Fish Gelatin Based Triboelectric Nanogenerator for Harvesting Biomechanical Energy and Self-Powered Sensing of Human Physiological Signals

A Triboelectric Sensor with High Sensitivity and Wide Detection Range by Tuning Electron Tunneling and Piezoelectric Charge

Triboelectric sensors have received extensive attention in wearable self-powered sensing, electronic skin, and smart medical treatment due to the characteristics of low-cost and diverse material choices, but the sensitivity and detected range are greatly limited to the development of scale and commercialization of triboelectric sensors. Herein, we propose a binary insulator/conductor electrification triboelectric sensor (BICS) assembling an aminated porous gelatin and aluminum (Al) as a positive tribolayer and an MXene@polyvinylidene fluoride (MXene@PVDF) nanofiber film as a negative tribolayer. Because of the positive layer, the Al can not only generate charges due to the triboelectric effect but also capture charges from gelatin due to the electron tunneling effect. And for the MXene@PVDF nanofiber negative layer, the MXene is embedded in PVDF film to enhance the generation of tribo- and piezocharge under contact with gelatin/Al film. Owing to the large number of charges generated, BICS shows an ultrahigh short current of 1.06 mA, which is 1000 times higher than previous related research (usually in ∼μA). BICS exhibits an excellent sensitivity of 3.33 V kPa-1 and a wide detection range from Pa to kPa, making it ideal for full pressure scale human activity monitoring. Our findings provide a novel and significant strategy for constructing high-performance triboelectric sensors.

Polyacrylonitrile/Polyaniline Composite Nanofibers for High-Performance Triboelectric Nanogenerator and Self-Powered Wireless Sensing Applications

Triboelectric nanogenerators (TENGs) are emerging as a sustainable and environmentally friendly approach for energy harvesting and self-powered sensing, because of their diverse material options, simple structure, and efficient energy conversion. However, developing tribopositive materials with both high-charge-inducing and high-charge-trapping capabilities remains a significant challenge. Herein, a high-performance TENG is developed based on a polyaniline (PANI) embedded polyacrylonitrile (PAN) nanofiber membrane (NM) (P/P NM) for energy harvesting and self-powered wireless sensing. The incorporation of PANI significantly enhanced the electrical performance, mechanical properties, and thermal stability of P/P NMs. The P/P NM-based TENG achieved an output voltage of 726 V, a short-circuit current density of 32 μA/cm2, and a peak power density of 23.3 W/m2, which were approximately 2.3, 3.6, and 4.6 times higher than those of the pristine PAN NM-based TENG, respectively. Detailed investigations revealed that the embedded PANI improved the electron-donating ability and dielectric constant (by 4.25 times) of P/P NMs, thereby significantly boosting the electrical output of the TENG. The mechanical energy harvesting ability was elucidated through capacitor charging and the operation of low-power devices. Furthermore, the P/P NM-based TENG was integrated into a self-powered wireless sensing system, which enabled the cross-scale monitoring of human signals ranging from tiny pulses to large-scale movements. The introduction of PANI nanofillers provides a simple, effective, and scalable strategy for developing high-performance positive tribomaterials, thus, advancing the practical application of TENGs in energy harvesting and self-powered sensing.

Engineering Triboelectric Paper for Energy Harvesting and Smart Sensing

Triboelectric nanogenerators (TENGs) represent a promising technology for energy harvesting and self-powered sensing with a wide range of applications. Despite their potential, challenges such as the need for cost-effective, large-area electrodes and engineering sustainable triboelectric materials remain, especially given the impending restrictions on single-use engineering plastics in Europe. To address these challenges, engineering nano-graphite-coated paper is presented as a sustainable and high-performance alternative for triboelectric layers. Moreover, this material, which can be produced on an industrial scale, offers a viable replacement for metal electrodes. The combination of nano-graphite and paper, with its large contact area and inherent surface roughness, enables ultra-high power densities exceeding 14 kW m-2, driven by electrostatic discharge at the surface. Beyond energy harvesting, smart sensors are developed for floors and walls that detect movements for security purposes and smart sheets that monitor body movements and physiological activities during sleep. The findings highlight the potential of this engineering paper to serve as an eco-friendly alternative to engineering plastics in TENGs and electrodes, opening new avenues for future applications.

Biowaste-Derived Triboelectric Nanogenerators for Emerging Bioelectronics

Triboelectric nanogenerators (TENGs) combine contact electrification and electrostatic induction effects to convert waste mechanical energy into electrical energy. As conventional devices contribute to electronic waste, TENGs based on ecofriendly and biocompatible materials have been developed for various energy applications. Owing to the abundance, accessibility, low cost, and biodegradability of biowaste (BW), recycling these materials has gained considerable attention as a green approach for fabricating TENGs. This review provides a detailed overview of BW materials, processing techniques for BW-based TENGs (BW-TENGs), and potential applications of BW-TENGs in emerging bioelectronics. In particular, recent progress in material design, fabrication methods, and biomechanical and environmental energy-harvesting performance is discussed. This review is aimed at promoting the continued development of BW-TENGs and their adoption for sustainable energy-harvesting applications in the field of bioelectronics.

