Porosity Modulated High-Performance Piezoelectric Nanogenerator Based on Organic/Inorganic Nanomaterials for Self-Powered Structural Health Monitoring

Inorganic Dielectric Materials Coupling Micro-/Nanoarchitectures for State-of-the-Art Biomechanical-to-Electrical Energy Conversion Devices

Biomechanical-to-electrical energy conversion technology rapidly developed with the emergence of nanogenerators (NGs) in 2006, which proves promising in distributed energy management for the Internet of Things, self-powered sensing, and human-computer interaction. Recently, researchers have increasingly integrated inorganic dielectric materials (IDMs) and micro-/nanoarchitectures into various types of NGs (i.e., triboelectric, piezoelectric, and flexoelectric NGs). This strategy significantly enhances the electrical performance, enabling near-theoretical energy harvesting capability and precise multiple physiological information detection. However, because micro-/nanoarchitectured IDMs function differently in each type of NG, numerous studies have focused on a single NG type and lack a unified perspective on their role across all types of biomechanical energy NGs. In this review, from an overall theoretical root of NGs, the performance enhancement mechanisms and effects of designs of IDMs coupling micro-/nanoarchitectures of various kinds of biomechanical energy NGs are systematically summarized. Next, advanced applications in human energy scavenging and physiological signal sensing are delved into. Finally, challenges and rational guidelines for designing future devices are discussed. This work provides researchers with in-depth insight into the development of high-performance personalized high-entropy power supplies and sensor networks via biomechanical-to-electrical energy conversion technologies based on IDMs coupling micro-/nanoarchitectures.

Advanced Energy Harvesters and Energy Storage for Powering Wearable and Implantable Medical Devices

Wearable and implantable active medical devices (WIMDs) are transformative solutions for improving healthcare, offering continuous health monitoring, early disease detection, targeted treatments, personalized medicine, and connected health capabilities. Commercialized WIMDs use primary or rechargeable batteries to power their sensing, actuation, stimulation, and communication functions, and periodic battery replacements of implanted active medical devices pose major risks of surgical infections or inconvenience to users. Addressing the energy source challenge is critical for meeting the growing demand of the WIMD market that is reaching valuations in the tens of billions of dollars. This review critically assesses the recent advances in energy harvesting and storage technologies that can potentially eliminate the need for battery replacements. With a key focus on advanced materials that can enable energy harvesters to meet the energy needs of WIMDs, this review examines the crucial roles of advanced materials in improving the efficiencies of energy harvesters, wireless charging, and energy storage devices. This review concludes by highlighting the key challenges and opportunities in advanced materials necessary to achieve the vision of self-powered wearable and implantable active medical devices, eliminating the risks associated with surgical battery replacement and the inconvenience of frequent manual recharging.

Ingenious Structure Engineering to Enhance Piezoelectricity in Poly(vinylidene fluoride) for Biomedical Applications

The future development of wearable/implantable sensing and medical devices relies on substrates with excellent flexibility, stability, biocompatibility, and self-powered capabilities. Enhancing the energy efficiency and convenience is crucial, and converting external mechanical energy into electrical energy is a promising strategy for long-term advancement. Poly(vinylidene fluoride) (PVDF), known for its piezoelectricity, is an outstanding representative of an electroactive polymer. Ingeniously designed PVDF-based polymers have been fabricated as piezoelectric devices for various applications. Notably, the piezoelectric performance of PVDF-based platforms is determined by their structural characteristics at different scales. This Review highlights how researchers can strategically engineer structures on microscopic, mesoscopic, and macroscopic scales. We discuss advanced research on PVDF-based piezoelectric platforms with diverse structural designs in biomedical sensing, disease diagnosis, and treatment. Ultimately, we try to give perspectives for future development trends of PVDF-based piezoelectric platforms in biomedicine, providing valuable insights for further research.

