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This study demonstrates fully solution‐processed polymeric multilayer piezoelectric devices. The key challenge, the effective control of the redissolution issue that will cause severe electrical shorting and inconsistent piezoelectric output, is overcome by searching for and using a solvent that offers adequate solubility but extremely slow dissolution for the piezoelectric polymer. The solvent screening methodology is established and demonstrated. The process parameters is systematically optimized to maximize the piezoelectric performance of the multilayer devices. The multilayer devices can output a high charge density of 376 µC m−2, even higher than the record charge density of 250 µC m−2 achieved by traditional contact electrification‐based triboelectric nanogenerators operated in ambient air. The crucial factors for increasing device fabrication yield, namely resistance to short circuits and poling‐induced breakdown, are analyzed. The potential of multilayer devices in practical applications is demonstrated using a five‐layer device as a direct power source and energy harvester. More importantly, the process developed here is transferrable for cost‐effective high‐throughput roll‐to‐roll production. This work thus lays the foundation for the mass production of polymeric multilayer piezoelectric devices and paves the way for their future commercialization. [ABSTRACT FROM AUTHOR]

A 3D-printable polymer can provide an effective solution for developing piezoelectric structures. However, their nanocomposite formulation and 3D printing processability must be optimized for fabricating complex geometries with high printability. In the present study, we optimized the 3D-printable piezoelectric composite formulation for developing complex geometries by an additive manufacturing approach. The zinc oxide (ZnO) nanomaterial was synthesized by the hydrothermal method. The ZnO loading in the 3D-printed flexible resin was optimized to exhibit good interfacial adhesion and enable 3D printing. The lattice structure was fabricated to improve the piezoelectric response compared with the solid structure. The lattice structure block printed with 10 wt% ZnO showed a good piezoelectric response, with a linear increase in the generated output voltage for an increase in force. The maximum power density of 0.065 μW/cm2 was obtained under 12 N force at 1 Hz. The fabricated structure generated a peak–peak voltage of ~3 V with a foot heel strike. [ABSTRACT FROM AUTHOR]

To mitigate the risks posed by noncommunicable chronic diseases (NCDs) to human health, the Internet of Healthcare (IoH) requires sensors with real‐time and long‐term monitoring capabilities. However, traditional pressure sensors, due to their high‐power consumption and non‐rechargeability, are unbale to meet the increasingly stringent requirements of physiological monitoring devices in the IoH. The emergence of self‐powered pressure sensing technology, exemplified by nanogenerators, provides a new strategy for the next generation of wearable health monitoring devices. This review begins by discussing the merits and drawbacks of different pressure‐sensing modes for healthcare monitoring. Then, it introduces the development and working mechanism of self‐powered triboelectric and piezoelectric sensors. Furthermore, it summarizes the optimizations of sensor structure and material selection aimed at improving sensing performance and achieving high accuracy in sensor networks within the IoH. Relevant application based on independent, or hybrid mechanisms are also covered. Finally, the challenges and prospects for achieving large‐scale commercial applications of self‐power sensing system in IoH are discussed. [ABSTRACT FROM AUTHOR]

A triboelectric nanogenerator (TENG) working on a contact electrification and electrostatic induction principle is a promising energy source for fulfilling the energy demand of low power electronic devices by converting the ambient mechanical energy to useful electrical energy. Here, a polymer nanocomposite film-based triboelectric nanogenerator has been designed by embedding reduced graphene oxide (rGO) nanosheets in a polyvinylidene fluoride (PVDF) matrix as one of the friction layers. The PVDF nanocomposite film-based TENG was constructed and examined for structural, electrical, and surface properties with varied weight percentages of rGO nanofillers (0.0 wt%, 0.5 wt%, 1.0 wt%, 1.5 wt%, and 2.0 wt%). The experimental results demonstrate that the addition of rGO in a PVDF matrix considerably increased the output performance of the TENG device. The TENG device with 1.5 wt% of rGO can deliver the maximum output voltage and current of 95.9 V, and 16.8 μA, respectively, which are ~ 3 and ~ 7 times the voltage and current produced by pristine PVDF film-based TENG. The enhanced performance of the nanogenerator is attributed to the addition of conductive nanofillers in the polymer matrix which improves the surface charge density of polymer nanocomposite films by forming a conduction network, resulting in more effective charge transfer. Moreover, the output of the nanogenerator is stored in the capacitor and used to drive commercial LEDs, revealing the TENGs' potential applications for designing self-powered electronic devices. [ABSTRACT FROM AUTHOR]

Articulus wound infection is a threat to human health. Existing medical materials have poor biocompatibility and may contain harmful chemicals, causing allergies and secondary infections. Therefore, there is an urgent need to develop innovative medical materials. Materials made of artificial spider silk proteins have been widely used in wound healing because of their good biocompatibility, biodegradability, cell adhesion and bioelectronic properties. [ABSTRACT FROM AUTHOR]

In recent years, the automotive industry has made significant progress in integrating multifunctional sensors to improve vehicle performance, safety, and efficiency. As the number of integrated sensors keeps increasing, there is a growing interest in alternative energy sources. Specifically, self‐powered sensor systems based on energy harvesting are drawing much attention, with a main focus on sustainability and reducing reliance on typical batteries. This paper demonstrates the use of triboelectric nanogenerators (TENGs) in a computer mouse for efficient energy harvesting and in automobile braking systems for safety applications using SrBi2Ta2O9 (SBTO) perovskite, blended PDMS composite operating in free‐standing mode with an interdigitated patterned aluminum electrode. This self‐powered sensor is capable of distinguishing between normal and abnormal braking patterns using digital signal processing techniques. It is noteworthy that the addition of 15% wt. of the SBTO in PDMS composite‐based TENG delivered 13.5 V, 45 nA, and an output power of 0.98 µW. This new combination of energy harvesting and safety applications enables real‐time monitoring and predictive maintenance in the automotive industry. [ABSTRACT FROM AUTHOR]

The transformation of environmentally benign waste energy into functional electricity holds profound implications for advancements in human progress. Herein, we detail the synthesis of tubular nanofibers featuring a hollow architecture through an innovative combination of sol-gel processing and electrospinning techniques, followed by surface modification with dopamine. These engineered PZT hollow nanotubes, upon integration into PVDF piezoelectric films, serve as potent reinforcing agents that amplify the piezoelectric active phase within the PVDF matrix. The introduction of these hollow PZT nanostructures alters the polarization electric field distribution, thereby augmenting the polarization dynamics of PVDF and significantly enhancing the piezoelectric performance of the resultant PVDF/PZT composite films. Our novel nano-generator exhibits an exceptional balance between a high piezoelectric coefficient, superior output characteristics, and commendable stability. Notably, the piezoelectric constant (d 33) of Neat PVDF films experiences a substantial elevation from 9 pC N−1 to 20 pC N−1, representing an impressive enhancement of approximately 122 %. Furthermore, the power density achieves a value of 0.54 μW cm−2. This study introduces an effective approach to augment the productive output capability of composite nanogenerators, paving the way for sustainable energy harvesting technologies. [ABSTRACT FROM AUTHOR]

