Boron Nitride Nanotube Addition Enhances the Crystallinity and Cytocompatibility of PVDF-TrFE

A Tympanic Piezo-Bioreactor Modulates Ion Channel-Associated Mechanosignaling to Stabilize Phenotype and Promote Tenogenesis in Human Tendon-Derived Cells

Preserving the function of human tendon-derived cells (hTDCs) during cell expansion is a significant challenge in regenerative medicine. In this study, a non-genetic approach is introduced to control the differentiation of hTDCs using a newly developed tympanic bioreactor. The system mimics the functionality of the human tympanic membrane, employing a piezoelectrically tuned acoustic diaphragm made of polyvinylidene fluoride-co-trifluoroethylene and boron nitride nanotubes. The diaphragm is vibrationally actuated to deliver targeted electromechanical stimulation to hTDCs. The results demonstrate that the system effectively maintains the tendon-specific phenotype of hTDCs, even under conditions that typically induce nonspecific differentiation, such as osteogenesis. This stabilization is achieved by modulating integrin-mediated mechanosignaling via ion channel-regulated calcium activity, potentially by TREK-1 and PIEZO1, yet targeted studies are required for confirmation. Finally, the system sustains the activation of key differentiation pathways (bone morphogenetic protein, BMP) while downregulating osteogenesis-associated (mitogen-ctivated protein kinase, MAPK and wingless integrated, WNT) pathways and upregulating Focal Adhesion Kinase (FAK) signaling. This approach offers a finely tunable, dose-dependent control over hTDC differentiation, presenting significant potential for non-genetic approaches in cell therapy, tendon tissue engineering, and the regeneration of other mechanosensitive tissues.

Electrospun polarity-controlled molecular orientation for synergistic performance of an artifact-free piezoelectric anisotropic sensor

Anisotropy in mechanical, optical and thermal sensors in a spatial direction has many applications in health care, robotics, aerospace, and tissue engineering. In particular, wearable and implantable sensors respond to stretching and bending strains that probe mechanical energy and track physiological signals. Hence, the development of anisotropic pressure sensors with true piezoelectric (PE) signals is of utmost importance to achieve efficient devices. Herein, a simple and efficient method is developed for high longitudinal and transverse responses, with an approach to isolating a true piezoelectric signal. The electrospun (ES) polarity of oriented dipoles inside flexible fibers gives rise to a high longitudinal/transverse PE response of both lateral and transverse strains. Nanofibers of poly(vinylidene-chlorotrifluoroethylene) copolymers contain poled dipoles, up to 86%, that promote an enhanced PE coefficient of 42 pm V-1 in the case of negative polarity-based electrospinning. It is 40% higher in composition than the commonly adopted positive polarity-biased electrospinning process. We demonstrated the advantage of such a high PE coefficient by the enhanced sensitivity of the longitudinal (VLs = 0.3 V kPa-1, ILs = 0.07 μA kPa-1) as well as transverse (VTs = 1.0 V kPa-1, ITs = 0.8 μA kPa-1) PE response. To counter the ambiguity of high transverse response as compared to longitudinal in electrospun fiber-based devices, a facile method is proposed to isolate the ferroelectret, triboelectric and piezoelectric signals in a fiber-based hybrid device with their independent charge generation mechanisms.

Progress in the development of piezoelectric biomaterials for tissue remodeling

Piezoelectric biomaterials have demonstrated significant potential in the past few decades to heal damaged tissue and restore cellular functionalities. Herein, we discuss the role of bioelectricity in tissue remodeling and explore ways to mimic such tissue-like properties in synthetic biomaterials. In the past decade, biomedical engineers have adopted emerging functional biomaterials-based tissue engineering approaches using innovative bioelectronic stimulation protocols based on dynamic stimuli to direct cellular activation, proliferation, and differentiation on engineered biomaterial constructs. The primary focus of this review is to discuss the concepts of piezoelectric energy harvesting, piezoelectric materials, and their application in soft (skin and neural) and hard (dental and bone) tissue regeneration. While discussing the prospective applications as an engineered tissue, an important distinction has been made between piezoceramics, piezopolymers, and their composites. The superiority of piezopolymers over piezoceramics to circumvent issues such as stiffness mismatch, biocompatibility, and biodegradability are highlighted. We aim to provide a comprehensive review of the field and identify opportunities for the future to develop clinically relevant and state-of-the-art biomaterials for personalized and remote health care.

