Active self-assembly of piezoelectric biomolecular films via synergistic nanoconfinement and in-situ poling

Piezoelectric materials for anti-infective bioapplications

Bacterial infection severely limits the effectiveness of biomaterials for tissue repair, posing a major challenge to modern medicine. Despite advances in novel antibiotics and their application in treatment, challenges remain in clinical practice. To address this issue, biomaterials are engineered to achieve desirable anti-infective performance and compatibility via adjusting their surface physicochemical properties. Recently, numerous studies on piezoelectric materials have been performed for anti-infective and regenerative therapies, but a comprehensive review is still lacking. This article provides a brief overview of the different types of piezoelectric materials and their characteristics. Building on this understanding, this review highlights the antibacterial mechanisms including orchestrating electric field and optimizing piezoelectric catalysis, which promote infective tissue regeneration, as well as discusses the anti-infective bioapplication of piezoelectric materials. Furthermore, this review concludes with perspectives into the challenges and future research directions of piezoelectric biomaterials.

Acoustofluidic precise manipulation: Recent advances in applications for micro/nano bioparticles

Acoustofluidic technologies that integrate acoustic waves and microfluidic chips have been widely used in bioparticle manipulation. As a representative technology, acoustic tweezers have attracted significant attention due to their simple manufacturing, contact-free operation, and low energy consumption. Recently, acoustic tweezers have enabled the efficient and smart manipulation of biotargets with sizes covering millimeters (such as zebrafish) and nanometers (such as DNA). In addition to acoustic tweezers, other related acoustofluidic chips including acoustic separating, mixing, enriching, and transporting chips, have also emerged to be powerful platforms to manipulate micro/nano bioparticles (cells in blood, extracellular vesicles, liposomes, and so on). Accordingly, some interesting applications were also developed, such as smart sensing. In this review, we firstly introduce the principles of acoustic tweezers and various related technologies. Second, we compare and summarize recent applications of acoustofluidics in bioparticle manipulation and sensing. Finally, we outlook the future development direction from the perspectives such as device design and interdisciplinary.

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.

Non-Centrosymmetric Single Crystalline Biomolecular Nano-Arrays for Responsive Electronics

Herein, a novel strategy is reported for synthesizing libraries of single crystalline amino acid (AA) nanocrystals with control over size, anisotropy, and polymorphism by leveraging dip-pen nanolithography (DPN) and recrystallization via solvent vapor annealing. The crystals are prepared by first depositing nanoreactors consisting of a solvent with AAs, followed by water vapor-induced recrystallization. This leads to isotropic structures that are non-centrosymmetric with strong piezoelectric (g33 coefficients >1000 mVm N-1), ferroelectric, and non-linear optical properties. However, recrystallizing arrays of isotropic DL-alanine nanodot features with a binary solvent (water and ethanol) leads to arrays of 1D piezoelectric nanorods with their long axis coincident with the polar axis. Moreover, positioning nanoreactors containing AAs (the nanodot features) between micro electrodes leads to capillary formation, making the reactors anisotropic and facilitating piezoelectric nanorod formation between the electrodes. This offers a facile route to device fabrication. These as-fabricated devices respond to ultrasonic stimulation in the form of a piezoelectric response. The technique described herein is significant as it provides a rapid way of investigating non-centrosymmetric nanoscale biocrystals, potentially pivotal for fabricating a new class of stimuli-responsive devices such as sensors, energy harvesters, and stimulators.

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.

Biodegradable Ferroelectric Molecular Plastic Crystal HOCH2(CF2)7CH2OH Structurally Inspired by Polyvinylidene Fluoride

Ferroelectric materials, traditionally comprising inorganic ceramics and polymers, are commonly used in medical implantable devices. However, their nondegradable nature often necessitates secondary surgeries for removal. In contrast, ferroelectric molecular crystals have the advantages of easy solution processing, lightweight, and good biocompatibility, which are promising candidates for transient (short-term) implantable devices. Despite these benefits, the discovered biodegradable ferroelectric materials remain limited due to the absence of efficient design strategies. Here, inspired by the polar structure of polyvinylidene fluoride (PVDF), a ferroelectric molecular crystal 1H,1H,9H,9H-perfluoro-1,9-nonanediol (PFND), which undergoes a cubic-to-monoclinic ferroelectric plastic phase transition at 339 K, is discovered. This transition is facilitated by a 2D hydrogen bond network formed through O-H···O interactions among the oriented PFND molecules, which is crucial for the manifestation of ferroelectric properties. In this sense, by reducing the number of -CF2- groups from ≈5 000 in PVDF to seven in PFND, it is demonstrated that this ferroelectric compound only needs simple solution processing while maintaining excellent biosafety, biocompatibility, and biodegradability. This work illuminates the path toward the development of new biodegradable ferroelectric molecular crystals, offering promising avenues for biomedical applications.

