Ultrasound-driven electrical stimulation of peripheral nerves based on implantable piezoelectric thin film nanogenerators

The development, use, and challenges of electromechanical tissue stimulation systems

BACKGROUND

Tissue stimulations greatly affect cell growth, phenotype, and function, and they play an important role in modeling tissue physiology. With the goal of understanding the cellular mechanisms underlying the response of tissues to external stimulations, in vitro models of tissue stimulation have been developed in hopes of recapitulating in vivo tissue function.

METHODS

Herein we review the efforts to create and validate tissue stimulators responsive to electrical or mechanical stimulation including tensile, compression, torsion, and shear.

RESULTS

Engineered tissue platforms have been designed to allow tissues to be subjected to selected types of mechanical stimulation from simple uniaxial to humanoid robotic stain through equal-biaxial strain. Similarly, electrical stimulators have been developed to apply selected electrical signal shapes, amplitudes, and load cycles to tissues, lending to usage in stem cell-derived tissue development, tissue maturation, and tissue functional regeneration. Some stimulators also allow for the observation of tissue morphology in real-time while cells undergo stimulation. Discussion on the challenges and limitations of tissue simulator development is provided.

CONCLUSIONS

Despite advances in the development of useful tissue stimulators, opportunities for improvement remain to better reproduce physiological functions by accounting for complex loading cycles, electrical and mechanical induction coupled with biological stimuli, and changes in strain affected by applied inputs.

Advanced Ultrasound Energy Transfer Technologies using Metamaterial Structures

Wireless energy transfer (WET) based on ultrasound-driven generators with enormous beneficial functions, is technologically in progress by the valuation of ultrasonic metamaterials (UMMs) in science and engineering domains. Indeed, novel metamaterial structures can develop the efficiency of mechanical and physical features of ultrasound energy receivers (US-ETs), including ultrasound-driven piezoelectric and triboelectric nanogenerators (US-PENGs and US-TENGs) for advantageous applications. This review article first summarizes the fundamentals, classification, and design engineering of UMMs after introducing ultrasound energy for WET technology. In addition to addressing using UMMs, the topical progress of innovative UMMs in US-ETs is conceptually presented. Moreover, the advanced approaches of metamaterials are reported in the categorized applications of US-PENGs and US-TENGs. Finally, some current perspectives and encounters of UMMs in US-ETs are offered. With this objective in mind, this review explores the potential revolution of reliable integrated energy transfer systems through the transformation of metamaterials into ultrasound-driven active mediums for generators.

Piezoelectric Biomaterials Inspired by Nature for Applications in Biomedicine and Nanotechnology

Bioelectricity provides electrostimulation to regulate cell/tissue behaviors and functions. In the human body, bioelectricity can be generated in electromechanically responsive tissues and organs, as well as biomolecular building blocks that exhibit piezoelectricity, with a phenomenon known as the piezoelectric effect. Inspired by natural bio-piezoelectric phenomenon, efforts have been devoted to exploiting high-performance synthetic piezoelectric biomaterials, including molecular materials, polymeric materials, ceramic materials, and composite materials. Notably, piezoelectric biomaterials polarize under mechanical strain and generate electrical potentials, which can be used to fabricate electronic devices. Herein, a review article is proposed to summarize the design and research progress of piezoelectric biomaterials and devices toward bionanotechnology. First, the functions of bioelectricity in regulating human electrophysiological activity from cellular to tissue level are introduced. Next, recent advances as well as structure-property relationship of various natural and synthetic piezoelectric biomaterials are provided in detail. In the following part, the applications of piezoelectric biomaterials in tissue engineering, drug delivery, biosensing, energy harvesting, and catalysis are systematically classified and discussed. Finally, the challenges and future prospects of piezoelectric biomaterials are presented. It is believed that this review will provide inspiration for the design and development of innovative piezoelectric biomaterials in the fields of biomedicine and nanotechnology.

Pristine MOF Materials for Separator Application in Lithium-Sulfur Battery

Lithium-sulfur (Li-S) batteries have attracted significant attention in the realm of electronic energy storage and conversion owing to their remarkable theoretical energy density and cost-effectiveness. However, Li-S batteries continue to face significant challenges, primarily the severe polysulfides shuttle effect and sluggish sulfur redox kinetics, which are inherent obstacles to their practical application. Metal-organic frameworks (MOFs), known for their porous structure, high adsorption capacity, structural flexibility, and easy synthesis, have emerged as ideal materials for separator modification. Efficient polysulfides interception/conversion ability and rapid lithium-ion conduction enabled by MOFs modified layers are demonstrated in Li-S batteries. In this perspective, the objective is to present an overview of recent advancements in utilizing pristine MOF materials as modification layers for separators in Li-S batteries. The mechanisms behind the enhanced electrochemical performance resulting from each design strategy are explained. The viewpoints and crucial challenges requiring resolution are also concluded for pristine MOFs separator in Li-S batteries. Moreover, some promising materials and concepts based on MOFs are proposed to enhance electrochemical performance and investigate polysulfides adsorption/conversion mechanisms. These efforts are expected to contribute to the future advancement of MOFs in advanced Li-S batteries.

Bioelectret Materials and Their Bioelectric Effects for Tissue Repair: A Review

Biophysical and clinical medical studies have confirmed that biological tissue lesions and trauma are related to the damage of an intrinsic electret (i.e., endogenous electric field), such as wound healing, embryonic development, the occurrence of various diseases, immune regulation, tissue regeneration, and cancer metastasis. As exogenous electrical signals, such as conductivity, piezoelectricity, ferroelectricity, and pyroelectricity, bioelectroactives can regulate the endogenous electric field, thus controlling the function of cells and promoting the repair and regeneration of tissues. Materials, once polarized, can harness their inherent polarized static electric fields to generate an electric field through direct stimulation or indirect interactions facilitated by physical signals, such as friction, ultrasound, or mechanical stimulation. The interaction with the biological microenvironment allows for the regulation and compensation of polarized electric signals in damaged tissue microenvironments, leading to tissue regeneration and repair. The technique shows great promise for applications in the field of tissue regeneration. In this paper, the generation and change of the endogenous electric field and the regulation of exogenous electroactive substances are expounded, and the latest research progress of the electret and its biological effects in the field of tissue repair include bone repair, nerve repair, drug penetration promotion, wound healing, etc. Finally, the opportunities and challenges of electret materials in tissue repair were summarized. Exploring the research and development of new polarized materials and the mechanism of regulating endogenous electric field changes may provide new insights and innovative methods for tissue repair and disease treatment in biological applications.