The exploration of energy harvesting encompasses a wide array of sources, with a specific focus on recovering mechanical and magnetic energy from overlooked outlets, driving current research endeavours. In this study, we developed highly flexible Magneto-Mechano-Electric (MME) harvesters by combining poly(vinylidene fluoride) (PVDF)/barium calcium zirconium titanate (BCT-BZT) composite films with metglas. The flexible piezoelectric polymer-ceramic composite films were fabricated using a solvent casting technique. The high piezoelectric BCT-BZT fillers were synthesized through a sol-gel reaction route. A thorough analysis was carried out on these composites to evaluate their structural, functional, microstructural, and dielectric properties. The composite film loaded with 20 wt% BCT-BZT filler achieved a 78 % β-phase with a significant enhancement in the dielectric properties, resulting in a high permittivity∼40 and low dielectric loss. Employing these films, we engineered nanogenerators capable of converting mechanical energy into electrical energy, yielding an output voltage of 11 V. Thereafter, to harvest mechanical and stray magnetic fields, we developed a MME generator comprising a magnetic Metglas layer and PVDF-BCT-BZT composite and achieved an output voltage of 3.3 V with a power density of 85 μW/m2 when subjected to an AC magnetic field of 5 Oe. Furthermore, the MME generator has demonstrated the ability to charge various capacitors showcasing its potential for usage in self-powered, non-contact, and implantable devices. [ABSTRACT FROM AUTHOR]

The flexoelectric effect describes phenomena where strain gradients induce electrical polarization and electric field gradients cause strain in materials. This specific type of electromechanical coupling effect is remarkable for being independent of material symmetry, Curie temperature, and it exhibits notable effects in small‐sized materials. The study of flexoelectric effects has provided fresh insights into materials science, particularly highlighting how thin‐film structures, with their unique geometrical and dimensional attributes, are highly responsive to flexoelectric influences, thereby offering significant opportunities for modulating electrical properties. Herein, this paper presents the fundamental concepts and theories underlying the flexoelectric effect are presented. Various methods for inducing this effect in thin films are explored, including the optimization of growth and deposition conditions, and the application of external mechanical stresses to create strain gradients. Additionally, recent advances in utilizing the flexoelectric effect to modulate ferroelectric domains, modify properties of thin films, and enhance functionalities in photovoltaic systems, nanogenerators, sensors, and actuators are reviewed. Finally, the challenges and future prospects for flexoelectric effects in advanced electronics are briefly presented. [ABSTRACT FROM AUTHOR]

The development of triboelectric nanogenerators (TENGs) using sustainable materials addresses the global electronic waste issue. This research focuses on fabricating a TENG device with biodegradable polylactic acid (PLA) as the tribopositive material and polytetrafluoroethylene (PTFE) as the tribonegative material. ZnFe2O4 nanoparticles are incorporated into the PLA matrix to enhance surface charge density and synthesised via a simple combustion method. PLA-ZnFe2O4 composite films were prepared by solvent casting with varying nanofiller content (0.25, 0.45, 0.65, and 0.85 g). Prepared composites were characterised by Powder X-ray Diffraction (PXRD) for crystalline nature and phase purity, Fourier Transform Infrared Spectroscopy (FTIR) for vibrational analysis, and Scanning Electron Microscopy (SEM) for surface morphology. The inclusion of ZnFe2O4 nanoparticles improves TENG output performance, with a maximum output voltage of 18.4 V and a current of 1.57 µA observed for a PLA (poly(lactic acid)) composite with 39.39% nanoparticle content. Electrical studies on the optimised device show successful charging of various capacitors and powering 20 LEDs and a calculator. Body movements like walking and jumping were also tested to measure voltage and current outputs. These findings highlight new possibilities for developing smart, self-powered electronic devices. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerators (TENGs) hold immense potential as sustainable energy sources, with waste materials serving as promising materials for their fabrication. Nearly 270 million tons of waste is produced yearly, most of which remains unrecycled. TENGs can utilize this wide range of waste to convert mechanical energy to electrical energy while providing a solution for the global issue of plastic waste. On the other hand, the enormous demand for wearable electronics and the Internet of Things (IoT) trigger the development of self‐reliant energy sources. Currently, TENGs are one of the preferred choices as they are easy to design and generate high output. In this regard, TENGs are promising for utilizing waste materials, particularly for self‐powered or energy‐autonomous applications. This review focuses on utilizing waste materials from diverse sources, including biowaste, household waste, medical, laboratory, pharmaceutical, textile, electronic waste (e‐waste), and automotive waste for TENG development. Different waste materials are detailed for their potential as materials for TENGs, their availability, and recycling methods. The review also highlights the applications of TENGs fabricated from waste materials. Finally, the challenges, limitations, and future perspectives of using waste materials for TENG fabrication are discussed to motivate further advances. [ABSTRACT FROM AUTHOR]

Subhasmita Swain,1 RDK Misra,2 Tapash R Rautray1 1Biomaterials and Tissue Regeneration Laboratory, Centre of Excellence, Siksha ‘O’ Anusandhan (Deemed to be University), Bhubaneswar, Odisha, India; 2Metallurgical, Materials and Biomedical Engineering Department, The University of Texas at El Paso, El Paso, Texas, 79968, USACorrespondence: Tapash R Rautray; RDK Misra, Email tapashrautray@soa.ac.in; dmisra2@utep.eduAbstract: Electroactive components can promote tissue healing and control neuronal activity with the support of the tissue environment and offer electrical impulses and biocompatible material habitats. Due to the increasing growth of portable electronics, it is imperative to generate tiny, lightweight power supply appliances with outstanding performance and sustainable energy conversion ability. In order to deal with the energy deficiency of electronic devices, self-powered systems based nanogenerators are committed to capturing ambient energy for electronic device consumption. Nanogenerator assemblies provide a range of benefits, including adjustable shape, flexibility, affordability, and transportability. As such, they represent a novel and intriguing area for biomedical investigation. In living organisms, bioelectrical mechanisms play an integral part in regulating the functions of cells and tissues. An essential component of electroactive assemblies includes self-powered nanogenerators. In conjunction with nanogenerators, biomedicine has contributed to the invention of medical devices based on self-powered system. Currently, one of the most significant energy-based technologies to guarantee the long-term functioning of implanted biomedical devices is the accumulation of biomechanical energy in vivo. This review covers the development of nanogenerators for biomedical applications. Piezoelectric and triboelectric materials, which could foster the evolution of potential applications in the field of bone regeneration and tissue engineering, are the primary focus of this review. These materials are electrically self-sustaining generators that encourage tissue repair involving osteogenic proliferation, differentiation, and microbial sterilization. Eventually, the discussion highlights the potential future scope and challenges related to the nanogenerators.Keywords: nanogenerator, piezoelectric, triboelectric, tissue engineering

