Applications In Wearable Devices Research Articles

LM-Gel Plasticine Based on Binary Cooperative with Kneadable Shaping and Conductivity.

Liquid metal (LM)-based polymers have received growing interest for wearable health monitoring, electronic skins, and soft robotics. However, fabricating multifunctional LM-based polymers, in particular, featuring a convenient shaping ability while offering excellent deformability and conductivity remains a challenge. To overcome this obstacle, here, we propose a strategy to prepare LM-Gel "plasticine" (LGP) with great deformability, which is composed of a PVA (poly(vinyl alcohol)) soft network and an LM conductive phase. LGP can be easily constructed into different shapes such as plasticine and can be applied to different conditions (such as building a 3D circuit, circuit repair, and switch). Meanwhile, LGP has great conductivity (2.3 × 104 S/m) after surface annealing. Besides, LGP has a good electric heating performance, which shows the potential for application in wearable heating devices. Thus, this approach not only provides a way to prepare LM-polymer plasticine but also provides a novel perspective toward extending the applied range of LM-polymer composites.

Dielectric Elastomer Actuators with Enhanced Durability by Introducing a Reservoir Layer

A Dielectric Elastomer Actuator (DEA) consists of electrodes with a dielectric layer between them. By controlling the design of the electrodes, voltage, and frequency, the operating range and speed of the DEA can be adjusted. These DEAs find applications in biomimetic robots, artificial muscles, and similar fields. When voltage is applied to the DEA, the dielectric layer undergoes compression and expansion due to electrostatic forces, which can lead to electrical breakdown. This phenomenon is closely related to the performance and lifespan of the DEA. To enhance stability and improve dielectric properties, a DEA Reservoir layer is introduced. Here, stability refers to the ability of the DEA to perform its functions even as the applied voltage increases. The Reservoir layer delays electrical breakdown and enhances stability due to its enhanced thickness. The proposed DEA in this paper is composed of a Reservoir layer and electrode layer. The Reservoir layer is placed between the electrode layers and is independently configured, not subjected to applied voltage like the electrode layers. The performance of the DEA was evaluated by varying the number of polymer layers in the Reservoir and electrode designs. Introducing the Reservoir layer improved the dielectric properties of the DEA and delayed electrical breakdown. Increasing the dielectric constant through the DEA Reservoir can enhance output characteristics in response to electrical signals. This approach can be utilized in various applications in wearable devices, artificial muscles, and other fields.

Evaluation of a Microcontroller-based Smart Wearable Device in College Students' Sports Forging Application

INTRODUCTION: The widespread use of smart wearable devices in various fields, including healthcare and sports, underscores the importance of their application in enhancing physical exercise among college students. Recent advancements in technology have facilitated the development of sophisticated methods to assess and predict physical activity outcomes, making their evaluation increasingly critical.OBJECTIVES: This study aims to develop a reliable assessment model for smart wearable devices used in college students' sports activities. The objective is to accurately predict and evaluate the effectiveness of these devices in improving students' physical health and promoting lifelong sports habits. Ultimately, the research seeks to integrate advanced computational methods to enhance the accuracy of physical exercise assessments.METHODS: The research introduces a novel assessment model that combines a zebra behavior-based heuristic optimization algorithm with a convolutional neural network (CNN). By analyzing user behavior data from wearable devices, the model constructs an evaluation index system tailored for college sports activities. The approach optimizes the parameters of the CNN using the zebra optimization algorithm, ensuring enhanced prediction accuracy.RESULTS: The evaluation model demonstrated high accuracy, with a significant improvement in predicting the outcomes of physical exercises among college students. Comparative analyses with traditional methods revealed that the new model reduced prediction errors and increased real-time performance metrics. Specifically, the model achieved a lower root mean square error (RMSE) in simulation tests, indicating more precise assessments. Figures and statistical data provided in the study illustrate the model's superior performance across various parameters.CONCLUSION: The developed assessment model significantly advances the application of smart wearable devices in monitoring and enhancing college students' physical activities. By integrating cutting-edge algorithms, the study not only improves the accuracy of exercise assessments but also contributes to the broader understanding of technology's role in health and fitness education. Future research could further refine this model by incorporating additional sensors and data points to expand its applicability and robustness.

