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Artificial peroxisomes (AP) with enzyme-mimetic catalytic activity and recruitment ability have drawn a great deal of attention in fabricating protocell systems for scavenging reactive oxygen species (ROS), modulating the inflammatory microenvironment, and reprogramming macrophages, which is of great potential in treating inflammatory diseases such as rheumatoid arthritis (RA). Herein, a macrophage membrane-cloaked Cu-coordinated polyphthalocyanine-based AP (CuAP) is prepared with a macrocyclic conjugated polymerized network and embedded Cu-single atomic active center, which mimics the catalytic activity and coordination environment of natural superoxide dismutase and catalase, possesses the inflammatory recruitment ability of macrophages, and performs photoacoustic imaging (PAI)-guided treatment. The results of both in vitrocellular and in vivoanimal experiments demonstrated that the CuAP under ultrasound and microbubbles could efficiently scavenge excess ROS in cells and tissues, modulate microenvironmental inflammatory cytokines such as interleukin-1β, tumor necrosis factor-α, and arginase-1, and reprogram macrophages by polarization of M1 (proinflammatory phenotype) to M2 (anti-inflammatory phenotype). We believe this study offers a proof of concept for engineering multifaceted AP and a promising approach for a PAI-guided treatment platform for RA.

Piezoceramics with global porosity and local compaction are highly desired to exploit the combination of mechanical and electrical properties. However, achieving such a functional combination is challenging because of the lack of techniques for applying uniform pressure inside porous ceramic green parts. Nature provides many examples of generating strong forces inside the macro and micro channels viathe state transformation of water. Inspired by these phenomena, we present a technique of “ice and fire”, that is, water freezing (ice pressing) and high-temperature sintering (fire), to produce ideal porous piezoceramics. We introduce a new compaction method called the “ice pressing method”, which manipulates liquid phase transition for compaction. This method has several advantages, including uniform pressure distribution, a wide pressure range, high effectiveness, and selective freezing. It can generate an ultrahigh pressure of up to 180 MPa on the piezoceramic green skeletons in minutes while retaining their functional pore structures. By exploiting the Mpemba phenomenon, we further accelerate the compaction procedure by 11%. The first ice-pressed and second fire-consolidated lead zirconate titanate (PZT) ceramics are highly densified and exhibit an outstanding piezoelectric response (d33= 531 pC N−1), comparable to conventional pressed bulk counterparts and 10–20 times higher than those of unpressed materials. The novel ice pressing method breaks the limitation of lacking a compaction technique for porous ceramics. The versatile and effective ice pressing method is a green and low-cost route promoting applications in sensors, acoustics, water filtration, catalyst substrates, and energy harvesting.

Enduring surface technologies draw much attention to improving friction performance and prolonging the lifespan of multi-alternative contact pairs. Laser surface texturing is smart to modify effectively the microscopic surface geometries and mechanical performances for the service's improvement of friction pair. This study explored the formation mechanisms and morphology evolution of hierarchical microtextures, with a focus on the thermal field and phase transformation resulting from the laser heating effect on the alloy surface. The controlling variates of laser machining were analyzed considering their influences on microtextures' height and diameter, the pulse numbers are 3 times and 1.7 times of the unit laser power, 81 times and 82.5 times of the unit pulse width. We contributed to the development of laser manufacturing techniques for creating hierarchical microtextures' controllable morphology and smart surface design for tribology engineering and energy management applications.

Improving the intrinsic film quality of metal halide perovskites is very critical to increase the power conversion efficiency and long-term stability of perovskite solar cells. Here we report a multifunctional, non-volatile additive that can be used to modulate the kinetics of perovskite film growth through a hydrogen-bond-bridged intermediate phase. The additive enables the formation of large perovskite grains and coherent grain growth from bottom to the surface of the film. The enhanced film morphology results in significantly reduced non-radiative recombinations, thus boosting the power conversion efficiency of inverted (p–i–n) solar cells to 24.8% (24.5% certified) with a low energy loss of 0.36 eV. The unencapsulated devices exhibit improved thermal stability with a T98lifetime beyond 1,000 h under continuous heating at 65 ± 5 °C in a nitrogen-filled glovebox. This effective approach can also be applied to wide-bandgap perovskites and large-area devices to show reduced voltage loss and high efficiency.

