The intrinsic piezoelectric properties of materials - a review with a focus on biological materials

One-step high-speed thermal-electric aerosol printing of piezoelectric bio-organic films for wirelessly powering bioelectronics

Piezoelectric biomaterials hold a pivotal role in the progression of bioelectronics and biomedicine, owing to their remarkable electromechanical properties, biocompatibility, and bioresorbability. However, their technological potential is restrained by certain challenges, including precise manipulation of nanobiomolecules, controlling their growth across nano-to-macro hierarchy, and tuning desirable mechanical properties. We report a high-speed thermal-electric driven aerosol (TEA) printing method capable of fabricating piezoelectric biofilms in a singular step. Electrohydrodynamic aerosolizing and in situ electrical poling allow instantaneous tuning of the spatial organization of biomolecular inks. We demonstrate TEA printing of β-glycine/polyvinylpyrrolidone films, and such films exhibit the piezoelectric voltage coefficient of 190 × 10-3 volt-meters per newton, surpassing that of industry-standard lead zirconate titanate by approximately 10-fold. Furthermore, these films demonstrate nearly two orders of magnitude improvement in mechanical flexibility compared to glycine crystals. We also demonstrate the ultrasonic energy harvesters based on the biofilms, providing the possibility of wirelessly powering bioelectronics.

Wearable Applicability of Respiratory Airflow Transducers: Current Approaches and Future Directions

Advanced technologies employed in modern respiratory airflow transducers have exhibited powerful capabilities in accurately measuring respiratory flow under controlled and sedentary conditions, particularly in clinical settings. However, the wearable applicability of these transducers as face-mounted electronics for use in occupational and sporting activities remains unexplored. The present review addresses the critical wearability issue associated with current respiratory airflow transducers, including pneumotachographs, orifice flowmeters, turbine flowmeters, hot wire anemometers, ultrasound flowmeters, and piezoelectric airflow transducers. Furthermore, a comprehensive analysis and comparison of all factors that impact the wearable applicability of respiratory airflow transducers are conducted, considering dynamic accuracy, long-term usability, power consumption, calibration frequency, and cleaning requirements. The findings indicate that the piezoelectric airflow transducer stands out as a more viable option for wearables compared to other devices. We expect that this review will serve as a valuable engineering reference, guiding future research efforts in designing and developing wearable respiratory airflow transducers for ambulatory respiratory flow monitoring.

Molded, Solid-State Biomolecular Assemblies with Programmable Electromechanical Properties

Piezoelectric and ferroelectric technologies are currently dominated by perovskite-based ceramics, not only due to their impressive figures of merit, but due to their versatility in size and shape. This allows the dimensions of, for example, lead zirconium titanate and potassium sodium niobate, to be tailored to the needs of thousands of applications across the automotive, medical device, and consumer electronics industries. In this Letter, we significantly advance the performance and customization of biomolecular crystal (nontoxic, biocompatible amino acids, viz., trans-4-hydroxy-L-proline, L-alanine, hydrates of L-arginine and L-asparagine, and γ-glycine) assemblies by growing them as molded, substrate-free piezoelectric elements. This methodology allows for electromechanical properties to be embedded in these assemblies by fine-tuning the chemistry of the biomolecules and thus the functional properties of the single crystal space group. Here, we report the piezoelectric, mechanical, thermal, and structural properties of these amino acid-based polycrystalline actuators. This versatile, low-cost, low-temperature growth method opens up the path to phase in biomolecular piezoelectrics as high-performance, eco-friendly alternatives to ceramics.

Advanced Materials for Energy Harvesting and Soft Robotics: Emerging Frontiers to Enhance Piezoelectric Performance and Functionality

Piezoelectric energy harvesting captures mechanical energy from a number of sources, such as vibrations, the movement of objects and bodies, impact events, and fluid flow to generate electric power. Such power can be employed to support wireless communication, electronic components, ocean monitoring, tissue engineering, and biomedical devices. A variety of self-powered piezoelectric sensors, transducers, and actuators have been produced for these applications, however approaches to enhance the piezoelectric properties of materials to increase device performance remain a challenging frontier of materials research. In this regard, the intrinsic polarization and properties of materials can be designed or deliberately engineered to enhance the piezo-generated power. This review provides insights into the mechanisms of piezoelectricity in advanced materials, including perovskites, active polymers, and natural biomaterials, with a focus on the chemical and physical strategies employed to enhance the piezo-response and facilitate their integration into complex electronic systems. Applications in energy harvesting and soft robotics are overviewed by highlighting the primary performance figures of merits, the actuation mechanisms, and relevant applications. Key breakthroughs and valuable strategies to further improve both materials and device performance are discussed, together with a critical assessment of the requirements of next-generation piezoelectric systems, and future scientific and technological solutions.