Synergistic Enhancement of Wearable Biosensor through Pt Single-Atom Catalyst for Sweat Analysis

Real-time monitoring of biological markers in sweat is a valuable tool for health assessment. In this study, we have developed an innovative wearable biosensor for precise analysis of glucose in sweat during physical activities. The sensor is based on a single-atom catalyst of platinum (Pt) uniformly dispersed on tricobalt tetroxide (Co3O4) nanorods and reduced graphene oxide (rGO), featuring a unique three-dimensional nanostructure and excellent glucose electrocatalytic performance with a wide detection range of 1-800 μM. Additionally, density functional theory calculations have revealed the synergetic role of Pt active sites in the Pt single-atom catalyst (Co3O4/rGO/Pt) in glucose adsorption and electron transfer, thereby enhancing sensor performance. To enable application in wearable devices, we designed an S-shaped microfluidic chip and a point-of-care testing (POCT) device, both of which were validated for effectiveness through actual use by volunteers. This research provides valuable insights and innovative approaches for analyzing sweat glucose using wearable devices, contributing to the advancement of personalized healthcare.

Capacitive BaTiO3-PDMS hand-gesture sensor: Insights into sensing mechanisms and signal classification with machine learning

Flexible sensors have gained extensive interest because of their versatile applications in healthcare, robotics, and wearable devices. This study introduces a capacitive sensor utilizing barium titanate oxide (BaTiO3)-polydimethylsiloxane (PDMS) for bending sensing and addresses crucial performance parameters including sensitivity, repeatability, response time, and durability. The sensor exhibited a notable capacitance change of 42.85% in conjunction with fast (1 s) responses and recovery times, and minimal hysteresis (<2%). Its reliable performance across varying bending rates and durability through extensive cyclic tests underscore its applicability in real-world scenarios. Importantly, the sensor's capabilities were enhanced by integrating machine learning (ML), achieving an impressive accuracy of 97.11% in recognizing hand-sign language gestures. Furthermore, finite element analysis was employed to validate the correlation between the increase in compression-induced packing density and capacitance enhancement. This holistic integration of advanced materials, computational simulations, and ML not only extends the boundaries of sensor technology but also holds promise for revolutionizing human–machine interactions, aiding speech-impaired individuals, and enriching virtual reality experiences. This study represents a pivotal advancement in the field of flexible sensors and the unlocking of new dimensions of their applications.

A Novel Dual-Band Circularly Polarized Wearable Antenna

A circularly polarized wearable antenna operating in the 2.45/5.8 GHz ISM dual bands is proposed, which consists of a coplanar waveguide-fed rectangular monopole antenna and two parasitic branches. The monopole rectangular radiation patch can generate 2.45 and 7 GHz frequency bands and has linear polarization characteristics. By adding L-shaped parasitic branches and L-like grounded branches on both sides of the monopole, the 7 GHz operating frequency band can be moved to the 5.8 GHz frequency band, and circular polarization characteristics can be achieved in both the 2.45 and 5.8 GHz frequency bands. The size of the antenna is 48.7 mm × 42.1 mm × 1.016 mm. The simulated −10 dB impedance bandwidths of the antenna are 1.8–2.66 GHz and 5.48–6.98 GHz, respectively. The 3 dB axial ratio bandwidths are 2.34–2.67 GHz and 5.58–6.39 GHz, respectively, and it has dual-band circular polarization characteristics. In addition, the radiation characteristics of the antenna and its safety performance near the human body were analyzed. The antenna prototype has been constructed, and the measurement and simulation results have good consistency. The proposed antenna is suitable for application in wearable devices.

Superwetting Capillary Tubes: Surface Science under Confined Space.

Capillarity is a crucial and pervasive phenomenon in nature and has found important applications in wearable electronics, medical devices, and miniature energy systems. Capillary tubes are the transport vessels in which the surface wettability plays an essential role in efficient and accurate liquid delivery. However, it remains a challenging issue to tailor and measure the surface wettability inside the tubes in view of the confined space. Herein, recent progress on the surface science under confined space is discussed, with a particular focus on surface modification, wettability evaluation, and advanced applications of the superwetting capillary tubes. This Perspective aims to highlight the emerging opportunities in surface science with spatial confinement toward flexible and portable devices.

