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Abstract The intriguing biomineralization process in nature endows the mineralized biological materials with intricate microarchitected structures in a facile and orderly way, which provides an inspiration for processing ceramics. Here, we propose a simple and efficient manufacturing process to fabricate cellular ceramics in programmed cell-based 3D configurations, inspired by the biomineralization process of the diatom frustule. Our approach separates the ingredient synthesis from architecture building, enabling the programmable manufacturing of cellular ceramics with various cell sizes, geometries, densities, metastructures, and constituent elements. Our approach exploits surface tension to capture precursor solutions in the architected cellular lattices, allowing us to control the liquid geometry and manufacture cellular ceramics with high precision. We investigate the geometry parameters for the architected lattices assembled by unit cells and unit columns, both theoretically and experimentally, to guide the 3D fluid interface creation in arranged configurations. We manufacture a series of globally cellular and locally compact piezoceramics, obtaining an enhanced piezoelectric constant and a designed piezoelectric anisotropy. This bioinspired, surface tension-assisted approach has the potential to revolutionize the design and processing of multifarious ceramic materials for structural and functional applications in energy, electronics and biomedicine.

Abstract The rapid-developing soft robots and wearable devices require flexible conductive materials to maintain electric functions over a large range of deformations. Considerable efforts are made to develop stretchable conductive materials; little attention is paid to the frequent failures of integrated circuits caused by the interface mismatch of soft substrates and rigid silicon-based microelectronics. Here, we present a stretchable solder with good weldability that can strongly bond with electronic components, benefiting from the hierarchical assemblies of liquid metal particles, small-molecule modulators, and non-covalently crosslinked polymer matrix. Our self-solder shows high conductivity (>2×105 S m−1), extreme stretchability (~1000%, and >600% with chip-integrated), and high toughness (~20 MJ m−3). Additionally, the dynamic interactions within our solder’s surface and interior enable a range of unique features, including ease of integration, component substitution, and circuit recyclability. With all these features, we demonstrated an application as thermoforming technology for three-dimensional (3D) conformable electronics, showing potential in reducing the complexity of microchip interfacing, as well as scalable fabrication of chip-integrated stretchable circuits and 3D electronics.

Abstract Nanoparticles, films, and patterns are three critical piezoelectric elements with widespread applications in sensing, actuations, catalysis and energy harvesting. High productivity and large-area fabrication of these functional elements is still a significant challenge, let alone the control of their structures and feature sizes on various substrates. Here, we report a fast and versatile electrostatic disc microprinting, enabled by triggering the instability of liquid-air interface of inks. The printing process allows for fabricating lead zirconate titanate free-standing nanoparticles, films, and micro-patterns. The as-fabricated lead zirconate titanate films exhibit a high piezoelectric strain constant of 560 pm V−1, one to two times higher than the state-of-the-art. The multiplexed tip jetting mode and the large layer-by-layer depositing area can translate into depositing speeds up to 109 μm3 s−1, one order of magnitude faster than current techniques. Printing diversified functional materials, ranging from suspensions of dielectric ceramic and metal nanoparticles, to insulating polymers, to solutions of biological molecules, demonstrates the great potential of the electrostatic disc microprinting in electronics, biotechnology and beyond.

Abstract 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.

Abstract Piezoelectric biomaterials have attracted great attention owing to the recent recognition of the impact of piezoelectricity on biological systems and their potential applications in implantable sensors, actuators, and energy harvesters. However, their practical use is hindered by the weak piezoelectric effect caused by the random polarization of biomaterials and the challenges of large-scale alignment of domains. Here, we present an active self-assembly strategy to tailor piezoelectric biomaterial thin films. The nanoconfinement-induced homogeneous nucleation overcomes the interfacial dependency and allows the electric field applied in-situ to align crystal grains across the entire film. The β-glycine films exhibit an enhanced piezoelectric strain coefficient of 11.2 pm V−1 and an exceptional piezoelectric voltage coefficient of 252 × 10−3 Vm N−1. Of particular significance is that the nanoconfinement effect greatly improves the thermostability before melting (192 °C). This finding offers a generally applicable strategy for constructing high-performance large-sized piezoelectric bio-organic materials for biological and medical microdevices.