Textile‐based wearable triboelectric nanogenerators (TENGs) have emerged as viable power sources for wearable electronics. However, it is still a daunting challenge to realize a high‐performing textile‐based nanogenerator without compromising its intrinsic textile‐like properties, such as stretchability, breathability, and conformability. The above challenge is addressed by fabricating a record high‐performing wearable, breathable and stretchable nanogenerator based on polarization‐induced ultra‐stretchable EVA/Nylon‐11 micro/nano‐fibers (1250%) as the triboelectric positive layer and polarization‐induced ultra‐stretchable EVA/PVDF/BA2CsAgBiBr7 micro/nano‐fibers (1480%) as the triboelectric negative layer. The excellent stretchability, breathability (1.15 Kgm−2d−1) and high energy‐harvesting performance (650 V, 19.5 µAcm−2) are attributed to the mechanically‐socketed structure of the aligned stretchable EVA microfibers with the polarized nanofibers, thus providing a universal framework to fabricate stretchable piezoelectric fibers. Compositional engineering and polarization‐induced surface charges coupled with triboelectric‐induced surface charges enabled enhanced performance compared to other wearable stretchable textile‐based nanogenerators. Additionally, it is utilized as a stretchable self‐powered pressure sensor with an ultra‐wide pressure sensing range (0.05–500 kPa) and high sensitivity (2.5 VkPa−1) even under deformations. To the best of the knowledge, PI‐STENG stands out amongst various stretchable self‐powered pressure sensors in terms of pressure sensing range and stretchability. The PI‐STENG is demonstrated as a machine learning‐enabled intellisensor for workforce safety monitoring. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerators (TENGs) have emerged as promising portable and sustainable energy sources in daily life, harvesting energy from human motion, water, and wind. However, they still face limitations in aspects such as contact area, deformability, wettability, and manufacturing method. Here, a wearable TENG incorporating an anisotropic domino structure based on a fluorinated elastomer blend is presented. Because of its thin, elongated structure with broad sides, the TENG achieves substantially larger contact areas and high bendability. Introducing a fluorinated elastomer into the polydimethylsiloxane matrix via a simple blending process not only enhances the triboelectric performance but also reduces surface energy and improves the stretchability of elastomers. The anisotropic arrangement of dominoes, in synergy with the fluorinated elastomer, mimics the surface physicochemical properties of natural rice leaves, resulting in anisotropic superhydrophobic wetting behavior with a self‐cleaning effect and controlled directional water flow for efficient water energy harvesting. Therefore, the TENG functions as an energy‐harvesting leaf that captures energy from wind and water droplets, as well as a wearable energy‐harvesting wristband that generates power from human motions such as touching, shaking, and hand washing. [ABSTRACT FROM AUTHOR]

In this study, both the optical and piezoelectric properties of polyvinylidene fluoride (PVDF) electrospun nanofibers were investigated at different needle-to-collector distances of the electrospinning process at constant applied high voltage. For piezoelectric characterization, the fabricated nanofiber mats were subjected to applied forces, including cyclic force, variable frequency-based loads, and free-falling masses (impulse loading), along with power density analysis for different load resistance values. In addition, both optical absorbance and transmittance measurements were conducted to evaluate the optical properties of the fabricated nanofibers. The piezoelectric analysis demonstrated the best piezoresponse of the fabricated nanomats at a needle-to-collector distance of 15 cm and high voltage of 22 kV. However, a trade-off between piezoelectric response and optical transmissivity was observed based on the electrospinning distance parameter. The relatively higher optically transparent sample exhibited only moderate piezoelectric response, while the less transparent sample displayed the highest piezoelectric activity. Based on the optimized sample and piezoelectric analysis, the synthesized nanofiber mat was subjected to applied mechanical stress in the form of variable velocity and momentum loads. A maximum potential of approximately 16 V was harvested through velocity and momentum impact, especially with the addition of a double-layer PVDF membrane. Furthermore, the sensing effect of airflow pressure on single/double-layer PVDF was studied. The single-layer PVDF membrane generated 79 mV under an airflow speed of 21 km/h, while the double-layer membrane produced 114 mV potential under the same airflow. This study highlights the diverse applications of PVDF nanofiber mats as multifunctional sensors and energy harvesting applications from mechanical shocks and airflow impact. [ABSTRACT FROM AUTHOR]

Layered transition metal dichalcogenides (TMDs) with high aspect ratios enhance the alignment of polymer chains and induce a preferred orientation of the polymeric crystallites when incorporated into polyvinylidene fluoride (PVDF). In addition to offering an effective charge‐transfer mechanism, TMDs give PVDF more rigidity and piezoelectric qualities. This work reports the non‐solvent induced phase separation (NIPS) introduced while developing the PVDF/MoS2 composites. During the NIPS, the PVDF chains become phase‐separated, which induces high polarization in the PVDF matrix. Phase‐separated PVDF/MoS2 composites show high porosity and charge distribution attributed to the enhanced piezoelectric output voltage. While the neat PVDF demonstrated very feeble output voltage generation, the hybrid composite containing 2 wt.% of MoS2/ZnO facilitated almost 20 times higher performance (peak‐to‐peak voltage of 2.4 V). This work yielded a phase‐separated composite that finds uses in energy harvesting, sensors, and actuators, among other fields. Highlights: NIPS creates high‐porosity composites with improved charge distribution.Layered TMDs improve charge‐transfer mechanism and PVDF's electrical properties.2 wt.% MoS2/ZnO exhibits nearly 20 times higher voltage generation than neat PVDF. [ABSTRACT FROM AUTHOR]