The human forearm is one of the most densely distributed parts of the human body, with the most irregular spatial distribution of muscles. A number of specific forearm muscles control hand motions. Acquiring high-fidelity sEMG signals from human forearm muscles is vital for human-machine interface (HMI) applications based on gesture recognition. Currently, the most commonly used commercial electrodes for detecting sEMG or other electrophysiological signals have a rigid nature without stretchability and cannot maintain conformal contact with the human skin during deformation, and the adhesive hydrogel used in them to reduce skin-electrode impedance may shrink and cause skin inflammation after long-term use. Therefore, developing elastic electrodes with stretchability and biocompatibility for sEMG signal recording is essential for developing HMI. Here, we fabricated a nanocomposite hybrid on-skin electrode by infiltrating silver nanowires (AgNWs), a one-dimensional (1D) nano metal material with conductivity, into polydimethylsiloxane (PDMS), a silicone elastomer with a similar Young’s modulus to that of the human skin. The AgNW on-skin electrode has a thickness of 300 μm and low sheet resistance of 0.481 ± 0.014 Ω/sq and can withstand the mechanical strain of up to 54% and maintain a sheet resistance lower than 1 Ω/sq after 1000 dynamic strain cycles. The AgNW on-skin electrode can record high signal-to-noise ratio (SNR) sEMG signals from forearm muscles and can reflect various force levels of muscles by sEMG signals. Besides, four typical hand gestures were recognized by the multichannel AgNW on-skin electrodes with a recognition accuracy of 92.3% using machine learning method. The AgNW on-skin electrode proposed in this study has great potential and promise in various HMI applications that employ sEMG signals as control signals.

Energy harvesters based on a piecewise linear system make it possible to extract more energy from environment vibrations. The amplitude truncation effect is a phenomenon of an energy harvester with a piecewise linear system. It shows a wider energy harvesting bandwidth and a lower voltage response than the purely linear counterpart. This work investigates the influence of spring length on the amplitude truncation effect and power density of electromagnetic energy harvesters. We first establish an analytical model of the piecewise linear system. Then, we apply the averaging method to explore the voltage responses in the frequency domain and compare the influence of various parameters. Later, we conduct a finite element simulation to analyze the voltage response at a constant frequency. The results obtained by the finite element simulation and averaging method match well with the experimental measurements. The experimental results demonstrate that the amplitude truncation effect is more visible at the shorter spring. Spring length plays a key role in the power density of an electromagnetic energy harvester. The case of 40 mm yields a maximum average power of 45.13 mW. The case of 30 mm displays a maximum power density of 2.35 mW/cm 3.

Piezoelectric shunt damping is promising in vibration suppression of thin structures. A Low-power direct adaptive synchronized switch damping on voltage (LDA-SSDV) circuit is designed to solve the stability problem of the SSDV without additional vibration strength monitoring devices. Based on the linear relationship between the maximum piezovoltage and the values of series voltage sources, we use simple envelope detectors and resistive voltage dividers to control the voltage sources. And the voltage sources are activated during the switching events for saving energy. The experimental results show that the LDA-SSDV circuit has a stable operation and similar vibration suppression level compared to SSDV.

Correction for ‘Exploring the Mpemba effect: a universal ice pressing enables porous ceramics’ by Xiaodan Yang et al., Mater. Horiz., 2024, DOI: https://doi.org/10.1039/d3mh01869e.

Piezoelectric materials enable emerging self-powered wearable and implantable devices. The sol–gel technology with the lowest cost for large-scale production has shown its potential for producing high-quality PZT thin films. However, fabricating PZT films with a sufficient thickness for different application scenarios requires a long and repeated coating and heat-treatment process. The traditional solution-based method usually requires at least 20 coating cycles to fabricate 2 μm-thick PZT thin films. To save cost and improve fabrication efficiency, we develop a simplified thin-film fabrication method assisted by PZT powder. The new method can fabricate 2 μm-thick PZT films in a single step, one spin coating and annealing. Experiments indicate that the powder-based PZT thin films have porous structures and outstanding piezoelectric performances. The measured d33of the powder-based PZT thin film is 47 pm/V. Both solution-based and powder-based PZT thin films show high flexibility and good fatigue resistance. Furthermore, we explore 2D mica as the substrate and achieve the transfer-free fabrication of flexible PZT thin-film nanogenerators that effectively simplify the complicated physical or chemical thin-film lift-off processes. The nanogenerator prototypes demonstrate the capability of accurately monitoring dynamic responses of flexible and soft human tissues.