Polymeric piezoelectric accelerometers with high sensitivity, broad bandwidth, and low noise density for organic electronics and wearable microsystems

Piezoelectric accelerometers excel in vibration sensing. In the emerging trend of fully organic electronic microsystems, polymeric piezoelectric accelerometers can be used as vital front-end components to capture dynamic signals, such as vocal vibrations in wearable speaking assistants for those with speaking difficulties. However, high-performance polymeric piezoelectric accelerometers suitable for such applications are rare. Piezoelectric organic compounds such as PVDF have inferior properties to their inorganic counterparts such as PZT. Consequently, most existing polymeric piezoelectric accelerometers have very unbalanced performance metrics. They often sacrifice resonance frequency and bandwidth for a flat-band sensitivity comparable to those of PZT-based accelerometers, leading to increased noise density and limited application potentials. In this study, a new polymeric piezoelectric accelerometer design to overcome the material limitations of PVDF is introduced. This new design aims to simultaneously achieve high sensitivity, broad bandwidth, and low noise. Five samples were manufactured and characterized, demonstrating an average sensitivity of 29.45 pC/g within a ± 10 g input range, a 5% flat band of 160 Hz, and an in-band noise density of 1.4 µg/Hz . These results surpass those of many PZT-based piezoelectric accelerometers, showing the feasibility of achieving comprehensively high performance in polymeric piezoelectric accelerometers to increase their potential in novel applications such as organic microsystems.

Hybrid Piezoelectric/Triboelectric Wearable Nanogenerator Based on Stretchable PVDF-PDMS Composite Films

Hybrid piezoelectric/triboelectric nanogenerators combine the merits of piezoelectric nanogenerators (PENGs) and triboelectric nanogenerators (TENGs), possessing enhanced electrical output and sensitivity. However, the structures of the majority of hybrid nanogenerators are rather complex in integrating both functions, limiting their practical application in wearable electronics. Herein, we propose to construct a piezoelectric/triboelectric hybrid nanogenerator (PT-NG) with a simple structure based on a composite film to simultaneously achieve the coupling of piezoelectric charge generation and triboelectrification with improved energy conversion efficiency. The composite film consists of electrospun PVDF nanofibers embedded in the surface of the PDMS film, which not only forms a rough nanomorphology on the surface of PDMS but also provides structural protection to the PVDF nanofibers by PDMS during compressive deformation. The results have shown that the PT-NG can generate much higher electrical outputs than individual TENG and PENG devices. The PT-NG devices exhibit a high level of mechanical-to-electrical energy conversion efficiency with superior performance in charging capacitors and functioning as self-powered wearable sensors for the detection of different signals from finger movement, the recognition of various gestures, and the monitoring of respiration. More importantly, the composite device possesses an impressive structure durability, maintaining its layered structure over 5000 testing cycles without noticing any obvious damage on the nanofibers or detachment between the layers. Our results have demonstrated that the combining of piezoelectric nanofibers and triboelectric substrate is an efficient way to fabricate highly efficient energy harvesting devices for intelligent identification and health monitoring.

Review of Piezoelectric Properties and Power Output of PVDF and Copolymer-Based Piezoelectric Nanogenerators

The highest energy conversion efficiencies are typically shown by lead-containing piezoelectric materials, but the harmful environmental impacts of lead and its toxicity limit future use. At the bulk scale, lead-based piezoelectric materials have significantly higher piezoelectric properties when compared to lead-free piezoelectric materials. However, at the nanoscale, the piezoelectric properties of lead-free piezoelectric material can be significantly larger than the bulk scale. The piezoelectric properties of Poly(vinylidene fluoride) (PVDF) and Poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) lead-free piezoelectric nanomaterials are reviewed and their suitability for use in piezoelectric nanogenerators (PENGs) is determined. The impact of different PVDF/PVDF-TrFE composite structures on power output is explained. Strategies to improve the power output are given. Overall, this review finds that PVDF/PVDF-TrFE can have significantly increased piezoelectric properties at the nanoscale. However, these values are still lower than lead-free ceramics at the nanoscale. If the sole goal in developing a lead-free PENG is to maximize output power, lead-free ceramics at the nanoscale should be considered. However, lead-free ceramics are brittle, and thus encapsulation of lead-free ceramics in PVDF is a way to increase the flexibility of these PENGs. PVDF/PVDF-TrFE offers the advantage of being nontoxic and biocompatible, which is useful for many applications.

Giant Piezoelectric Output and Stability Enhancement in Piezopolymer Composites with Liquid Metal Nanofillers

Integrating nanomaterials into the polymer matrix is an effective strategy to optimize the performance of polymer-based piezoelectric devices. Nevertheless, the trade-off between the output enhancement and stability maintenance of piezoelectric composites usually leads to an unsatisfied overall performance for the high-strength operation of devices. Here, by setting liquid metal (LM) nanodroplets as the nanofillers in a poly(vinylidene difluoride) (PVDF) matrix, the as-formed liquid-solid/conductive-dielectric interfaces significantly promote the piezoelectric output and the reliability of this piezoelectric composite. A giant performance improvement featured is obtained with, nearly 1000% boosting on the output voltage (as high as 212 V), 270% increment on the piezoelectric coefficient (d33 ∼51.1 pC N-1 ) and long-term reliability on both structure and output (over 36 000 cycles). The design of a novel heterogenous interface with both mechanical matching and electric coupling can be the new orientation for developing high performance piezoelectric composite-based devices.