The unique 3D structure of spider silk protein (spidroin) determines the excellent mechanical properties of spidroin fiber, but the difficulty of heterologous expression and poor spinning performance of recombinant spider silk protein limit its application. A high‐yield low‐molecular‐weight biomimetic spidroin (Amy‐6rep) is obtained by sequence modification, and its excellent spinning performance is verified by electrospinning it for use as a nanogenerator. Amy‐6rep increases the highly fibrogenic microcrystalline region in the core repeat region of natural spidroin with limited sequence length and replaces the polyalanine sequence with an amyloid polypeptide through structural similarity. Due to sequence modification, the expression of Amy‐6rep increased by ≈200%, and the self‐assembly performance of Amy‐6rep significantly increased. After electrospinning with Amy‐6rep, the nanofibers exhibit good tribopower generation capacity. In this paper, a biomimetic spidroin sequence design with high yield and good spinning performance is reported, and a strategy for electrospinning to produce an artificial nanogenerator is explored. [ABSTRACT FROM AUTHOR]

Flexible piezoelectric nanogenerator (PENG) and triboelectric nanogenerators (TENG) have gained prodigious attention due to the increasing demand of nano and micro energy for driving of miniaturized electronic devices, sensors, and various internet of things. The key challenges that are currently in focus are material selection and simple fabrication techniques for improved electrical performance along with good mechanical properties and flexibility. Herein, a ferroelectric polymer, poly(vinylidenefluoride-co-trifluoroethyne) (PVDF-TrFE), is chosen as a flexible material due to its promising prospect for energy harvesting. To improve the performance, a ceramic material, 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 (PMN-PT), with very high piezoelectric properties has been selected as the reinforcement. Further, reduced graphene oxide has been added as a conducting filler to promote charge conduction. A remarkable enhancement in output voltage of nearly 3 fold is achieved in PVDF-TrFE/PMN-PT (PP) polymer composite as compared to the base polymer PVDF-TrFE (P) TENG device. Furthermore, the PVDF-TrFE/rGO/PMN-PT (PPR) as a PENG illustrates a great improvement in output current of the order of 2 as compared to the pristine polymer. The maximum output voltage as shown by the TENG is 200 V and the maximum current that is shown by the PENG is 30 µA. Therefore, the fabricated PMN-PT based PVDF-TrFE nanogenerators have an immense prospect for applications in self-powered systems.

Ferroelectret nanogenerators (FENGs), recognized for their porous structures that facilitate charge retention, thereby creating giant electric dipoles and exhibiting remarkable piezoelectric properties, are utilized in the development of various flexible transducers. However, despite their flexibility, most developed ferroelectret nanogenerators lack adequate stretchability and satisfactory transverse piezoelectric properties, significantly inhibiting their widespread deployment in wearable or skin-mounted electronics. Here, we introduce a highly stretchable ferroelectret nanogenerator (HS-FENG) built from laser-induced graphene (LIG), Ecoflex and anhydrous ethanol, demonstrating exceptional flexibility and stretchability, along with longitudinal and transverse piezoelectric effects. The stretchability of HS-FENG can reach a record of 468 %, while the quasi-static piezoelectric coefficients d33 and d31 are approximately 120 pC/N and 70 pC/N, respectively. To our knowledge, this is the first demonstration of the developed FENG with remarkably high stretchability. Furthermore, leveraging the performance of the created HS-FENG, we construct a skin-mounted intelligent kinesiology tape capable of effectively monitoring motion signals from human muscles and joints, thereby offering a deeper understanding of movement for users across different levels of physical activity, from professional athletes to individuals undergoing rehabilitation. The development of intelligent kinesiology tape exemplifies the potential of HS-FENG technology in enhancing professional athletic training and personalized healthcare. It contributes to the advancement of inconspicuous skin-mounted biomechanical feedback systems and human-machine interfaces, marking progress in the field.

Flexible, lead-free piezoelectric nanogenerators are gaining prominence as viable alternatives with remarkable potential in the backdrop of increasing demand for sustainable energy solutions, particularly in the field of microelectronic systems and sensing technologies. In this context, the synergistic impact of utilizing reduced graphene oxide (rGO) nanosheets decorated with zinc oxide (ZnO) nanorods, in conjunction with a low-temperature phase-inversion technique aimed at augmenting the polar β-phase of poly-(vinylidene fluoride) (PVDF) was explored. The nanofiller concentrations of rGO and ZnO were systematically varied to ascertain the optimal concentration in the PVDF matrix. These optimal concentrations were further used to fabricate PVDF/ZnO/rGO hybrid and PVDF/ZnO-decorated rGO nanocomposites. Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), and differential scanning calorimetry (DSC) characterizations were employed to examine the electroactive crystal phase in synthesized nanocomposites, confirming enhancement in polar β-phase and crystallinity, thereby improving piezoelectric, dielectric, and ferroelectric properties of the nanocomposites as confirmed by a dielectric broadband spectrometer (BDS) and piezoresponse force microscopy (PFM). A comparative analysis of optimized nanocomposites supplemented with related characterizations was performed to assess their piezoelectric performance. Additionally, systematic variations in force and frequency were carried out to understand their correlation with the piezoelectric performance of PENGs. The optimized PENG showcased the exceptional piezoelectric energy harvesting potential, generating an open circuit voltage of 23 V (at 1 Hz and 1 N), 98 V (at 5 Hz and 10 N), and 153 V (at 15 Hz and 50 N). Further, the PENG produced an instantaneous power density of ∼28 μW/cm2, charged a range of capacitors, sensed human body motions, successfully illuminating 50 LEDs in series and 36 in combination of series and parallel connections. This fabricated PENG henceforth showcases the immense potential for energy harvesting applications. [ABSTRACT FROM AUTHOR]

Tribovoltaic effect is a phenomenon of the generation of direct voltage and current by the mechanical friction on semiconductor interface, which exhibits a brand‐new energy conversion mechanism by the coupling of semiconductor and triboelectrification. Here, the origin, interfaces, characteristics, mechanism, coupling effect and application of the tribovoltaic effect is summarized and reviewed. The tribovoltaic effect is first proposed in 2019, which has developed in various forms tribovoltaic nanogenerator (TVNG) including metal‐semiconductor, metal‐insulator‐semiconductor, semiconductor‐semiconductor, liquid‐solid and flexible interfaces. Compared with triboelectric nanogenerator, the TVNG has the characteristics of direct‐current, high current density (mA‐A cm−2) and low impedance (Ω‐kΩ). The two mainstream views on the tribovoltaic generation mechanism, one dominated by built‐in electric fields and the other dominated by interface electric fields, have been elaborated and summarized in detail. The tribo‐photovoltaic effect and tribo‐thermoelectric effect are also discovered and introduced because they can easily interact with other multi‐physical field effects. The TVNGs are suitable for making energy harvesting and self‐powered sensing devices for micro‐nano energy applications. This paper not only revisit the development of the tribovoltaic effect, but also makes prospects for mechanism research, device fabrication and integrated application, which can accelerate the evolution of smart wearable electronics and intelligent industrial components. [ABSTRACT FROM AUTHOR]