Flexible Electronics: Advancements and Applications of Flexible Piezoelectric Composites in Modern Sensing Technologies

The piezoelectric effect refers to a physical phenomenon where piezoelectric materials generate an electric field when subjected to mechanical stress or undergo mechanical deformation when subjected to an external electric field. This principle underlies the operation of piezoelectric sensors. Piezoelectric sensors have garnered significant attention due to their excellent self-powering capability, rapid response speed, and high sensitivity. With the rapid development of sensor techniques achieving high precision, increased mechanical flexibility, and miniaturization, a range of flexible electronic products have emerged. As the core constituents of piezoelectric sensors, flexible piezoelectric composite materials are commonly used due to their unique advantages, including high conformability, sensitivity, and compatibility. They have found applications in diverse domains such as underwater detection, electronic skin sensing, wearable sensors, targeted therapy, and ultrasound diagnostics for deep tissue. The advent of flexible piezoelectric composite materials has revolutionized the design concepts and application scenarios of traditional piezoelectric materials, playing a crucial role in the development of next-generation flexible electronic products. This paper reviews the research progress on flexible piezoelectric composite materials, covering their types and typical fabrication techniques, as well as their applications across various fields. Finally, a summary and outlook on the existing issues and future development of these composite materials are provided.

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.

Multimaterial Printing of Serpentine Microarchitectures with Synergistic Mechanical/Piezoelectric Stimulation for Enhanced Cardiac-Specific Functional Regeneration

Recreating the natural heart's mechanical and electrical environment is crucial for engineering functional cardiac tissue and repairing infarcted myocardium in vivo. In this study, multimaterial-printed serpentine microarchitectures are presented with synergistic mechanical/piezoelectric stimulation, incorporating polycaprolactone (PCL) microfibers for mechanical support, polyvinylidene fluoride (PVDF) microfibers for piezoelectric stimulation, and magnetic PCL/Fe3O4 for controlled deformation via an external magnet. Rat cardiomyocytes in piezoelectric constructs, subjected to dynamic mechanical stimulation, exhibit advanced maturation, featuring superior sarcomeric structures, improved calcium transients, and upregulated maturation genes compared to non-piezoelectric constructs. Furthermore, these engineered piezoelectric cardiac constructs demonstrate significant structural and functional repair of infarcted myocardium, as evidenced by enhanced ejection and shortening fraction, reduced fibrosis and inflammation, and increased angiogenesis. The findings underscore the therapeutic potential of piezoelectric cardiac constructs for myocardial infarction therapy.

Flexible, biodegradable ultrasonic wireless electrotherapy device based on highly self-aligned piezoelectric biofilms

Biodegradable piezoelectric devices hold great promise in on-demand transient bioelectronics. Existing piezoelectric biomaterials, however, remain obstacles to the development of such devices due to difficulties in large-scale crystal orientation alignment and weak piezoelectricity. Here, we present a strategy for the synthesis of optimally orientated, self-aligned piezoelectric γ-glycine/polyvinyl alcohol (γ-glycine/PVA) films via an ultrasound-assisted process, guided by density functional theory. The first-principles calculations reveal that the negative piezoelectric effect of γ-glycine originates from the stretching and compression of glycine molecules induced by hydrogen bonding interactions. The synthetic γ-glycine/PVA films exhibit a piezoelectricity of 10.4 picocoulombs per newton and an ultrahigh piezoelectric voltage coefficient of 324 × 10-3 volt meters per newton. The biofilms are further developed into flexible, bioresorbable, wireless piezo-ultrasound electrotherapy devices, which are demonstrated to shorten wound healing by ~40% and self-degrade in preclinical wound models. These encouraging results offer reliable approaches for engineering piezoelectric biofilms and developing transient bioelectronics.

Glycine/alginate-based piezoelectric film consisting of a single, monolithic β-glycine spherulite towards flexible and biodegradable force sensor

Development of piezoelectric biomaterials with high piezoelectric performance, while possessing excellent flexibility, biocompatibility, and biodegradability still remains a great challenge. Herein, a flexible, biocompatible and biodegradable piezoelectric β-glycine-alginate-glycerol (Gly-Alg-Glycerol) film with excellent in vitro and in vivo sensing performance was developed. Remarkably, a single, monolithic β-glycine spherulite, instead of more commonly observed multiple spherulites, was formed in alginate matrix, thereby resulting in outstanding piezoelectric property, including high piezoelectric constant (7.2 pC/N) and high piezoelectric sensitivity (1.97 mV/kPa). The Gly-Alg-Glycerol film exhibited superior flexibility, enabling complex shape-shifting, e.g. origami pigeon, 40% tensile strain, and repeated bending and folding deformation without fracture. In vitro, the flexible Gly-Alg-Glycerol film sensor could detect subtle pulse signal, sound wave and recognize shear stress applied from different directions. In addition, we have demonstrated that the Gly-Alg-Glycerol film sensor sealed by polylactic acid and beeswax could serve as an in vivo sensor to monitor physiological pressure signals such as heartbeat, respiration and muscle movement. Finally, the Gly-Alg-Glycerol film possessed good biocompatibility, supporting the attachment and proliferation of rat mesenchymal stromal cells, and biodegradability, thereby showing great potential as biodegradable piezoelectric biomaterials for biomedical sensing applications.

