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Triboelectric nanogenerators (TENGs) have attracted widespread attention as a promising candidate for energy harvesting due to their flexibility and high power density. To meet diverse application scenarios, a highly stretchable (349%), conductive (1.87 S m-1), and antibacterial electrode composed of carbon quantum dots/LiCl/agar-polyacrylamide (CQDs/LiCl/agar-PAAm) dual-network (DN) hydrogel is developed for wearable TENGs. Notably, the concentration of agar alters the pore spacing and pore size of the DN hydrogel, thereby impacting the network cross-linking density and the migration of conductive ions (Li+ and Cl-). This variation further affects the mechanical strength and conductivity of the hydrogel electrode, thus modulating the mechanical stability and electrical output performance of the TENGs. With the optimal agar content, the tensile strength and conductivity of the hydrogel electrode increase by 211 and 719%, respectively. This enhancement ensures the stable output of TENGs during continuous operation (6000 cycles), with open-circuit voltage, short-circuit current, and transferred charge increasing by 200, 530, and 155%, respectively. Additionally, doping with CQDs enables the hydrogel electrode to effectively inhibit the Gram-negative bacterium Escherichia coli. Finally, the TENGs are utilized as a self-power smart ring for efficient and concise information transmission via Morse code. Consequently, this study introduces a creative approach for designing and implementing multifunctional, flexible wearable devices.

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Heart failure (HF) represents a cardiovascular disease that significantly threatens global well-being and quality of life. Electroactive nanomaterials, characterized by their distinctive physical and chemical properties, emerge as promising candidates for HF prevention and management. This review comprehensively examines electroactive nanomaterials and their applications in HF intervention. It presents the definition, classification, and intrinsic characteristics of conductive, piezoelectric, and triboelectric nanomaterials, emphasizing their mechanical robustness, electrical conductivity, and piezoelectric coefficients. The review elucidates their applications and mechanisms: 1) early detection and diagnosis, employing nanomaterial-based sensors for real-time cardiac health monitoring; 2) cardiac tissue repair and regeneration, providing mechanical, chemical, and electrical stimuli for tissue restoration; 3) localized administration of bioactive biomolecules, genes, or pharmacotherapeutic agents, using nanomaterials as advanced drug delivery systems; and 4) electrical stimulation therapies, leveraging their properties for innovative pacemaker and neurostimulation technologies. Challenges in clinical translation, such as biocompatibility, stability, and scalability, are discussed, along with future prospects and potential innovations, including multifunctional and stimuli-responsive nanomaterials for precise HF therapies. This review encapsulates current research and future directions concerning the use of electroactive nanomaterials in HF prevention and management, highlighting their potential to innovating in cardiovascular medicine.

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Electronic skin (e-skin) is considered as a highly promising interface for human-computer interaction systems and wearable electronic devices. Through elaborate design and assembly of various materials, it possesses multiple characteristics similar to human skin, including remarkable flexibility, stretchability, sensitivity to temperature and humidity, biocompatibility, and efficient interfacial ion/electron transport capabilities. Here, we innovatively integrate multifunctional carbon quantum dots (CQDs), which exhibit conductivity, antibacterial properties, ultraviolet absorption, and fluorescence emission, with poly(acrylic acid) and glycerin (Gly) into a three-dimensional network structure of natural goatskin collagen fibers. Through a top-down design strategy enhanced by hydrogen bond reconstruction, we successfully fabricated a novel transparent e-skin (PAC-eSkin). This e-skin exhibited significant tensile properties (4.94 MPa of tensile strength and 263.42% of a maximum breaking elongation), while also possessing Young's modulus similar to human skin (2.32 MPa). It is noteworthy that the functionalized CQDs used was derived from discarded goat hair, and the addition of Gly gave PAC-eSkin excellent antifreezing and moisturizing properties. Due to the presence of ultrasmall CQDs, which creates efficient ion/electron transport channels within PAC-eSkin, it could rapidly sense human motion and physiological signals (with a gauge factor (GF) of 1.88). Furthermore, PAC-eSkin had the potential to replace traditional electrode patches for real-time monitoring of electrocardiogram, electromyogram, and electrooculogram signals, with a higher SNR (signal-to-noise ratio) of 25.1 dB. Additionally, the customizable size and shape of PAC-eSkin offer vast possibilities for the construction of single-electrode triboelectric nanogenerator systems. We have reason to believe that the design and development of this transparent e-skin based on CQDs-functionalized dermal collagen matrices can pave a new way for innovations in human-computer interaction interfaces and their sensing application in diverse scenarios.