Enhancing Ultrasound Power Transfer: Efficiency, Acoustics, and Future Directions

Implantable medical devices (IMDs), like pacemakers regulating heart rhythm or deep brain stimulators treating neurological disorders, revolutionize healthcare. However, limited battery life necessitates frequent surgeries for replacements. Ultrasound power transfer (UPT) emerges as a promising solution for sustainable IMD operation. Current research prioritizes implantable materials, with less emphasis on sound field analysis and maximizing energy transfer during wireless power delivery. This review addresses this gap. A comprehensive analysis of UPT technology, examining cutting-edge system designs, particularly in power supply and efficiency is provided. The review critically examines existing efficiency models, summarizing the key parameters influencing energy transmission in UPT systems. For the first time, an energy flow diagram of a general UPT system is proposed to offer insights into the overall functioning. Additionally, the review explores the development stages of UPT technology, showcasing representative designs and applications. The remaining challenges, future directions, and exciting opportunities associated with UPT are discussed. By highlighting the importance of sustainable IMDs with advanced functions like biosensing and closed-loop drug delivery, as well as UPT's potential, this review aims to inspire further research and advancements in this promising field.

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.

In Situ Phosphorization for Constructing Ni5P2-Ni Heterostructure Derived from Bimetallic MOF for Li-S Batteries

Heterostructured materials commonly consist of bifunctions due to the different ingredients. For host material in the sulfur cathode of lithium-sulfur (Li-S) batteries, the chemical adsorption and catalytic activity for lithium polysulfides (LiPS) are important. This work obtains a Ni5P2-Ni nanoparticle (Ni5P2-NiNPs) heterostructure through a confined self-reduction method followed by an in situ phosphorization process using Al/Ni-MOF as precursors. The Ni5P2-Ni heterostructure not only has strong chemical adsorption, but also can effectively catalyze LiPS conversion. Furthermore, the synthetic route can keep Ni5P2-NiNPs inside of the nanocomposites, which have structural stability, high conductivity, and efficient adsorption/catalysis in LiPS conversion. These advantages make the assembled Li-S battery deliver a reversible specific capacity of 619.7 mAh g- 1 at 0.5 C after 200 cycles. The in situ ultraviolet-visible technique proves the catalytic effect of Ni5P2-Ni heterostructure on LiPS conversion during the discharge process.

Advances in Material-Assisted Electromagnetic Neural Stimulation

Bioelectricity plays a crucial role in organisms, being closely connected to neural activity and physiological processes. Disruptions in the nervous system can lead to chaotic ionic currents at the injured site, causing disturbances in the local cellular microenvironment, impairing biological pathways, and resulting in a loss of neural functions. Electromagnetic stimulation has the ability to generate internal currents, which can be utilized to counter tissue damage and aid in the restoration of movement in paralyzed limbs. By incorporating implanted materials, electromagnetic stimulation can be targeted more accurately, thereby significantly improving the effectiveness and safety of such interventions. Currently, there have been significant advancements in the development of numerous promising electromagnetic stimulation strategies with diverse materials. This review provides a comprehensive summary of the fundamental theories, neural stimulation modulating materials, material application strategies, and pre-clinical therapeutic effects associated with electromagnetic stimulation for neural repair. It offers a thorough analysis of current techniques that employ materials to enhance electromagnetic stimulation, as well as potential therapeutic strategies for future applications.

Porous Organic Framework Materials (MOF, COF, and HOF) as the Multifunctional Separator for Rechargeable Lithium Metal Batteries

The separator is an important component in batteries, with the primary function of separating the positive and negative electrodes and allowing the free passage of ions. Porous organic framework materials have a stable connection structure, large specific surface area, and ordered pores, which are natural places to store electrolytes. And these materials with specific functions can be designed according to the needs of researchers. The performance of porous organic framework-based separators used in rechargeable lithium metal batteries is much better than that of polyethylene/propylene separators. In this paper, the three most classic organic framework materials (MOF, COF, and HOF) are analyzed and summarized. The applications of MOF, COF, and HOF separators in lithium-sulfur batteries, lithium metal anode, and solid electrolytes are reviewed. Meanwhile, the research progress of these three materials in different fields is discussed based on time. Finally, in the conclusion, the problems encountered by MOF, COF, and HOF in different fields as well as their future research priorities are presented. This review will provide theoretical guidance for the design of porous framework materials with specific functions and further stimulate researchers to conduct research on porous framework materials.

Ultra-low frequency magnetic energy focusing for highly effective wireless powering of deep-tissue implantable electronic devices

The limited lifespan of batteries is a challenge in the application of implantable electronic devices. Existing wireless power technologies such as ultrasound, near-infrared light and magnetic fields cannot charge devices implanted in deep tissues, resulting in energy attenuation through tissues and thermal generation. Herein, an ultra-low frequency magnetic energy focusing (ULFMEF) methodology was developed for the highly effective wireless powering of deep-tissue implantable devices. A portable transmitter was used to output the low-frequency magnetic field (<50 Hz), which remotely drives the synchronous rotation of a magnetic core integrated within the pellet-like implantable device, generating an internal rotating magnetic field to induce wireless electricity on the coupled coils of the device. The ULFMEF can achieve energy transfer across thick tissues (up to 20 cm) with excellent transferred power (4-15 mW) and non-heat effects in tissues, which is remarkably superior to existing wireless powering technologies. The ULFMEF is demonstrated to wirelessly power implantable micro-LED devices for optogenetic neuromodulation, and wirelessly charged an implantable battery for programmable electrical stimulation on the sciatic nerve. It also bypassed thick and tough protective shells to power the implanted devices. The ULFMEF thus offers a highly advanced methodology for the generation of wireless powered biodevices.

Revealing an important role of piezoelectric polymers in nervous-tissue regeneration: A review

Nerve injuries pose a drastic threat to nerve mobility and sensitivity and lead to permanent dysfunction due to low regenerative capacity of mature neurons. The electrical stimuli that can be provided by electroactive materials are some of the most effective tools for the formation of soft tissues, including nerves. Electric output can provide a distinctly favorable bioelectrical microenvironment, which is especially relevant for the nervous system. Piezoelectric biomaterials have attracted attention in the field of neural tissue engineering owing to their biocompatibility and ability to generate piezoelectric surface charges. In this review, an outlook of the most recent achievements in the field of piezoelectric biomaterials is described with an emphasis on piezoelectric polymers for neural tissue engineering. First, general recommendations for the design of an optimal nerve scaffold are discussed. Then, specific mechanisms determining nerve regeneration via piezoelectric stimulation are considered. Activation of piezoelectric responses via natural body movements, ultrasound, and magnetic fillers is also examined. The use of magnetoelectric materials in combination with alternating magnetic fields is thought to be the most promising due to controllable reproducible cyclic deformations and deep tissue permeation by magnetic fields without tissue heating. In vitro and in vivo applications of nerve guidance scaffolds and conduits made of various piezopolymers are reviewed too. Finally, challenges and prospective research directions regarding piezoelectric biomaterials promoting nerve regeneration are discussed. Thus, the most relevant scientific findings and strategies in neural tissue engineering are described here, and this review may serve as a guideline both for researchers and clinicians.