A historical timeline of the development and evolution of medical diagnostic ultrasonography

Diagnostic ultrasonography has evolved to become an indispensable imaging tool that permits non-invasive evaluation of the whole body. In this narrative review, we present a historical timeline of the invention, development, and evolution of diagnostic medical ultrasound. It includes interesting fun facts that may help the reader identify with many of the incredible researchers in this field. This review is a tribute to the researchers who contributed to this amazing invention.

A review of recent advances of piezoelectric poly-L-lactic acid for biomedical applications

Poly-L-lactic acid (PLLA), recognized as a piezoelectric material, not only demonstrates exceptional piezoelectric properties but also exhibits commendable biocompatibility and biodegradability. These properties render PLLA highly promising for diverse applications, including sensors, wearable devices, biomedical engineering, and related domains. This review offers a comprehensive overview of the distinctive piezoelectric effect of PLLA-based material and delves into the latest advancements in its preparation strategies as a piezoelectric material. It further presents recent research progress in PLLA-based piezoelectric materials, particularly in the realms of health monitoring, skin repair, nerve regeneration, and tissue repair. The discourse extends to providing insights into potential future trajectories for the development of PLLA-based piezoelectric materials.

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.

Ultrasonic controllable synthesis of sulfur-functionalized metal-organic frameworks (S-MOFs) and their application in piezo-photocatalytic rapid reduction of hexavalent chromium (Cr)

The United Nations' Sustainable Development Goals (SDGs) are significant in guiding modern scientific research. In recent years, scholars have paid much attention to MOFs materials as green materials. However, piezo catalysis of MOFs materials has not been widely studied. Piezoelectric materials can convert mechanical energy into electrical energy, while MOFs are effective photocatalysts for removing pollutants. Therefore, it is crucial to design MOFs with piezoelectric properties and photosensitivity. In this study, sulfur-functionalized metal-organic frameworks (S-MOFs) were prepared using organic sulfur-functionalized ligand (H2TDC) ultrasonic synthesis to enhance their piezoelectric properties and visible light absorption. The study demonstrated that the S-MOFs significantly enhanced the reduction of a 10 mg/L solution of hexavalent chromium to 99.4 % within 10 min, using only 15 mg of catalyst. The orbital energy level differences of the elements were analyzed using piezo response force microscopy (PFM) and X-ray photoelectron spectroscopy (XPS). The results showed that MOFs functionalized with sulfur atom ligands have a built-in electric field that facilitates charge separation and migration. This study presents a new approach to enhance the piezoelectric properties of MOFs, which broadens their potential applications in piezo catalysis and piezo-photocatalysis. Additionally, it provides a sustainable method for reducing hexavalent chromium, contributing to the achievement of sustainable development goals, specifically SDG-6, SDG-7, SDG-9, and SDG-12.

All-Textile Piezoelectric Nanogenerator Based on 3D Knitted Fabric Electrode for Wearable Applications

Flexible, air permeable and elastic self-powered sensors for human motion monitoring and assisted medical rehabilitation have recently become a hot research topic. However, most current piezoelectric sensors can not account for many characteristics. Addressing this challenge, an all-textile piezoelectric sensor (ATPS) based on 3D structured knitted fabric electrodes is reported. The ATPS consists of a piezoelectric element polyvinylidene fluoride nanofiber membrane, flexible knitted fabric electrodes, and an elastic self-adhesive bandage. Based on the flexible and efficient knitting technology, the sensor has the advantages of low cost, flexibility, simple structure, and convenient large-area manufacturing. Experimental and finite element simulation results show that the knitting pattern of fabric electrodes can enhance the piezoelectric output of ATPS. The optimal ATPS has a high voltage response sensitivity of up to 0.68 V/kPa. The proposed ATPS responds to a wide range of input forces from 0.098 to 724 N in self-powered mode, verifying its feasibility as a tactile sensor for human motion detection and recognition (throat swallowing, wrist bending, elbow bending, knee bending, walking slowly, running fast) and as a pressure sensor (Morse code, digit recognition) and demonstrating its potential for motion tracking, medical rehabilitation, and human-computer interaction.