Extensive efforts have been made to harvest energy from water in the form of raindrops1–6, river and ocean waves7,8, tides9and others10–17. However, achieving a high density of electrical power generation is challenging. Traditional hydraulic power generation mainly uses electromagnetic generators that are heavy, bulky, and become inefficient with low water supply. An alternative, the water-droplet/solid-based triboelectric nanogenerator, has so far generated peak power densities of less than one watt per square metre, owing to the limitations imposed by interfacial effects—as seen in characterizations of the charge generation and transfer that occur at solid–liquid1–4or liquid–liquid5,18interfaces. Here we develop a device to harvest energy from impinging water droplets by using an architecture that comprises a polytetrafluoroethylene film on an indium tin oxide substrate plus an aluminium electrode. We show that spreading of an impinged water droplet on the device bridges the originally disconnected components into a closed-loop electrical system, transforming the conventional interfacial effect into a bulk effect, and so enhancing the instantaneous power density by several orders of magnitude over equivalent devices that are limited by interfacial effects.

Harnessing abundant kinetic water energy in diverse forms of river flows, ocean waves, tidal currents, raindrops, and others, is highly attractive to ease the energy crisis and satisfy the demands of scattered sensor network nodes in the Internet of things. Among them, raindrops, widely and ubiquitously distributed in nature and ambient living life, have been extensively explored and regarded as significant renewable energy carriers. Extensive efforts have been made to investigate droplet‐based electricity nanogenerators in fundamental mechanism, performance, and applications for achieving sustainable energy demands of the rapidly developing society over the past decade. In this review, we introduce the remarkable progress in this field and discuss the fundamental mechanisms of droplet energy harvesting technology for achieving high‐power generation. More significantly, a systematic review of droplet energy harvesting in different two‐phase interfaces, including liquid–solid, liquid–liquid, and liquid–gas interfaces, is provided. Finally, this survey reveals that droplet‐based electricity generators present vast potential in the power supply. At the same time, several development challenges and prospective solutions are discussed to spur future technological advancements. Schematic of the large‐scale droplet energy harvesting devices in practice application. Water, droplet widely and ubiquitously distributed in nature and ambient living life, have been considered as one of the most potential candidates of sustainable power source due to its enormous energy. Extensive efforts have been made to investigate droplet‐based electricity nanogenerators in diverse aspects over the past decade. Therefore, comprehensively understanding the mechanism of energy conversion and different phase interface fundamentals is urgent, as well as revealing the further research trends for achieving sustainable energy demands of the rapidly developing society.

Optimal orthodontic forces need to be applied to induce appropriate biological and mechanical reactions in the periodontium, thus leading to proper tooth movements, while excessive orthodontic forces could harm the tooth roots and periodontal tissues during treatment. However, estimating orthodontic forces currently relies on clinical experience, lacking objective data and analysis; thus monitoring the in-vivo orthodontic force is essential to reducing side effects and improving orthodontic treatment. Unfortunately, in-vivo orthodontic force sensor systems are currently not available, and in-vitro ones are mostly bulky and costly. Here, we report a battery-free and wireless orthodontic force sensing system (BWS) designed for in-vivo, contactless, and real-time measurement of the orthodontic force. We developed a 915MHz far-field RF energy harvesting system to power the intraoral BWS, and achieved an in vivo wireless measurement distance of 220mm. This system allows in-vivo orthodontic force monitoring at anytime and anywhere, so it can be applied to improve clinical treatments and orthodontic research. Besides, in vivo experiments demonstrate that the system can harvest a voltage of 2V even at a 350mm distance, which highlights the device's potential to serve as a versatile platform for monitoring various oral environmental parameters through different sensors.

Freestanding lead-free piezoceramic thin films can be derived via water peeling. Thed33value of the freestanding BCZT thin film reaches 209 pm V−1. The freestanding piezoceramic films obtain versatile application scenarios such as energy harvest and virus detection.

