Improved Energy Harvesting Ability of Single-Layer Binary Fiber Nanocomposite Membrane for Multifunctional Wearable Hybrid Piezoelectric and Triboelectric Nanogenerator and Self-Powered Sensors

Recent Advances in Polyvinylidene Fluoride with Multifunctional Properties in Nanogenerators

Amid the global energy crisis and rising emphasis on sustainability, efficient energy harvesting has become a research priority. Nanogenerators excel in converting abundant mechanical and thermal energy into electricity, offering a promising path for sustainable solutions. Among various nanogenerator's materials, Polyvinylidene fluoride (PVDF), with its distinctive molecular structure, exhibits multifunctional electrical properties including dielectric, piezoelectric and pyroelectric characteristics. These properties combined with its excellent flexibility make PVDF a prime candidate material for nanogenerators. In nanogenerators, this material is capable of efficiently collecting and converting energy. This paper discusses how PVDF's properties are manifested in three types of nanogenerators and compares the performance of these nanogenerators. In addition, strategies to improve the output performance of nanogenerators are demonstrated, including physical and chemical modification of materials, as well as structural optimization strategies such as hybrid structures and external circuits. It also introduces the application of this material in natural and human energy harvesting, as well as its promising prospects in medical technologies and smart home systems. The aim is to promote the use of PVDF in self-powered sensing, energy harvesting and smart monitoring, thereby providing valuable insights for designing more efficient and versatile nanogenerators.

External strategies for enhanced sensing performance of self-powered polyvinylidene fluoride-based sensors

The era of the Internet of Things has created an increasing demand for self-powered, flexible sensors. Among various intelligent materials, poly(vinylidene fluoride) (PVDF) has emerged as a promising candidate due to its flexibility, processability, biocompatibility, and unique electroactive properties. PVDF's distinctive piezoelectric, pyroelectric and triboelectric characteristics make it particularly suitable for self-powered flexible sensing applications. While research has primarily focused on enhancing the electroactive β phase, PVDF-based sensors still face limitations in their piezoelectric and pyroelectric performance. External strategies such as electrode design, stress/heat transfer improvements, microstructure optimization, and multifunctional synergy show great potential for improving sensing performance. Although numerous reviews address PVDF's polar phase enhancement, there is limited literature overviewing external strategies for performance optimization. This review focuses on external strategies for enhancing the sensing performance of PVDF-based sensors and their emerging applications. It also addresses practical challenges and future directions in PVDF-based sensor development.

3D printed shape-memory piezoelectric scaffolds with in-situ self-power properties for bone defect repair

Electrical stimulation has been shown to regulate early immunity and late-stage osteogenesis in bone repair. However, achieving in-situ electrical stimulation in the form of self-power in vivo during the initial postoperative stages when the patients have limited mobility remains challenging. In this study, we developed a 3D-printed in-situ self-powered composite scaffold composed of shape memory polyurethane elastomers (SMPU) and polyvinylidene fluoride (PVDF) piezoelectric nanofibers. The composite scaffold demonstrates excellent shape memory performance, allowing for minimally invasive implantation. During the shape memory process, the composite scaffold can provide mechanical force stimulation to PVDF nanofibers to generate charge. Therefore, self-power was achieved through the integration of the shape memory process and piezoelectric effects, and it can be used for in-situ electrical stimulation during the initial postoperative period. Additionally, the composite scaffold can output voltage under continuous mechanical force stimulation, indicating that the patients can apply sustained mechanical force stimulation to the composite scaffold to output voltage through rehabilitation exercises when the patients regain mobility. Both cell experiments and animal studies confirmed that this composite scaffold can effectively regulate the immune microenvironment and enhance osteogenesis. This study successfully achieves in-situ electrical stimulation in the form of self-power by integrating the shape memory process and piezoelectric effects, which is expected to be an effective repair strategy for bone tissue engineering.

A novel ultrasound-driven piezoelectric GBR membrane dispersed with boron nitride nanotubes promotes bone regeneration and anti-bacterial properties

Bone graft absorption and infection are the major challenges to guided bone regeneration(GBR), yet the GBR membrane is neither osteogenic nor antibacterial. Hence, we followed sono-piezo therapy strategy by fabricating an electrospun membrane dispersed with boron nitride nanotubes. The PLLA/Gelatine/PDA@BNNT (PGBT) membrane has improved mechanical and biocompatible properties and generate piezovoltages of 130 mV when activated by ultrasound stimulation under 100 mW/cm2 without extra polarization. The PGBT with ultrasound is conducive to cellular osteogenesis, barrier function, and shows antibacterial rate of about 40 %. The rat cranial defect experiments revealed that PGBT with ultrasound could promote osteogenesis in-vivo and show great potentials for vertical bone defect repair.

Electrospun multifunctional nanofibers for advanced wearable sensors

The multifunctional extension of fiber-based wearable sensors determines their integration and sustainable development, with electrospinning technology providing reliable, efficient, and scalable support for fabricating these sensors. Despite numerous studies on electrospun fiber-based wearable sensors, further attention is needed to leverage composite structural engineering for functionalizing electrospun fibers. This paper systematically reviews the research progress on fiber-based multifunctional wearable sensors in terms of design concept, device fabrication, mechanism exploration, and application potential. Firstly, the basics of electrospinning are briefly introduced, including its development, principles, parameters, and material selection. Tactile sensors, as crucial components of wearable sensors, are discussed in detail, encompassing their performance parameters, transduction mechanisms, and preparation strategies for pressure, strain, temperature, humidity, and bioelectrical signal sensors. The main focus of the article is on the latest research progress in multifunctional sensing design concepts, multimodal decoupling mechanisms, sensing mechanisms, and functional extensions. These extensions include multimodal sensing, self-healing, energy harvesting, personal thermal management, EMI shielding, antimicrobial properties, and other capabilities. Furthermore, the review assesses existing challenges and outlines future developments for multifunctional wearable sensors, highlighting the need for continued research and innovation.