Highlights Freestanding lead-free piezoceramic thin films can be derived via water peeling. The d 33 value 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.

Anthropogenetic environmental deterioration and climate change caused by energy production and consumption pose a significant threat to the future of humanity. Renewable, environmentally friendly, and cost-effective energy sources are becoming increasingly important for addressing future energy demands. Mechanical power is the most common type of external energy that can be converted into useful electric power. Because of its strong electromechanical coupling ability, the piezoelectric mechanism is a far more successful technique for converting mechanics energy to electrical energy when compared to electrostatic, electromagnetic, and triboelectric transduction systems. Currently, the scientific community has maintained a strong interest in piezoelectric micro-power generators because of their great potential for powering a sensor unit in the distributed network nodes. A national network usually has a large mass of sensor units distributed in each city, and a self-powered sensor network is eagerly required. This paper presents a comprehensive review of the development of piezoelectric micro-power generators. The fundamentals of piezoelectric energy conversion, including operational modes and working mechanisms, are introduced. Current research progress in piezoelectric materials including zinc oxide, ceramics, single crystals, organics, composite, bio-inspired and foam materials are reviewed. Piezoelectric energy harvesting at the nano- and microscales, and its applications in a variety of fields such as wind, liquid flow, body movement, implantable and sensing devices are discussed. Finally, the future development of multi-field coupled, hybrid piezoelectric micropower generators and their potential applications are discussed.

Abstract 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.

The decay of electrostatic charges largely reduces the protective efficacy of electret masks. Here, the authors report a triboelectrification-based self-charging electrostatic face mask with high airborne particle capture efficiency and prolonged stability.

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.

Abstract The lack of stable p-type van der Waals (vdW) semiconductors with high hole mobility severely impedes the step of low-dimensional materials entering the industrial circle. Although p-type black phosphorus (bP) and tellurium (Te) have shown promising hole mobilities, the instability under ambient conditions of bP and relatively low hole mobility of Te remain as daunting issues. Here we report the growth of high-quality Te nanobelts on atomically flat hexagonal boron nitride (h-BN) for high-performance p-type field-effect transistors (FETs). Importantly, the Te-based FET exhibits an ultrahigh hole mobility up to 1370 cm2 V−1 s−1 at room temperature, that may lay the foundation for the future high-performance p-type 2D FET and metal–oxide–semiconductor (p-MOS) inverter. The vdW h-BN dielectric substrate not only provides an ultra-flat surface without dangling bonds for growth of high-quality Te nanobelts, but also reduces the scattering centers at the interface between the channel material and the dielectric layer, thus resulting in the ultrahigh hole mobility .

Fabricating geometrically complex piezoceramics in compact sintered bodies has been difficult to achieve. Here the authors demonstrate a gravity-driven sintering strategy where high-temperature viscous behavior of piezoceramic allows for forming of complex shaped sintered bodies.

Abstract Wearing masks has been a recommended protective measure due to the risks of coronavirus disease 2019 (COVID‐19) even in its coming endemic phase. Therefore, deploying a “smart mask” to monitor human physiological signals is highly beneficial for personal and public health. This work presents a smart mask integrating an ultrathin nanocomposite sponge structure‐based soundwave sensor (≈400 µm), which allows the high sensitivity in a wide‐bandwidth dynamic pressure range, i.e., capable of detecting various respiratory sounds of breathing, speaking, and coughing. Thirty‐one subjects test the smart mask in recording their respiratory activities. Machine/deep learning methods, i.e., support vector machine and convolutional neural networks, are used to recognize these activities, which show average macro‐recalls of ≈95% in both individual and generalized models. With rich high‐frequency (≈4000 Hz) information recorded, the two‐/tri‐phase coughs can be mapped while speaking words can be identified, demonstrating that the smart mask can be applicable as a daily wearable Internet of Things (IoT) device for respiratory disease identification, voice interaction tool, etc. in the future. This work bridges the technological gap between ultra‐lightweight but high‐frequency response sensor material fabrication, signal transduction and processing, and machining/deep learning to demonstrate a wearable device for potential applications in continual health monitoring in daily life.

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.