Biocompatible triboelectric energy generators (BT-TENGs) for energy harvesting and healthcare applications

Electronic waste (e-waste) has become a significant environmental and societal challenge, necessitating the development of sustainable alternatives. Biocompatible and biodegradable electronic devices offer a promising solution to mitigate e-waste and provide viable alternatives for various applications, including triboelectric nanogenerators (TENGs). This review provides a comprehensive overview of recent advancements in biocompatible, biodegradable, and implantable TENGs, emphasizing their potential as energy scavengers for healthcare devices. The review delves into the fabrication processes of self-powered TENGs using natural biopolymers, highlighting their biodegradability and compatibility with biological tissues. It further explores the biomedical applications of ultrasound-based TENGs, including their roles in wound healing and energy generation. Notably, the review presents the novel application of TENGs for vagus nerve stimulation, demonstrating their potential in neurotherapeutic interventions. Key findings include the identification of optimal biopolymer materials for TENG fabrication, the effectiveness of TENGs in energy harvesting from physiological movements, and the potential of these devices in regenerative medicine. Finally, the review discusses the challenges in scaling up the production of implantable TENGs from biomaterials, addressing issues such as mechanical stability, long-term biocompatibility, and integration with existing medical devices, outlining future research opportunities to enhance their performance and broaden their applications in the biomedical field.

Polyurethanes synthesized using biomass-derived furan diols as sustainable triboelectric materials

This work shows that various polyurethanes (FPUs) prepared using biomass-derived furan diols can be applied as promising tribopositive materials. The elastic FPUs having appropriate glass transition temperature (Tg) could be incorporated into polyethylene terephthalate (PET) fabrics to form FPU/PET films. The optimal FPU-4/PET film showed promising triboelectric performance with output voltages (Vp-p) up to 405 V and a maximum power density (Pmax) of 32 mW cm-2.

Advanced Triboelectric Applications of Biomass-Derived Materials: A Comprehensive Review

The utilization of triboelectric materials has gained considerable attention in recent years, offering a sustainable approach to energy harvesting and sensing technologies. Biomass-derived materials, owing to their abundance, renewability, and biocompatibility, offer promising avenues for enhancing the performance and versatility of triboelectric devices. This paper explores the synthesis and characterization of biomass-derived materials, their integration into triboelectric nanogenerators (TENGs), and their applications in energy harvesting, self-powered sensors, and environmental monitoring. This review presents an overview of the emerging field of advanced triboelectric applications that utilize the unique properties of biomass-derived materials. Additionally, it addresses the challenges and opportunities in employing biomass-derived materials for triboelectric applications, emphasizing the potential for sustainable and eco-friendly energy solutions.

Charge Dispersion Strategy for High-Performance and Rain-Proof Triboelectric Nanogenerator

Triboelectric nanogenerator (TENG) is becoming a sustainable and renewable way of energy harvesting and self-powered sensing because of low cost, simple structure, and high efficiency. However, the output current of existing TENGs is still low. It is proposed that the output current of TENGs can be dramatically improved if the triboelectric charges can distribute inside the triboelectric layers. Herein, a novel single-electrode conductive network-based TENG (CN-TENG) is developed by introducing a conductive network of multiwalled carbon nanotubes in dielectric triboelectric layer of thermoplastic polyurethane (TPU). In this CN-TENG, the contact electrification-induced charges distribute on both the surface and interior of the dielectric TPU layer. Thus, the short-circuit current of CN-TENG improves for 100-fold, compared with that of traditional dielectric TENG. In addition, this CN-TENG, even without packing, can work stably in high-humidity environments and even in the rain, which is another main challenge for conventional TENGs due to charge leakage. Further, this CN-TENG is applied for the first time, to successfully distinguish conductive and dielectric materials. This work provides a new and effective strategy to fabricate TENGs with high output current and humidity-resistivity, greatly expanding their practical applications in energy harvesting, movement sensing, human-machine interaction, and so on.

Survey on Energy Harvesting for Biomedical Devices: Applications, Challenges and Future Prospects for African Countries

Self-powered biomedical devices, which are the new vision of Internet Of Things (IOT) healthcare, are facing many technical and application challenges. Many research works have reported biomedical devices and self-powered applications for healthcare, along with various strategies to improve the monitoring time of self-powered devices or to eliminate the dependence on electrochemical batteries. However, none of these works have especially assessed the development and application of healthcare devices in an African context. This article provides a comprehensive review of self-powered devices in the biomedical research field, introduces their applications for healthcare, evaluates their status in Africa by providing a thorough review of existing biomedical device initiatives and available financial and scientific cooperation institutions in Africa for the biomedical research field, and highlights general challenges for implementing self-powered biomedical devices and particular challenges related to developing countries. The future perspectives of the aforementioned research field are provided, as well as an architecture for improving this research field in developing countries.