Rational Design of a Surface Acoustic Wave Device for Wearable Body Temperature Monitoring

Continuous monitoring of vital signs based on advanced sensing technologies has attracted extensive attention due to the ravages of COVID-19. A maintenance-free and low-cost passive wireless sensing system based on surface acoustic wave (SAW) device can be used to continuously monitor temperature. However, the current SAW-based passive sensing system is mostly designed at a low frequency around 433 MHz, which leads to the relatively large size of SAW devices and antenna, hindering their application in wearable devices. In this paper, SAW devices with a resonant frequency distributed in the 870 MHz to 960 MHz range are rationally designed and fabricated. Based on the finite-element method (FEM) and coupling-of-modes (COM) model, the device parameters, including interdigital transducer (IDT) pairs, aperture size, and reflector pairs, are systematically optimized, and the theoretical and experimental results show high consistency. Finally, SAW temperature sensors with a quality factor greater than 2200 are obtained for real-time temperature monitoring ranging from 20 to 50 °C. Benefitting from the higher operating frequency, the size of the sensing system can be reduced for human body temperature monitoring, showing its potential to be used as a wearable monitoring device in the future.

Silver nanoparticles reinforced on silk fibroin/carboxymethylcellulose composite films for electrical applications

This study proposes the fabrication of silver nanoparticles (AgNPs) on silk fibroin-carboxymethylcellulose (SF-CMC) composite films for advancement in electronic device applications. Bombyx mori silk fibroin is a biopolymer that is used as a bio-template in the fabrication of AgNPs. Various silver nitrate (AgNO3) combinations are added to the prepared SF solution to synthesize AgNPs. To develop stand-alone biopolymer-nanocomposite (SF-CMC/AgNPs) films, SF-AgNPs colloidal solution is blended with CMC solution. Ultra Violet – Visible (UV–Vis), Photoluminescence (PL), Fourier Transform Infra-red Spectroscopy (FT-IR), X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM) have been employed to the prepared SF-CMC/AgNPs composites toevaluate the physical, chemical, structural, morphological, and topographical information of the composite films. Furthermore, the composites are subjected to LCR Hi-tester and electrochemical workstation CH instrument to analyze the AC, DC conductivity, dielectric characteristics, and electrochemical impedance analysis of SF-CMC/AgNPs composites. The UV–visible spectra reveals the formed nanoparticles in spherical shape with average particle size 35–40 nm. XRD reveals the formed AgNPs in face centred cubic (FCC) structure; TEM reveals the average particle size of 35 nm. AC conductivity of the SF-CMC/AgNPs composite found to be 4.0 × 10−4 to 8.04 × 10−4 S/cm. In spite of the presence of AgNPs, measurements of the dielectric behaviourof pure CMC and SF-CMC materials exhibit good dielectric performance. The obtained results demonstrated that the SF-CMCfilms exhibit significant conductivity following AgNPs incorporation and may therefore be used in biosensor and wearable electronic device applications.

Surface Energy-Assisted Patterning of Vapor Deposited All-Inorganic Perovskite Arrays for Wearable Optoelectronics.

Solution-based methods for fabricating all-inorganic perovskite film arrays often suffer from limited control over nucleation and crystallization, resulting in poor homogeneity and coverage. To improve film quality, advanced vapor deposition techniques are employed for continuous film. Here, the vapor deposition strategy to the all-inorganic perovskite films array, enabling area-selective deposition of perovskite through substrate modulation is expanded. It can yield a high-quality perovskite film array with different pixel shapes, various perovskite compositions, and a high resolution of 423dpi. The resulting photodetector arrays exhibit remarkable optoelectronic performance with an on/off ratio of 13 887 and responsivity of 47.5AW-1. The device also displays long-term stability in a damp condition for up to 12h. Moreover, a pulse monitoring sensor based on the perovskite films array demonstrates stable monitoring for pulse signals after being worn for 12h and with a low illumination of 0.055mWcm-2, highlighting the potential application in wearable optoelectronic devices.

Wearable EMI Shielding Composite Films with Integrated Optimization of Electrical Safety, Biosafety and Thermal Safety.