Abstract Piezoceramic films are an essential class of energy‐conversion materials that have been widely used in the electronics industry. Although current methods create a great freedom for fabricating high‐quality piezoceramic films, it requires well‐controlled synthesis conditions, including special high‐cost equipment and planar substrates particularly. The limited substrate selections hinder the applications of piezoceramic films in 3D conformal structures where most objects possess complex curvilinear surfaces. To overcome such limitations, a fast, energy‐efficient, and cost‐effective approach, named flame treated spray (FTS) coating, is developed for preparing piezoceramic films on free‐form surfaces. The flame treatment significantly enhances the hydrophilicity of a substrate, assisting in forming a uniform and continuous thin film. The followed spray coating deposits hundreds of nanometers to several micrometers thick films on 3D free‐form surfaces. Given the size controllability and arbitrary surface compatibility of the FTS method, a highly conformal piezoelectric tactile sensor array (4 × 4) is assembled on a spherical surface for mimicking robot fingers and an on‐site thin‐film sensor on the wing of an aircraft model to monitor the vibration in real‐time during flight. The FTS film deposition offers a highly promising methodology for the application of functional thin‐film from micro‐ to marcoscale devices, regardless of conformal problems.

In this paper, we present a simple metasurface based multiband reflective polarization converter for both linear and circular polarizations. We show that, on one hand, the proposed structure can convert the polarization of linearly polarized waves to the orthogonal direction at four frequency bands — 4.3 GHz, 7.2 GHz, 12.3 GHz, and 15.15 GHz. On the other hand, this metasurface can achieve linear to circular or circular to linear polarization conversion at 4 GHz, 4.75–5.95 GHz, 8.35–8.8 GHz and 14.35–14.6 GHz frequency bands. Such multiband operation originates from multiple resonances occurring in the structure based on meandered square ring and diagonal split strip resonator. Moreover, the polarization transforming capability is stable for oblique incident angle up to $15^{o}$ , for both transverse electric (TE) and transverse-magnetic (TM) polarizations. Furthermore, the proposed structure acts as a meta-reflector that maintains the handedness of the circular polarization upon reflection. Finally, a prototype of the proposed meta-structure is fabricated and measured for both normal and oblique incidence of electromagnetic waves. All the results present excellent resonant stability with respect to the different polarization and incident angles. In addition, we have also performed the tolerance analysis of different material parameters to understand the robustness of the structure. Due to the ability of the structure to perform three functionalities through a single layout, the proposed design can pave its way in different microwave applications such as satellite, radar, and 5G communications.

Vortex-induced vibration (VIV) is used by piezoelectric energy harvesters to generate electricity from wind and water flow. In this study, we introduce the nonlinear magnetic force into piezoelectric energy harvesters and develop a nonlinear monostable piezoelectric VIV transducer. We build a distributed-parameter model based on the Euler-Bernoulli beam theory and Kirchhof's law to analyze the dynamic responses of the magnetic-coupling piezoelectric energy harvester (MCPEH). Model results show that the performance of the MCPEH varies greatly with the increase of the load resistance and the length of the used PZT. There are two optimal resistance values for the MCPEH. When $R

Dental caries and traumatic injuries to teeth may cause irreversible inflammation and eventual death of the dental pulp. Nevertheless, predictably, repair and regeneration of the dentin-pulp complex remain a formidable challenge. In recent years, smart multifunctional materials with antimicrobial, anti-inflammatory, and pro-regenerative properties have emerged as promising approaches to meet this critical clinical need. As a unique class of smart materials, piezoelectric materials have an unprecedented advantage over other stimuli-responsive materials due to their inherent capability to generate electric charges, which have been shown to facilitate both antimicrobial action and tissue regeneration. Nonetheless, studies on piezoelectric biomaterials in the repair and regeneration of the dentin-pulp complex remain limited. In this review, we summarize the biomedical applications of piezoelectric biomaterials in dental applications and elucidate the underlying molecular mechanisms contributing to the biological effect of piezoelectricity. Moreover, we highlight how this state-of-the-art can be further exploited in the future for dental tissue engineering.