The Modification of Activated Carbon for the Performance Enhancement of a Natural-Rubber-Based Triboelectric Nanogenerator

Increasing energy demands and growing environmental concerns regarding the consumption of fossil fuels are important motivations for the development of clean and sustainable energy sources. A triboelectric nanogenerator (TENG) is a promising energy technology that harnesses mechanical energy from the ambient environment by converting it into electrical energy. In this work, the enhancement of the energy conversion performance of a natural rubber (NR)-based TENG has been proposed by using modified activated carbon (AC). The effect of surface modification techniques, including acid treatments and plasma treatment for AC material on TENG performance, are investigated. The TENG fabricated from the NR incorporated with the modified AC using N2 plasma showed superior electrical output performance, which was attributed to the modification by N2 plasma introducing changes in the surface chemistry of AC, leading to the improved dielectric property of the NR-AC composite, which contributes to the enhanced triboelectric charge density. The highest power density of 2.65 mW/m2 was obtained from the NR-AC (N2 plasma-treated) TENG. This research provides a key insight into the modification of AC for the development of TENG with high energy conversion performance that could be useful for other future applications such as PM2.5 removal or CO2 capture.

Recent Advances in Triboelectric Nanogenerators: From Technological Progress to Commercial Applications

Serious climate changes and energy-related environmental problems are currently critical issues in the world. In order to reduce carbon emissions and save our environment, renewable energy harvesting technologies will serve as a key solution in the near future. Among them, triboelectric nanogenerators (TENGs), which is one of the most promising mechanical energy harvesters by means of contact electrification phenomenon, are explosively developing due to abundant wasting mechanical energy sources and a number of superior advantages in a wide availability and selection of materials, relatively simple device configurations, and low-cost processing. Significant experimental and theoretical efforts have been achieved toward understanding fundamental behaviors and a wide range of demonstrations since its report in 2012. As a result, considerable technological advancement has been exhibited and it advances the timeline of achievement in the proposed roadmap. Now, the technology has reached the stage of prototype development with verification of performance beyond the lab scale environment toward its commercialization. In this review, distinguished authors in the world worked together to summarize the state of the art in theory, materials, devices, systems, circuits, and applications in TENG fields. The great research achievements of researchers in this field around the world over the past decade are expected to play a major role in coming to fruition of unexpectedly accelerated technological advances over the next decade.

Chicken skin based Milli Watt range biocompatible triboelectric nanogenerator for biomechanical energy harvesting

This work reports a high-performance, low-cost, biocompatible triboelectric nanogenerator (TENG) using chicken skin (CS). The device is suitable to power wearable devices, which is critical to adapt electronics in monitoring, predicting, and treating people. It also supports sustainability by providing a cost-effective way to reduce the poultry industry's waste. It has been shown here that CS-derived biowaste is an effective means of generating tribopositive material for TENGs. The CS contains amino acid functional groups based on (Glycine, Proline, and Hydroxyproline), which are essential to demonstrate the electron-donating ability of collagen. The skin was cut into 3 × 3 cm2 and used as the raw material for fabricating the TENG device with a stacking sequence of Al/Kapton/spacing/CS/Al. The chicken skin-based TENG (CS-TENG) is characterized at different frequencies (4-14 HZ) using a damping system. The CS-TENG produces an open-circuit voltage of 123 V, short-circuit current of 20 µA and 0.2 mW/cm2 of a power density at 20 MΩ. The biocompatible CS-TENG presents ultra-robust and stable endurance performance with more than 52,000 cycles. The CS-TENG is impressively capable of scavenging energy to light up to 55 commercial light-emitting diodes (LEDs), a calculator, and to measure the physiological motions of the human body. CS-TENG is a step toward sustainable, battery-less devices or augmented energy sources, especially when using traditional power sources, such as in wearable devices, remote locations, or mobile applications is not practical or cost-effective.

A Portable Triboelectric Nanogenerator Based on Dehydrated Nopal Powder for Powering Electronic Devices

Triboelectric nanogenerators (TENGs) based on organic materials can harvest green energy to convert it into electrical energy. These nanogenerators could be used for Internet-of-Things (IoT) devices, substituting solid-state chemical batteries that have toxic materials and limited-service time. Herein, we develop a portable triboelectric nanogenerator based on dehydrated nopal powder (NOP-TENG) as novel triboelectric material. In addition, this nanogenerator uses a polyimide film tape adhered to two copper-coated Bakelite plates. The NOP-TENG generates a power density of 2309.98 μW·m^-2 with a load resistance of 76.89 MΩ by applying a hand force on its outer surface. Furthermore, the nanogenerator shows a power density of 556.72 μW·m^-2 with a load resistance of 76.89 MΩ and under 4g acceleration at 15 Hz. The output voltage of the NOP-TENG depicts a stable output performance even after 27,000 operation cycles. This nanogenerator can light eighteen green commercial LEDs and power a digital calculator. The proposed NOP-TENG has a simple structure, easy manufacturing process, stable electric behavior, and cost-effective output performance. This portable nanogenerator may power electronic devices using different vibration energy sources.