Piezoelectric catalytic driven advanced oxidation process using two-dimensional metal dichalcogenides for wastewater pollutants remediation

The public and society have increasingly recognized numerous grave environmental issues, including water pollution, attributed to the rapid expansion of industrialization and agriculture. Renewable energy-driven catalytic advanced oxidation processes (AOPs) represent a green, sustainable, and environmentally friendly approach to meet the demands of environmental remediation. In this context, 2D transition metal dichalcogenides (TMDCs) piezoelectric materials, with their non-centrosymmetric crystal structure, exhibit unique features. They create dipole polarization, inducing a built-in electric field that generates polarized holes and electrons and triggers redox reactions, thereby facilitating the generation of reactive oxygen species for wastewater pollutant remediation. A broad spectrum of 2D TMDCs piezoelectric materials have been explored in self-integrated Fenton-like processes and persulfate activation processes. These materials offer a more simplistic and practical method than traditional approaches. Consequently, this review highlights recent advancements in 2D TMDCs piezoelectric catalysts and their roles in wastewater pollutant remediation through piezocatalytic-driven AOPs, such as Fenton-like processes and sulfate radicals-based oxidation processes.

Pyroelectric Polyelectrolyte Brushes

Piezo- and pyroelectric materials are of interest, for example, for energy harvesting applications, for the development of tactile sensors, as well as neuromorphic computing. This study reports the observation of pyro- and piezoelectricity in thin surface-attached polymer brushes containing zwitterionic and electrolytic side groups that are prepared via surface-initiated polymerization. The pyro- and piezoelectric properties of the surface-grafted polyelectrolyte brushes are found to sensitively depend on and can be tuned by variation of the counterion. The observed piezo- and pyroelectric properties reflect the structural complexity of polymer brushes, and are attributed to a complex interplay of the non-uniform segment density within these films, together with a non-uniform distribution of counterions and specific ion effects. The fabrication of thin pyroelectric films by surface-initiated polymerization is an important addition to the existing strategies toward such materials. Surface-initiated polymerization, in particular, allows for facile grafting of polar thin polymer films from a wide range of substrates via a straightforward two-step protocol that obviates the need for multistep laborious synthetic procedures or thin film deposition protocols. The ability to produce polymer brushes with piezo- and pyroelectric properties opens up new avenues of application of these materials, for example, in energy harvesting or biosensing.

Organic Polar Crystals, Second Harmonic Generation, and Piezoelectric Effects from Heteroadamantanes in the Space Group R3m

Polar crystalline materials, a subset of the non-centrosymmetric materials, are highly sought after. Their symmetry properties make them pyroelectric and also piezoelectric and capable of second-harmonic generation (SHG). For SHG and piezoelectric applications, metal oxides are commonly used. The advantages of oxides are durability and hardness - downsides are the need for high-temperature synthesis/processing and often the need to include toxic metals. Organic polar crystals, on the other hand, can avoid toxic metals and can be amenable to solution-state processing. While the vast majority of polar organic molecules crystallize in non-polar space groups, we found that both 7-chloro-1,3,5-triazaadamantane, for short Cl-TAA, and also the related Br-TAA (but not I-TAA) form polar crystals in the space group R3m, easily obtained from dichloromethane solution. Measurements confirm piezoelectric and SHG properties for Cl-TAA and Br-TAA. When the two species are crystallized together, solid solutions form, suggesting that properties of future materials can be tuned continuously.

Computational design and evaluation of the mechanical and electrical behavior of a piezoelectric scaffold: a preclinical study

Piezoelectric scaffolds have been recently developed to explore their potential to enhance the bone regeneration process using the concept of piezoelectricity, which also inherently occurs in bone. In addition to providing mechanical support during bone healing, with a suitable design, they are supposed to produce electrical signals that ought to favor the cell responses. In this study, using finite element analysis (FEA), a piezoelectric scaffold was designed with the aim of providing favorable ranges of mechanical and electrical signals when implanted in a large bone defect in a large animal model, so that it could inform future pre-clinical studies. A parametric analysis was then performed to evaluate the effect of the scaffold design parameters with regard to the piezoelectric behavior of the scaffold. The designed scaffold consisted of a porous strut-like structure with piezoelectric patches covering its free surfaces within the scaffold pores. The results showed that titanium or PCL for the scaffold and barium titanate (BT) for the piezoelectric patches are a promising material combination to generate favorable ranges of voltage, as reported in experimental studies. Furthermore, the analysis of variance showed the thickness of the piezoelectric patches to be the most influential geometrical parameter on the generation of electrical signals in the scaffold. This study shows the potential of computer tools for the optimization of scaffold designs and suggests that patches of piezoelectric material, attached to the scaffold surfaces, can deliver favorable ranges of electrical stimuli to the cells that might promote bone regeneration.