Capillary‐enabled water energy harvesters (WEHs) are capable of generating direct‐current electricity continuously. However, active‐metal electrodes can introduce metal–air batteries in these WEHs. Given the nearly identical device structures and output characteristics of these two technologies, it is essential to distinguish between them. Herein, we present a systematic study of the water‐activated metal–air battery (WMB) through theoretical analyses and experimental verifications. We conclude the general formation rules of the WMB from a material and device‐structure perspective. Furthermore, we provide a comparative summary of various WEHs and WMBs for easy identification. We aim to improve the comprehension of metal–air batteries in the field of WEHs and assist in distinguishing between these technologies. Identification of metal–air batteries from water energy harvesters by electrode materials.

Energy harvesting holds great potential to achieve long-lifespan self-powered operations of wireless sensor networks, wearable devices, and medical implants, and thus has attracted substantial interest from both academia and industry. This paper presents a comprehensive review of piezoelectric energy-harvesting techniques developed in the last decade. The piezoelectric effect has been widely adopted to convert mechanical energy to electricity, due to its high energy conversion efficiency, ease of implementation, and miniaturization. From the viewpoint of applications, we are most concerned about whether an energy harvester can generate sufficient power under a variable excitation. Therefore, here we concentrate on methodologies leading to high power output and broad operational bandwidth. Different designs, nonlinear methods, optimization techniques, and harvesting materials are reviewed and discussed in depth. Furthermore, we identify four promising applications: shoes, pacemakers, tire pressure monitoring systems, and bridge and building monitoring. We review new high-performance energy harvesters proposed for each application.

Humans have evolved to walk highly efficiently to conserve energy, making it challenging to develop assistive and energy-harvesting devices for walking. Herein, we report a heel pad-based assistance device for walking that not only optimizes the energetic economy of walking and prevents plantar fasciitis but also harvests energy from heel impact. Our footwear-embedded device improves the walking economy by offering shock absorption and walking assistance, while simultaneously providing energy-harvesting functions. We demonstrate that the use of our device reduces the activation of the gastrocnemius and soleus muscles during the foot strike by 5.8 ± 1.0 % and 4.1 ± 0.6 %, respectively. The collisional energy conserved from the impact at the touchdown is transformed into 3.8 ± 0.3 watts of electrical power (mean ± SEM). Compared with walking in normal shoes, the energy savings with the device imply that walking endurance could be increased by as much as 10 % without extra effort from the wearer. Our findings demonstrate the potential of the heel pad-based device that enhances the energy economy of walking and human bipedal locomotion.

Energy harvesting is an essential technology for enabling low-power, maintenance-free electronic devices, and thus has attracted a great deal of attention in recent years. A variety of designs and approaches have been proposed to harvest ambient vibration energy, but crucial questions remain regarding figures of merit characterizing the performance of energy harvesters. Of primary importance is the energy conversion efficiency. There are large discrepancies in the definition and tested values of efficiency in the literature. This study is intended to answer the fundamental question for energy harvesters: how to define and calculate the energy conversion efficiency. We first review studies on efficiency and analyze the energy flow in an energy harvesting system. Based on the analysis, we derive an efficiency expression for linear cantilever energy harvesters. The developed efficiency expression transparently and quantitatively reveals the relationship between efficiency and key parameters. Experiments are performed to validate the efficiency expression. Furthermore nonlinear energy harvesters are tested in both on-resonance and off-resonance conditions. Both experimental and theoretical studies manifest that the energy conversion efficiency tends to decrease as the excitation frequency rises and its value is related to the phase difference between excitations and responses. Around resonance states where the phase difference of both linear and nonlinear energy harvesters is about 90 degrees, the efficiency calculation is much simplified.

Although the crystal phase of two-dimensional (2D) transition metal dichalcogenides (TMDs) has been proven to play an essential role in fabricating high-performance electronic devices in the past decade, its effect on the performance of 2D material-based flash memory devices still remains unclear. Here, we report the exploration of the effect of MoTe2in different phases as the charge-trapping layer on the performance of 2D van der Waals (vdW) heterostructure-based flash memory devices, where a metallic 1T′-MoTe2or semiconducting 2H-MoTe2nanoflake is used as the floating gate. By conducting comprehensive measurements on the two kinds of vdW heterostructure-based devices, the memory device based on MoS2/h-BN/1T′-MoTe2presents much better performance, including a larger memory window, faster switching speed (100 ns), and higher extinction ratio (107), than that of the device based on the MoS2/h-BN/2H-MoTe2heterostructure. Moreover, the device based on the MoS2/h-BN/1T′-MoTe2heterostructure also shows a long cycle (>1200 cycles) and retention (>3000 s) stability. Our study clearly demonstrates that the crystal phase of 2D TMDs has a significant impact on the performance of nonvolatile flash memory devices based on 2D vdW heterostructures, which paves the way for the fabrication of future high-performance memory devices based on 2D materials.