Triboelectricity has emerged as a promising and novel method for low-power systems. In this study, a novel system is presented that converts wind energy into electrical energy through triboelectric energy conversion. The proposed system is based on the principle of a Van de Graaff machine. As is known, the required mechanical energy in a Van de Graaff generator is supplied by a DC motor. In this study, the required mechanical energy is provided by the wind using a propeller system, where the mechanical energy from the wind rotates a belt system, storing static charges generated by the friction of different materials and converting them into electrical energy. A laboratory-scale generator was manufactured, and data were collected under various experimental conditions. It was observed that the experimental generator could charge a 100 µF capacitor to 20.7 V within 6 min at a wind speed of 7 m/s. Furthermore, it was observed that the presented generator exhibited an energy generation capacity of 21.4 mJ over the same duration. Although the obtained energy is low, the simplicity of the system, absence of a traditional electric generator, and the potential to provide necessary energy production for off-grid, remote, low-power applications with improvements are considered its main advantages. [ABSTRACT FROM AUTHOR]

Humans generate a lot of irregular movements in their daily lives, and much of the movement energy is difficult to collect. This paper develops a wearable device based on a liquid metal (LM)‐based frictional electric nanogenerator, including: flexible power‐generating fiber, power‐generating surface, and power‐generating insole. Friction nano power generation fibers are prepared using LM, epoxy resin, and silicone. The power generation device could be formed by weaving the fibers in cross, mesh and spiral arrangement, with a maximum open circuit voltage of 142 mV and current of 1.06 A, which could be coded into intelligent clothing. Power generating surfaces use LM, nylon,polycaprolactone (PCL), and polyethylene terephthalate (PET) as friction electrodes. The LM‐PCL produces a maximum open‐circuit voltage of 2.4 V and a maximum current of 1.23 A when they form a friction electrode. Electricity‐generating insoles are composed of silicone holes filled with LM, and the movement of the human foot generates electricity. With a friction area of 18.75 cm2, a maximum output voltage of 221 mV is obtained. These friction nano power devices have the advantages of a green environment, and low cost, which could be widely used in medical, biological, and clothing formulation fields. [ABSTRACT FROM AUTHOR]

Ubiquitous energy harvesting technologies require new types of renewable, sustainable, and clean energy to solve the problems of fossil fuels. Although various nanogenerators have been developed over the last decade, low current density, requirements for complicated management circuits, generation of direct current (DC) outputs, and significant performance degradation under humid atmospheres have been problems limiting practical applications. This paper reports that the tribovoltaic and moisture‐enabled electricity generation effects can be achieved in a layered double hydroxide (LDH) by applying a metal brushing mode. The ZnAl‐LDH shows enhanced tribovoltaic nanogenerator (TVNG) performance even in a high‐humidity environment coupled with the moisture‐enabled electricity generated by the concentration gradient of a water molecule through the interlamellar structures of the LDHs. The spontaneous dissociation of water in the interior of LDHs removes the hole generated by the tribovoltaic effect, allowing high efficiency of an output voltage of 693.38 mV and current density of 65.48 mA m−2 even under low‐applied force (≈3.5 mN) at relative humidity 80%. The proposed TVNG provides a proof of concept for an all‐in‐one device consisting of a generator and capacitor because the LDH reveals a spontaneous charging performance similar to that of a capacitor. [ABSTRACT FROM AUTHOR]

Precision medicine requires precise regulation of drugs in terms of time, space, and dosage. Exogenous control systems, such as electrical responsiveness, have made great progress. However, wearable or implantable controlled drug release devices still face major challenges due to limitations including limited battery life, large size, and fixed power supply. To overcome these limitations, the fabrication of autonomous devices is available to endure extended periods without reliance on external power sources. As a promising strategy, nanogenerators (NGs) turn body mechanical energy into electricity, powering long‐term drug release. In this review, the current status of drug delivery systems (DDS) is briefly outlined and the importance of self‐driven controlled drug release systems is emphasized. The main types and operational mechanisms of various nanogenerators are introduced. This review also focuses on summarizing the latest progress of self‐powered controlled drug release systems based on nanogenerators (NG‐based CDRs). Additionally, their applications in the field of drug release are introduced in detail. Finally, the existing challenges and future trends of self‐powered NG‐based CDRs are discussed from the perspectives of clinical needs and practical translation. [ABSTRACT FROM AUTHOR]

This study explores the impact of CaTiO3 and LiNbO3 crystals on the optical and dielectric properties of polyvinylidene fluoride (PVDF) films. Our investigation employs UV–Visible Spectroscopy to characterize the n-π* C-F related electronic transition within the PVDF matrix. We find that CaTiO3 crystals significantly decrease the composite’s band gap and dielectric properties, enhancing its electronic and optical attributes. Conversely, LiNbO3 crystals increase the band gap energy. These variations align with observed DC conductivity changes, suggesting novel functionalities for optoelectronic, sensing, and energy storage applications.

Piezoelectricity or piezoelectric effect is a phenomenon by which mechanical energy is converted into electrical energy and vice versa. Piezoelectric effect has been observed in several organic materials. Therefore, in past few years organic piezoelectric materials have received significant research interests in biomedical applications and specifically for fabrication of implantable biomedical devices because of their high piezoelectric performance, excellent biocompatibility and biodegradability, superior mechanical properties, and cheap fabrication process. This article provides a comprehensive review of the recent research progress on organic piezoelectric materials. It extensively covers the piezoelectric properties and preparation methods of different organic piezoelectric materials including amino acids, peptides, proteins, polysaccharides, and polymers (such as PVDF, PLLA, PHB), as well as their representative implantable biomedical device applications namely biosensing, tissue regeneration, and drug delivery. Finally, the article discusses the challenges and future directions of this research field.

Abstract The unique 3D structure of spider silk protein (spidroin) determines the excellent mechanical properties of spidroin fiber, but the difficulty of heterologous expression and poor spinning performance of recombinant spider silk protein limit its application. A high‐yield low‐molecular‐weight biomimetic spidroin (Amy‐6rep) is obtained by sequence modification, and its excellent spinning performance is verified by electrospinning it for use as a nanogenerator. Amy‐6rep increases the highly fibrogenic microcrystalline region in the core repeat region of natural spidroin with limited sequence length and replaces the polyalanine sequence with an amyloid polypeptide through structural similarity. Due to sequence modification, the expression of Amy‐6rep increased by ≈200%, and the self‐assembly performance of Amy‐6rep significantly increased. After electrospinning with Amy‐6rep, the nanofibers exhibit good tribopower generation capacity. In this paper, a biomimetic spidroin sequence design with high yield and good spinning performance is reported, and a strategy for electrospinning to produce an artificial nanogenerator is explored.