Biodegradable ferroelectric molecular crystal with large piezoelectric response

Transient implantable piezoelectric materials are desirable for biosensing, drug delivery, tissue regeneration, and antimicrobial and tumor therapy. For use in the human body, they must show flexibility, biocompatibility, and biodegradability. These requirements are challenging for conventional inorganic piezoelectric oxides and piezoelectric polymers. We discovered high piezoelectricity in a molecular crystal HOCH2(CF2)3CH2OH [2,2,3,3,4,4-hexafluoropentane-1,5-diol (HFPD)] with a large piezoelectric coefficient d33 of ~138 picocoulombs per newton and piezoelectric voltage constant g33 of ~2450 × 10-3 volt-meters per newton under no poling conditions, which also exhibits good biocompatibility toward biological cells and desirable biodegradation and biosafety in physiological environments. HFPD can be composite with polyvinyl alcohol to form flexible piezoelectric films with a d33 of 34.3 picocoulombs per newton. Our material demonstrates the ability for molecular crystals to have attractive piezoelectric properties and should be of interest for applications in transient implantable electromechanical devices.

Piezoelectric Applications of Low-Dimensional Composites and Porous Materials

Low-dimensional (LD) materials, with atomically thin anisotropic structures, exhibit remarkable physical and chemical properties, prominently featuring piezoelectricity resulting from the absence of centrosymmetry. This characteristic has led to diverse applications, including sensors, actuators, and micro- and nanoelectromechanical systems. While piezoelectric effects are observed across zero-dimensional (0D), one-dimensional (1D), and two-dimensional (2D) LD materials, challenges such as effective charge separation and crystal structure imperfections limit their full potential. Addressing these issues requires innovative solutions, with the integration of LD materials with polymers, ceramics, metals, and other porous materials proving a key strategy to significantly enhance piezoelectric properties. This review comprehensively covers recent advances in synthesizing and characterizing piezoelectric composites based on LD materials and porous materials. The synergistic combination of LD materials with other substances, especially porous materials, demonstrates notable performance improvements, addressing inherent challenges. The review also explores future directions and challenges in developing these composite materials, highlighting potential applications across various technological domains.

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.

Bioinspired Amino Acid Based Materials in Bionanotechnology: From Minimalistic Building Blocks and Assembly Mechanism to Applications

Inspired by natural hierarchical self-assembly of proteins and peptides, amino acids, as the basic building units, have been shown to self-assemble to form highly ordered structures through supramolecular interactions. The fabrication of functional biomaterials comprised of extremely simple biomolecules has gained increasing interest due to the advantages of biocompatibility, easy functionalization, and structural modularity. In particular, amino acid based assemblies have shown attractive physical characteristics for various bionanotechnology applications. Herein, we propose a review paper to summarize the design strategies as well as research advances of amino acid based supramolecular assemblies as smart functional materials. We first briefly introduce bioinspired reductionist design strategies and assembly mechanism for amino acid based molecular assembly materials through noncovalent interactions in condensed states, including self-assembly, metal ion mediated coordination assembly, and coassembly. In the following part, we provide an overview of the properties and functions of amino acid based materials toward applications in nanotechnology and biomedicine. Finally, we give an overview of the remaining challenges and future perspectives on the fabrication of amino acid based supramolecular biomaterials with desired properties. We believe that this review will promote the prosperous development of innovative bioinspired functional materials formed by minimalistic building blocks.

Robust Piezoelectric Biomolecular Membranes from Eggshell Protein for Wearable Sensors

Flexible and wearable devices are drawing increasing attention due to their promising applications in energy harvesting and sensing. However, the application of wearable devices still faces great challenges, such as flexibility, repeatability, and biodegradability. Biopiezoelectric materials have been regarded as favorable energy-harvesting sources due to their nontoxicity and biocompatibility. Here, a wearable and biodegradable sensor is proposed to monitor human activities. The proposed sensor is fabricated via a low-cost, facile, and scalable electrospinning technology from nanofibers composed of eggshell membranes mixed with polyethylene oxide. It is shown that the sensor exhibits excellent flexibility, outstanding degradability, and mechanical stability over 3000 cycles under periodic stimulation. The device displays multiple potential applications, including the recognition of different objects, human motion monitoring, and active voice recognition. Finally, it is shown that the composite nanofiber membrane has good degradability and breathability. With excellent sensing performance, environmental friendliness, and ease of processing, the eggshell membrane-based sensor could be a promising candidate for greener and more environmentally friendly devices for application in implantable and wearable electronics.