that are hard-coded into the device and do not change throughout the entire lifetime of the deployment. The inability to refresh these two keys is as a weak point in terms of the overall security of the network especially when considering deployments that are expected to operate for at least 10–15 years. In this paper, the security issues of OTAA are presented in detail highlighting the vulnerabilities against the specific type of attacks. A new scheme for network activation is proposed that builds upon the current LoRaWAN architecture in a way that maintains backwards compatibility while resolving certain vulnerabilities. Under the new mechanism, the devices periodically negotiate new keys securely based on elliptic-curve cryptography. The security properties of the proposed mechanism are analyzed against a specific type of attacks. The analysis indicates that the new secure rejoin mechanism guarantees (i) computational key secrecy, (ii) decisional key secrecy, and (iii) key independence, forward and backward, for both root keys thus properly addressing the considered security vulnerabilities of LoRaWAN. Moreover, the method is implemented in software using the RIOT-OS, a hardware-independent operating system that supports many different architectures for 8 bit, 16 bit, 32 bit and 64 bit processors. The resulting software is evaluated on the FIT IoT-Lab real-world experimentation facility under a diverse set of ARM Cortex-M* devices targeting a broad range of IoT applications, ranging from advanced wearable devices to interactive entertainment devices, home automation and industrial cyber-physical systems. The experiments indicate that the overall overhead incurred in terms of energy and time by the proposed rejoin mechanism is acceptable given the low frequency of execution and the improvements to the overall security of the LoRaWAN1.1 OTAA method.

A Highly Stretchable, Self-Healing Elastomer with Rate Sensing Capability Based on a Dynamic Dual Network.

Flexible sensing materials have attracted tremendous attention in recent years because of their potential applications in the fields of health monitoring, artificial intelligence, and so on. However, the preparation of rate sensing materials with self-healing performance is always a huge challenge. Herein, we first report the design and synthesis of a highly stretchable, recyclable, self-healing polysiloxane elastomer with rate sensing capability. The elastomer is composed of a dynamic dual network with boron/oxygen dative bonds and hydrogen bonds, which overcomes the structural instability of conventional solid-liquid materials. It exhibits certain adhesion, satisfactory mechanical robustness, and superior elongation at break (up to 1171%). After heating treatment at 80 °C for 2-4 h, the mechanical properties of damaged materials can be almost completely restored. Because of the "solid-liquid" property of the elastomer, it has irreplaceable functions which can sense different rates by resistance change after blending with multiwalled carbon nanotubes, principally in the range of 10 mm/min-150 mm/min. Especially, this rate sensing elastomer can be personalized by 3D printing at room temperature. This rate sensing strategy coupled with the introduction of dynamic dual-network structure is expected to help design advanced wearable devices for human rhythmic movement.