Gas therapy is emerging as a highly promising therapeutic strategy for cancer treatment. However, there are limitations, including the lack of targeted subcellular organelle accuracy and spatiotemporal release precision, associated with gas therapy. In this study, we developed a series of photoactivatable nitric oxide (NO) donors NRh-R-NO (R = Me, Et, Bn, iPr, and Ph) based on an N-nitrosated upconversion luminescent rhodamine scaffold. Under the irradiation of 808 nm light, only NRh-Ph-NO could effectively release NO and NRh-Ph with a significant turn-on frequency upconversion luminescence (FUCL) signal at 740 nm, ascribed to lower N–N bond dissociation energy. We also investigated the involved multistage near-infrared-controlled cascade release of gas therapy, including the NO released from NRh-Ph-NO along with one NRh-Ph molecule generation, the superoxide anion O2⋅− produced by the photodynamic therapy (PDT) effect of NRh-Ph, and highly toxic peroxynitrite anion (ONOO‒) generated from the co-existence of NO and O2⋅−. After mild nano-modification, the nanogenerator (NRh-Ph-NO NPs) empowered with superior biocompatibility could target mitochondria. Under an 808 nm laser irradiation, NRh-Ph-NO NPs could induce NO/ROS to generate RNS, causing a decrease in the mitochondrial membrane potential and initiating apoptosis by caspase-3 activation, which further induced tumor immunogenic cell death (ICD). In vivo therapeutic results of NRh-Ph-NO NPs showed augmented RNS-potentiated gas therapy, demonstrating excellent biocompatibility and effective tumor inhibition guided by real-time FUCL imaging. Collectively, this versatile strategy defines the targeted RNS-mediated cancer therapy.

The coupling of pyroelectricity, semiconductor, and optical excitation yields the pyro-phototronic effect, which has been extensively utilized in photodetectors. It can also enhance the performance of light energy harvesting nanogenerators. In this work, a pyro-phototronic effect-enhanced MXene/ZnO heterojunction nanogenerator has been successfully demonstrated, which can harvest broadband light energy (from deep UV to near-infrared) and still operate at 200 °C. The morphology of the ZnO layer and the MXene layer’s thickness have been further optimized for better light energy harvesting performance. For the optimized heterojunction nanogenerator, the responsivity can be improved from ~0.2 mA/W to ~3.5 mA/W by pyro-phototronic effect, under 0.0974 mW/cm2 365 nm UV illumination. Moreover, the coupling of pyro-phototronic and piezo-phototronic effects in MXene/ZnO heterojunction nanogenerators has been investigated. The results indicate that only a small tensile strain could improve the nanogenerator’s performance. The working mechanisms have been carefully analyzed, and the modulation of piezoelectric charges on the Schottky barrier height is found to be the key factor. These results demonstrate the enormous potential of the pyro-phototronic effect in light energy harvesting nanogenerators and illustrate the coupling of pyro-phototronic and piezo-phototronic effects for further performance improvement.

A 3D-printable polymer can provide an effective solution for developing piezoelectric structures. However, their nanocomposite formulation and 3D printing processability must be optimized for fabricating complex geometries with high printability. In the present study, we optimized the 3D-printable piezoelectric composite formulation for developing complex geometries by an additive manufacturing approach. The zinc oxide (ZnO) nanomaterial was synthesized by the hydrothermal method. The ZnO loading in the 3D-printed flexible resin was optimized to exhibit good interfacial adhesion and enable 3D printing. The lattice structure was fabricated to improve the piezoelectric response compared with the solid structure. The lattice structure block printed with 10 wt% ZnO showed a good piezoelectric response, with a linear increase in the generated output voltage for an increase in force. The maximum power density of 0.065 μW/cm2 was obtained under 12 N force at 1 Hz. The fabricated structure generated a peak–peak voltage of ~3 V with a foot heel strike.

Recently, triboelectric nanogenerators (TENGs) are getting considerable attention as an energy harvesting tool that can convert random mechanical energy into electricity due to the wide material selection, low cost, and easy fabrication. TENGs work by contact electrification on the interface and electrostatic induction on the electrodes when two surfaces contact and separate. Herein, the study of the contact electrification process on the metal–polyvinylidene difluoride (PVDF) interface is conducted focusing on the effect of β phase content on the electrical properties of the PVDF films. It is found through the EFM and KPFM surface electrical studies that a higher β phase promotes stronger electrostatic interactions and enhances electron‐cloud overlap with the metal coated cantilever tip that leads to higher amount of charge transfer. Additionally, there is overall enhancement of the TENGs electric output performance for a higher β phase containing PVDF films and the maximum electric output of 8.1 V and 12.2 nA is obtained for the TENG made with 79% β phase PVDF film. [ABSTRACT FROM AUTHOR]

Gas therapy is emerging as a highly promising therapeutic strategy for cancer treatment. However, there are limitations, including the lack of targeted subcellular organelle accuracy and spatiotemporal release precision, associated with gas therapy. In this study, we developed a series of photoactivatable nitric oxide (NO) donors NRh-R-NO (R = Me, Et, Bn, i Pr, and Ph) based on an N -nitrosated upconversion luminescent rhodamine scaffold. Under the irradiation of 808 nm light, only NRh-Ph-NO could effectively release NO and NRh-Ph with a significant turn-on frequency upconversion luminescence (FUCL) signal at 740 nm, ascribed to lower N–N bond dissociation energy. We also investigated the involved multistage near-infrared-controlled cascade release of gas therapy, including the NO released from NRh-Ph-NO along with one NRh-Ph molecule generation, the superoxide anion O 2 ⋅− produced by the photodynamic therapy (PDT) effect of NRh-Ph, and highly toxic peroxynitrite anion (ONOO‒) generated from the co-existence of NO and O 2 ⋅−. After mild nano-modification, the nanogenerator (NRh-Ph-NO NPs) empowered with superior biocompatibility could target mitochondria. Under an 808 nm laser irradiation, NRh-Ph-NO NPs could induce NO/ROS to generate RNS, causing a decrease in the mitochondrial membrane potential and initiating apoptosis by caspase-3 activation, which further induced tumor immunogenic cell death (ICD). In vivo therapeutic results of NRh-Ph-NO NPs showed augmented RNS-potentiated gas therapy, demonstrating excellent biocompatibility and effective tumor inhibition guided by real-time FUCL imaging. Collectively, this versatile strategy defines the targeted RNS-mediated cancer therapy. The peroxynitrite upconversion nanogenerator NRh-Ph-NO nanoparticles empowered with superior mitochondrial targeting could induce reactive nitrogen species-potentiated precision gas therapy guided by frequency upconversion luminescence imaging upon 808 nm laser irradiation. [Display omitted] [ABSTRACT FROM AUTHOR]