Biomaterial-based flexible electromagnetic interference (EMI) shielding composite films are desirable in many applications of wearable electronic devices. However, much research focuses on improving the EMI shielding performance of materials, while optimizing the comprehensive safety of wearable EMI shielding materials has been neglected. Herein, wearable cellulose nanofiber@boron nitride nanosheet/silver nanowire/bacterial cellulose (CNF@BNNS/AgNW/BC) EMI shielding composite films with sandwich structure are fabricated via a simple sequential vacuum filtration method. For the first time, the electrical safety, biosafety, and thermal safety of EMI shielding materials are optimized integratedly. Since both sides of the sandwich structure contain CNF and BC electrical insulation layers, the CNF@BNNS/AgNW/BC composite films exhibit excellent electrical safety. Furthermore, benefiting from the AgNW conductive networks in the middle layer, the CNF@BNNS/AgNW/BC exhibit excellent EMI shielding effectiveness of 49.95dB and ultra-fast response Joule heating performance. More importantly, the antibacterial property of AgNW ensures the biosafety of the composite films. Meanwhile, the AgNW and the CNF@BNNS layers synergistically enhance the thermal conductivity of the CNF@BNNS/AgNW/BC composite film, reaching a high value of 8.85W m‒1 K‒1, which significantly enhances its thermal safety when used in miniaturized electronic device. This work offers new ideas for fabricating biomaterial-based EMI shielding composite films with high comprehensive safety.

Robust ultrahigh electromagnetic interference shielding effectiveness based on engineered structures of carbon nanotube films

High-performance electromagnetic interference (EMI) shielding materials with ultrathin, flexible, and pliable mechanical properties are highly desired for high-end equipments, yet there remain large challenges in the manufacture of these materials. Here, carbon nanotube film (CNTF)/copper (Cu) nanoparticle (NP) composite films are fabricated via a facile electrodeposition method to achieve high electromagnetic shielding efficiency. Notably, a CNTF/Cu NP composite film with 15μm thickness can achieve excellent EMI shielding efficiency of ∼248 dB and absolute EMI shielding effectiveness as high as 2.17×105 dB cm2 g-1, which are the best values for composite EMI shielding materials with similar or greater thicknesses. These engineered composite films exhibit excellent deformation tolerance, which ensures the robust reliability of EMI shielding efficiency after 20,000 cycles of repeated bending. Our results represent a critical breakthrough in the preparation of ultrathin, flexible, and pliable shielding films for applications in smart, portable and wearable electronic devices, and 5G communication.

Nickel-cobalt metal-organic frameworks based flexible hydrogel as a wearable contact lens for electrochemical sensing of urea in tear samples.

Aflexible, wearable, non-invasivecontact lens sensor utilizing nickel-cobalt metal-organic framework (Ni-Co-MOF) based hydrogel is introducedfor urea monitoring in tear samples. The synthesized Ni-Co-MOF hydrogel exhibits a porous structure with interconnected voids, as visualized by Scanning Electron Microscopy (SEM). Detailed structural and vibrational properties of the material were characterized using X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR)spectroscopy, and Raman spectroscopy. The developed Ni-Co-MOF hydrogel sensor showcases a detection limit of 0.445 mM for urea within a linear range of 0.5-70 mM. Notably, it demonstrates exceptional selectivity, effectively distinguishing against interfering species like UA, AA, glucose, dopamine, Cl-, K+, Na+, Ca2+, and IgG. The enhanced electrocatalytic performance of the Ni-Co-MOF hydrogel electrode is attributed to the presence of Ni and Co, fostering Ni2+ oxidation on the surface and forming a Co2+ complex that acts as a catalyst for urea oxidation. The fabricated sensor exhibits successful detection and retrieval of urea in simulated tear samples, showcasing promising potential for bioanalytical applications. The binder-free, non-toxic nature of the Ni-Co-MOF hydrogel sensor presents exciting avenues for future utilization in non-enzymatic electrochemical sensing, including applications in wearable devices, point-of-care diagnostics, and personalized healthcare monitoring.

Ultrasensitive Biomimetic Skin with Multimodal and Photoelectric Dual-Signal Sensing.