Density-of-States Matching-Induced Ultrahigh Current Density and High-Humidity Resistance in a Simply Structured Triboelectric Nanogenerator

Triboelectric nanogenerators (TENGs) can covert mechanical energy into electricity in a clean and sustainable manner. However, traditional TENGs are mainly limited by the low output current, and thus their practical applications are still limited. Herein, a new type of TENG is developed by using conductive materials as the triboelectric layers and electrodes simultaneously. Because of the matched density of states between the two triboelectric layers, this simply structured device reaches an open-circuit voltage of 1400 V and an ultrahigh current density of 1333 mA m^-2 when poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) film and copper (Cu) or aluminum (Al) foil are used as the triboelectric pair. The current density increases by nearly three orders of magnitude compared with traditional TENGs. More importantly, this device can work stably in high-humidity environments, which is always a big challenge for traditional TENGs. Surprisingly, this TENG can even perform well in the presence of water droplets. This work provides a new and effective strategy for constructing high-performance TENGs, which can be used in many practical applications in the near future.

Biodegradable Polymers in Triboelectric Nanogenerators

Triboelectric nanogenerators (TENGs) have attracted much attention because they not only efficiently harvest energy from the surrounding environment and living organisms but also serve as multifunctional sensors toward the detection of various chemical and physical stimuli. In particular, biodegradable TENG (BD-TENG) represents an emerging type of self-powered device that can be degraded, either in physiological environments as an implantable power source without the necessity of second surgery for device retrieval, or in the ambient environment to minimize associated environmental pollution. Such TENGs or TNEG-based self-powered devices can find important applications in many scenarios, such as tissue regeneration, drug release, pacemakers, etc. In this review, the recent progress of TENGs developed on the basis of biodegradable polymers is comprehensively summarized. Material strategies and fabrication schemes of biodegradable and self-powered devices are thoroughly introduced according to the classification of plant-degradable polymer, animal-degradable polymer, and synthetic degradable polymer. Finally, current problems, challenges, and potential opportunities for the future development of BD-TENGs are discussed. We hope this work may provide new insights for modulating the design of BD-TNEGs that can be beneficial for both environmental protection and healthcare.

Eco-Friendly Keratin-Based Additives in the Polymer Matrix to Enhance the Output of Triboelectric Nanogenerators

A triboelectric nanogenerator (TENG) is an energy generator that converts mechanical energy into electrical energy using triboelectricity at a nanoscale. Given their potential application as power sources in electronic devices, various attempts have been made to improve their output performance. Here, we present an eco-friendly, low-cost, and facile fabrication method to enhance TENG characteristics with keratin protein additives. Keratin sources, human and cat hair, are processed into powder and added to the friction layer, which increases their positive charge affinity, thereby boosting the output performance of the TENG. The output performances of the keratin-added TENG (K-TENG) are measured in the vertical contact-separation mode, with both additives having the highest output values at 5 wt % load. The K-TENG generates more output voltage and current values than the pristine TENG by 90 and 208%, respectively. Hence, we conclude that this method would potentially promote TENG as a strong candidate for a competitive "green" energy harvesting device in future electronics applications.

Triboelectric and Piezoelectric Nanogenerators for Self-Powered Healthcare Monitoring Devices: Operating Principles, Challenges, and Perspectives

The internet of medical things (IoMT) is used for the acquisition, processing, transmission, and storage of medical data of patients. The medical information of each patient can be monitored by hospitals, family members, or medical centers, providing real-time data on the health condition of patients. However, the IoMT requires monitoring healthcare devices with features such as being lightweight, having a long lifetime, wearability, flexibility, safe behavior, and a stable electrical performance. For the continuous monitoring of the medical signals of patients, these devices need energy sources with a long lifetime and stable response. For this challenge, conventional batteries have disadvantages due to their limited-service time, considerable weight, and toxic materials. A replacement alternative to conventional batteries can be achieved for piezoelectric and triboelectric nanogenerators. These nanogenerators can convert green energy from various environmental sources (e.g., biomechanical energy, wind, and mechanical vibrations) into electrical energy. Generally, these nanogenerators have simple transduction mechanisms, uncomplicated manufacturing processes, are lightweight, have a long lifetime, and provide high output electrical performance. Thus, the piezoelectric and triboelectric nanogenerators could power future medical devices that monitor and process vital signs of patients. Herein, we review the working principle, materials, fabrication processes, and signal processing components of piezoelectric and triboelectric nanogenerators with potential medical applications. In addition, we discuss the main components and output electrical performance of various nanogenerators applied to the medical sector. Finally, the challenges and perspectives of the design, materials and fabrication process, signal processing, and reliability of nanogenerators are included.