Harvesting the dissipated environmental mechanical energy to generate electrical energy is subject of the new research in the field of clean energy. In this paper, a triboelectric nanogenerator based on vertical two-electrode structure was fabricated using KAPTON and PDMS polymers. The nanogenerator outputs were measured and plotted by applying a mechanical vibration with the frequency of 8 Hz. The results indicated the ability of producing a voltage of 3.5 V and a current of 0.025 μA by this nanogenerator. To effectively simulate the performance of the device in different structural and environmental conditions, the ordinary capacitance model of the device was modified considering three effective capacitances. The simulation results showed a very good agreement between calculated and actual outputs when the edge effect capacitor was included in the ordinary model. Finally, based on the corrected model for the nanogenerator, the effect of the environmental conditions on the device output was studied. The innovative point of this text is the investigation of the effect of edge capacitors in the performance of triboelectric nanogenerators, and it has also been tried to collect a collection of studies that I have done in the field of triboelectric nanogenerators. [ABSTRACT FROM AUTHOR]

The coupling of pyroelectricity, semiconductor, and optical excitation yields the pyro-phototronic effect, which has been extensively utilized in photodetectors. It can also enhance the performance of light energy harvesting nanogenerators. In this work, a pyro-phototronic effect-enhanced MXene/ZnO heterojunction nanogenerator has been successfully demonstrated, which can harvest broadband light energy (from deep UV to near-infrared) and still operate at 200 °C. The morphology of the ZnO layer and the MXene layer's thickness have been further optimized for better light energy harvesting performance. For the optimized heterojunction nanogenerator, the responsivity can be improved from ~0.2 mA/W to ~3.5 mA/W by pyro-phototronic effect, under 0.0974 mW/cm2 365 nm UV illumination. Moreover, the coupling of pyro-phototronic and piezo-phototronic effects in MXene/ZnO heterojunction nanogenerators has been investigated. The results indicate that only a small tensile strain could improve the nanogenerator's performance. The working mechanisms have been carefully analyzed, and the modulation of piezoelectric charges on the Schottky barrier height is found to be the key factor. These results demonstrate the enormous potential of the pyro-phototronic effect in light energy harvesting nanogenerators and illustrate the coupling of pyro-phototronic and piezo-phototronic effects for further performance improvement. [ABSTRACT FROM AUTHOR]

Abstract Tribovoltaic effect is a phenomenon of the generation of direct voltage and current by the mechanical friction on semiconductor interface, which exhibits a brand‐new energy conversion mechanism by the coupling of semiconductor and triboelectrification. Here, the origin, interfaces, characteristics, mechanism, coupling effect and application of the tribovoltaic effect is summarized and reviewed. The tribovoltaic effect is first proposed in 2019, which has developed in various forms tribovoltaic nanogenerator (TVNG) including metal‐semiconductor, metal‐insulator‐semiconductor, semiconductor‐semiconductor, liquid‐solid and flexible interfaces. Compared with triboelectric nanogenerator, the TVNG has the characteristics of direct‐current, high current density (mA‐A cm−2) and low impedance (Ω‐kΩ). The two mainstream views on the tribovoltaic generation mechanism, one dominated by built‐in electric fields and the other dominated by interface electric fields, have been elaborated and summarized in detail. The tribo‐photovoltaic effect and tribo‐thermoelectric effect are also discovered and introduced because they can easily interact with other multi‐physical field effects. The TVNGs are suitable for making energy harvesting and self‐powered sensing devices for micro‐nano energy applications. This paper not only revisit the development of the tribovoltaic effect, but also makes prospects for mechanism research, device fabrication and integrated application, which can accelerate the evolution of smart wearable electronics and intelligent industrial components.

Lead-free piezoelectric ceramic is a promising material for energy harvesters, as they have superior electromechanical, ferroelectric, and piezoelectric properties. In addition, piezoelectric ceramics can be blended with polymer to achieve high-flexibility polymer-ceramic composites, providing mechanical robustness and stability. In this context, a new lead-free ferroelectric material, having the chemical formula SrTi2O5 (STO), was synthesized using a high-temperature solid-state reaction. Detailed analyses of the structural, morphological, and electrical properties of the synthesized material were performed. STO crystallizes with orthorhombic symmetry and space group of Cmm2. The frequency and temperature-dependent dielectric parameters were evaluated, and impedance spectroscopy shed light on the charge dynamics. The PDMS-STO composites at different mass fraction of the STO were prepared using a solvent casting route, and a corresponding piezoelectric nanogenerator (PENG) was developed. The electrical output of the different PENG by varying massfractions of STO in PDMS and varying force were investigated. The 15% (in mass) PENG device delivered the highest peak-to-peak voltage, current, and power density of 25 V, 92 nA, and 0.64 μW @ 500 MΩ, respectively. The biomechanical energy harvesting using the PENG device by daily human motions, bending of the device, and attaching the device to laboratory equipment was demonstrated. Later the PENG device was attached to the human throat region, and snoring signals were recorded. A classification model was designed employing the convolutional neural network (CNN) model. Efforts have been laid to differentiate between normal and abnormal snores, which could help the patient with screening and early disease detection, contributing to self-powered healthcare applications.

Abstract Recently, triboelectric nanogenerators (TENGs) are getting considerable attention as an energy harvesting tool that can convert random mechanical energy into electricity due to the wide material selection, low cost, and easy fabrication. TENGs work by contact electrification on the interface and electrostatic induction on the electrodes when two surfaces contact and separate. Herein, the study of the contact electrification process on the metal–polyvinylidene difluoride (PVDF) interface is conducted focusing on the effect of β phase content on the electrical properties of the PVDF films. It is found through the EFM and KPFM surface electrical studies that a higher β phase promotes stronger electrostatic interactions and enhances electron‐cloud overlap with the metal coated cantilever tip that leads to higher amount of charge transfer. Additionally, there is overall enhancement of the TENGs electric output performance for a higher β phase containing PVDF films and the maximum electric output of 8.1 V and 12.2 nA is obtained for the TENG made with 79% β phase PVDF film.