Polymer Nanocomposite Sensors with Improved Piezoelectric Properties through Additive Manufacturing

Additive manufacturing (AM) technology has recently seen increased utilization due to its versatility in using functional materials, offering a new pathway for next-generation conformal electronics in the smart sensor field. However, the limited availability of polymer-based ultraviolet (UV)-curable materials with enhanced piezoelectric properties necessitates the development of a tailorable process suitable for 3D printing. This paper investigates the structural, thermal, rheological, mechanical, and piezoelectric properties of a newly developed sensor resin material. The polymer resin is based on polyvinylidene fluoride (PVDF) as a matrix, mixed with constituents enabling UV curability, and boron nitride nanotubes (BNNTs) are added to form a nanocomposite resin. The results demonstrate the successful micro-scale printability of the developed polymer and nanocomposite resins using a liquid crystal display (LCD)-based 3D printer. Additionally, incorporating BNNTs into the polymer matrix enhanced the piezoelectric properties, with an increase in the voltage response by up to 50.13%. This work provides new insights for the development of 3D printable flexible sensor devices and energy harvesting systems.

Self-Polarized P(VDF-TrFE)/Carbon Black Composite Piezoelectric Thin Film

Self-polarized energy harvesting materials have seen increasing research interest in recent years owing to their simple fabrication method and versatile application potential. In this study, we systematically investigated self-polarized P(VDF-TrFE)/carbon black (CB) composite thin films synthesized on flexible substrates, with the CB content varying from 0 to 0.6 wt.% in P(VDF-TrFE). The presence of -OH functional groups on carbon black significantly enhances its crystallinity, dipolar orientation, and piezoelectric performance. Multiple characterization techniques were used to investigate the crystalline quality, chemical structure, and morphology of the composite P(VDF-TrFE)/CB films, which indicated no significant changes in these parameters. However, some increase in surface roughness was observed when the CB content increased. With the application of an external force, the piezoelectrically generated voltage was found to systematically increase with higher CB content, reaching a maximum value at 0.6 wt.%, after which the sample exhibited low resistance. The piezoelectric voltage produced by the unpoled 0.6 wt.% CB composite film significantly exceeded the unpoled pure P(VDF-TrFE) film when subjected to the same applied strain. Furthermore, it exhibited exceptional stability in the piezoelectric voltage over time, exceeding the output voltage of the poled pure P(VDF-TrFE) film. Notably, P(VDF_TrFE)/CB composite-based devices can be used in energy harvesting and piezoelectric strain sensing to monitor human motions, which has the potential to positively impact the field of smart wearable devices.

Surface-Modified Piezoelectric Copolymer Poly(vinylidene fluoride-trifluoroethylene) Supporting Physiological Extracellular Matrixes to Enhance Mesenchymal Stem Cell Adhesion for Nanoscale Mechanical Stimulation

There is an unmet clinical need to provide viable bone grafts for clinical use. Autologous bone, one of the most commonly transplanted tissues, is often used but is associated with donor site morbidity. Tissue engineering strategies to differentiate an autologous cell source, such as mesenchymal stromal cells (MSCs), into a potential bone-graft material could help to fulfill clinical demand. However, osteogenesis of MSCs can typically require long culture periods that are impractical in a clinical setting and can lead to significant cost. Investigation into strategies that optimize cell production is essential. Here, we use the piezoelectric copolymer poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE), functionalized with a poly(ethyl acrylate) (PEA) coating that drives fibronectin network formation, to enhance MSC adhesion and to present growth factors in the solid phase. Dynamic electrical cues are then incorporated, via a nanovibrational bioreactor, and the MSC response to electromechanical stimulation is investigated.