Achieving High Piezoelectric Performance across a Wide Composition Range in Tetragonal (Bi,Na)TiO3-BaTiO3 Films for Micro-electromechanical Systems

Tetragonal (1-x)(Bi,Na)TiO3-xBaTiO3 films exhibit enhanced piezoelectric properties due to domain switching over a wide composition range. These properties were observed over a significantly wider composition range than the morphotropic phase boundary (MPB), which typically has a limited composition range of 1-2%. The polarization axis was found to be along the in-plane direction for the tetragonal composition range x = 0.06-1.0, attributed to the tensile thermal strain from the substrate during cooling after the film formation. A "two-step increase" in remanent polarization against an applied maximum electric field was observed at the high-field region due to the domain switching, and a very high piezoelectric response (effective d33 value, denoted as d33,f) over 220 pm/V was achieved for a wide composition range of x = 0.2-0.5 with high tetragonality, exceeding previously reported values for bulk ceramics. Moreover, a transverse piezoelectric coefficient, e31,f, of 19 C/m2 measured using a cantilever structure was obtained for a composition range of at least 10 atom % (for both x = 0.2 and 0.3). This value is the highest reported for Pb-free piezoelectric thin films and is comparable to the best data for Pb-based thin films. Reversible domain switching eliminates the need for conventional MPB compositions, allowing an improvement in the piezoelectric properties over a wider composition range. This strategy could provide a guideline for the development of environmentally acceptable lead-free piezoelectric films with composition-insensitive piezoelectric performance to replace Pb-based materials with MPB composition, such as PZT.

Review of Piezoelectrical Materials Potentially Useful for Peripheral Nerve Repair

It has increasingly been recognized that electrical currents play a pivotal role in cell migration and tissue repair, in a process named "galvanotaxis". In this review, we summarize the current evidence supporting the potential benefits of electric stimulation (ES) in the physiology of peripheral nerve repair (PNR). Moreover, we discuss the potential of piezoelectric materials in this context. The use of these materials has deserved great attention, as the movement of the body or of the external environment can be used to power internally the electrical properties of devices used for providing ES or acting as sensory receptors in artificial skin (e-skin). The fact that organic materials sustain spontaneous degradation inside the body means their piezoelectric effect is limited in duration. In the case of PNR, this is not necessarily problematic, as ES is only required during the regeneration period. Arguably, piezoelectric materials have the potential to revolutionize PNR with new biomedical devices that range from scaffolds and nerve-guiding conduits to sensory or efferent components of e-skin. However, much remains to be learned regarding piezoelectric materials, their use in manufacturing of biomedical devices, and their sterilization process, to fine-tune their safe, effective, and predictable in vivo application.

Flexoelectric and piezoelectric effects in micro- and nanocellulose films

In this work, we evaluated the flexoelectric and piezoelectric contributions to the overall macroscopic polarization in cellulose films. To this end, the flexoelectric μ31 and transverse effective piezoelectric e31,f coefficients of cellulose films were determined using cantilever beam bending. The experiments were based on theoretical developments allowing to separate the flexoelectric from the piezoelectric contribution, represented by an effective flexoelectric coefficient, μeff, depending on both e31,f and μ31. Five free-standing and stainless steel/cellulose bilayer films were prepared from cellulose showing different morphologies and surface charge degrees: two almost neutral cellulose microfibers (CMF) and three (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO)-oxidized cellulose micro- (TCMF) and nanofibers (TCNF) bearing negative charged groups on the surface. The dielectric properties of the films indicated a low dielectric constant for unmodified CMF, and a huge increase for TEMPO-oxidized samples, which were up to 9 times higher than poly(vinylidene fluoride)-based polymers. TEMPO-oxidized cellulose films exhibited the largest flexoelectric coefficients (almost 7 times higher than those of synthetic polymer dielectrics), which evidenced that the presence of polar groups and surface charge boosted both flexoelectricity and piezoelectricity in unpoled cellulose films. These findings pave the way towards sustainable cellulose-based curvature sensors with large effective flexoelectric coefficients, without the need of preliminary energy consuming poling step.

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.

Recent advances in tailoring stimuli-responsive hybrid scaffolds for cardiac tissue engineering and allied applications

To recapitulate bio-physical properties and functional behaviour of native heart tissues, recent tissue engineering-based approaches are focused on developing smart/stimuli-responsive materials for interfacing cardiac cells. Overcoming the drawbacks of the traditionally used biomaterials, these smart materials portray outstanding mechanical and conductive properties while promoting cell-cell interaction and cell-matrix transduction cues in such excitable tissues. To date, a large number of stimuli-responsive materials have been employed for interfacing cardiac tissues alone or in combination with natural/synthetic materials for cardiac tissue engineering. However, their comprehensive classification and a comparative analysis of the role played by these materials in regulating cardiac cell behaviour and in vivo metabolism are much less discussed. In an attempt to cover the recent advances in fabricating stimuli-responsive biomaterials for engineering cardiac tissues, this review details the role of these materials in modulating cardiomyocyte behaviour, functionality and surrounding matrix properties. Furthermore, concerns and challenges regarding the clinical translation of these materials and the possibility of using such materials for the fabrication of bio-actuators and bioelectronic devices are discussed.