Biomimetic Exogenous "Tissue Batteries" as Artificial Power Sources for Implantable Bioelectronic Devices Manufacturing

Implantable bioelectronic devices (IBDs) have gained attention for their capacity to conformably detect physiological and pathological signals and further provide internal therapy. However, traditional power sources integrated into these IBDs possess intricate limitations such as bulkiness, rigidity, and biotoxicity. Recently, artificial "tissue batteries" (ATBs) have diffusely developed as artificial power sources for IBDs manufacturing, enabling comprehensive biological-activity monitoring, diagnosis, and therapy. ATBs are on-demand and designed to accommodate the soft and confining curved placement space of organisms, minimizing interface discrepancies, and providing ample power for clinical applications. This review presents the near-term advancements in ATBs, with a focus on their miniaturization, flexibility, biodegradability, and power density. Furthermore, it delves into material-screening, structural-design, and energy density across three distinct categories of TBs, distinguished by power supply strategies. These types encompass innovative energy storage devices (chemical batteries and supercapacitors), power conversion devices that harness power from human-body (biofuel cells, thermoelectric nanogenerators, bio-potential devices, piezoelectric harvesters, and triboelectric devices), and energy transfer devices that receive and utilize external energy (radiofrequency-ultrasound energy harvesters, ultrasound-induced energy harvesters, and photovoltaic devices). Ultimately, future challenges and prospects emphasize ATBs with the indispensability of bio-safety, flexibility, and high-volume energy density as crucial components in long-term implantable bioelectronic devices.

Wireless Electric Cues Mediate Autologous DPSC-Loaded Conductive Hydrogel Microspheres to Engineer the Immuno-Angiogenic Niche for Homologous Maxillofacial Bone Regeneration

Stem cell therapy serves as an effective treatment for bone regeneration. Nevertheless, stem cells from bone marrow and peripheral blood are still lacking homologous properties. Dental pulp stem cells (DPSCs) are derived from neural crest, in coincidence with maxillofacial tissues, thus attracting great interest in in situ maxillofacial regenerative medicine. However, insufficient number and heterogenous alteration of seed cells retard further exploration of DPSC-based tissue engineering. Electric stimulation has recently attracted great interest in tissue regeneration. In this study, a novel DPSC-loaded conductive hydrogel microspheres integrated with wireless electric generator is fabricated. Application of exogenous electric cues can promote stemness maintaining and heterogeneity suppression for unpredictable differentiation of encapsulated DPSCs. Further investigations observe that electric signal fine-tunes regenerative niche by improvement on DPSC-mediated paracrine pattern, evidenced by enhanced angiogenic behavior and upregulated anti-inflammatory macrophage polarization. By wireless electric stimulation on implanted conductive hydrogel microspheres, loaded DPSCs facilitates the construction of immuno-angiogenic niche at early stage of tissue repair, and further contributes to advanced autologous mandibular bone defect regeneration. This novel strategy of DPSC-based tissue engineering exhibits promising translational and therapeutic potential for autologous maxillofacial tissue regeneration.

Flexible and Stretchable Light-Emitting Diodes and Photodetectors for Human-Centric Optoelectronics

Optoelectronic devices with unconventional form factors, such as flexible and stretchable light-emitting or photoresponsive devices, are core elements for the next-generation human-centric optoelectronics. For instance, these deformable devices can be utilized as closely fitted wearable sensors to acquire precise biosignals that are subsequently uploaded to the cloud for immediate examination and diagnosis, and also can be used for vision systems for human-interactive robotics. Their inception was propelled by breakthroughs in novel optoelectronic material technologies and device blueprinting methodologies, endowing flexibility and mechanical resilience to conventional rigid optoelectronic devices. This paper reviews the advancements in such soft optoelectronic device technologies, honing in on various materials, manufacturing techniques, and device design strategies. We will first highlight the general approaches for flexible and stretchable device fabrication, including the appropriate material selection for the substrate, electrodes, and insulation layers. We will then focus on the materials for flexible and stretchable light-emitting diodes, their device integration strategies, and representative application examples. Next, we will move on to the materials for flexible and stretchable photodetectors, highlighting the state-of-the-art materials and device fabrication methods, followed by their representative application examples. At the end, a brief summary will be given, and the potential challenges for further development of functional devices will be discussed as a conclusion.

Recent Advances in Implantable Neural Interfaces for Multimodal Electrical Neuromodulation

Electrical neuromodulation plays a pivotal role in enhancing patient outcomes among individuals suffering from neurological disorders. Implantable neural interfaces are vital components of the electrical neuromodulation system to ensure desirable performance; However, conventional devices are limited to a single function and are constructed with bulky and rigid materials, which often leads to mechanical incompatibility with soft tissue and an inability to adapt to the dynamic and complex 3D structures of biological systems. In addition, current implantable neural interfaces utilized in clinical settings primarily rely on wire-based techniques, which are associated with complications such as increased risk of infection, limited positioning options, and movement restrictions. Here, the state-of-art applications of electrical neuromodulation are presented. Material schemes and device structures that can be employed to develop robust and multifunctional neural interfaces, including flexibility, stretchability, biodegradability, self-healing, self-rolling, or morphing are discussed. Furthermore, multimodal wireless neuromodulation techniques, including optoelectronics, mechano-electrics, magnetoelectrics, inductive coupling, and electrochemically based self-powered devices are reviewed. In the end, future perspectives are given.

An Emerging Era: Conformable Ultrasound Electronics

Conformable electronics are regarded as the next generation of personal healthcare monitoring and remote diagnosis devices. In recent years, piezoelectric-based conformable ultrasound electronics (cUSE) have been intensively studied due to their unique capabilities, including nonradiative monitoring, soft tissue imaging, deep signal decoding, wireless power transfer, portability, and compatibility. This review provides a comprehensive understanding of cUSE for use in biomedical and healthcare monitoring systems and a summary of their recent advancements. Following an introduction to the fundamentals of piezoelectrics and ultrasound transducers, the critical parameters for transducer design are discussed. Next, five types of cUSE with their advantages and limitations are highlighted, and the fabrication of cUSE using advanced technologies is discussed. In addition, the working function, acoustic performance, and accomplishments in various applications are thoroughly summarized. It is noted that application considerations must be given to the tradeoffs between material selection, manufacturing processes, acoustic performance, mechanical integrity, and the entire integrated system. Finally, current challenges and directions for the development of cUSE are highlighted, and research flow is provided as the roadmap for future research. In conclusion, these advances in the fields of piezoelectric materials, ultrasound transducers, and conformable electronics spark an emerging era of biomedicine and personal healthcare.