Biopolymer-based electrospun fibers in electrochemical devices: versatile platform for energy, environment, and health monitoring

Electrochemical power tools are regarded as essential keys in a world that is becoming increasingly reliant on fossil fuels in order to meet the challenges of rapidly depleting fossil fuel supplies. Additionally, due to the industrialization of societies and the growth of diseases, the need for sensitive, reliable, inexpensive, and portable sensors and biosensors for noninvasive monitoring of human health and environmental pollution is felt more than ever before. In recent decades, electrospun fibers have emerged as promising candidates for the fabrication of highly efficient electrochemical devices, such as actuators, batteries, fuel cells, supercapacitors, and biosensors. Meanwhile, the use of synthetic polymers in the fabrication of versatile electrochemical devices has raised environmental concerns, leading to an increase in the quest for natural polymers. Natural polymers are primarily derived from microorganisms and plants. Despite the challenges of processing bio-based electrospun fibers, employing natural nanofibers in the fabrication of electrochemical devices has garnered tremendous attention in recent years. Here, various natural polymers and the strategies employed to fabricate various electrospun biopolymers are briefly covered. The recent advances and research strategies used to apply the bio-based electrospun membranes in different electrochemical devices are carefully summarized, along with the scopes in various advanced technologies. A comprehensive and critical discussion about the use of biopolymer-based electrospun fibers as the potential alternative to non-renewable ones in future technologies is briefly highlighted. This review will serve as a field opening platform for using different biopolymer-based electrospun fibers to advance the electrochemical device-based renewable and sustainable technologies, which will be of high interest to a large community. Accordingly, future studies should focus on feasible and cost-effective extraction of biopolymers from natural resources as well as fabrication of high-performance nanofibrous biopolymer-based components applicable in various electrochemical devices.

Eco-friendly pectin polymer film-based triboelectric nanogenerator for energy scavenging

Inspired by the desire to solve the energy-related issues in remote sensing applications, internet of things, wireless autonomous devices, and self-powered portable electronic devices, triboelectric nanogenerators (TENGs) have been highly promoted. However, for use in the specified applications, especially in wearable and biomedical devices, environmental-friendly materials are required. Herein, an eco-friendly pectin polymer is used as a positive triboelectric material to fabricate a TENG with excellent output performance. Working in conjunction with a polyimide, the polyimide and microarchitected pectin (MA@pectin) polymer film-based TENG (PP-TENG) generated open circuit voltage (V_OC), short circuit current (I_SC), and charge density (Q_SC) of ∼300 V, 14 μA, and 70 μC cm^-2, respectively, exhibiting remarkable enhancement compared to the TENG based on polyimide/pristine pectin polymer (V_OC, I_SC, and Q_SC of 170 V, 7.6 μA, and 47 μC cm^-2, respectively) under similar operating conditions. The output performance of the PP-TENG is particularly reliant on the pectin concentration, indicating an optimum concentration of 9 wt%. The improved performance of the PP-TENG was systematically analyzed and explained in terms of pectin concentration, dielectric constant, and surface roughness. Furthermore, the PP-TENG can power portable electronic devices and light-emitting diodes to prove the capability of the TENG in practical applications. The fabricated PP-TENG is anticipated to be a sustainable energy harvester via a low-cost and facile approach.

Emerging Development of Auto-Charging Sensors for Respiration Monitoring

In recent years, the development of biomedical monitoring systems, including respiration monitoring systems, has been accelerated. Wearable and implantable medical devices are becoming increasingly important in the diagnosis and management of disease and illness. Respiration can be monitored using a variety of biosensors and systems. Auto-charged sensors have a number of advantages, including low cost, ease of preparation, design flexibility, and a wide range of applications. It is possible to use the auto-charged sensors to directly convert mechanical energy from the airflow into electricity. The ability to monitor and diagnose one's own health is a major goal of auto-charged sensors and systems. Respiratory disease model output signals have not been thoroughly investigated and clearly understood. As a result, figuring out their exact interrelationship is a difficult and important research question. This review summarized recent developments in auto-charged respiratory sensors and systems in terms of their device principle, output property, detecting index, and so on. Researchers with an interest in auto-charged sensors can use the information presented here to better understand the difficulties and opportunities that lie ahead.

From Triboelectric Nanogenerator to Polymer-Based Biosensor: A Review

Nowadays, self-powered wearable biosensors that are based on triboelectric nanogenerators (TENGs) are playing an important role in the continuous efforts towards the miniaturization, energy saving, and intelligence of healthcare devices and Internets of Things (IoTs). In this review, we cover the remarkable developments in TENG−based biosensors developed from various polymer materials and their functionalities, with a focus on wearable and implantable self-powered sensors for health monitoring and therapeutic devices. The functions of TENGs as power sources for third-party biosensors are also discussed, and their applications in a number of related fields are concisely illustrated. Finally, we conclude the review with a discussion of the challenges and problems of leveraging TENG−based intelligent biosensors.