Ultrasonocoverslip: In-vitro platform for high-throughput assay of cell type-specific neuromodulation with ultra-low-intensity ultrasound stimulation

Brain stimulation with ultra-low-intensity ultrasound has rarely been investigated due to the lack of a reliable device to measure small neuronal signal changes made by the ultra-low intensity range. We propose Ultrasonocoverslip, an ultrasound-transducer-integrated-glass-coverslip that determines the minimum intensity for brain cell activation. Brain cells can be cultured directly on Ultrasonocoverslip to simultaneously deliver uniform ultrasonic pressure to hundreds of cells with real-time monitoring of cellular responses using fluorescence microscopy and single-cell electrophysiology. The sensitivity for detecting small responses to ultra-low-intensity ultrasound can be improved by averaging simultaneously obtained responses. Acoustic absorbers can be placed under Ultrasonocoverslip, and stimuli distortions are substantially reduced to precisely deliver user-intended acoustic stimulations. With the proposed device, we discover the lowest acoustic threshold to induce reliable neuronal excitation releasing glutamate. Furthermore, mechanistic studies on the device show that the ultra-low-intensity ultrasound stimulation induces cell type-specific neuromodulation by activating astrocyte-mediated neuronal excitation without direct neuronal involvement. The performance of ultra-low-intensity stimulation is validated by in vivo experiments demonstrating improved safety and specificity in motor modulation of tail movement compared to that with supra-watt-intensity.

MXene-Functionalized Ferroelectric Nanocomposite Membranes with Modulating Surface Potential Enhance Bone Regeneration

Rapid and effective bone defect repair remains a challenging issue for clinical treatment. Applying biomaterials with endogenous surface potential has been widely studied to enhance bone regeneration, but how to regulate the electric potential and surface morphology of the implanted materials precisely to achieve an optimal bioelectric microenvironment is still a major challenge. The aim of this study is to develop electroactive biomaterials that better mimic the extracellular microenvironment for bone regeneration. Hence, MXene/polyvinylidene fluoride (MXene/PVDF) ferroelectric nanocomposite membranes were prepared by electrospinning. Physicochemical characterization demonstrated that Ti₃C₂T_x MXene nanosheets were wrapped in PVDF shell layer and the surface morphology and potential were modulated by altering the content of MXene, where uniform distribution of fibers and enhanced electric potential can be obtained and precisely assembled into a natural extracellular matrix (ECM) in bone tissue. Consequently, the MXene/PVDF membranes facilitated cell adhesion, stretching, and growth, showing good biocompatibility; meanwhile, their intrinsic electric potential promoted the recruitment of osteogenic cells and accelerated the differentiation of osteoblast. Furthermore, 1 wt % MXene/PVDF membrane with a suitable surface potential and better topographical structure for bone regeneration qualitatively and quantitatively promoted bone tissue formation in a rat calvarial bone defect after 4 and 8 weeks of healing. The fabricated MXene/PVDF ferroelectric nanocomposite membranes show a biomimetic microenvironment with a sustainable electric potential and optimal 3D topographical structure, providing an innovative and well-suited strategy for application in bone regeneration.

Inhibition of Zinc Dendrites Realized by a β-P(VDF-TrFE) Nanofiber Layer in Aqueous Zn-Ion Batteries

Uncontrollable Zn dendrite formations and parasitic side reactions on Zn electrodes induce poor cycling stability and safety issues, preventing the large-scale commercialization of Zn-ion batteries. Herein, to achieve uniform Zn deposition and suppress side reactions, an electrospun ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) copolymer, a P(VDF-TrFE) nanofiber layer, is introduced as an artificial solid-electrolyte interface on a Cu substrate acting as a current collector. The aligned molecular structure of β-P(VDF-TrFE) can effectively suppress localized current density on the Cu surface, lead to uniform Zn deposition, and suppress side reactions by preventing direct contact between electrodes and aqueous electrolytes. The half-cell configuration formed by the newly fabricated electrode can achieve an average coulombic efficiency of 99.2% over 300 cycles without short-circuiting at a current density of 1 mA cm-2 and areal capacity of 1 mAh cm-2. Stable cycling stability is also maintained for 200 cycles at a current density of 0.5 A g-1 in a full-cell test using MnO2 as a cathode.