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The escalating energy and environmental challenges have catalyzed a global shift toward seeking more sustainable, economical, and eco-friendly energy solutions. Water, capturing 35% of the Earth's solar energy, represents a vast reservoir of clean energy. However, current industrial capabilities harness only a fraction of the energy within the hydrological cycle. The past decade has seen rapid advancements in nanoscience and nanomaterials leading to a comprehensive exploration of liquid-solid triboelectrification as a low-carbon, efficient method for water energy harvesting. This review explores two fundamental principle models involved in liquid-solid triboelectrification. On the basis of these models, two distinct types of water energy harvesting devices, including droplet-based nanogenerators and water evaporation-induced nanogenerators, are summarized from their working principles, recent developments, materials, structures, and performance optimization techniques. Additionally, the applications of these nanogenerators in energy harvesting, self-powered sensing, and healthcare are also discussed. Ultimately, the challenges and future prospects of liquid-solid triboelectrification are further explored.

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This study presents the fabrication of an ultralight, porous, and high-performance triboelectric nanogenerator (TENG) utilizing silk fibroin (SF) aerogels and PDMS sponges as the friction layer. The transition from two-dimensional film friction layers to three-dimensional porous aerogels significantly increased the specific surface area, offering an effective strategy for designing high-performance SF aerogel-based TENGs. The TENG incorporating the porous SF aerogel exhibited optimal output performance at a 3% SF concentration, achieving a maximum open circuit voltage of 365 V, a maximum short-circuit current of 11.8 µA, and a maximum power density of 7.52 W/m2. In comparison to SF-film-based TENGs, the SF-aerogel based TENG demonstrated a remarkable 6.5-fold increase in voltage and a 4.5-fold increase in current. Furthermore, the power density of our SF-based TENG surpassed the previously reported optimal values for SF-based TENGs by 2.4 times. Leveraging the excellent mechanical stability and biocompatibility of TENGs, we developed an SF-based TENG self-powered sensor for the real-time monitoring of subtle biological movements. The SF-based TENG exhibits promising potential as a wearable bioelectronic device for health monitoring.

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The state-of-the-art triboelectric nanogenerator (TENG) technology has numerous advantages and creates new prospects for the rapid development of the Internet of Things (IoT) in marine environments. Here, to accelerate the application process of TENG, an elaborately designed multilayered sleeve-structured hybrid nanogenerator (M-HNG) is developed to efficiently and persistently harvest marine energy. The M-HNG integrates an electromagnetic nanogenerator (EMG) with four coils and a multilayered sleeve-structured TENG (MS-TENG) with three freestanding layer units to increase spatial utilization efficiency. Moreover, rabbit fur strips are introduced to enhance the output performance and strengthen the durability of TENG. Therefore, the MS-TENG has high durability due to its soft-contact structure, maintaining its performance even after 240,000 cycles. When a 1000 µF capacitor is charged by M-HNG utilizing a power management circuit (PMC), the stored energy is increased from 2.62 mJ to 140.11 mJ, representing a significant improvement of 52-fold. The M-HNG triggered by water waves has successfully powered various small electronic devices, including 1200 LED lights, nine thermo-hygrometers, a water quality testing pen, and water level alarms. The proposed M-HNG effectively harvests low-frequency water wave energy, introducing an innovative concept for constructing a hybrid TENG with enhanced density and durability.