Perinatal Tissue-Derived Stem Cells: An Emerging Therapeutic Strategy for Challenging Neurodegenerative Diseases

Over the past 20 years, stem cell therapy has been considered a promising option for treating numerous disorders, in particular, neurodegenerative disorders. Stem cells exert neuroprotective and neurodegenerative benefits through different mechanisms, such as the secretion of neurotrophic factors, cell replacement, the activation of endogenous stem cells, and decreased neuroinflammation. Several sources of stem cells have been proposed for transplantation and the restoration of damaged tissue. Over recent decades, intensive research has focused on gestational stem cells considered a novel resource for cell transplantation therapy. The present review provides an update on the recent preclinical/clinical applications of gestational stem cells for the treatment of protein-misfolding diseases including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD) and amyotrophic lateral sclerosis (ALS). However, further studies should be encouraged to translate this promising therapeutic approach into the clinical setting.

Rehabilitation exercise-driven symbiotic electrical stimulation system accelerating bone regeneration

Electrical stimulation can effectively accelerate bone healing. However, the substantial size and weight of electrical stimulation devices result in reduced patient benefits and compliance. It remains a challenge to establish a flexible and lightweight implantable microelectronic stimulator for bone regeneration. Here, we use self-powered technology to develop an electric pulse stimulator without circuits and batteries, which removes the problems of weight, volume, and necessary rigid packaging. The fully implantable bone defect electrical stimulation (BD-ES) system combines a hybrid tribo/piezoelectric nanogenerator to provide biphasic electric pulses in response to rehabilitation exercise with a conductive bioactive hydrogel. BD-ES can enhance multiple osteogenesis-related biological processes, including calcium ion import and osteogenic differentiation. In a rat model of critical-sized femoral defects, the bone defect was reversed by electrical stimulation therapy with BD-ES and subsequent bone mineralization, and the femur completely healed within 6 weeks. This work is expected to advance the development of symbiotic electrical stimulation therapy devices without batteries and circuits.

Biomaterials and bioelectronics for self-powered neurostimulation

Self-powered neurostimulation via biomaterials and bioelectronics innovation has emerged as a compelling approach to explore, repair, and modulate neural systems. This review examines the application of self-powered bioelectronics for electrical stimulation of both the central and peripheral nervous systems, as well as isolated neurons. Contemporary research has adeptly harnessed biomechanical and biochemical energy from the human body, through various mechanisms such as triboelectricity, piezoelectricity, magnetoelasticity, and biofuel cells, to power these advanced bioelectronics. Notably, these self-powered bioelectronics hold substantial potential for delivering neural stimulations that are customized for the treatment of neurological diseases, facilitation of neural regeneration, and the development of neuroprosthetics. Looking ahead, we expect that the ongoing advancements in biomaterials and bioelectronics will drive the field of self-powered neurostimulation toward the realization of more advanced, closed-loop therapeutic solutions, paving the way for personalized and adaptable neurostimulators in the coming decades.

Wireless Deep Brain Stimulation by Ultrasound-Responsive Molecular Piezoelectric Nanogenerators

Implantable neural stimulation devices are becoming prevalent in bioelectronic medicine for the precise treatment of various clinical diseases. Nevertheless, the limited lifespan and buckling size of the implanted devices remain significant obstacles for chronic clinical application. In this study, we developed an ultrasound-driven battery-free neurostimulator based on a high-performance mini-sized nanogenerator and demonstrated its successful application for the deep-brain-stimulation (DBS) therapy of Parkinson's disease in a rat model. This soft piezoelectric-triboelectric hybrid nanogenerators (PTNG) are made of porous thin-films of molecular piezoelectric materials, which have great advantages of facile, scalable, low-temperature, and flexible processing. Without any bucky accessory control circuits, the subcutaneously implanted soft PTNG can function as a wirelessly powered neurostimulator, allowing for the adjustment of stimulation parameters through external programmable ultrasound pulses. This DBS electroceutical application of energy-harvesting thin-film devices based on molecular piezoelectric materials provides valuable insight into the development of a soft high-performance bioelectronic device.

Supershear Rayleigh wave imaging for quantitative assessment of biomechanical properties of brain using air-coupled optical coherence elastography

Recently, supershear Rayleigh waves (SRWs) have been proposed to characterize the biomechanical properties of soft tissues. The SRWs propagate along the surface of the medium, unlike surface Rayleigh waves, SRWs propagate faster than bulk shear waves. However, their behavior and application in biological tissues is still elusive. In brain tissue elastography, shear waves combined with magnetic resonance elastography or ultrasound elastography are generally used to quantify the shear modulus, but high spatial resolution elasticity assessment in 10 μm scale is still improving. Here, we develop an air-coupled ultrasonic transducer for noncontact excitation of SRWs and Rayleigh waves in brain tissue, use optical coherent elastography (OCE) to detect, and reconstruct the SRW propagation process; in combing with a derived theoretical model of SRWs on a free boundary surface, we quantify the shear modulus of brain tissue with high spatial resolution. We first complete validation experiments using a homogeneous isotropic agar phantom, and the experimental results clearly show the SRW is 1.9649 times faster than the bulk shear waves. Furthermore, the propagation velocity of SRWs in both the frontal and parietal lobe regions of the brain is all 1.87 times faster than the bulk shear wave velocity. Finally, we evaluated the anisotropy in different brain regions, and the medulla oblongata region had the highest anisotropy index. Our study shows that the OCE system using the SRW model is a new potential approach for high-resolution assessment of the biomechanical properties of brain tissue.

Temporal Immunomodulation via Wireless Programmed Electric Cues Achieves Optimized Diabetic Bone Regeneration

Mimicking the temporal pattern of biological behaviors during the natural repair process is a promising strategy for biomaterial-mediated tissue regeneration. However, precise regulation of dynamic cell behaviors allocated in a microenvironment post-implantation remains challenging until now. Here, remote tuning of electric cues is accomplished by wireless ultrasound stimulation (US) on an electroactive membrane for bone regeneration under a diabetic background. Programmable electric cues mediated by US from the piezoelectric membrane achieve the temporal regulation of macrophage polarization, satisfying the pattern of immunoregulation during the natural healing process and effectively promoting diabetic bone repair. Mechanistic insight reveals that the controllable decrease in AKT2 expression and phosphorylation could explain US-mediated macrophage polarization. This study exhibits a strategy aimed at precisely biosimulating the temporal regenerative pattern by controllable and programmable electric output for optimized diabetic tissue regeneration and provides basic insights into bionic design-based precision medicine achieved by intelligent and external field-responsive biomaterials.