Wires with Continuous Sabal Leaf-Patterned Micropores Constructed by Freeze Printing for a Wearable Sensor Responsible to Multiple Deformations

The design of porous structure in wearable sensors is very important for the detection of mechanical signals. However, it remains challenging to construct a porous structure capable of detecting all kinds of mechanical signals. Here, round wire with long-range orientated micropores (RW-LOM) is fabricated by a newly established freeze printing technique and constructed into a wearable sensor by the incorporation of carbon nanotubes and polydimethylsiloxane. The Sabal leaf-like lamellar structure in RW-LOM is realized and can be tuned by the proper coordination of slurry concentration and the printing parameters. The fine structures in RW-LOM allow the wearable sensor to detect compression, stretching, twisting, and bending with a high sensitivity, stability, and broad detecting range. This work not only provides a wearable sensor with high stability and high sensitivity but also establishes a technique to construct porous wires that could find applications in the fields like intelligent industry and healthcare.

Eco-Friendly Triboelectric Material Based on Natural Rubber and Activated Carbon from Human Hair

The triboelectric nanogenerator (TENG) has emerged as a novel energy technology that converts mechanical energy from surrounding environments to electricity. The TENG fabricated from environmentally friendly materials would encourage the development of next-generation energy technologies that are green and sustainable. In the present work, a green triboelectric material has been fabricated from natural rubber (NR) filled with activated carbon (AC) derived from human hair. It is found that the TENG fabricated from an NR-AC composite as a tribopositive material and a poly-tetrafluoroethylene (PTFE) sheet as a tribonegative one generates the highest peak-to-peak output voltage of 89.6 V, highest peak-to-peak output current of 6.9 µA, and can deliver the maximum power density of 242 mW/m². The finding of this work presents a potential solution for the development of a green and sustainable energy source.

Metal-Free Transparent Three-Dimensional Flexible Electronics by Selective Molecular Bridges

Flexible and transparent electronics is a new generation of device enabling modern interactive designs, which facilitates the recent development of low-cost, lightweight, and flexible materials. Although conventional indium tin oxide material still dominates the major market, its brittleness and steadily increasing price drive scientists to search for other alternatives. To meet the high demand, numerous metallic or organic conductive materials have been developed, but their poor adhesion toward supporting substrates and the subsequent circuit patterning approach remains problematic. In this study, a robust metal-free flexible conductive film fabrication strategy is introduced. The flexible polyethylene terephthalate (PET) film is utilized as the base, where a poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) conductive layer is tightly linked onto this supporting substrate. An interface activation process, i.e., oxygen plasma treatment, generates PET surface active spots to react with the subsequently introduced poly(vinyl alcohol) (PVA) molecule functional groups. This spatially selective PVA molecular bridge therefore acts as a dual-function intermediate layer through covalent bonding toward PET and hydrogen bonding toward PEDOT:PSS to conjugate two distinct materials. This PEDOT:PSS/PVA/PET film delivers superior physical properties, such as a high conductivity of 38.2 Ω/sq and great optical transmittance of 84.1%, which are well tunable under conductive polymer thickness controls. The film is also durable and can maintain original electrical properties even under serious bending for hundreds of cycles. Relying on these outstanding performances, arbitrary conductive circuits are built on this flexible substrate and can function as normal electronics when integrated with multiple electronic parts, e.g., light-emitting diodes (LEDs). Superior electrical signal outputs are achieved when complicated stereo structures including folding, splicing, interlacing, and braiding are incorporated, enabling the use of these films for flexible three-dimensional electronics assembling. Space identifying smart key and lock pair, origami rabbit-carrot touch response, pressure-stimulated jumping frog, and moving dinosaur recognition designs realize these PEDOT:PSS/PVA/PET film-based human-machine interactive devices. This flexible, transparent, and conductive film generation approach by molecular bridge creation should facilitate future development of flexible or foldable devices with complex circuits.

Recent progress of self-powered respiration monitoring systems

Wearable and implantable medical devices are playing more and more key roles in disease diagnosis and health management. Various biosensors and systems have been used for respiration monitoring. Among them, self-powered sensors have some special characteristics such as low-cost, easy preparation, highly designable, and diversified. The respiratory airflow can drive the self-powered sensors directly to convert mechanical energy of the airflow into electricity. One of the major goals of the self-powered sensors and systems is realizing health monitoring and diagnosis. The relationship between the output signals and the models of respiratory diseases has not been studied deeply and clearly. Therefore, how to find an accurate relationship between them is a challenging and significant research topic. This review summarized the recent progress of the self-powered respiratory sensors and systems from aspects of device principle, output property, detecting index and so on. The challenges and perspectives have also been discussed for reference to the researchers who are interested in the field of self-powered sensors.