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Human-machine interactions (HMIs) have penetrated into various academic and industrial fields, such as robotics, virtual reality, and wearable electronics. However, the practical application of most human-machine interfaces faces notable obstacles due to their complex structure and materials, high power consumption, limited effective skin adhesion, and high cost. Herein, we report a self-powered, skin adhesive, and flexible human-machine interface based on a triboelectric nanogenerator (SSFHMI). Characterized by its simple structure and low cost, the SSFHMI can easily convert touch stimuli into a stable electrical signal at the trigger pressure from a finger touch, without requiring an external power supply. A skeleton spacer has been specially designed in order to increase the stability and homogeneity of the output signals of each TENG unit and prevent crosstalk between them. Moreover, we constructed a hydrogel adhesive interface with skin-adhesive properties to adapt to easy wear on complex human body surfaces. By integrating the SSFHMI with a microcontroller, a programmable touch operation platform has been constructed that is capable of multiple interactions. These include medical calling, music media playback, security unlocking, and electronic piano playing. This self-powered, cost-effective SSFHMI holds potential relevance for the next generation of highly integrated and sustainable portable smart electronic products and applications.

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Stretchable triboelectric nanogenerators (TENGs) represent a new class of energy-harvesting devices for powering wearable devices. However, most of them are associated with poor stretchability, low stability, and limited substrate material choices. This work presents the design and demonstration of highly stretchable and stable TENGs based on liquid metalel ectrodes with different phases. The conductive and fluidic properties of eutectic gallium-indium (EGaIn) in the serpentine microfluidic channel ensure the robust performance of the EGaIn-based TENG upon stretching over several hundred percent. The bi-phasic EGaIn (bGaIn) from oxidation lowers surface tension and increases adhesion for printing on diverse substrates with high output performance parameters. The optimization of the electrode shapes in the bGaIn-based TENGs can reduce the device footprint and weight, while enhancing stretchability. The applications of the EGaIn- and bGaIn-based TENG include smart elastic bands for human movement monitoring and smart carpets with integrated data transmission/processing modules for headcount monitoring/control. Combining the concept of origami in the paper-based bGaIn TENG can reduce the device footprint to improve output performance per unit area. The integration of bGaIn-TENG on a self-healing polymer substrate with corrosion resistance against acidic and alkaline solutions further facilitates its use in various challenging and extreme environments.

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Piezoelectric effect produces an electrical signal when stress is applied to the bone. When the integrity of the bone is destroyed, the biopotential within the defect site is reduced and several physiological responses are initiated to facilitate healing. During the healing of the bone defect, the bioelectric potential returns to normal levels. Treatment of fractures that exceed innate regenerative capacity or exhibit delayed healing requires surgical intervention for bone reconstruction. For bone defects that cannot heal on their own, exogenous electric fields are used to assist in treatment. This paper reviews the effects of exogenous electrical stimulation on bone healing, including osteogenesis, angiogenesis, reduction in inflammation and effects on the peripheral nervous system. This paper also reviews novel electrical stimulation methods, such as small power supplies and nanogenerators, that have emerged in recent years. Finally, the challenges and future trends of using electrical stimulation therapy for accelerating bone healing are discussed.