Bistable nonlinear energy harvesters are effective structures for scavenging broadband energy from frequency-varying vibration sources. The bistable characteristic of such structures is typically induced by introducing magnetic fields, prestress, and nonuniform geometries or fixtures. However, the complicated structures or single deformation modes of these structures limit their practical application. Inspired by the structure of soybean pods, a bionic metallic nanomaterial-based bistable piezoelectric energy harvester is developed in this study. The nanoplate substrate with a local bistable region mimics the configuration of a soybean pod. To the best of the authors’ knowledge, the local bistable configuration represents a novel energy harvesting strategy. The local bistable nanoplate is fabricated using a mature surface mechanical attrition treatment technique that generates a gradient nanostructure to enhance the mechanical properties of the bistable structure. The energy harvesting performance and nonlinear dynamic characteristics of the energy harvester are evaluated through frequency-sweep and fixed-frequency vibration tests and numerical simulations with a new two-step finite element (FE) model. The harvester characteristics in three vibration modes (single-well vibration (SV), intermittent cross-well vibration (ICV), and continuous cross-well vibration (CCV)) are discussed. The experimental and numerical results demonstrate that the voltage output and working bandwidth of the proposed harvester increase by five times in the ICV and CCV modes when the excitation acceleration increases from 0.5 gto 3.0 g. The bionic nanomaterial-based bistable piezoelectric energy harvester can be potentially used in various applications such as vehicle suspension systems, tires, and vehicle-bridge systems.

The growth of high-quality single-crystalline Te nanobelts is reported by introducing atomically flat hexagonal boron nitride (h-BN) nanoflakes into the chemical vapor deposition system as the growth substrate.The field-effect transistor based on Te grown on h-BN exhibits an ultrahigh hole mobility up to 1370 cm2V−1s−1at room temperature.

Extensive work have been done to harvest untapped water energy in formats of raindrops, flows, waves, and others. However, attaining stable and efficient electricity generation from these low-frequency water kinetic energies at both individual device and large-scale system level remains challenging, partially owing to the difficulty in designing a unit that possesses stable liquid and charge transfer properties, and also can be seamlessly integrated to achieve preferential collective performances without the introduction of tortuous wiring and redundant node connection with external circuit. Here, we report the design of water electricity generators featuring the combination of lubricant layer and transistor-like electrode architecture that endows enhanced electrical performances in different working environments. Such a design is scalable in manufacturing and suitable for facile integration, characterized by significant reduction in the numbers of wiring and nodes and elimination of complex interfacing problems, and represents a significant step toward large-scale, real-life applications.

Previous droplet-based electricity generator has made breakthroughs in efficient water energy harvesting through taking advantage of the contact electrification, however, the kinetic energy of water remains to be tapped into. In this work, we develop a leaf-mimic rain energy harvester (REH) that allows for the collection of electrostatic and kinetic energy simultaneously based on the synergy of the liquid-solid contact electrification and the piezoelectric effect. Impinged by a water droplet, the REH generates a boosted transferred charge value (101 nC) and high output power density (82.66 W m−2). We also show that such performances enable the construction of self-charged wireless sensor systems with continuous operational capability. The REH is also low-cost and facile for fabrication, paving a new way towards high-efficiency power generation from raindrops as well as other water sources.

