Tailored Poly(vinylidene fluoride-co-trifluoroethylene) Crystal Orientation for a Triboelectric Nanogenerator through Epitaxial Growth on a Chitin Nanofiber Film

Self-Powered Pressure-Temperature Bimodal Sensing Based on the Piezo-Pyroelectric Effect for Robotic Perception

Multifunctional sensors have played a crucial role in constructing high-integration electronic networks. Most of the current multifunctional sensors rely on multiple materials to simultaneously detect different physical stimuli. Here, we demonstrate the large piezo-pyroelectric effect in ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) single crystals for simultaneous pressure and temperature sensing. The outstanding piezoelectric and pyroelectric properties of PMN-PT result in rapid response speed and high sensitivity, with values of 46 ms and 28.4 nA kPa-1 for pressure sensing, and 1.98 s and 94.66 nC °C-1 for temperature detection, respectively. By leveraging the distinct differences in the response speed of piezoelectric and pyroelectric responses, the piezo-pyroelectric effect of PMN-PT can effectively detect pressure and temperature from mixed-force thermal stimuli, which enables a robotic hand for stimuli classification. With appealing multifunctionality, fast speed, high sensitivity, and compact structure, the proposed self-powered bimodal sensor therefore holds significant potential for high-performance artificial perception.

Preparation of Chitin Nanofibers and Natural Rubber Composites and Their Triboelectric Nanogenerator Applications

Triboelectric nanogenerators (TENGs) have gained significant attention as promising energy-harvesting devices that convert mechanical energy into electrical energy through charge separation induced by friction and electrostatic induction. In this study, we explore the utilization of biowaste shrimp shell-extracted chitin nanofiber (ChNF) as a viable eco-friendly material for TENG applications. Composite materials were prepared by incorporating ChNF into natural rubber (NRL) at loading levels of 0.1 and 0.2 wt% (NRL/ChNF) to form the TENG triboelectric layer. ChNFs with a uniform width of approximately 10-20 nm were successfully extracted from the shrimp shells through a simple mechanical procedure. The NRL/ChNF composites exhibited enhanced mechanical properties, as evidenced by a higher Young's modulus (3.4 GPa) compared to pure NRL. Additionally, the NRL/ChNF composites demonstrated an increased dielectric constant of 3.3 at 0.1 MHz. Moreover, the surface potential difference of NRL increased from 0.182 V to 1.987 V in the NRL/ChNF composite. When employed as the triboelectric layer in TENG, the NRL/ChNF composites exhibited significant improvement in their output voltage, with it reaching 106.04 ± 2.3 V. This enhancement can be attributed to the increased dielectric constant of NRL/ChNF, leading to enhanced charge exchange and charge density. This study presents a straightforward and environmentally friendly technique for preparing sustainable natural materials suitable for energy-harvesting devices.

Outstanding Synergy of Sensitivity and Linear Range Enabled by Multigradient Architectures

Flexible pressure sensors are devices that mimic the sensory capabilities of natural human skin and enable robots to perceive external stimuli. One of the main challenges is maintaining high sensitivity over a broad linear pressure range due to poor structural compressibility. Here, we report a flexible pressure sensor with an ultrahigh sensitivity of 153.3 kPa-1 and linear response over an unprecedentedly broad pressure range from 0.0005 to 1300 kPa based on interdigital-shaped, multigradient architectures, featuring modulus, conductivity, and microstructure gradients. Such multigradient architectures and interdigital-shaped configurations enable effective stress transfer and conductivity regulation, evading the pressure sensitivity-linear range trade-off dilemma. Together with high pressure resolution, high frequency response, and good reproducibility over the ultrabroad linear range, proof-of-concept applications such as acoustic wave detection, high-resolution pressure measurement, and healthcare monitoring in diverse scenarios are demonstrated.

Piezoelectric materials for neuroregeneration: a review

The purpose of nerve regeneration via tissue engineering strategies is to create a microenvironment that mimics natural nerve growth for achieving functional recovery. Biomaterial scaffolds offer a promising option for the clinical treatment of large nerve gaps due to the rapid advancement of materials science and regenerative medicine. The design of biomimetic scaffolds should take into account the inherent properties of the nerve and its growth environment, such as stiffness, topography, adhesion, conductivity, and chemical functionality. Various advanced techniques have been employed to develop suitable scaffolds for nerve repair. Since neuronal cells have electrical activity, the transmission of bioelectrical signals is crucial for the functional recovery of nerves. Therefore, an ideal peripheral nerve scaffold should have electrical activity properties similar to those of natural nerves, in addition to a delicate structure. Piezoelectric materials can convert stress changes into electrical signals that can activate different intracellular signaling pathways critical for cell activity and function, which makes them potentially useful for nerve tissue regeneration. However, a comprehensive review of piezoelectric materials for neuroregeneration is still lacking. Thus, this review systematically summarizes the development of piezoelectric materials and their application in the field of nerve regeneration. First, the electrical signals and natural piezoelectricity phenomenon in various organisms are briefly introduced. Second, the most commonly used piezoelectric materials in neural tissue engineering, including biocompatible piezoelectric polymers, inorganic piezoelectric materials, and natural piezoelectric materials, are classified and discussed. Finally, the challenges and future research directions of piezoelectric materials for application in nerve regeneration are proposed.