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State-of-the-art triboelectric nanogenerators (TENGs) typically employ fluoropolymers, highly negative chargeable materials in triboelectric series. However, many researchers nowadays are concerned about environmental pollution caused by poly-and per-fluoroalkyl substances (PFAS) due to their critical immunotoxicity as fluoropolymers are likely to release PFAS into the ecosystem during their life cycle. Herein, a sulfur-rich polymer (SRP)/MXene composite, offering high-performance yet sustainable TENG is developed. Value-addition of sulfur into SRP-based TENG has huge advantages since sulfur is abundant waste from petroleum refining and possesses the highest electron affinity (-200 kJ mol-1) among polymerizable atoms. MXene segregated structure is introduced into SRP to achieve homogeneous distribution without electrical percolation by utilizing below 0.5 wt% of MXene, resulting in a significantly enhanced dielectric constant without a drastic increase of dielectric loss. Due to homogeneous MXene distribution, SRP/MXene composite-based TENG demonstrates 2.9 times and 19.5 times enhances peak voltage and peak current compared to previous SRP-based TENGs. Additionally, it exhibits reusability without critical reduction of modulus and TENG performance due to dynamically exchangeable disulfide bonds. Finally, after the corona discharging and scaling-up process to a 4-inch wafer size, SRP/MXene composite-based TENG exhibits an 8.4 times improvement in peak power density, reaching 3.80 W m-2 compared to previous SRP-based TENGs.

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Triboelectric nanogenerators (TENG) are promising alternatives for clean energy harvesting. However, the material utilization in the development of TENG relies majorly on polymers derived from non-renewable resources. Therefore, minimizing the carbon footprint associated with such TENG development demands a shift toward usage of sustainable materials. This study pioneers using natural rubber (NR) as a sustainable alternative in TENG development. Infusing graphene in NR, its dielectric constant and tribonegativity are optimized, yielding a remarkable enhancement. The optimized sample exhibits a dielectric constant of 411 (at 103 Hz) and a contact potential difference (CPD) value of 1.85 V. In contrast, the pristine NR sample showed values of 6 and 3.06 V for the dielectric constant and CPD. Simulation and experimental studies fine-tune the TENG's performance, demonstrating excellent agreement between theoretical predictions and practical studies. Sensors developed via stencil printing technique possess a remarkably low layer thickness of 270 µm, and boast a power density of 420 mW m-2, a staggering 250% increase over conventional NR. Moreover, the material is pressure sensitive, enabling precise real-time human motion detection, including finger contact, finger bending, neck bending, and arm bending. This versatile sensor offers wireless monitoring, empowering healthcare monitoring based on the Internet of Things.

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A vast majority of electrical devices have integrated magnetic units, which generate constant magnetic fields with noticeable vibrations. The majority of existing nanogenerators acquire energy through friction/mechanical forces and most of these instances overlook acoustic vibrations and magnetic fields. Magnetic two-dimensional (2D) tellurides present a wide range of possibilities for devising a potential flexible energy harvester. 2D chromium telluride (2D CrTe3) is synthesized, which exhibits ferromagnetic behavior with a higher T c of ≈224 K. The structure exhibits stable high remnant magnetization, making 2D CrTe3 a potential material for harvesting magneto-acoustic waves. A magneto-acoustic nanogenerator (MANG) is fabricated and the basic mechanical stability and sensitivity of the device with change in load conditions are tested. A high surface charge density of 2.919 mC m-2 is obtained for the device. The thermal strain created in the lattice structure is examined using in-situ Raman spectroscopy. The magnetic anisotropy energy (MAE) responsible for long-range FM ordering is calculated by theoretical modelling with insights into opening of electronic bandgap which enhances the flexoelectric effects. The MANG can be a potential NG to synergistically tap into the magneto-acoustic vibrations generated from the frequency changes of a vibrating device such as loudspeakers.

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Extrusion-based 3D printing is a facile technology to construct complex structures of hydrogels, especially for tough hydrogels that have shown demonstrated potential in load-bearing materials and tissue engineering. However, 3D-printed hydrogels often possess mechanical properties that do not guarantee their usage in tissue-mimicking, load-bearing components, and motion sensors. This study proposes a novel strategy to construct high-strength and anisotropic Fe3+ cross-linked poly(acrylamide-co-acrylic acid)/sodium alginate double network hydrogels. The semi-flexible sodium alginate chains act as a "conformation regulator" to promote the formation of strong intermolecular interactions between polymer chains and lock the more extended conformation exerted by the pre-stretch, enabling the construction of 3D-printed hydrogel structures with high orientation. The equilibrated anisotropic hydrogel filaments with a water content of 50-60 wt.% exhibit outstanding mechanical properties (tensile strength: 9-44 MPa; elongation at break: 120-668%; Young's modulus: 7-62 MPa; toughness: 26-52 MJ m- 3). 3D-printed anisotropic hydrogel structures with high mechanical performance show demonstrated potential as loading-bearing structures and electrodes of flexible triboelectric nanogenerators for versatile human motion sensing.