Wrist-worn smart devices such as smartwatches and wristbands are rapidly penetrating our daily life for health, security and fashion purposes. However, the battery-powered wearables have a limited lifetime and need to be frequently recharged, which degrades user experience and further poses environmental problems. Inspired by the structure of the woodpecker’s head, this paper reports a bionic two-layer band piezoelectric energy harvester for self-powered smartwatches and wristbands. An inner band and an outer band of the harvester mimic two branches of the hyoid bone of the woodpecker. The energy harvesting unit employs a piezoelectric array structure. A finite element analysis is conducted to identify the optimal positions of piezoelectric patches in the array and an improved rectifier circuit is developed to manage the multiple AC inputs. We design two operation modes, i.e., movement mode and impact mode, to accommodate energy harvesters in different human activities. A maximum power output of 15.41 mW is achieved in experiments when tapping the prototype, corresponding to an equivalent power density of 1049.01 μW/cm3, around five times higher than previous wrist-worn harvesters. The design demonstrates its capability of continuously powering a watch and a screen during a normal walking process. The concept of shifting from the watch body to watch bands provides the design of energy harvesters a larger space and higher user-friendliness, which, fused with the piezoelectric array method, shows the potential to merge the gap of the power generation of energy harvesters and the power consumption of wrist wearables.

As a typical ferroelectric material, the PbZr1−xTixO3(PZT) thin film with a homogeneous component has drawn extensive attention to the application in self-powered flexible electronics. The design of compositionally graded PZT thin films (i.e. artificially control the Zr/Ti ratio in different compositional layers in one film) has shown its immense potentials due to some novel phenomena induced by strain gradient, such as the shifted hysteresis loop, generation of the built-in electric field, enhancement in the motion of domain wall. However, the effect of the compositionally graded heterostructure on the piezoelectric response and its performance on the device level has seldom been investigated. To fill this knowledge gap, we prepare PZT thin films with the compositionally graded structure and based on that, fabricate flexible piezoelectric nanogenerators (PENGs). Furthermore, we explore the 2D mica as the substrate of PENGs and avoid the commonly used costly and troublesome laser-lifting or etching transfer procedure. The PENG prototypes integrated with 1 µm thick PZT films are flexible, translucent, and show high electric responses under different mechanical stimuli. Experiments indicate that up-graded PZT films, of which Zr composition varies from 20% near the bottom to 80% at the top, outperforms the down-graded counterpart. The up-graded PENG achieves a maximum voltage response of 2 V and a current density of 10.0 μA/cm2when bent by 90°. This work demonstrates that the strain-tuned compositionally graded structure is an effective approach to improve the PENG performance.

In this article, we report a wearable millimeter-size energy generator that yields instantaneous power of 2.1 W level from kinetic energy of human running motions. The generator, with a hybridization of piezoelectric and electromagnetic transductions, integrates mainly two major novel techniques: impact induced frequency up conversion effect for the piezoelectric generation and abrupt magnetic flux density change for the electromagnetic generation. The generator proves to be able to effectively harness energy from human motions, producing a power density over one order of magnitude higher than that of state-of-the-art work. This result is further validated by the charging performance, i.e. high charging rate and voltage into mF-level capacitors. Moreover, this wearable generator demonstrates the capability to charge a Li-on battery in dozens of minutes. This work can be of much significance for the development of self-charging battery powered wearable electronic devices.

Sensors that provide critical information about jet engine performance are widely installed on static components but are rarely found on rotors because of their inaccessibility and extremely high rotation speeds. We present a new monitoring method, integrating energy harvesting technology with wireless sensors to achieve real-time self-powered engine monitoring. Energy harvesters, used to generate power from ambient vibration, are sustainable alternatives to batteries for achieving self-sustained long-term operation of electronic devices. By utilising structural nonlinearity, force amplification mechanism, and the piezoelectric effect, we show a 22.52-g energy harvester capable of high power output (78.87 mW), broad working bandwidth (22.5 Hz), and strong reliability (2100 RPM). Our approach breaks limitations from wired connections that are weighty and vulnerable to failures. We theoretically and experimentally analyse the nonlinear responses and demonstrate the harvester by constantly lighting 112 LEDs and a self-powered wireless sensor system in a jet engine. This work paves a new way for developing future monitoring systems for advanced jet engines and other rotating machinery applications.

Energy harvesting in uniflow fluid environment aims at ambient energy that can be used in water environment for monitor equipment. In this paper, we focus on coupling both bending vibration and torsional vibration to gain better power generation. A novel structure of energy converter(arc-shaped) was designed and manufactured. Meanwhile the influence of vibrator with and without a pelvic fin was tested. Mathematical analyse due to vibration phenomenon and experimental result are reported. The 270-degree arc-shaped ring size piezoelectric ceramic is verified capable of producing an effective voltage over 10 V with the power of 0.5 mW.