Spider-Web and Ant-Tentacle Doubly Bio-Inspired Multifunctional Self-Powered Electronic Skin with Hierarchical Nanostructure

For the practical applications of wearable electronic skin (e-skin), the multifunctional, self-powered, biodegradable, biocompatible, and breathable materials are needed to be assessed and tailored simultaneously. Integration of these features in flexible e-skin is highly desirable; however, it is challenging to construct an e-skin to meet the requirements of practical applications. Herein, a bio-inspired multifunctional e-skin with a multilayer nanostructure based on spider web and ant tentacle is constructed, which can collect biological energy through a triboelectric nanogenerator for the simultaneous detection of pressure, humidity, and temperature. Owing to the poly(vinyl alcohol)/poly(vinylidene fluoride) nanofibers spider web structure, internal bead-chain structure, and the collagen aggregate nanofibers based positive friction material, e-skin exhibits the highest pressure sensitivity (0.48 V kPa-1 ) and high detection range (0-135 kPa). Synchronously, the nanofibers imitating the antennae of ants provide e-skin with short response and recovery time (16 and 25 s, respectively) to a wide humidity range (25-85% RH). The e-skin is demonstrated to exhibit temperature coefficient of resistance (TCR = 0.0075 °C-1 ) in a range of the surrounding temperature (27-55 °C). Moreover, the natural collagen aggregate and the all-nanofibers structure ensure the biodegradability, biocompatibility, and breathability of the e-skin, showing great promise for practicability.

High-Performance Foam-Shaped Strain Sensor Based on Carbon Nanotubes and Ti3C2Tx MXene for the Monitoring of Human Activities

The flexible strain sensor is of significant importance in wearable electronics, since it can help monitor the physical signals from the human body. Among various strain sensors, the foam-shaped ones have received widespread attention owing to their light weight and gas permeability. However, the working range of these sensors is still not large enough, and the sensitivity needs to be further improved. In this work, we develop a high-performance foam-shaped strain sensor composed of Ti₃C₂T_x MXene, multiwalled carbon nanotubes (MWCNTs), and thermoplastic polyurethane (TPU). MXene sheets are adsorbed on the surface of a composite foam of MWCNTs and TPU (referred to as TPU/MWCNTs foam), which is prefabricated by using a salt-templating method. The obtained TPU/MWCNTs@MXene foam works effectively as a lightweight, easily processable, and sensitive strain sensor. The TPU/MWCNTs@MXene device can deliver a wide working strain range of ∼100% and an outstanding sensitivity as high as 363 simultaneously, superior to the state-of-the-art foam-shaped strain sensors. Moreover, the composite foam shows an excellent gas permeability and suitable elastic modulus close to those of skin, indicating its being highly comfortable as a wearable sensor. Owing to these advantages, the sensor works effectively in detecting both subtle and large human movements, such as joint motion, finger motion, and vocal cord vibration. In addition, the sensor can be used for gesture recognition, demonstrating its perspective in human-machine interaction. Because of the high sensitivity, wide working range, gas permeability, and suitable modulus, our foam-shaped composite strain sensor may have great potential in the field of flexible and wearable electronics in the near future.

Compressible and Stretchable Magnetoelectric Sensors Based on Liquid Metals for Highly Sensitive, Self-Powered Respiratory Monitoring

Healthcare monitoring, especially for respiration, has attracted tremendous attention from academics considering the great significance of health information feedback. The respiratory rate, as a critical health indicator, has been used to screen and evaluate potential illness risks in early medical diagnoses. A self-powered sensing system for medical monitoring is critical and imperative due to needless battery replacement and simple assembly. However, the development of a self-powered respiratory sensor with highly sensitive performance is still a daunting challenge. In this work, a compressible and stretchable magnetoelectric sensor (CSMS) with an arch-shaped air gap is reported, enabling self-powered respiratory monitoring driven by exhaled/inhaled breath. The CSMS contains two key functional materials: liquid metals and magnetic powders both with low Young's modulus, allowing for sensing compressibility and stretchability simultaneously. More importantly, such a magnetoelectric sensor exhibits mechanoelectrical converting capacity under an external force, which has been verified by Maxwell numerical simulation. Owing to the air-layer introduction, the magnetoelectric sensors achieve high sensitivity (up to 17.73 kPa^-1), fast response, and long-term stability. The highly sensitive and self-powered magnetoelectric sensor can be further applied as a noninvasive, miniaturized, and portable respiratory monitoring system with the aim of warning for potential health risks. We anticipate that this technique will create an avenue for self-powered respiratory monitoring fields.

Embedding Silver Nanowires into a Hydroxypropyl Methyl Cellulose Film for Flexible Electrochromic Devices with High Electromechanical Stability

Transparent conductive films (TCFs) based on silver nanowires (AgNWs) are becoming one of the best candidates in realizing flexible optoelectronic devices. The AgNW-based TCF is usually prepared by coating AgNWs on a transparent polymer film; however, the coated AgNWs easily detach from the polymer underneath because of the weak adhesion between them. Herein, a network of AgNWs is embedded in the transparent hydroxypropyl methyl cellulose film, which has a strong adhesion with the AgNWs. The obtained TCF shows high optical transmittance (>85%), low roughness (rms = 4.8 ± 0.5 nm), and low haze (<0.2%). More importantly, owing to the embedding structure and strong adhesion, this TCF also shows excellent electromechanical stability, which is superior to the reported ones. Employing this TCF in a flexible electrochromic device, the obtained device exhibits excellent cyclic electromechanical stability and high coloring efficiency. Our work demonstrates a promising TCF with superior electromechanical stability for future applications in flexible optoelectronics.