Functional material-mediated wireless physical stimulation for neuro-modulation and regeneration

Nerve injuries and neurological diseases remain intractable clinical challenges. Despite the advantages of stem cell therapy in treating neurological disorders, uncontrollable cell fates and loss of cell function in vivo are still challenging. Recently, increasing attention has been given to the roles of external physical signals, such as electricity and ultrasound, in regulating stem cell fate as well as activating or inhibiting neuronal activity, which provides new insights for the treatment of neurological disorders. However, direct physical stimulations in vivo are short in accuracy and safety. Functional materials that can absorb energy from a specific physical field exerted in a wireless way and then release another localized physical signal hold great advantages in mediating noninvasive or minimally invasive accurate indirect physical stimulations to promote the therapeutic effect on neurological disorders. In this review, the mechanism by which various physical signals regulate stem cell fate and neuronal activity is summarized. Based on these concepts, the approaches of using functional materials to mediate indirect wireless physical stimulation for neuro-modulation and regeneration are systematically reviewed. We expect that this review will contribute to developing wireless platforms for neural stimulation as an assistance for the treatment of neurological diseases and injuries.

Tissue-Matchable and Implantable Batteries Toward Biomedical Applications

Implantable electronic devices can realize real-time and reliable health monitoring, diagnosis, and treatment of human body, which are expected to overcome important bottlenecks in the biomedical field. However, the commonly used energy supply devices for them are implantable batteries based on conventional rigid device design with toxic components, which both mechanically and biologically mismatch soft biological tissues. Therefore, the development of highly soft, safe, and implantable tissue-matchable flexible batteries is of great significance and urgency for implantable bioelectronics. In this work, the recent advances of tissue-matchable and implantable flexible batteries are overviewed, focusing on the design strategies of electrodes/batteries and their biomedical applications. The mechanical flexibility, biocompatibility, and electrochemical performance in vitro and in vivo of these flexible electrodes/batteries are then discussed. Finally, perspectives are provided on the current challenges and possible directions of this field in the future.

Implantable Zinc-Oxygen Battery for In Situ Electrical Stimulation-Promoted Neural Regeneration

Electrical stimulation is a promising strategy for treating neural diseases. However, current energy suppliers cannot provide effective power for in situ electrical stimulation. Here, an implantable tubular zinc-oxygen battery is reported as the power source for in situ electrical stimulation during the neural repair. The battery exhibited a high volumetric energy density of 231.4 mWh cm-3 based on the entire anode and cathode in vivo. Due to its superior electrochemical properties and biosafety, the battery can be directly wrapped around the nerve to provide in situ electrical stimulation with a minimal size of 0.86 mm3 . The cell and animal experiments demonstrated that the zinc-oxygen battery-based nerve tissue engineering conduit effectively promoted regeneration of the injured long-segment sciatic nerve, proving its promising applications for powering implantable neural electronics in the future.

The marriage of immunomodulatory, angiogenic, and osteogenic capabilities in a piezoelectric hydrogel tissue engineering scaffold for military medicine

BACKGROUND

Most bone-related injuries to grassroots troops are caused by training or accidental injuries. To establish preventive measures to reduce all kinds of trauma and improve the combat effectiveness of grassroots troops, it is imperative to develop new strategies and scaffolds to promote bone regeneration.

METHODS

In this study, a porous piezoelectric hydrogel bone scaffold was fabricated by incorporating polydopamine (PDA)-modified ceramic hydroxyapatite (PDA-hydroxyapatite, PHA) and PDA-modified barium titanate (PDA-BaTiO₃, PBT) nanoparticles into a chitosan/gelatin (Cs/Gel) matrix. The physical and chemical properties of the Cs/Gel/PHA scaffold with 0-10 wt% PBT were analyzed. Cell and animal experiments were performed to characterize the immunomodulatory, angiogenic, and osteogenic capabilities of the piezoelectric hydrogel scaffold in vitro and in vivo.

RESULTS

The incorporation of BaTiO₃ into the scaffold improved its mechanical properties and increased self-generated electricity. Due to their endogenous piezoelectric stimulation and bioactive constituents, the as-prepared Cs/Gel/PHA/PBT hydrogels exhibited cytocompatibility as well as immunomodulatory, angiogenic, and osteogenic capabilities; they not only effectively induced macrophage polarization to M2 phenotype but also promoted the migration, tube formation, and angiogenic differentiation of human umbilical vein endothelial cells (HUVECs) and facilitated the migration, osteo-differentiation, and extracellular matrix (ECM) mineralization of MC3T3-E1 cells. The in vivo evaluations showed that these piezoelectric hydrogels with versatile capabilities significantly facilitated new bone formation in a rat large-sized cranial injury model. The underlying molecular mechanism can be partly attributed to the immunomodulation of the Cs/Gel/PHA/PBT hydrogels as shown via transcriptome sequencing analysis, and the PI3K/Akt signaling axis plays an important role in regulating macrophage M2 polarization.

CONCLUSION

The piezoelectric Cs/Gel/PHA/PBT hydrogels developed here with favorable immunomodulation, angiogenesis, and osteogenesis functions may be used as a substitute in periosteum injuries, thereby offering the novel strategy of applying piezoelectric stimulation in bone tissue engineering for the enhancement of combat effectiveness in grassroots troops.

Oxidative Stress: A Suitable Therapeutic Target for Optic Nerve Diseases?

Optic nerve disorders encompass a wide spectrum of conditions characterized by the loss of retinal ganglion cells (RGCs) and subsequent degeneration of the optic nerve. The etiology of these disorders can vary significantly, but emerging research highlights the crucial role of oxidative stress, an imbalance in the redox status characterized by an excess of reactive oxygen species (ROS), in driving cell death through apoptosis, autophagy, and inflammation. This review provides an overview of ROS-related processes underlying four extensively studied optic nerve diseases: glaucoma, Leber's hereditary optic neuropathy (LHON), anterior ischemic optic neuropathy (AION), and optic neuritis (ON). Furthermore, we present preclinical findings on antioxidants, with the objective of evaluating the potential therapeutic benefits of targeting oxidative stress in the treatment of optic neuropathies.