Emerging Trends in Soft Electronics: Integrating Machine Intelligence with Soft Acoustic/Vibration Sensors

In the last decade, soft acoustic/vibration sensors have gained tremendous research interest due to their unique ability to detect broadband acoustic/vibration stimuli, potentializing futuristic applications including voice biometrics, voice-controlled human-machine-interfaces, electronic skin, and skin-mountable healthcare devices. Importantly, to benefit most from these sensors, it is inevitable to use machine learning (ML) to process their output signals; with ML, a more accurate and efficient interpretation of original data is possible. This paper is dedicated to offering an overview of recent advances empowering the development of soft acoustic/vibration sensors and their signal processing using ML. First, the key performance parameters of the sensors are discussed. Second, popular transduction mechanisms for the sensors are addressed, followed by an in-depth overview of each type, covering materials used, structural designs, and sensing performances. Third, potential applications of the sensors are elaborated and fourth, a thorough discussion on ML is conducted, exploring different types of ML, specific ML algorithms suitable for processing acoustic/vibration signals, and current trends in ML-assisted applications. Finally, the challenges and potential opportunities in soft acoustic/vibration sensor and ML research are revealed to offer new insights into future prospects in these fields.

Flexible, Wash-Resistant Human Mechanical Energy Harvesting and Storage System for Monitoring Human Movement

The rapid development of personal portable electronic devices has brought an increasingly urgent need for flexible and portable power sources. Herein, a low-cost, wearable, efficient, sustainable energy harvesting and storage system for human motion detection has been developed, based on a supercapacitor (SC) and triboelectric nanogenerator (TENG). Carbon cloth (CC)-loaded ZnO/ZnS nanoarrays and a PVD-treated polyurethane conductive sponge are employed as positive and negative triboelectric friction layers, respectively. Besides, flexible and robust silicone rubber provides stable output performance and enables the TENG to harvest mechanical energy from human motion even under complex conditions. As a result, it shows excellent electrical output performance in terms of the open-circuit voltage, short-circuit current, and average power density, reaching 175 V, 12 μA, and 816.7 mW m^-2, respectively. These outstanding performances enable the TENG to effectively charge an all-solid-state symmetrical SC (MnO₂/LiMn₂O₄@CC//MnO₂/LiMn₂O₄@CC) and subsequently store it as electrochemical energy for sustainable power supply. Because of the flexible all-texture-type structure of the entire system, it is capable of monitoring the human body's movement. This work has a promising future in random mechanical energy harvesting and storage, as well as human motion tracking.

Modulus-Modulated All-Organic Core-Shell Nanofiber with Remarkable Piezoelectricity for Energy Harvesting and Condition Monitoring

The low piezoelectricity of piezoelectric polymers significantly restricts their applications. Introducing inorganic fillers can slightly improve the piezoelectricity of polymers, whereas it is usually at the cost of flexibility and durability. In this work, using a modulus-modulated core-shell structure strategy, all-organic nanofibers with remarkable piezoelectricity were designed and prepared by a coaxial electrospinning method. It was surprisingly found that the introduction of a nonpiezoelectric polymeric core (e.g., polycarbonate, PC) can result in 110% piezoelectric coefficient (d₃₃) enhancement in a poly(vinylidenefluoride-co-trifluoroethylene) (PVDF-TrFE) nanofiber. Accordingly, the all-organic PVDF-TrFE@PC core-shell nanofiber exhibits record-high energy-harvesting performance (i.e., 126 V output voltage, 710 mW m^-2 power density) among the reported organic piezoelectric materials. In addition, the excellent sensing capability of the core-shell nanofiber enabled us to develop a wireless vibration monitoring and analyzing system, which realizes the real-time vibration detection of a power transformer.

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.