Piezoelectric nanogenerators for self-powered wearable and implantable bioelectronic devices

One of the recent innovations in the field of personalized healthcare is the piezoelectric nanogenerators (PENGs) for various clinical applications, including self-powered sensors, drug delivery, tissue regeneration etc. Such innovations are perceived to potentially address some of the unmet clinical needs, e.g., limited life-span of implantable biomedical devices (e.g., pacemaker) and replacement related complications. To this end, the generation of green energy from biomechanical sources for wearable and implantable bioelectronic devices gained considerable attention in the scientific community. In this perspective, this article provides a comprehensive state-of-the-art review on the recent developments in the processing, applications and associated concerns of piezoelectric materials (synthetic/biological) for personalized healthcare applications. In particular, this review briefly discusses the concepts of piezoelectric energy harvesting, piezoelectric materials (ceramics, polymers, nature-inspired), and the various applications of piezoelectric nanogenerators, such as, self-powered sensors, self-powered pacemakers, deep brain stimulators etc. Important distinction has been made in terms of the potential clinical applications of PENGs, either as wearable or implantable bioelectronic devices. While discussing the potential applications as implantable devices, the biocompatibility of the several hybrid devices using large animal models is summarized. This review closes with the futuristic vision of integrating data science approaches in developmental pipeline of PENGs as well as clinical translation of the next generation PENGs. STATEMENT OF SIGNIFICANCE: Piezoelectric nanogenerators (PENGs) hold great promise for transforming personalized healthcare through self-powered sensors, drug delivery systems, and tissue regeneration. The limited battery life of implantable devices like pacemakers presents a significant challenge, leading to complications from repititive surgeries. To address such a critical issue, researchers are focusing on generating green energy from biomechanical sources to power wearable and implantable bioelectronic devices. This comprehensive review critically examines the latest advancements in synthetic and nature-inspired piezoelectric materials for PENGs in personalized healthcare. Moreover, it discusses the potential of piezoelectric materials and data science approaches to enhance the efficiency and reliability of personalized healthcare devices for clinical applications.

Recent development of piezoelectric biosensors for physiological signal detection and machine learning assisted cardiovascular disease diagnosis

As cardiovascular disease stands as a global primary cause of mortality, there has been an urgent need for continuous and real-time heart monitoring to effectively identify irregular heart rhythms and to offer timely patient alerts. However, conventional cardiac monitoring systems encounter challenges due to inflexible interfaces and discomfort during prolonged monitoring. In this review article, we address these issues by emphasizing the recent development of the flexible, wearable, and comfortable piezoelectric passive sensor assisted by machine learning technology for diagnosis. This innovative device not only harmonizes with the dynamic mechanical properties of human skin but also facilitates continuous and real-time collection of physiological signals. Addressing identified challenges and constraints, this review provides insights into recent advances in piezoelectric cardiac sensors, from devices to circuit systems. Furthermore, this review delves into the integration of machine learning technologies, showcasing their pivotal role in facilitating continuous and real-time assessment of cardiac status. The synergistic combination of flexible piezoelectric sensor design and machine learning holds substantial potential in automating the detection of cardiac irregularities with minimal human intervention. This transformative approach has the power to revolutionize patient care paradigms.

Reactive oxygen species for therapeutic application: Role of piezoelectric materials

This perspective article emphasizes the significant role of reactive oxygen species (ROS) in in vivo remedial therapy of various diseases and complications, capitalizing on their potential reactivity. Among the various influencers, herein, piezoelectric materials driven ROS generation activity is primarily considered. Intrinsic non-centrosymmetry of piezoelectric materials makes them suitable for distinct dipole formation in the presence of external mechanical stimuli. Such characteristics prompt the positioning of opposite charged carriers to execute associated redox transformations that effectively participate to generate ROS in the aqueous media of the cell cytoplasm, organelles and nucleus. The immense reactivity of piezoelectric material driven ROS is fostered to terminate cellular toxicity or curtail tumor cell growth, due to their higher specificity. This perspective considers the conjugated performance of piezoelectric materials and ultrasound which can remotely generate electrical charges that promote ROS production for therapeutic application. In particular, a substantial synopsis is provided for the remedial activity of numerous piezocatalytic materials in tumor cell apoptosis, antibacterial treatment, dental care and neurological disorders. Subsequently, the report precisely demonstrates the methods involving various spectrophotometric approaches for the analysis of the ROS. Finally, the key challenges of piezoelectric material-based therapy are discussed and systematic future progress is outlined.