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Eutectogels have garnered considerable attention for the development of wearable devices, owing to their inherent mechanical elasticity, ionic conductivity, affordability, and environmental compatibility. However, the low conductivity of existing eutectogels has impeded their progression in electronic applications. Here, we report a zwitterionic eutectogel with an impressive ionic conductivity of up to 15.7 mS cm-1. The incorporation of zwitterionic groups into the eutectogel creates ample mobile charges by dissociating the cation and anion of solvents, thereby yielding exceptional ionic conductivity. Moreover, the abundant electrostatic and hydrogen bonding interactions within the eutectogel endow it with prominent self-healing and adhesive properties. By integrating the eutectogel with a roughly patterned polydimethylsiloxane film, we have successfully constructed a triboelectric nanogenerator (TENG) with a maximum output power density of 112 mW m-2. This TENG is capable of generating stable electrical signals even in extreme temperature conditions ranging from -80 to 100 °C and effectively powering electronic devices. Furthermore, the assembled TENG displays high sensitivity as a self-powered sensor, enabling real-time and precise monitoring of signals derived from human motions. This study establishes a promising approach for the development of sustainable and multifunctional flexible electronics that are resilient in extreme environments.

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Within the domain of wearable devices that are self-powered and sensory, triboelectric nanogenerators (TENGs) have surfaced as a notable solution to meet the growing needs for energy harvesting. This study unveils an innovative wearable and stretchable multifunctional double-layered TENG, based on PDMS/MXene, known as PM-TENG. Furthermore, PM-TENG can also be used as a joint sensor to monitor the movement of athletes' joints during volleyball training. By augmenting the matrix with PDMS/MXene, which possesses dual capabilities-namely, charge capture and charge movement-the intermediary layer is integrated. This leads to a two fold increase in the ability to trap charges and the overall triboelectric performance. With a power density reaching 11.27 mW, it notably exceeds the performance of its counterparts that solely utilize PDMS, by nearly 11 times. This academic effort elucidates the important role of PM-TENG in biomechanical energy capture and autonomous wearable sports motion sensing.

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Triboelectric nanogenerators (TENGs) as an avant-garde technology that transforms mechanical energy into electrical energy, offering a new direction for green energy and sustainable development. By means of high-efficiency TENGs, conventional materials as new triboelectric materials have exhibited multi-attribute characteristics, achieving innovative applications in the field of micro-nano energy harvesting and self-powered sensing. The progress of TENGs technology with the triboelectric materials is complementary and mutually promoting. On the one hand, one of the cruxes of TENGs lies in the triboelectric materials, which have a decisive impact on their performance. On the other hand, as the research and application of TENGs continue to deepen, higher demands are placed on triboelectric materials, which in turn promotes the advancement of the entire material system as well as the fields of materials science and physics. This work aims to delve into the characteristics, types, preferred choices, and modification treatments of triboelectric materials on the performances of TENGs, hoping to provide guidance and insights for future research and applications.

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Wireless energy transfer (WET) based on ultrasound-driven generators with enormous beneficial functions, is technologically in progress by the valuation of ultrasonic metamaterials (UMMs) in science and engineering domains. Indeed, novel metamaterial structures can develop the efficiency of mechanical and physical features of ultrasound energy receivers (US-ETs), including ultrasound-driven piezoelectric and triboelectric nanogenerators (US-PENGs and US-TENGs) for advantageous applications. This review article first summarizes the fundamentals, classification, and design engineering of UMMs after introducing ultrasound energy for WET technology. In addition to addressing using UMMs, the topical progress of innovative UMMs in US-ETs is conceptually presented. Moreover, the advanced approaches of metamaterials are reported in the categorized applications of US-PENGs and US-TENGs. Finally, some current perspectives and encounters of UMMs in US-ETs are offered. With this objective in mind, this review explores the potential revolution of reliable integrated energy transfer systems through the transformation of metamaterials into ultrasound-driven active mediums for generators.