Abstract Real‐time detection and differentiation of diverse external stimuli with one tactile senor remains a huge challenge and largely restricts the development of electronic skins. Although different sensors have been described based on piezoresistivity, capacitance, and triboelectricity, and these devices are promising for tactile systems, there are few, if any, piezoelectric sensors to be able to distinguish diverse stimuli in real time. Here, a human skin‐inspired piezoelectric tactile sensor array constructed with a multilayer structure and row+column electrodes is reported. Integrated with a signal processor and a logical algorithm, the tactile sensor array achieves to sense and distinguish the magnitude, positions, and modes of diverse external stimuli, including gentle slipping, touching, and bending, in real time. Besides, the unique design overcomes the crosstalk issues existing in other sensors. Pressure sensing and bending sensing tests show that the proposed tactile sensor array possesses the characteristics of high sensitivity (7.7 mV kPa−1), long‐term durability (80 000 cycles), and rapid response time (10 ms) (less than human skin). The tactile sensor array also shows a superior scalability and ease of massive fabrication. Its ability of real‐time detection and differentiation of diverse stimuli for health monitoring, detection of animal movements, and robots is demonstrated.

Abstract The soft millirobot is a promising candidate for emerging applications in various in‐vivo/vitro biomedical settings. Despite recent success in its design and actuation, the absence of sensing ability makes it still far from being a reality. Here, a radio frequency identification (RFID) based battery‐less soft millirobot that can move, sense, and communicate remotely by coupling the magnetic and piezoelectric effects is reported. This design integrates the robot actuation and power generation units within a thin multilayer film (

Electronic skin made of thin, soft, stretchable devices that can mimic the human skin and reconstruct the tactile sensation and perception offers great opportunities for prosthesis sensing, robotics controlling, and human-machine interfaces. Advanced materials and mechanics engineering of thin film devices has proven to be an efficient route to enable and enhance flexibility and stretchability of various electronic skins; however, the density of devices is still low owing to the limitation in existing fabrication techniques. Here, we report a high-throughput one-step process to fabricate large tactile sensing arrays with a sensor density of 25 sensors/cm2 for electronic skin, where the sensors are based on intrinsically stretchable piezoelectric lead zirconate titanate (PZT) elastomer. The PZT elastomer sensor arrays with great uniformity and passive-driven manner enable high-resolution tactile sensing, simplify the data acquisition process, and lower the manufacturing cost. The high-throughput fabrication process provides a general platform for integrating intrinsically stretchable materials into large area, high device density soft electronics for the next-generation electronic skin.

Flow-induced energy harvesting has attracted more and more attention among researchers in both fields of the wind and the fluid. Piezoelectric energy harvesters and triboelectric nanogenerators are exploited to obtain superior performance and sustainability, and the electromagnetic conversion has been continuously improved in the meantime. Aiming at different circumstances, researchers have designed, manufactured, and tested a variety of energy harvesters. In this paper, we analyze the state-of-the-art energy harvesting techniques and categorize them based on the working environment, application targets, and energy conversion mechanisms. The trend of research endeavors is analyzed, and the advantages, existing problems of energy harvesters, and corresponding solutions of energy harvesters are assessed.

Bistable morphing structures are widely used as actuation mechanisms in soft actuators, soft robotics, energy absorbers, mechanical computers, optical lenses, meta materials, and flexible electronics. However, untethered actuators, repetitive actuators, and hybrid-assembly (containing in-plane-assembly and out-of-plane-assembly) actuators remain challenging to realize using existing bistable structures, which hinders the novel application of such actuators in research, engineering, and daily life. This problem is solved by fabricating a magnet-driven soft bistable actuator (MSBA) unit. The self-buckling of the circular polydimethylsiloxane (PDMS) sheet ensures the bistability of the actuator and allows it to operate as an independent unit, free of external constraints. The reorientation of neodymium-iron-boron (NdFeB) microparticles embedded in the PDMS sheet enables the dome-shaped actuators to exhibit repetitive snapping under the stimulus of a direction-switching magnetic field. The potential of this MSBA unit in bionics, electronics, and biomechanics applications is demonstrated in systematic studies involving modification of the buckling deflection and magnetic moment density. The MSBA unit exhibits excellent performance in hybrid designs and intelligent systems. [ABSTRACT FROM AUTHOR]