3D Printed Polymer Piezoelectric Materials: Transforming Healthcare through Biomedical Applications

Three-dimensional (3D) printing is a promising manufacturing platform in biomedical engineering. It offers significant advantages in fabricating complex and customized biomedical products with accuracy, efficiency, cost-effectiveness, and reproducibility. The rapidly growing field of three-dimensional printing (3DP), which emphasizes customization as its key advantage, is actively searching for functional materials. Among these materials, piezoelectric materials are highly desired due to their linear electromechanical and thermoelectric properties. Polymer piezoelectrics and their composites are in high demand as biomaterials due to their controllable and reproducible piezoelectric properties. Three-dimensional printable piezoelectric materials have opened new possibilities for integration into biomedical fields such as sensors for healthcare monitoring, controlled drug delivery systems, tissue engineering, microfluidic, and artificial muscle actuators. Overall, this review paper provides insights into the fundamentals of polymer piezoelectric materials, the application of polymer piezoelectric materials in biomedical fields, and highlights the challenges and opportunities in realizing their full potential for functional applications. By addressing these challenges, integrating 3DP and piezoelectric materials can lead to the development of advanced sensors and devices with enhanced performance and customization capabilities for biomedical applications.

Advances in Wearable Piezoelectric Sensors for Hazardous Workplace Environments

Recent advances in wearable energy harvesting technology as solutions to occupational health and safety programs are presented. Workers are often exposed to harmful conditions-especially in the mining and construction industries-where chronic health issues can emerge over time. While wearable sensors technology can aid in early detection and long-term exposure tracking, powering them and the associated risks are often an impediment for their widespread use, such as the need for frequent charging and battery safety. Repetitive vibration exposure is one such hazard, e.g., whole body vibration, yet it can also provide parasitic energy that can be harvested to power wearable sensors and overcome the battery limitations. This review can critically analyze the vibration effect on workers' health, the limitations of currently available devices, explore new options for powering different personal protective equipment devices, and discuss opportunities and directions for future research. The recent progress in self-powered vibration sensors and systems from the perspective of the underlying materials, applications, and fabrication techniques is reviewed. Lastly, the challenges and perspectives are discussed for reference to the researchers who are interested in self-powered vibration sensors.

Thin-Film Platinum Resistance Temperature Detector with a SiCN/Yttria-Stabilized Zirconia Protective Layer by Direct Ink Writing for High-Temperature Applications

In situ temperature monitoring of curved high-temperature components in extreme environments is challenging for a variety of applications in fields such as aero engines and gas turbines. Recently, extrusion-based direct ink writing (DIW) has been utilized to fabricate platinum (Pt) resistance temperature detectors (RTDs). However, the current Pt RTD prepared by DIW technology suffers from a limited temperature range and poor high-temperature stability. Here, DIW technology and yttria-stabilized zirconia (YSZ)-modified precursor ceramic film packaging have been used to build a Pt RTD with high-temperature resistance, small disturbance, and high stability. The results indicate that the protective layer formed by the liquid phase anchors the Pt particles and reduces the agglomeration and volatilization of the Pt sensitive layer at high temperature. Attributed to the SiCN/YSZ protective layer, the temperature resistance curve of the Pt RTD in the range of 50-800 °C has little deviation from the fitting curve, and the fitting correlation coefficient is above 0.9999. Interestingly, the Pt RTD also has high repeatability and stability. The high temperature resistance drift rate is only 0.05%/h after 100 h of long-term testing at 800 °C and can withstand butane flame up to ∼1300 °C without damage. Moreover, the Pt RTD can be conformally deposited on the outer ring of aerospace bearings by DIW technology and then realize on-site, nondestructive, and real-time monitoring of bearing temperature. The fabricated Pt RTD shows great potential for high-temperature applications, and the novel technology proposed provides a feasible pathway for temperature monitoring of aeroengine internal curved hot-end components.