Physical mechanisms of emerging neuromodulation modalities

One of the ultimate goals of neurostimulation field is to design materials, devices and systems that can simultaneously achieve safe, effective and tether-free operation. For that, understanding the working mechanisms and potential applicability of neurostimulation techniques is important to develop noninvasive, enhanced, and multi-modal control of neural activity. Here, we review direct and transduction-based neurostimulation techniques by discussing their interaction mechanisms with neurons via electrical, mechanical, and thermal means. We show how each technique targets modulation of specific ion channels (e.g. voltage-gated, mechanosensitive, heat-sensitive) by exploiting fundamental wave properties (e.g. interference) or engineering nanomaterial-based systems for efficient energy transduction. Overall, our review provides a detailed mechanistic understanding of neurostimulation techniques together with their applications toin vitro, in vivo, and translational studies to guide the researchers toward developing more advanced systems in terms of noninvasiveness, spatiotemporal resolution, and clinical applicability.

Non-Invasive Hybrid Ultrasound Stimulation of Visual Cortex In Vivo

The optic nerve is the second cranial nerve (CN II) that connects and transmits visual information between the retina and the brain. Severe damage to the optic nerve often leads to distorted vision, vision loss, and even blindness. Such damage can be caused by various types of degenerative diseases, such as glaucoma and traumatic optic neuropathy, and result in an impaired visual pathway. To date, researchers have not found a viable therapeutic method to restore the impaired visual pathway; however, in this paper, a newly synthesized model is proposed to bypass the damaged portion of the visual pathway and set up a direct connection between a stimulated visual input and the visual cortex (VC) using Low-frequency Ring-transducer Ultrasound Stimulation (LRUS). In this study, by utilizing and integrating various advanced ultrasonic and neurological technologies, the following advantages are achieved by the proposed LRUS model: 1. This is a non-invasive procedure that uses enhanced sound field intensity to overcome the loss of ultrasound signal due to the blockage of the skull. 2. The simulated visual signal generated by LRUS in the visual-cortex-elicited neuronal response in the visual cortex is comparable to light stimulation of the retina. The result was confirmed by a combination of real-time electrophysiology and fiber photometry. 3. VC showed a faster response rate under LRUS than light stimulation through the retina. These results suggest a potential non-invasive therapeutic method for restoring vision in optic-nerve-impaired patients using ultrasound stimulation (US).

Piezoelectric biomaterials for neural tissue engineering

Nerve injury caused by trauma or iatrogenic trauma can lead to loss of sensory and motor function, resulting in paralysis of patients. Inspired by endogenous bioelectricity and extracellular matrix, various external physical and chemical stimuli have been introduced to treat nerve injury. Benefiting from the self-power feature and great biocompatibility, piezoelectric biomaterials have attracted widespread attention in biomedical applications, especially in neural tissue engineering. Here, we provide an overview of the development of piezoelectric biomaterials for neural tissue engineering. First, several types of piezoelectric biomaterials are introduced, including inorganic piezoelectric nanomaterials, organic piezoelectric polymers, and their derivates. Then, we focus on the in vitro and in vivo external energy-driven piezoelectric effects involving ultrasound, mechanical movement, and other external field-driven piezoelectric effects. Neuroengineering applications of the piezoelectric biomaterials as in vivo grafts for the treatment of central nerve injury and peripheral nerve injury are also discussed and highlighted. Finally, the current challenges and future development of piezoelectric biomaterials for promoting nerve regeneration and treating neurological diseases are presented.

Ultrasound-mediated piezoelectric nanoparticle modulation of intrinsic cardiac autonomic nervous system for rate control in atrial fibrillation

Rate control is a cornerstone of atrial fibrillation treatment. Barium titanate nanoparticles (BTNPs) are piezoelectric nanomaterials that can generate local electromagnetic fields under ultrasound activation, stimulating nearby neuronal tissue. This study aimed to modulate the inferior right ganglionated plexus (IRGP) of the heart and reduce the ventricular rate during rapid atrial pacing (RAP)-induced atrial fibrillation using ultrasound-mediated BTNPs. Adult male beagles were randomly divided into a phosphate-buffered saline (PBS) group (n = 6) and a BTNP group (n = 6). PBS or nanoparticles were injected into the IRGP of both groups before RAP. The biological safety of the material was evaluated according to electrophysiology recordings, thermal effects and level of inflammation. Compared to the PBS group, the BaTiO₃ piezoelectric nanoparticle group had reduced ventricular rates in the sinus rhythm and atrial fibrillation models after stimulating the IRGP by applying ultrasound. In addition, transient stimulation by BTNPs did not lead to sustained neuronal excitation in the IRGP. The activation of the BTNPs did not induce inflammation or thermal damage effects in the IRGP. Ultrasound-mediated BTNP neuromodulation can significantly reduce the ventricular rate by stimulating the IRGP. Thus, ultrasound-mediated BTNP neuromodulation is a potential therapy for atrial fibrillation rate control.

Triboelectric and Piezoelectric Nanogenerators for Self-Powered Healthcare Monitoring Devices: Operating Principles, Challenges, and Perspectives

The internet of medical things (IoMT) is used for the acquisition, processing, transmission, and storage of medical data of patients. The medical information of each patient can be monitored by hospitals, family members, or medical centers, providing real-time data on the health condition of patients. However, the IoMT requires monitoring healthcare devices with features such as being lightweight, having a long lifetime, wearability, flexibility, safe behavior, and a stable electrical performance. For the continuous monitoring of the medical signals of patients, these devices need energy sources with a long lifetime and stable response. For this challenge, conventional batteries have disadvantages due to their limited-service time, considerable weight, and toxic materials. A replacement alternative to conventional batteries can be achieved for piezoelectric and triboelectric nanogenerators. These nanogenerators can convert green energy from various environmental sources (e.g., biomechanical energy, wind, and mechanical vibrations) into electrical energy. Generally, these nanogenerators have simple transduction mechanisms, uncomplicated manufacturing processes, are lightweight, have a long lifetime, and provide high output electrical performance. Thus, the piezoelectric and triboelectric nanogenerators could power future medical devices that monitor and process vital signs of patients. Herein, we review the working principle, materials, fabrication processes, and signal processing components of piezoelectric and triboelectric nanogenerators with potential medical applications. In addition, we discuss the main components and output electrical performance of various nanogenerators applied to the medical sector. Finally, the challenges and perspectives of the design, materials and fabrication process, signal processing, and reliability of nanogenerators are included.