The flexible polyvinylidene difluoride (PVDF)/6H–SiC composite films are fabricated to overcome the natural brittleness of hexagonal SiC. Yet the electrical output of the piezoelectric nanogenerator (PENG) based on the composite film needs to be further improved. Here, PENG and hybrid nanogenerator exploiting both triboelectric and piezoelectric effects (T-PENG) based on PVDF/6H–SiC composite films are assembled. The PENG based on the PVDF/15 wt% 6H–SiC composite film shows the open circuit voltage (V oc) of 16.81 V. The T-PENG achieves the bridge rectified voltage of 65.70 and 136.58 V when subjected to the external force of 1.1 and 4.9 N, indicating 3.91 and 7.39 times the output of the PENG under the same force, which is the highest value compared with the reported nanogenerators based on SiC and SiC composites. This work breaks through the limitation of low mechanical energy utilization efficiency of film-based PENG and provides a feasible way to enhance the electrical output of nano power sources. [ABSTRACT FROM AUTHOR]

Existing self-powered generators with substantial volume can generate tens of V using triboelectric, piezoelectric, and pyroelectric effects. However, there is a growing need for more robust, cost-effective, smaller-sized, and easier-to-produce generators for onboard and distributed sensor applications. In this article, we introduce for the first time a minute renewable energy source based on a single zinc oxide nanowire (ZnONW) to power multiple common bulk sensors. A nanomanipulator within a scanning electron microscope (SEM) was utilized to manipulate and provide mechanical energy by deforming a single suspended ZnONW under specific scenarios. Piezoelectric properties of the ZnONW, including the effects of deformation magnitude and bending frequency, were investigated. A voltage output of up to 22.3 mV was obtained and was used to power external sensing elements practically for the first time, with the sensing signal measured using the voltage-division principle. 0–180° bending angle of a flexible strain gauge (sensitivity: −1.07 mV/rad), 30–90 °C temperature, and light on/off were successfully tested. Simulations were conducted to evaluate the influence of the mass block on the first resonant frequency of the nanogenerator and to enhance power generation performance. Our work offers a fresh method for studying the piezoelectric properties of a single ZnONW-based nanogenerator and demonstrates its potential for self-powered microdevices in various real-time, flexible, and portable sensing applications. [ABSTRACT FROM AUTHOR]

Wound healing is a highly orchestrated biological process characterized by sequential phases involving inflammation, proliferation, and tissue remodeling, and the role of endogenous electrical signals in regulating these phases has been highlighted. Recently, external electrostimulation has been shown to enhance these processes by promoting cell migration, extracellular matrix formation, and growth factor release while suppressing pro-inflammatory signals and reducing the risk of infection. Among the innovative approaches, piezoelectric and triboelectric nanogenerators have emerged as the next generation of flexible and wireless electronics designed for energy harvesting and efficiently converting mechanical energy into electrical power. In this review, we discuss recent advances in the emerging field of nanogenerators for harnessing electrical stimulation to accelerate wound healing. We elucidate the fundamental mechanisms of wound healing and relevant bioelectric physiology, as well as the principles underlying each nanogenerator technology, and review their preclinical applications. In addition, we address the prominent challenges and outline the future prospects for this emerging era of electrical wound-healing devices. [ABSTRACT FROM AUTHOR]

The development of self-powered water purification technologies for decentralized applications is crucial for ensuring the provision of drinking water in resource-limited regions. The elimination of the dependence on external energy inputs and the attainment of self-powered status significantly expands the applicability of the treatment system in real-world scenarios. Hybrid energy harvesters, which convert multiple ambient energies simultaneously, show the potential to drive self-powered water purification facilities under fluctuating actual conditions. Here, we propose recent advancements in hybrid energy systems that simultaneously harvest various ambient energies (e.g., photo irradiation, flow kinetic, thermal, and vibration) to drive water purification processes. The mechanisms of various energy harvesters and point-of-use water purification treatments are first outlined. Then we summarize the hybrid energy harvesters that can drive water purification treatment. These hybrid energy harvesters are based on the mechanisms of mechanical and photovoltaic, mechanical and thermal, and thermal and photovoltaic effects. This review provides a comprehensive understanding of the potential for advancing beyond the current state-of-the-art of hybrid energy harvester-driven water treatment processes. Future endeavors should focus on improving catalyst efficiency and developing sustainable hybrid energy harvesters to drive self-powered treatments under unstable conditions (e.g., fluctuating temperatures and humidity). [ABSTRACT FROM AUTHOR]

Malignant tumors have the capability to metastasize and colonize, meaning that they can spread to other organs and tissues, distributing metastatic focus and are hard to target. Although significant advances have been made in cancer treatment, it remains one of the leading causes of death around the globe. In recent years, new-emerging implantable systems and devices have been developed to tackle the challenge of metastatic tumors. In this review, implantable systems for suppressing tumors and preventing tumor recurrence are reported. In particular, we emphasize the responsive drug delivery systems and the external field assisted catalytic therapy for tumor treatment, as well as implantable biosensors for tumor microenvironment monitoring. We also conclude the open challenges and future perspectives of implantable systems and devices for cancer therapy and sensing. [ABSTRACT FROM AUTHOR]

Sensor-based human action recognition (HAR) is considered to have broad practical prospects. It applies to wearable devices to collect plantar pressure or acceleration information at human joints during human actions, thereby identifying human motion patterns. Existing related works have mainly focused on improving recognition accuracy, and have rarely considered energy-efficient management of portable HAR systems. Considering the high sensitivity and energy harvesting ability of triboelectric nanogenerators (TENGs), in this research a TENG which achieved output performance of 9.98 mW/cm 2 was fabricated using polydimethylsiloxane and carbon nanotube film for sensor-based HAR as a wearable sensor. Considering real-time identification, data are acquired using a sliding window approach. However, the classification accuracy is challenged by quasi-periodic characteristics of the intercepted sequence. To solve this problem, compensatory dynamic time warping (C-DTW) is proposed, which adjusts the DTW result based on the proportion of points separated by small distances under DTW alignment. Our simulation results show that the classification accuracy of C-DTW is higher than that of DTW and its improved versions (e.g., WDTW, DDTW and softDTW), with almost the same complexity. Moreover, C-DTW is much faster than shapeDTW under the same classification accuracy. Without loss of generality, the performance of the existing DTW versions can be enhanced using the compensatory mechanism of C-DTW. [ABSTRACT FROM AUTHOR]

Owing to their biocompatibility, chemical stability, film-forming ability, cost-effectiveness, and excellent electroactive properties, poly(vinylidene fluoride) (PVDF) and PVDF-based polymers are widely used in sensors, actuators, energy harvesters, etc. In this review, the recent research progress on the PVDF phase structures and identification of different phases is outlined. Several approaches for obtaining the electroactive phase of PVDF and preparing PVDF-based nanocomposites are described. Furthermore, the potential applications of these materials in wearable sensors and human energy harvesters are discussed. Finally, some challenges and perspectives for improving the properties and boosting the applications of these materials are presented. [ABSTRACT FROM AUTHOR]