Advantages and Prospective Implications of Smart Materials in Tissue Engineering: Piezoelectric, Shape Memory, and Hydrogels

Conventional biomaterial is frequently used in the biomedical sector for various therapies, imaging, treatment, and theranostic functions. However, their properties are fixed to meet certain applications. Smart materials respond in a controllable and reversible way, modifying some of their properties because of external stimuli. However, protein-based smart materials allow modular protein domains with different functionalities and responsive behaviours to be easily combined. Wherein, these "smart" behaviours can be tuned by amino acid identity and sequence. This review aims to give an insight into the design of smart materials, mainly protein-based piezoelectric materials, shape-memory materials, and hydrogels, as well as highlight the current progress and challenges of protein-based smart materials in tissue engineering. These materials have demonstrated outstanding regeneration of neural, skin, cartilage, bone, and cardiac tissues with great stimuli-responsive properties, biocompatibility, biodegradability, and biofunctionality.

Simulation and Performance Evaluation of a Bio-Inspired Nanogenerator for Medical Applications

Providing sufficient energy for autonomous systems at the nanoscale is one of the major challenges of the Internet of Nano Things (IoNT). Existing battery technologies and conventional integrated circuits cannot be used in such small dimensions. Even if they are small enough to be used at the nano level, they still cannot be used in medical applications due to biocompatibility issues. M13 is a very promising virus with piezoelectric properties, which has attracted much interest in the scientific community as a bioenergy harvester. However, M13 studies presented so far in the literature are designed only for macroscale systems. In this paper, we simulate two designs of a bio-inspired nanogenerator based on the properties of M13 for nanosystems. We derive the stiffness matrix of M13, its dielectric and piezoelectric matrices and its density. We verify our calculated values by comparing our simulations with the results of experimental studies presented in the literature. We also evaluate the system's performance in terms of frequency response and loading characteristics. The results presented in this study show that a single M13 is a very promising nano-generator that can be used for medical applications.

Ultrasound-Mediated Ocular Drug Delivery: From Physics and Instrumentation to Future Directions

Drug delivery to the anterior and posterior segments of the eye is impeded by anatomical and physiological barriers. Increasingly, the bioeffects produced by ultrasound are being proven effective for mitigating the impact of these barriers on ocular drug delivery, though there does not appear to be a consensus on the most appropriate system configuration and operating parameters for this application. In this review, the fundamental aspects of ultrasound physics most pertinent to drug delivery are presented; the primary phenomena responsible for increased drug delivery efficacy under ultrasound sonication are discussed; an overview of common ocular drug administration routes and the associated ocular barriers is also given before reviewing the current state of the art of ultrasound-mediated ocular drug delivery and its potential future directions.

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.

Mussel-inspired polydopamine decorated silane modified-electroconductive gelatin-PEDOT:PSS scaffolds for bone regeneration

This study seeks to simulate both the chemistry and piezoelectricity of bone by synthesizing electroconductive silane-modified gelatin-poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) scaffolds using the freeze drying technique. In order to enhance hydrophilicity, cell interaction, and biomineralization, the scaffolds were functionalized with polydopamine (PDA) inspired by mussels. Physicochemical, electrical, and mechanical analyses were conducted on the scaffolds, as well as in vitro evaluations using the osteosarcoma cell line MG-63. It was found that scaffolds had interconnected porous structures, so the PDA layer formation reduced the size of pores while maintaining scaffold uniformity. PDA functionalization reduced the electrical resistance of the constructs while improving their hydrophilicity, compressive strength, and modulus. As a result of the PDA functionalization and the use of silane coupling agents, higher stability and durability were achieved as well as an improvement in biomineralization capability after being soaked in SBF solution for a month. Additionally, the PDA coating enabled the constructs to enhance viability, adhesion, and proliferation of MG-63 cells, as well as to express alkaline phosphatase and deposit HA, indicating that scaffolds can be used for bone regeneration. Therefore, the PDA-coated scaffolds developed in this study and the non-toxic performance of PEDOT:PSS present a promising approach for further in vitro and in vivo studies.