Modular pulse synthesizer for transcranial magnetic stimulation with fully adjustable pulse shape and sequence

The temporal shape of a pulse in transcranial magnetic stimulation (TMS) influences which neuron populations are activated preferentially as well as the strength and even direction of neuromodulation effects. Furthermore, various pulse shapes differ in their efficiency, coil heating, sensory perception, and clicking sound. However, the available TMS pulse shape repertoire is still very limited to a few biphasic, monophasic, and polyphasic pulses with sinusoidal or near-rectangular shapes. Monophasic pulses, though found to be more selective and stronger in neuromodulation, are generated inefficiently and therefore only available in simple low-frequency repetitive protocols. Despite a strong interest to exploit the temporal effects of TMS pulse shapes and pulse sequences, waveform control is relatively inflexible and only possible parametrically within certain limits. Previously proposed approaches for flexible pulse shape control, such as through power electronic inverters, have significant limitations: The semiconductor switches can fail under the immense electrical stress associated with free pulse shaping, and most conventional power inverter topologies are incapable of generating smooth electric fields or existing pulse shapes. Leveraging intensive preliminary work on modular power electronics, we present a modular pulse synthesizer (MPS) technology that can, for the first time, flexibly generate high-power TMS pulses (one-side peak ∼4000 V, ∼8000 A) with user-defined electric field shape as well as rapid sequences of pulses with high output quality. The circuit topology breaks the problem of simultaneous high power and switching speed into smaller, manageable portions, distributed across several identical modules. In consequence, the MPS TMS techology can use semiconductor devices with voltage and current ratings lower than the overall pulse voltage and distribute the overall switching of several hundred kilohertz among multiple transistors. MPS TMS can synthesize practically any pulse shape, including conventional ones, with fine quantization of the induced electric field (⩽17% granularity without modulation and ∼300 kHz bandwidth). Moreover, the technology allows optional symmetric differential coil driving so that the average electric potential of the coil, in contrast to conventional TMS devices, stays constant to prevent capacitive artifacts in sensitive recording amplifiers, such as electroencephalography. MPS TMS can enable the optimization of stimulation paradigms for more sophisticated probing of brain function as well as stronger and more selective neuromodulation, further expanding the parameter space available to users.

Wirelessly Powered Electrical-Stimulation Based on Biodegradable 3D Piezoelectric Scaffolds Promotes the Spinal Cord Injury Repair

An electroactive scaffold integrated with noninvasive in vivo electrical-stimulation (ES) capability shows great promise in the repair and regeneration of damaged tissues. Developing high-performance piezoelectric biomaterials which can simultaneously serve as both a biodegradable tissue scaffold and controllable electrical stimulator remains a great challenge. Herein, we constructed a biodegradable high-performance 3D piezoelectric scaffold with ultrasound (US)-driven wireless ES capability, and demonstrated its successful application for the repair of spinal cord injuries in a rat model. The 3D multichannel piezoelectric scaffold was prepared by electrospinning of poly(lactic acid) (PLA) nanofibers incorporated with biodegradable high-performance piezoelectric potassium sodium niobate (K_0.5Na_0.5NbO₃, KNN) nanowires. With programmed US irradiation as a remote mechanical stimulus, the on-demand in vivo ES with an adjustable timeline, duration, and strength can be delivered by the 3D piezoelectric scaffold. Under proper US excitation, the 3D tissue scaffolds made of the piezoelectric composite nanofibers can accelerate the recovery of motor functions and enhance the repair of spinal cord injury. The immunohistofluorescence investigation indicated that the 3D piezoelectric scaffolds combined with the US-driven in vivo ES promoted neural stem cell differentiation and endogenous angiogenesis in the lesion. This work highlights the potential application of a biodegradable high-performance piezoelectric scaffold providing US-driven on-demand electrical cues for regenerative medicine.

Electroceuticals for peripheral nerve regeneration

Electroceuticals provide promising opportunities for peripheral nerve regeneration, in terms of modulating the extensive endogenous tissue repair mechanisms between neural cell body, axons and target muscles. However, great challenges remain to deliver effective and controllable electroceuticals via bioelectronic implantable device. In this review, the modern fabrication methods of bioelectronic conduit for bridging critical nerve gaps after nerve injury are summarized, with regard to conductive materials and core manufacturing process. In addition, to deliver versatile electrical stimulation, the integration of implantable bioelectronic device is discussed, including wireless energy harvesters, actuators and sensors. Moreover, a comprehensive insight of beneficial mechanisms is presented, including up-to-date in vitro, in vivo and clinical evidence. By integrating conductive biomaterials, 3D engineering manufacturing process and bioelectronic platform to deliver versatile electroceuticals, the modern biofabrication enables comprehensive biomimetic therapies for neural tissue engineering and regeneration in the new era.

Electrical Stimulation Enabled via Electrospun Piezoelectric Polymeric Nanofibers for Tissue Regeneration

Electrical stimulation has demonstrated great effectiveness in the modulation of cell fate in vitro and regeneration therapy in vivo. Conventionally, the employment of electrical signal comes with the electrodes, battery, and connectors in an invasive fashion. This tedious procedure and possible infection hinder the translation of electrical stimulation technologies in regenerative therapy. Given electromechanical coupling and flexibility, piezoelectric polymers can overcome these limitations as they can serve as a self-powered stimulator via scavenging mechanical force from the organism and external stimuli wirelessly. Wireless electrical cue mediated by electrospun piezoelectric polymeric nanofibers constitutes a promising paradigm allowing the generation of localized electrical stimulation both in a noninvasive manner and at cell level. Recently, numerous studies based on electrospun piezoelectric nanofibers have been carried out in electrically regenerative therapy. In this review, brief introduction of piezoelectric polymer and electrospinning technology is elucidated first. Afterward, we highlight the activating strategies (e.g., cell traction, physiological activity, and ultrasound) of piezoelectric stimulation and the interaction of piezoelectric cue with nonelectrically/electrically excitable cells in regeneration medicine. Then, quantitative comparison of the electrical stimulation effects using various activating strategies on specific cell behavior and various cell types is outlined. Followingly, this review explores the present challenges in electrospun nanofiber-based piezoelectric stimulation for regeneration therapy and summarizes the methodologies which may be contributed to future efforts in this field for the reality of this technology in the clinical scene. In the end, a summary of this review and future perspectives toward electrospun nanofiber-based piezoelectric stimulation in tissue regeneration are elucidated.

Wireless interfaces for brain neurotechnologies

Wireless interfaces enable brain-implanted devices to remotely interact with the external world. They are critical components in modern research and clinical neurotechnologies and play a central role in determining their overall size, lifetime and functionality. Wireless interfaces use a wide range of modalities-including radio-frequency fields, acoustic waves and light-to transfer energy and data to and from an implanted device. These forms of energy interact with living tissue through distinct mechanisms and therefore lead to systems with vastly different form factors, operating characteristics, and safety considerations. This paper reviews recent advances in the development of wireless interfaces for brain neurotechnologies. We summarize the requirements that state-of-the-art brain-implanted devices impose on the wireless interface, and discuss the working principles and applications of wireless interfaces based on each modality. We also investigate challenges associated with wireless brain neurotechnologies and discuss emerging solutions permitted by recent developments in electrical engineering and materials science. This article is part of the theme issue 'Advanced neurotechnologies: translating innovation for health and well-being'.