High-Efficiency Poly(Vinylidene Fluoride-Co-Hexafluoropropylene) Loaded 3D Marigold Flower-Like Bismuth Tungstate Triboelectric Films for Mechanical Energy Harvesting and Sensing Applications

Triboelectric nanogenerators (TENGs) are one of the most trending energy harvesting devices because of their efficient and simple mechanism in harvesting mechanical energy from the environment into electricity. Herein, ferroelectric and dielectric bismuth tungstate (Bi₂ WO₆ (BWO)) with a marigold flower-like structure is prepared via a hydrothermal method, which is embedded in poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), forming a PVDF-HFP/BWO composite polymer film (CPF) to fabricate TENGs. Generally, the ferroelectric materials exhibit a large piezoelectric coefficient, high electrostatic dipole moment, and high dielectric constant. The prepared PVDF-HFP/BWO CPF reveals a high polar crystalline β-phase which leads to enhanced piezoelectric and ferroelectric properties of the CPF, thus resulting in the increased electrical performance of the fabricated TENG. The electrical output performance of the proposed TENG is systematically investigated by varying the amount of BWO material embedded in the PVDF-HFP polymer. The fabricated PVDF-HFP/2.5 wt% BWO CPF-based TENG device exhibits the highest electrical output performance. Additionally, the robust test of the TENG device is conducted to investigate the electrical performance for long-term durability and mechanical stability. Finally, the proposed TENG is operated as a self-powered sensor, harvesting mechanical energy from daily life human activities, and powering various low-power portable electronics.

An ultra high performance, lead-free Bi2WO6:P(VDF-TrFE)-based triboelectric nanogenerator for self-powered sensors and smart electronic applications

Obtaining sustainable, high output power supply from triboelectric nanogenerators still remains a major issue that restricts their widespread use in self-powered electronic applications. In this work, an ultra-high performance, non-toxic, flexible triboelectric nanogenerator based on bismuth tungstate (Bi₂WO₆):polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE)) is fabricated. A hydrothermal technique is used to synthesize highly crystalline Bi₂WO₆ nanoparticles that are then incorporated inside the P(VDF-TrFE) matrix nanofiber mat using electrospinning over an aluminum-coated PET substrate to yield a nanogenerator with a device configuration of Cu-coated PET/(Bi₂WO₆:P(PVDF-TrFE)) nanofiber mat/Al-coated PET. The highly crystalline nature of the biconcave shaped Bi₂WO₆ nanoparticles and β - P(VDF-TrFE) is confirmed by X-ray powder diffraction (XRD) and Raman spectroscopic techniques. The dielectric constant of the Bi₂WO₆:P(PVDF-TrFE) nanofiber mat was studied and a high dielectric constant of 44 was observed. The as-fabricated nanogenerator delivers a very high output voltage (open circuit) of 205 V and current density (short circuit) of 11.91 mA m^-2 at ∼0.15 kgf without any electric poling, which is higher than all the prior reports in this field. The fabricated nanogenerator possesses very high output stability and ultra-sensitivity with a swift response time of 60 ms. This outstanding performance of the nanogenerator can be ascribed to the synergistic combination of the β-phase P(VDF-TrFE) polymer and non-centrosymmetric nature of Bi₂WO₆ nanoparticles. Furthermore, a Bi₂WO₆-based pH sensor is driven by the energy obtained from the as-fabricated nanogenerator and the real time demonstration of the nanogenerator powering a calculator is also demonstrated. The strategy outlined here presents a cost-effective, high performance alternative for driving various portable bio-compatible self-powered electronic devices.

Fluorinated Graphene-Enabled Durable Triboelectric Coating for Water Energy Harvesting

The durability issue of triboelectric nanogenerators (TENGs) still limits its practical application for long-term operation, especially in harvesting water energy, which is one of the most widespread energies in nature. Attempting to ameliorate this, fluorinated graphene (FG) with unique triboelectric negativity and superhydrophobic property is introduced to serve as a new triboelectric and protective layer for TENG construction. The self-cleaning as well as anti-corrosion property and durability of the FG coating-enabled TENG device is then demonstrated. Furthermore, this novel triboelectronegative material candidate is applied for consecutively coating on Cu mesh and the inner wall of sewage pipe to fabricate TENGs for water energy harvesting and working as a metal protective layer in the meantime. Through the extraordinary output performance, the feasibility of FG-enabled triboelectric coating to be used in the field of interference screening, filtering, and sewage pipes is proved. This developed triboelectronegative coating not only broadens the material selection of TENG but also significantly enhances the durability and robustness of TENG for water energy harvesting, which possesses great potential in applying in metal protection and water energy harvesting under extreme conditions (e.g., strong acid and strong alkaline environments).