Effects of Electrical Stimulation on Articular Cartilage Regeneration with a Focus on Piezoelectric Biomaterials for Articular Cartilage Tissue Repair and Engineering

There is increasing evidence that chondrocytes within articular cartilage are affected by endogenous force-related electrical potentials. Furthermore, electrical stimulation (ES) promotes the proliferation of chondrocytes and the synthesis of extracellular matrix (ECM) molecules, which accelerate the healing of cartilage defects. These findings suggest the potential application of ES in cartilage repair. In this review, we summarize the pathogenesis of articular cartilage injuries and the current clinical strategies for the treatment of articular cartilage injuries. We then focus on the application of ES in the repair of articular cartilage in vivo. The ES-induced chondrogenic differentiation of mesenchymal stem cells (MSCs) and its potential regulatory mechanism are discussed in detail. In addition, we discuss the potential of applying piezoelectric materials in the process of constructing engineering articular cartilage, highlighting the important advances in the unique field of tissue engineering.

Vacuum and Electromagnetic Fields Treatment to Regenerate a Diffuse Mature Facial Scar Caused by Sulfuric Acid Assault

Acid attacks are on the rise, and they cause extensive and deep burns, especially on the face. The treatments used to improve the aesthetic, functional and social impact of non-acid scars do not always prove useful for acid scars. This article reports the case of a woman with an extended, mature, acid facial scar, caused by sulfuric acid assault, treated with a recent new procedure that combines the application of vacuum and electromagnetic fields. Before and after the treatment, the aesthetic appearance, and motor function of the face and neck were evaluated, as well as the level of hydration, the amount of sebum, the elasticity, and the pH of the skin. The improvements highlighted after the treatment of the aesthetic and functional characteristics of the face and neck, and of the physical parameters of the skin seemed to indicate that this particular treatment induces tissue regeneration, even in the nerve component. However, it is evident that the rehabilitation pathways of facial wounds and scars must be personalized, and must include continuous psychological support for the patient.

Natural Piezoelectric Biomaterials: A Biocompatible and Sustainable Building Block for Biomedical Devices

The piezoelectric effect has been widely observed in biological systems, and its applications in biomedical field are emerging. Recent advances of wearable and implantable biomedical devices bring promise as well as requirements for the piezoelectric materials building blocks. Owing to their biocompatibility, biosafety, and environmental sustainability, natural piezoelectric biomaterials are known as a promising candidate in this emerging field, with a potential to replace conventional piezoelectric ceramics and synthetic polymers. Herein, we provide a thorough review of recent progresses of research on five major types of piezoelectric biomaterials including amino acids, peptides, proteins, viruses, and polysaccharides. Our discussion focuses on their structure- and phase-related piezoelectric properties and fabrication strategies to achieve desired piezoelectric phases. We compare and analyze their piezoelectric performance and further introduce and comment on the approaches to improve their piezoelectric property. Representative biomedical applications of this group of functional biomaterials including energy harvesting, sensing, and tissue engineering are also discussed. We envision that molecular-level understanding of the piezoelectric effect, piezoelectric response improvement, and large-scale manufacturing are three main challenges as well as research and development opportunities in this promising interdisciplinary field.

An Experimental Investigation on Polarization Process of a PZT-52 Tube Actuator with Interdigitated Electrodes

The manipulator is the key component of the micromanipulator. Using the axial expansion and contraction properties, the piezoelectric tube can drive the manipulator to achieve micro-motion positioning. It is widely used in scanning probe microscopy, fiber stretching and beam scanning. The piezoceramic tube actuator used to have continuous electrodes inside and outside. It is polarized along the radial direction. There are relatively high polarization voltages, but poor axial mechanical properties. A new tubular actuator is presented in this paper by combining interdigitated electrodes and piezoceramic tubes. The preparation, polarization and mesoscopic mechanical properties were investigated. Using Lead Zirconate Titanate (PZT-52) as a substrate, the preparation process of interdigitated electrodes by screen printing was studied. For initial polarization voltage determination, the local characteristic model of the actuator was extracted and the electric field was analyzed by a finite element method. By measuring the actuator's axial displacement, we measured the actuator's polarization effect. Various voltages, times and temperatures were evaluated to determine how polarization affects the actuator's displacement. Optimal polarization conditions are 800 V, 60 min and 150 °C, with a maximum displacement of 0.88 μm generated by a PZT-52 tube actuator with interdigitated electrodes. PZT-52 tube actuators with a continuous electrode cannot be polarized under these conditions. The maximum displacement is 0.47 μm after polarization at 4 kV. Based on the results, the new actuator has a more convenient polarization process and a greater axial displacement from an application standpoint. It provides technical guidance for the preparation and polarization of the piezoceramic tube actuator. There is potential for piezoelectric tubular actuators to be used in a broader range of applications.