Advances in integrated power supplies for self-powered bioelectronic devices

Bioelectronic devices with medical functions have attracted widespread attention in recent years. Power supplies are crucial components in these devices, which ensure their stable operation. Biomedical devices that utilize external power supplies and extended electrical wires limit patient mobility and increase the risk of discomfort and infection. To address these issues, self-powered devices with integrated power supplies have emerged, including triboelectric nanogenerators, piezoelectric nanogenerators, thermoelectric generators, batteries, biofuel cells, solar cells, wireless power transfer, and hybrid energy systems. This mini-review highlights the recent advances in the power supplies utilized in these self-powered devices. A concluding section discusses the subsisting challenges and future perspectives in integrated power supply technologies and design and manufacturing of self-powered devices.

Flexible Pressure Sensor Composed of Multi-Layer Textile Materials for Human-Machine Interaction Applications

Flexible pressure sensors have shown significant application prospects in fields such as artificial intelligence and precision manufacturing. However, most flexible pressure sensors are often prepared using polymer materials and precise micronano processing techniques, which greatly limits the widespread application of sensors. Here, this work chooses textile material as the construction material for the sensor, and its latitude and longitude structure endows the sensor with a natural structure. The flexible pressure sensor was designed using a multilayer stacking strategy by combining multilayer textile materials with two-dimensional MXene materials. The experiment shows that its sensitivity is 52.08 kPa-1 at 30 and 7.29 kPa-1 within 30-120 kPa. As a demonstration, these sensors are applied to wireless human motion monitoring, as well as related applications involving auxiliary communication and robotic arm integration. Furthermore, relevant demonstrations of sensor array applications are presented. This work provides inspiration for the design and application of flexible pressure sensors.

Co-doped MOF-5 and carbon nanotube nanoparticles enhancing stability and high output performance in core-shell nanofibers for piezoelectric nanogenerators

The interfacial interaction of carbon nanotubes (CNTs) significantly enhances the output capability of piezoelectric nanogenerators (PENGs). However, overcoming the limitation of low specific surface area in one-dimensional materials remains a significant challenge. This paper introduces a hydrothermal method for composite MOF (C-M) using CNTs and MOF-5, demonstrating localized co-doping between them. Coaxial electrospun piezoelectric fiber membranes (C-MNF) were then prepared using PVDF/PAN as the matrix. Benefiting from C-M's excellent crystallinity and its synergistic interaction with the polymer matrix, the C-MNF-based PENG showed a 125 % increase in output voltage, reaching ∼25 V, compared to coaxial membranes simply mixing MOF-5 and CNTs. As a result, its short-circuit current was ∼1.8 μA, with a piezoelectric coefficient d33 of ∼400 pC N-1. Consequently, this material exhibits superior piezoelectric output capabilities, paving the way for future functional material fabrication.

Charge Generation and Enhancement of Key Components of Triboelectric Nanogenerators: A Review

The past decade has witnessed remarkable progress in high-performance Triboelectric nanogenerators (TENG) with the design and synthesis of functional dielectric materials, the exploration of novel dynamic charge transport mechanisms, and the innovative design of architecture, making it one of the most crucial technologies for energy harvesting. High output charge density is fundamental for TENG to expand its application scope and accelerate industrialization; it depends on the dynamic equilibrium of charge generation, trapping, de-trapping, and migration within its core components. Here, this review classifies and summarizes innovative approaches to enhance the charge density of the charge generation, charge trapping, and charge collection layers. The milestone of high charge density TENG is reviewed based on material selection and innovative mechanisms. The state-of-the-art principles and techniques for generating high charge density and suppressing charge decay are discussed and highlighted in detail, and the distinct charge transport mechanisms, the technologies of advanced materials preparation, and the effective charge excitation strategy are emphatically introduced. Lastly, the bottleneck and future research priorities for boosting the output charge density are summarized. A summary of these cutting-edge developments intends to provide readers with a deep understanding of the future design of high-output TENG.

3D Printing of Flexible BaTiO3/Polydimethylsiloxane Piezocomposite with Aligned Particles for Enhanced Energy Harvesting

With the rapid development of human-machine interactions and artificial intelligence, the demand for wearable electronic devices is increasing uncontrollably all over the world; however, an unsustainable power supply for such sensors continues to restrict their applications. In the present work, piezoelectric barium titanate (BaTiO3) ceramic powder with excellent properties was prepared from milled precursors through a solid-state reaction. To fabricate a flexible device, the as-prepared BaTiO3 powder was mixed with polydimethylsiloxane (PDMS) polymer. The BaTiO3/PDMS ink with excellent rheological properties was extruded smoothly by direct ink writing technology (DIW). BaTiO3 particles were aligned due to the shear stress effect during the printing process. Subsequently, the as-printed composite was assembled into a sandwich-type device for effective energy harvesting. It was observed that the maximum output voltage and current of this device reached 68 V and 720 nA, respectively, for a BaTiO3 content of 6 vol %. Therefore, the material extrusion-based three-dimensional (3D) printing technique can be used to prepare flexible piezoelectric composites for efficient energy harvesting.