In Vitro and In Vivo Cytotoxicity of Boron Nitride Nanotubes: A Systematic Review

Boron nitride nanotubes (BNNTs) are an exciting class of nanomaterials due to their unique chemical and physical characteristics. In recent decades, BNNTs have gained huge attention in research and development for various applications, including as nano-fillers for composites, semiconductor devices, hydrogen storage, and as an emerging material in biomedical and tissue engineering applications. However, the toxicity of BNNTs is not clear, and the biocompatibility is not proven yet. In this review, the role of BNNTs in biocompatibility studies is assessed in terms of their characteristics: cell viability, proliferation, therapeutic outcomes, and genotoxicity, which are vital elements for their prospective use in biomedical applications. A systematic review was conducted utilising the databases Scopus and Web of Science (WOS) (2008-2022). Additional findings were discovered manually by snowballing the reference lists of appropriate reviews. Only English-language articles were included. Finally, the significant analysis and discussion of the chosen articles are presented.

Properties and applications of boron nitride nanotubes

Nanomaterials have received increasing attention due to their controllable physical and chemical properties and their improved performance over their bulk structures during the last years. Carbon nanostructures are one of the most widely searched materials for use in different applications ranging from electronic to biomedical because of their exceptional physical and chemical properties. However, BN nanostructures surpassed the attention of the carbon-based nanostructure because of their enhanced thermal and chemical stabilities in addition to structural similarity with the carbon nanomaterials. Among these nanostructures, one dimensional-BN nanostructures are on the verge of development as new materials to fulfill some necessities for different application areas based on their excellent and unique properties including their tunable surface and bandgap, electronic, optical, mechanical, thermal, and chemical stability. Synthesis of high-quality boron nitride nanotubes (BNNTs) in large quantities with novel techniques provided greater access, and increased their potential use in nanocomposites, biomedical fields, and nanodevices as well as hydrogen uptake applications. In this review, properties and applications of one-dimensional BN (1D) nanotubes, nanofibers, and nanorods in hydrogen uptake, biomedical field, and nanodevices are discussed in depth. Additionally, research on native and modified forms of BNNTs and also their composites with different materials to further improve electronic, optical, structural, mechanical, chemical, and biological properties are also reviewed. BNNTs find many applications in different areas, however, they still need to be further studied for improving the synthesis methods and finding new possible future applications.

Improved drug delivery and competitive adsorption of paclitaxel and mitomycin C anticancer drugs on the Boron-nitride nanoparticles: A molecular dynamics insight

The competitive aggregated adsorption and molecular interactions between paclitaxel (PX) and mitomycin C (MMC) molecules on the surface of boron nitride nanosheet (BNNS) was investigated using molecular dynamics method. BNNS...

A Self-Powered Piezo-Bioelectric Device Regulates Tendon Repair-Associated Signaling Pathways through Modulation of Mechanosensitive Ion Channels

Tendon disease constitutes an unmet clinical need and remains a critical challenge in the field of orthopaedic surgery. Innovative solutions are required to overcome the limitations of current tendon grafting approaches, and bioelectronic therapies show promise in treating musculoskeletal diseases, accelerating functional recovery through the activation of tissue regeneration-specific signaling pathways. Self-powered bioelectronic devices, particularly piezoelectric materials, represent a paradigm shift in biomedicine, negating the need for battery or external powering and complementing existing mechanotherapy to accelerate the repair processes. Here, the dynamic response of tendon cells to a piezoelectric collagen-analogue scaffold comprised of aligned nanoscale fibers made of the ferroelectric material poly(vinylidene fluoride-co-trifluoroethylene) is shown. It is demonstrated that motion-powered electromechanical stimulation of tendon tissue through piezo-bioelectric device results in ion channel modulation in vitro and regulates specific tissue regeneration signaling pathways. Finally, the potential of the piezo-bioelectronic device in modulating the progression of tendinopathy-associated processes in vivo, using a rat Achilles acute injury model is shown. This study indicates that electromechanical stimulation regulates mechanosensitive ion channel sensitivity and promotes tendon-specific over non-tenogenic tissue repair processes.