Innovative antibacterial electrospun nanofibers mats depending on piezoelectric generation

This paper introduces a new approach of testing piezoelectric nanofibers as antibacterial mat. In this work, both Polyvinylidene fluoride (PVDF) and PVDF embedded with thermoplastic polyurethane nanofibers are synthesized as nanofibers mat via electrospinning technique. Then, such mat is analyzed as piezoelectric material to generate electric voltage under different mechanical excitations. Furthermore, morphological and chemical characteristics have been operated to prove the existence of beta sheets piezoelectricity of the synthesized nanofibers mats. Then, the synthesized nanofibers surfaces have been cyclically stretched and exposed to bacteria specimen. It has been noticed that the generated voltage and the corresponding localized electric field positively affect the growth of bacteria and reduces the formation of K. penomenue samples bacteria colonies. In addition, the effect of both stretching frequency and pulses numbers have been studied on the bacteria count, growth kinetics, and protein leakage. Our contribution here is to introduce an innovative way of the direct impact of the generated electric field from piezoelectric nanofibers on the reduction of bacteria growth, without depending on traditional anti-bacterial nanoparticles. This work can open a new trend of the usability of piezoelectric nanofibers through masks, filters, and wound curing mats within anti-bacterial biological applications.

Flexible PVDF-TrFE Nanocomposites with Ag-decorated BCZT Heterostructures for Piezoelectric Nanogenerator Applications

Flexible piezoelectric nanogenerators are playing an important role in delivering power to next-generation wearable electronic devices due to their high-power density and potential to create self-powered sensors for the Internet of Things. Among the range of available piezoelectric materials, poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE)-based piezoelectric composites exhibit significant potential for flexible piezoelectric nanogenerator applications. However, the high electric fields that are required for poling cannot be readily applied to polymer composites containing piezoelectric fillers due to the high permittivity contrast between the filler and matrix, which reduces the dielectric strength. In this paper, novel Ag-decorated BCZT heterostructures were synthesized via a photoreduction method, which were introduced at a low level (3 wt %) into the matrix of PVDF-TrFE to fabricate piezoelectric composite films. The effect of Ag nanoparticle loading content on the dielectric, ferroelectric, and piezoelectric properties was investigated in detail, where a maximum piezoelectric energy-harvesting figure of merit of 5.68 × 10^-12 m²/N was obtained in a 0.04Ag-BCZT NWs/PVDF-TrFE composite film, where 0.04 represents the concentration of the AgNO₃ solution. Modeling showed that an optimum performance was achieved by tailoring the fraction and distribution of the conductive silver nanoparticles to achieve a careful balance between generating electric field concentrations to increase the level of polarization, while not degrading the dielectric strength. This work therefore provides a strategy for the design and manufacture of highly polarized piezoelectric composite films for piezoelectric nanogenerator applications.

Stretchable nanofibers of polyvinylidenefluoride (PVDF)/thermoplastic polyurethane (TPU) nanocomposite to support piezoelectric response via mechanical elasticity

Interest in piezoelectric nanocomposites has been vastly growing in the energy harvesting field. They are applied in wearable electronics, mechanical actuators, and electromechanical membranes. In this research work, nanocomposite membranes of different blend ratios from PVDF and TPU have been synthesized. The PVDF is responsible for piezoelectric performance where it is one of the promising polymeric organic materials containing β-sheets, to convert applied mechanical stress into electric voltage. In addition, the TPU is widely used in the plastic industry due to its superior elasticity. Our work investigates the piezoresponse analysis for different blending ratios of PVDF/TPU. It has been found that TPU blending ratios of 15–17.5% give higher output voltage at different stresses conditions along with higher piezosensitivity. Then, TPU addition with its superior mechanical elasticity can partially compensate PVDF to enhance the piezoelectric response of the PVDF/TPU nanocomposite mats. This work can help reducing the amount of added PVDF in piezoelectric membranes with enhanced piezo sensitivity and mechanical elasticity.

Poly(vinylidene fluoride)-Stabilized Black γ-Phase CsPbI3 Perovskite for High-Performance Piezoelectric Nanogenerators