Metal-Free Perovskite Piezoelectric Nanogenerators for Human-Machine Interfaces and Self-Powered Electrical Stimulation Applications

Single crystal metal-free halide perovskites have received great attention in recent years owing to their excellent piezoelectric and ferroelectric properties. However, the nanotoxicity and piezoelectricity within the nanoscale of such materials have yet been reported for the demonstration of practical applications. In this work, the observation of intrinsic piezoelectricity in metal-free perovskite (MDABCO-NH₄ I₃ ) films using piezoresponse force microscopy (PFM) is reported. A cytotoxicity test is also performed on MDABCO-NH₄ I₃ to evaluate its low-toxic nature. The as-synthesized MDABCO-NH₄ I₃ is further integrated into a piezoelectric nanogenerator (PENG). The MDABCO-NH₄ I₃ -based PENG (MN-PENG) exhibits optimal output voltage and current of 15.9 V and 54.5 nA, respectively. In addition, the MN-PENG can serve as a self-powered strain sensor for human-machine interface applications or be adopted in in vitro electrical stimulation devices. This work demonstrates a path of perovskite-based PENG with high performance, low toxicity, and multifunctionality for future advanced wearable sensors and portable therapeutic systems.

Characterization of Pannexin1, Connexin32, and Connexin43 in Spotted Sea Bass (Lateolabrax maculatus): They Are Important Neuro-Related Immune Response Genes Involved in Inflammation-Induced ATP Release

Many immunological diseases can be treated by regulating neurobehavior, in which extracellular ATP is a vital member of endogenous danger-associated molecular pattern signaling molecule that plays a crucial part in innate neuro-related immunity. It is actively released through pannexin (Panx) and connexin (Cx) hemichannels from activated or stressed cells during inflammation, injury, or apoptosis. In addition to participating in ATP release, Panxs and Cxs also have crucial immune functions. In this study, pannexin1, three connexin32 isoforms and connexin43 were identified and characterized in spotted sea bass (Lateolabrax maculatus), which were named LmPanx1, LmCx32.2, LmCx32.3, LmCx32.7, and LmCx43. Their similar topological structures were discovered by sequence analysis: a relatively unconserved C-terminal region and four highly conserved transmembrane (TM) domains, and so on. Each extracellular (ECL) region of Panx1 has two conserved cysteine residues. Unlike Panx1, each ECL region of Cx32 and Cx43 contains three conserved cysteine residues, forming two conserved motifs: CX6CX3C motif in ECL1 and CX4CX5C motif in ECL2. Furthermore, Panx1 and Cx43 share similar genomic organization and synteny with their counterparts in selected vertebrates. Cx32 and CX43 were located in the same locus in fish, but diverged into two loci from amphibian. Moreover, despite varying expression levels, the identified genes were constitutively expressed in all examined tissues. All genes were upregulated by PAMP [lipopolysaccharide and poly(I:C)] stimulation or bacterial infection in vivo and in vitro, but they were downregulated in the brain at 6 or 12 h after stimulation. Especially, the three LmCx32 isoforms and LmCx43 were upregulated by ATP stimulation in primary head kidney leukocytes; however, downregulation of LmCx32.3 and LmCx43 expression were noted at 12 h. Conversely, ATP treatment inhibited the expression of LmPanx1. Importantly, we showed that the spotted sea bass Panx1, Cx43, and Cx32 were localized on the cellular membrane and involved in inflammation-induced ATP release. Taken together, our results demonstrated that Panx1, Cx32, and Cx43 are important neuro-related immune response genes involved in inflammation-induced ATP release.

Wearable Piezoelectric Nanogenerators Based on Core-Shell Ga-PZT@GaOx Nanorod-Enabled P(VDF-TrFE) Composites

High-output flexible piezoelectric nanogenerators (PENGs) have achieved great progress and are promising applications for harvesting mechanical energy and supplying power to flexible electronics. In this work, unique core-shell structured Ga-PbZr_xTi_1-xO₃ (PZT)@GaO_x nanorods were synthesized by a simple mechanical mixing method and then were applied as fillers in a poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) matrix to obtain highly efficient PENGs with excellent energy-harvesting properties. The decoration of gallium nanoparticles on PZT @GaO_x nanorods can amplify the local electric field, facilitate the increment of polar β-phase fraction in P(VDF-TrFE), and strengthen the polarizability of PZT and P(VDF-TrFE). The interfacial interactions of GaO_x and P(VDF-TrFE) are also in favor of an increased β-phase fraction, which results in a remarkable improvement of PENG performance. The optimized Ga-PZT@GaO_x/P(VDF-TrFE) PENG delivers a maximum open-circuit voltage of 98.6 V and a short-circuit current of 0.3 μA with 9.8 μW instantaneous power under a vertical force of 12 N at a frequency of 30 Hz. Such a PENG exhibits a stable output voltage after 6 000 cycles by the durability test. Moreover, the liquid gallium metal offers a mechanical matching interface between rigid PZT and the soft polymer matrix, which benefits the effective, durable mechanical energy-harvesting capability from the physical activities of elbow joint bending and walking. This research renders a deep association between a liquid metal and piezoelectric ceramics in the field of piezoelectric energy conversion, offering a promising approach toward self-powered smart wearable devices.

Recent progress on polyvinylidene difluoride based nanocomposite: Applications in energy harvesting and sensing

Discovered in 2006, Nanogenerators have attracted much attention as promising energy-harvesting devices. It harnesses energy by utilizing piezoelectric, pyroelectric thermoelectric properties of nanomaterials to produce electricity and have potential to...

Recent Advances in Self-Powered Piezoelectric and Triboelectric Sensors: From Material and Structure Design to Frontier Applications of Artificial Intelligence

The development of artificial intelligence and the Internet of things has motivated extensive research on self-powered flexible sensors. The conventional sensor must be powered by a battery device, while innovative self-powered sensors can provide power for the sensing device. Self-powered flexible sensors can have higher mobility, wider distribution, and even wireless operation, while solving the problem of the limited life of the battery so that it can be continuously operated and widely utilized. In recent years, the studies on piezoelectric nanogenerators (PENGs) and triboelectric nanogenerators (TENGs) have mainly concentrated on self-powered flexible sensors. Self-powered flexible sensors based on PENGs and TENGs have been reported as sensing devices in many application fields, such as human health monitoring, environmental monitoring, wearable devices, electronic skin, human–machine interfaces, robots, and intelligent transportation and cities. This review summarizes the development process of the sensor in terms of material design and structural optimization, as well as introduces its frontier applications in related fields. We also look forward to the development prospects and future of self-powered flexible sensors.