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Renewable energy sources, such as wind, tide, solar cells, etc, are the primary research areas that deliver enormous amounts of energy for our daily usage and minimize the dependency upon fossil fuel. Paralley, harnessing ambient energy from our surroundings must be prioritized for small powered systems. Nanogenerators, which use waste energy to generate electricity, are based on such concepts. We refer to these nanogenerators as energy harvesters. The purpose of energy harvesters is not to outcompete traditional renewable energy sources. It aims to reduce reliance on primary energy sources and enhance decentralized energy production. Energy storage is another area that needs to be explored for quickly storing the generated energy. Supercapacitor is a familiar device with a unique quick charging and discharging feature. Encouraging advancements in energy storage and harvesting technologies directly supports the efficient and comprehensive use of sustainable energy. Yet, self-optimization from independent energy harvesting and storage devices is challenging to overcome. It includes instability, insufficient energy output, and reliance on an external power source, preventing their direct application and future development. Coincidentally, integrating energy harvesters and storage devices can address these challenges, which demand their inherent action. This review intends to offer a complete overview of supercapacitor-based integrated energy harvester and storage systems and identify opportunities and directions for future research in this subject.

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Linear polyamides, known as nylons, are a class of synthetic polymers with a wide range of applications due to their outstanding properties, such as chemical and thermal resistance or mechanical strength. These polymers have been used in various fields: from common and domestic applications, such as socks and fishing nets, to industrial gears or water purification membranes. By their durability, flexibility and wear resistance, nylons are now being used in addictive manufacturing technology as a good material choice to produce sophisticated devices with precise and complex geometric shapes. Furthermore, the emergence of triboelectric nanogenerators and the development of biomaterials have highlighted the versatility and utility of these materials. Due to their ability to enhance triboelectric performance and the range of applications, nylons show a potential use as tribo-positive materials. Because of the easy control of their shape, they can be subsequently integrated into nanogenerators. The use of nylons has also extended into the field of biomaterials, where their biocompatibility, mechanical strength and versatility have paved the way for groundbreaking advances in medical devices as dental implants, catheters and non-absorbable surgical sutures. By means of 3D bioprinting, nylons have been used to develop scaffolds, joint implants and drug carriers with tailored properties for various biomedical applications. The present paper aims to collect evidence of these recently specific applications of nylons by reviewing the literature produced in recent decades, with a special focus on the newer technologies in the field of energy harvesting and biomedicine.

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Piezoelectric nanogenerators (PENGs) are booming for energy collection and wearable energy supply as one of the next generations of green energy-harvesting devices. Balancing the output, safety, degradation, and cost is the key to solving the bottleneck of PENG application. In this regard, yttrium (Y)-doped zinc oxide (ZnO) (Y-ZnO) was synthesized and embedded into polylactide (PLLA) for developing degradable piezoelectric composite films with an enhanced energy-harvesting performance. The synthesized Y-ZnO exhibits high piezoelectric properties benefiting from the stronger polarity of the Y-O bond and regulation of oxygen vacancy concentration, which improve the output performance of the composite film with Y-ZnO and PLLA (Y-Z-PLLA). The obtained open-circuit voltage (Voc), short-circuit current (Isc), and instantaneous power density of the optimized Y-Z-PLLA PENG reach 17.52 V, 2.45 µA, and 1.76 µW/cm2, respectively. The proposed PENG also shows good degradability. In addition, practical applications of the proposed PENG were demonstrated by converting biomechanical energy, such as walking, running, and jumping, into electricity.