Ultrasound-Powered Implants: A Critical Review of Piezoelectric Material Selection and Applications

Ultrasound-powered implants (UPIs) represent cutting edge power sources for implantable medical devices (IMDs), as their powering strategy allows for extended functional lifetime, decreased size, increased implant depth, and improved biocompatibility. IMDs are limited by their reliance on batteries. While batteries proved a stable power supply, batteries feature relatively large sizes, limited life spans, and toxic material compositions. Accordingly, energy harvesting and wireless power transfer (WPT) strategies are attracting increasing attention by researchers as alternative reliable power sources. Piezoelectric energy scavenging has shown promise for low power applications. However, energy scavenging devices need be located near sources of movement, and the power stream may suffer from occasional interruptions. WPT overcomes such challenges by more stable, on-demand power to IMDs. Among the various forms of WPT, ultrasound powering offers distinct advantages such as low tissue-mediated attenuation, a higher approved safe dose (720 mW cm^-2 ), and improved efficiency at smaller device sizes. This study presents and discusses the state-of-the-art in UPIs by reviewing piezoelectric materials and harvesting devices including lead-based inorganic, lead-free inorganic, and organic polymers. A comparative discussion is also presented of the functional material properties, architecture, and performance metrics, together with an overview of the applications where UPIs are being deployed.

Boron nitride nanotube scaffolds: emergence of a new era in regenerative medicine

Tissue engineering scaffolds have transformed from passive geometrical supports for cell adhesion, extension and proliferation to active, dynamic systems that can in addition, trigger functional maturation of the cells in response to external stimuli. Such 'smart' scaffolds require the incorporation of active response elements that can respond to internal or external stimuli. One of the key elements that direct the cell fate processes is mechanical stress. Different cells respond to various types and magnitudes of mechanical stresses. The incorporation of a pressure-sensitive element in the tissue engineering scaffold therefore, will aid in tuning the cell response to the desired levels. Boron nitride nanotubes (BNNTs) are analogous to carbon nanotubes and have attracted considerable attention due to their unique amalgamation of chemical inertness, piezoelectric property, biocompatibility and, thermal and mechanical stability. Incorporation of BNNTs in scaffolds confers them with piezoelectric property that can be used to stimulate the cells seeded on them. Biorecognition and solubilization of BNNTs can be engineered through surface functionalization with different biomolecules. Over the years, the importance of BNNT has grown in the realm of healthcare nanotechnology. This review discusses the salient properties of BNNTs, the influence of functionalization on theirin vitroandin vivobiocompatibility, and the uniqueness of BNNT-incorporated tissue engineering scaffolds.

Functionalized BaTiO3 enhances piezoelectric effect towards cell response of bone scaffold

Piezoelectric effect of polyvinylidene fluoride (PVDF) plays a crucial role in restoring the endogenous electrical microenvironment of bone tissue, whereas more β phase in PVDF leads to higher piezoelectric performance. Nanoparticles can induce the nucleation of the β phase. However, they are prone to aggregate in PVDF matrix, resulting in weakened nucleation ability of β phase. In this work, the hydroxylated BaTiO₃ nanoparticles were functionalized with polydopamine to promote their dispersion in PVDF scaffolds fabricated via selective laser sintering. On one hand, the catechol groups of polydopamine could form hydrogen bonding with the hydroxyl groups of the BaTiO₃. On the other hand, the amino groups of polydopamine were able to bond with CF group of PVDF. As a result, the functionalized BaTiO₃ nanoparticles homogeneously distributed in PVDF matrix, which significantly increased the β phase fraction from 46% to 59% with an enhanced output voltage by 356%. Cell testing confirmed the enhanced surface electric cues significantly promoted cell adhesion, proliferation and differentiation. Furthermore, the scaffolds exhibited enhanced tensile strength and modulus, which was ascribed to the rigid particle strengthening effect and the improved interfacial adhesion. This study suggested that the piezoelectric scaffolds shown a potential application in bone repair.