Halide perovskite materials have been recently recognized as promising materials for piezoelectric nanogenerators (PENGs) due to their potentially strong ferroelectricity and piezoelectricity. Here, we report a new method using a poly(vinylidene fluoride) (PVDF) polymer to achieve excellent long-term stable black γ-phase CsPbI₃ and explore the piezoelectric performance on a CsPbI₃@PVDF composite film. The PVDF-stabilized black-phase CsPbI₃ perovskite composite film can be stable under ambient conditions for more than 60 days and over 24 h while heated at 80 °C. Piezoresponse force spectroscopy measurements revealed that the black CsPbI₃/PVDF composite contains well-developed ferroelectric properties with a high piezoelectric charge coefficient (d ₃₃) of 28.4 pm/V. The black phase of the CsPbI₃-based PVDF composite exhibited 2 times higher performance than the yellow phase of the CsPbI₃-based composite. A layer-by-layer stacking method was adopted to tune the thickness of the composite film. A five-layer black-phase CsPbI₃@PVDF composite PENG exhibited a voltage output of 26 V and a current density of 1.1 μA/cm². The output power can reach a peak value of 25 μW. Moreover, the PENG can be utilized to charge capacitors through a bridge rectifier and display good durability without degradation for over 14 000 cyclic tests. These results reveal the feasibility of the all-inorganic perovskite for the design and development of high-performance piezoelectric nanogenerators.

Acoustic Core-Shell Resonance Harvester for Application of Artificial Cochlea Based on the Piezo-Triboelectric Effect

The demand for flexible, efficient, and self-powered cochlear implants applied to remedy sensorineural hearing loss caused by dysfunctional hair cells remains urgent. Herein, we report an acoustic core-shell resonance harvester for the application of artificial cochleae based on the piezo-triboelectric effect. Integrating dispersed BaTiO₃ particles as cores and porous PVDF-TrFE as shells, the acoustic harvest devices with ingenious core-shell structures exhibit outstanding piezo-triboelectric properties (V_oc = 15.24 V, DA_sc = 9.22 mA/m²). The acoustic harvest principle reveals that BaTiO₃ nanocores resonate with sound waves and bounce against porous PVDF-TrFE microshells, thereby generating piezo-triboelectric signals. By experimental measurement and numerical modeling, the vibration process and resonance regulation of acoustic harvest devices were intensively investigated to regulate the influential parameters. Furthermore, the acoustic harvesters exhibit admirable feasibility and sensitivity for sound recording and show potential application for artificial cochlea.

Two-Step Regulation Strategy Improving Stress Transfer and Poling Efficiency Boosts Piezoelectric Performance of 0-3 Piezocomposites

The rapid development of flexible micropower electronics has aided the opportunity for the broader application of flexible piezoelectric composites (PCs) but has also led to higher requirements for their power generation. Among them, 0-3 PCs with embedded zero-dimension piezoparticle fillers, although low cost and easy to prepare, suffer from suboptimal output performance because of inherent structural defects. In this work, the voltage output was increased from 3.4 to 12.7 V under a force of 7 N, through first-step regulation by aligning the KNbO₃ (KN) particles in the polydimethylsiloxane (PDMS) matrix; then, a significantly enhanced current output (from 0.7 to 4.5 μA) through second-step regulation by introducing copper nanorods (Cu NRs) interspersed in the gaps between the KN chains. Consequently, the proposed PC exhibits much higher power density, 37.3 μW/cm², than that of random KN/PDMS and thus shows good potential for high-performance, flexible piezoelectric energy harvesters.

Boosting Performance of Self-Polarized Fully Printed Piezoelectric Nanogenerators via Modulated Strength of Hydrogen Bonding Interactions

Self-polarized piezoelectric devices have attracted significant interest owing to their fabrication processes with low energy consumption. Herein, novel poling-free piezoelectric nanogenerators (PENGs) based on self-polarized polyvinylidene difluoride (PVDF) induced by the incorporation of different surface-modified barium titanate nanoparticles (BTO NPs) were prepared via a fully printing process. To reveal the effect of intermolecular interactions between PVDF and NP surface groups, BTO NPs were modified with hydrophilic polydopamine (PDA) and hydrophobic 1H,1H,2H,2H-perfluorodecyltriethoxysilane (PFDTES) to yield PDA-BTO and PFD-BTO, respectively. This study demonstrates that the stronger hydrogen bonding interactions existed in PFD-BTO/PVDF composite film comparative to the PDA-BTO/PVDF composite film induced the higher β-phase formation (90%), which was evidenced by the XRD, FTIR and DSC results, as well as led to a better dispersion of NPs and improved mechanical properties of composite films. Consequently, PFD-BTO/PVDF-based PENGs without electric poling exhibited a significantly improved output voltage of 5.9 V and power density of 102 μW cm-3, which was 1.8 and 2.9 times higher than that of PDA-BTO/PVDF-based PENGs, respectively. This study provides a promising approach for advancing the search for high-performance, self-polarized PENGs in next-generation electric and electronic industries.