Mimicking biological skin enabling direct, intelligent interaction between users and devices, multimodal sensing with optical/electrical (OE) output signals is urgently required. Owing to this, this work aims to logically design a stretchable OE biomimetic skin (OE skin), which can sensitively sense complex external stimuli of pressure, strain, temperature, and localization. The OE skin consists of elastic thin polymer-stabilized cholesteric liquid crystal films, an ion-conductive hydrogel layer, and an elastic protective membrane formed with thin polydimethylsiloxane. The as-designed OE skin exhibits customizable structural color on demand, good thermochromism, and excellent mechanochromism, with the ability to extend the full visible spectrum, a good linearity of over 0.99, fast response speed of 93 ms, and wide temperature range of 119 °C. In addition, the conduction resistance variation of ion-conductive hydrogel exhibits excellent sensing capabilities under pressure, stretch, and temperature, endowing a good linearity of 0.99998 (stretching from 0 to 150%) and high thermal sensitivity of 0.86% per °C. Such an outstanding OE skin provides design concepts for the development of multifunctional biomimetic skin used in human-machine interaction and can find wide applications in intelligent wearable devices and human-machine interactions.

Fluorine-Containing Ionogels with Stretchable, Solvent-Resistant, Wide Temperature Tolerance, and Transparent Properties for Ionic Conductors.

Stretchable ionogels, as soft ion-conducting materials, have generated significant interest. However, the integration of multiple functions into a single ionogel, including temperature tolerance, self-adhesiveness, and stability in diverse environments, remains a challenge. In this study, a new class of fluorine-containing ionogels was synthesized through photo-initiated copolymerization of fluorinated hexafluorobutyl methacrylate and butyl acrylate in a fluorinated ionic liquid 1-butyl-3-methyl imidazolium bis (trifluoromethylsulfonyl) imide. The resulting ionogels demonstrate good stretchability with a fracture strain of ~1300%. Owing to the advantages of the fluorinated network and the ionic liquid, the ionogels show excellent stability in air and vacuum, as well as in various solvent media such as water, sodium chloride solution, and hexane. Additionally, the ionogels display impressive wide temperature tolerance, functioning effectively within a wide temperature range from -60 to 350 °C. Moreover, due to their adhesive properties, the ionogels can be easily attached to various substrates, including plastic, rubber, steel, and glass. Sensors made of these ionogels reliably respond to repetitive tensile-release motion and finger bending in both air and underwater. These findings suggest that the developed ionogels hold great promise for application in wearable devices.

Reviews on Flexible Force Sensors Based on Fiber Assemblies with Mass Production Efficiency

AbstractFlexible force sensors show great potential applications in smart wearable devices based on their softness and ease of deformation. Textiles are extremely compatible with the human body, where mechanical forces generated by human movements and physiological activities create rich application scenarios for flexible force sensors. Currently, the bottleneck in the development of flexible sensors depends on the breakthrough of mass production efficiency, which has been a research focus in recent years to accelerate the application of smart textiles in various fields. This work reviews the research progress of flexible force sensors based on fiber assemblies with mass production efficiency, which is discussed in four aspects: sensing mechanisms, structure design, preparation methods, and application. Finally, the challenges faced by mass production of flexible force sensors are analyzed and summarized, and a few inspirations for their future development direction are provided.

Ultra-stretchable, high conductive, fatigue resistance, and self-healing strain sensor based on mussel-inspired adhesive hydrogel for human motion monitoring

Conductive hydrogels have been widely applied in various electronics, such as artificial skin, flexible devices, and implantable bioelectronics. However, it is still a challenge to develop high-performance hydrogel with high conductivity without compromising the toughness, stretchability, self-healing, and adhesion properties. Herein, inspired by the mussel-adhesion mechanism, an adhesive hydrogel that simultaneously achieves high conductivity (27.0 S·m−1), ultra stretchability (strain ˃ 3700 %), and strong toughness (1930 kJ·m−3) was developed by incorporating polydopamine (PDA)/sodium caseinate (SC) cross-linked network into the poly(acrylamide-co-acrylic acid) (P(AM-co-AA))/Al3+ network. Due to the abundant metal coordination and hydrogen bonds in the network, the obtained hydrogel displayed rapid self-healing capability (healing efficiency, HE > 97 %) and excellent fatigue resistance. Moreover, the introduction of PDA-SC cross-linked network endowed the hydrogels with robust adhesion (36.5 kPa for pigskin) and high conductivity. The conductive hydrogel was assembled into a strain sensor, which demonstrated prominent sensing performance with a wide detection range (∼2500%), high sensitivity (gauge factor (GF) of 23.7), fast response time and reliable repeatability. The hydrogel strain sensor can be attached on human body to distinguish and monitor both large and subtle movement signals. The developed conductive hydrogel strain sensor is expected to have promising applications in wearable devices, human–machine interaction, and electrical skin, and to extend for use in other portable and wearable energy related devices with multifunction.