Bio-piezoelectricity: fundamentals and applications in tissue engineering and regenerative medicine

In recent years, smart materials have piqued the interest of scientists and physicians in the biomedical community owing to their ability to modify their properties in response to an external stimulation or changes in their surroundings. Biocompatible piezoelectric materials are an interesting group of smart materials due to their ability to produce electrical charges without an external power source. Electric signals produced by piezoelectric scaffolds can renew and regenerate tissues through special pathways like that found in the extracellular matrix. This review summarizes the piezoelectric phenomenon, piezoelectric effects generated within biological tissues, piezoelectric biomaterials, and their applications in tissue engineering and their use as biosensors.

Electrospun piezoelectric scaffolds for cardiac tissue engineering

The use of smart materials in tissue engineering is becoming increasingly appealing to provide additional functionalities and control over cell fate. The stages of tissue development and regeneration often require various electrical and electromechanical cues supported by the extracellular matrix, which is often neglected in most tissue engineering approaches. Particularly, in cardiac cells, electrical signals modulate cell activity and are responsible for the maintenance of the excitation-contraction coupling. Addition of electroconductive and topographical cues improves the biomimicry of cardiac tissues and plays an important role in driving cells towards the desired phenotype. Current platforms used to apply electrical stimulation to cells in vitro often require large external equipment and wires and electrodes immersed in the culture media, limiting the scalability and applicability of this process. Piezoelectric materials represent a shift in paradigm in materials and methods aimed at providing electrical stimulation to cardiac cells since they can produce and deliver electrical signals to cells and tissues by mechanoelectrical transduction. Despite the ability of piezoelectric materials to mimic the mechanoelectrical transduction of the heart, the use of these materials is limited in cardiac tissue engineering and methods to characterise piezoelectricity are often built in-house, which poses an additional difficulty when comparing results from the literature. In this work, we aim at providing an overview of the main challenges in cardiac tissue engineering and how piezoelectric materials could offer a solution to them. A revision on the existing literature in electrospun piezoelectric materials applied to cardiac tissue engineering is performed for the first time, as electrospinning plays an important role in the manufacturing of scaffolds with enhanced piezoelectricity and extracellular matrix native-like morphology. Finally, an overview of the current techniques used to evaluate piezoelectricity and their limitations is provided.

Microstructure and Piezoelectric Properties of Lead Zirconate Titanate Nanocomposites Reinforced with In-Situ Formed ZrO2 Nanoparticles

Lead zirconate titanate (PZT)-based ceramics are used in numerous advanced applications, including sensors, displays, actuators, resonators, chips; however, the poor mechanical characteristics of these materials severely limits their utility in composite materials. To address this issue, we herein fabricate transgranular type PZT ceramic nanocomposites by a novel method. Thermodynamically metastable single perovskite-type Pb0.99(Zr0.52+xTi0.48)0.98Nb0.02O3+1.96x powders are prepared from a citrate precursor before both monoclinic and tetragonal ZrO2 nanoparticles ranging from 20 to 80 nm are precipitated in situ at a sintering temperature of 1260 °C. The effects of ZrO2 content on the microstructure, dielectric, and piezoelectric properties are investigated and the mechanism, by which ZrO2 toughened PZT is analyzed in detail. The ZrO2 nanoparticles underwent a tetragonal to monoclinic phase transition upon cooling. The fracture mode changed from intergranular to transgranular with increasing ZrO2 content. The incorporation of ZrO2 nanoparticles improved the mechanical and piezoelectric properties. The optimized piezoelectric properties (εT33/ε0 = 1398, tan δ = 0.024 d33 = 354 pC N-1, kp = 0.66 Qm = 78) are obtained when x = 0.02. Tc initially increased and subsequently decreased with increasing ZrO2 content. The highest Tc = (387 °C) and lowest εT33/ε0 was obtained at x = 0.01.

Facile preparation of high loading filled PVDF/BaTiO3 piezoelectric composites for selective laser sintering 3D printing

3D printed piezoelectric devices, due to their sufficient multidimensional deformation and excellent piezoelectric properties, are one of the most promising research directions. However, the lack of high loaded piezoelectric composites is the key bottleneck restricting the enhancement of the piezoelectric output. In this work, we successfully prepared a novel high loaded polyvinylidene fluoride (PVDF)/barium titanate (BaTiO3) piezoelectric composite suitable for selective laser sintering (SLS) 3D printing via solid state shear milling (S3M) technology. The 50 wt% BaTiO3 filling made the most outstanding contribution to the piezoelectric properties of the composites. The 3D printed cymbal parts with a stress amplification effect exhibited outstanding piezoelectric conversion efficiency and responsiveness, whose open circuit voltage and short circuit current could reach 20 V and 1.1 μA, respectively. This work not only contributed a new high loaded piezoelectric composite for SLS processing, but also provided a novel piezoelectric performance enhancement strategy by the construction of 3D structure.