An acid and alkali-resistant triboelectric nanogenerator

With the development of technology, environmental problems have become more and more acute and the use of electronic devices in harsh environments has gradually attracted attention. For example, the friction layer of triboelectric nanogenerators (TENGs) may be contaminated and corroded in harsh environments (such as acidic, alkaline or oily environments), resulting in damage or destruction of the TENGs. In this study, we use electrospinning followed by a sintering process to prepare a super-hydrophobic sintered polyvinyl alcohol-polytetrafluoroethylene (S-PVA-PTFE) composite membrane and general industrial oil-absorbing paper to construct a TENG. The maximum power density of the TENG is 261 mW m-2, it can light up 100 blue LEDs, and can power a variety of small electronic devices. Moreover, after 72 h of soaking the friction layer in a strong acid solution followed by a strong alkali solution, the performance of the TENG has no obvious change. The TENG can work stably in an oily working environment. The TENG provides a novel approach for self-powered sensors that work in harsh environments.

Advances in triboelectric nanogenerators for biomedical sensing

Biomedical sensors have been essential in improving healthcare outcomes over the past 30 years, though limited power source access and user wearability restraints have prevented them from taking a constant and active biomedical sensing role in our daily lives. Triboelectric nanogenerators (TENGs) have demonstrated exceptional capabilities and versatility in delivering self-powered and wear-optimized biomedical sensors, and are paving the way for a novel platform technology able to fully integrate into the developing 5G/Internet-of-Things ecosystem. This novel paradigm of TENG-based biomedical sensors aspires to provide ubiquitous and omnipresent real-time biomedical sensing for us all. In this review, we cover the remarkable developments in TENG-based biomedical sensing which have arisen in the last octennium, focusing on both in-body and on-body biomedical sensing solutions. We begin by covering TENG as biomedical sensors in the most relevant, mortality-associated clinical fields of pneumology and cardiology, as well as other organ-related biomedical sensing abilities including ambulation. We also include an overview of ambient biomedical sensing as a field of growing interest in occupational health monitoring. Finally, we explore TENGs as power sources for third party biomedical sensors in a number of fields, and conclude our review by focusing on the future perspectives of TENG biomedical sensors, highlighting key areas of attention to fully translate TENG-based biomedical sensors into clinically and commercially viable digital and wireless consumer and health products.

Single-Layer Triboelectric Nanogenerators Based on Ion-Doped Natural Nanofibrils

As emerging ambient energy harvesting technology, triboelectric nanogenerators (TENGs) have proven to be a robust power source and have demonstrated the unique ability to power micro-nano electronics autonomously to form self-powered devices. Although four working modes of TENGs have been developed to promote the feasibility of self-powered micro-nano systems, the relatively complicated structure composed of multilayer and movable components limits the practical applications of TENGs. Herein, we propose a single-layer triboelectric nanogenerator (SL-TENG) based on ion-doped natural nanofibrils. Compared with the simplest mode of currently existing TENGs, i.e., the single-electrode type, this novel single-electrode TENG further simplifies the configuration by the removal of the dielectric layer. The underlying mechanism of the proposed SL-TENG is comprehensively investigated through electrical measurements and the analysis of the effect of ion species at different concentrations. In contrast to conventional TENGs that require electrodes to realize charge transfer, it is revealed that the ions doped into natural nanofibrils effectively realize charge transfer due to the separation and migration of cations and anions. This new working principle based on the combination of electrons and ions enables TENGs to show greater potential for applications since the ultrasimple single-layer configuration enables them to be more easily integrated with other electronic components; additionally, the whole device of the proposed SL-TENG is biodegradable because the natural nanofibrils are completely extracted from carrots.

Triboelectric nanogenerator based on Teflon/vitamin B1 powder for self-powered humidity sensing

Recently, there has been growing interest in triboelectric nanogenerators (TENGs) that can effectively convert various forms of mechanical energy input into electrical energy. In the present study, a novel Teflon/vitamin B1 powder based triboelectric nanogenerator (TVB-TENG) is proposed. Paper is utilized as a supporting platform for triboelectrification between a commercial Teflon tape and vitamin B1 powder. The measured open-circuit voltage was approximately 340 V. The TVB-TENG can be applied as a humidity sensor and exhibits a linear and reversible response to the relative humidity of the environment. Moreover, the change in relative humidity is also indicated by the change in luminosity of a set of light-emitting diodes (LEDs) integrated in the TVB-TENG system. The TVB-TENG proposed in this study illustrates a cost-effective method for portable power supply and sensing devices.