3D printed dual network Cross-Linked hydrogel electrolytes for high area capacity flexible zinc ion Micro-Batteries

Hydrogel electrolytes have wide applications in flexible zinc ion micro-batteries (FZIMBs) due to their excellent mechanical flexibility, biocompatibility, and ionic conductivity. However, traditional templating methods are limited to fabricating two-dimensional and simple three-dimensional structures, making them insufficient for preparing complex structures in FZIMBs. Here, we report a printable hydrogel electrolyte ink with excellent rheological properties. By utilizing 3D printing technology, we achieve the preparation of a custom-shaped, double-network crosslinked polyacrylamide-hydroxypropyl methylcellulose hydrogel electrolyte (PHHE). The PHHE exhibits high ionic conductivity (31.72 mS cm−1), good cycling stability, and mechanical flexibility. Furthermore, we constructed FZIMBs with high areal capacities (6.45 mAh cm−2 at 0.5 mA cm−2) and good mechanical flexibility by leveraging PHHE and 3D printing technology. Integrating FZIMBs with a pressure sensing component, we establish a sensing interaction system, demonstrating practical applications of flexible wearable devices. This work presents a novel method for the preparation of customized hydrogel electrolytes and highlights the significant potential of FZIMBs in practical applications.

Recent Progress in Wearable Near-Sensor and In-Sensor Intelligent Perception Systems.

As the Internet of Things (IoT) becomes more widespread, wearable smart systems will begin to be used in a variety of applications in people's daily lives, not only requiring the devices to have excellent flexibility and biocompatibility, but also taking into account redundant data and communication delays due to the use of a large number of sensors. Fortunately, the emerging paradigms of near-sensor and in-sensor computing, together with the proposal of flexible neuromorphic devices, provides a viable solution for the application of intelligent low-power wearable devices. Therefore, wearable smart systems based on new computing paradigms are of great research value. This review discusses the research status of a flexible five-sense sensing system based on near-sensor and in-sensor architectures, considering material design, structural design and circuit design. Furthermore, we summarize challenging problems that need to be solved and provide an outlook on the potential applications of intelligent wearable devices.

Electrical, optical and mechanical properties of monolayer MoTe2 for applications in wearable optoelectronic devices

Transition metal dichalcogenides (TMDs) have excellent optical and mechanical properties and have potential application value in wearable optoelectronic response devices. MoTe2, a representative material of TMDs, is studied by first-principles calculation in this paper. The results show that the MoTe2 monolayer has a direct band gap of 1.110eV, which has a strong light absorption capacity and can produce a high concentration of photogenerated charge carriers after light absorption. The material is soft and exhibits the unique mechanical properties of layered materials. The effects of biaxial strain and defects on the properties of the materials were analyzed. The results show that the biaxial compression strain can enhance the light absorption curve of the material, enhance the light absorption of the photogenerated carrier, and expand the range of its energy distribution. The tensile strain decreases the value of the photon absorption curve and decreases the range of energy distribution of photogenerated carriers. The Mo vacancy defect increases the absorption curve value in the low energy region and broadens the optical response range of the material. The two types of vacancy defects both induce a ‘discrete’ distribution of photogenerated carriers. The Mo vacancy significantly affects the elastic modulus and anisotropy properties of the material, resulting in the material changing from ductile to brittle. When Mo vacancy is added, the spatial distribution of the elastic modulus of the material also changes greatly. Therefore, MoTe2 has potential application in flexible optoelectronic devices, and its performance can be controlled by strains and defects.