Lead-Free Perovskite Cs3Bi2I9-Derived Electroactive PVDF Composite-Based Piezoelectric Nanogenerators for Physiological Signal Monitoring and Piezo-Phototronic-Aided Strain Modulated Photodetectors

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.

A Spin-Charge-Regulated Self-Powered Nanogenerator for Simultaneous Pyro-Magneto-Electric Energy Harvesting

In view of the depletion of natural energy resources, harvesting energy from waste is a revolution to simultaneously capture, unite, and recycle various types of waste energies in flexible devices. Thus, in this work, a spin-charge-regulated pyro-magneto-electric nanogenerator is devised at a well-known ferroelectric P(VDF-TrFE) copolymer. It promptly stores thermal-magnetic energies in a "capacitor" that generates electricity at room temperature. The ferroelectric domains are regulated to slip at the interfaces (also twins) of duly promoting polarization and other properties. An excellent pyroelectric coefficient p ∼ 615 nC·m-2·K-1 is obtained, with duly enhanced stimuli of a thermal sensitivity ∼1.05 V·K-1, a magnetoelectric coefficient αme ∼8.8 mV·cm-1·Oe-1 at 180 Hz (resonance frequency), and a magnetosensitivity ∼473 V/T. It is noteworthy that a strategy of further improving p (up to 41.2 μC·m-2·K-1) and αme (up to 23.6 mV·cm-1·Oe-1) is realized in the electrically poled dipoles. In a model hybrid structure, the spins lead to switch up the electric dipoles parallel at the polymer chains in a cohesive charged layer. It is an innovative approach for efficiently scavenging waste energies from electric vehicles, homes, and industries, where abundant thermal and magnetic energies are accessible. This sustainable strategy could be useful in next-generation self-powered electronics.

Electroactive properties and piezo-tribo hybrid energy harvesting performances of PVDF-AlFeO3 composites: role of crystal symmetry and agglomeration of fillers

Inorganic filler-loaded PVDF-based composites have been very widely used for electrical and energy harvesting applications in recent times. In this regard, the effects of different parameters of fillers like size, shape, chemical states, distribution, functional properties, and many others on the output performance of PVDF have been widely studied. However, the effect of another important parameter, namely the crystal symmetry of the filler, in tuning the energy harvesting performance of PVDF has been rarely explored. Therefore, to explore this fact, here we develop PVDF-based composite films by using two types of AlFeO3 fillers, one with rhombohedral R3̄c symmetry (AFRH) and another with an orthorhombic Pc21n structure. Ferrite-based oxides have been chosen here as fillers due to their good dielectric compatibility with PVDF. On the other hand, AlFeO3 has been chosen due to the simplicity of synthesizing it with both centrosymmetric and non-centrosymmetric crystal structures and the scarcity of reports exploring the energy-harvesting performance of AlFeO3-based polymer composites. A significant difference in particle agglomeration has also been observed here between the mentioned two types of AlFeO3 fillers which was mainly due to their specific synthesis conditions. The electroactive properties of PVDF have been observed to be mostly dependent on filler agglomeration. However, the crystal symmetry has shown a strong effect on the piezoelectric energy harvesting performances. As a result of these facts, the piezo-tribo hybrid energy harvesting performance, which depends on both the dielectric permittivity and piezoelectric activity, has been observed to be better for the AFRH5-based hybrid device (AFRH5H) (with ∼72 V open circuit voltage and ∼45 μW cm-2 power density) compared to that of the AFOR5-based hybrid device (AFOR5H). The real-life applications of all the energy harvesting devices have also been demonstrated here.

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.

Hydrogen Bonding-Assisted Complete Ferroelectric β-Phase Conversion in Poly(vinylidene fluoride) Thin Films: Exhibiting an Excellent Memory Window and Long Retention

Organic nonvolatile memory with low power consumption is a critical research demand for next-generation memory applications. Ferroelectric switching characteristics of poly(vinylidene fluoride) (PVDF) thin films modified with a trace amount of hydrated Cu salt (CuCl2·2H2O) are explored in the present study. Herein, a Cu salt-mediated PVDF (Cu/PVDF) thin film with preferential edge-on β-crystallites is fabricated through the orientation-controlled spin coating (OCSC) technique. This work proposes a convenient and effective approach to produce edge-on-oriented electroactive PVDF thin films with a high degree of polar β-phase, so as to realize the favorable switching under low operating voltages. Herein, chemically modified PVDF is anticipated to form a complex intermediate, which attains its stability by undergoing favorable hydrogen bonding that reorients the C-C structure of PVDF to obtain the β-conformation. Such information is verified by X-ray photoelectron spectroscopy (XPS). Grazing incidence Fourier transform infrared (GI-FTIR) spectroscopy revealed that the Cu salt incorporated into the PVDF matrix favored the formation of the electroactive β-phase with edge-on crystallite lamellae. Consequently, the Cu/PVDF thin film demonstrates a good contrast between electric field-assisted written and erased data bits in the piezoresponse force microscopy (PFM) phase image. Furthermore, to obtain the ferroelectric memory window, a metal-ferroelectric-insulator-semiconductor (MFIS) diode with Cu/PVDF as a ferroelectric layer has been fabricated. The capacitance-voltage (C-V) characteristic of the MFIS diode exhibits a memory window of 12 V with a long-term retention behavior (∼longer than 7 days). In a nutshell, we tried to represent a clear understanding of the interfacial interactions of the Cu salt with PVDF, which favor the edge-on formation that results in the promising low-voltage ferroelectric switching and excellent retention response, where any additional electrical poling and/or external stretching is completely possible to be ruled out, thus offering a new prospect for the evolution of devices with long-lasting nonvolatile memories.

Preferential perovskite surface-termination induced high piezoresponse in lead-free in situ fabricated Cs3Bi2Br9-PVDF nanocomposites promotes biomechanical energy harvesting

Lead-free halide perovskites have gained immense popularity in photovoltaic and energy harvesting applications because of their excellent optical and electrical attributes with minimal toxicity. We synthesized composite films of lead-free Cs₃Bi₂Br₉ perovskite embedded in the polyvinylidene fluoride (PVDF) matrix and have investigated their piezoelectric energy harvesting. Five PVDF@Cs₃Bi₂Br₉ composite films were fabricated with varying wt% of the perovskite in the PVDF. The composite with a 4 wt% of the perovskite shows 85% activation of the electroactive β-phase of PVDF. Additionally, this composite exhibits a maximum polarisation of ∼0.1 μC cm^-2 and the best energy storage density of ∼0.8 mJ cm^-3 at an applied field of ∼16 kV cm^-1 among all the synthesized composites. A nanogenerator fabricated using 4 wt% loading in the composite film produced an instantaneous output voltage of ∼40 V, an instantaneous current of ∼4.1 μA, and a power density of ∼17.8 μW cm^-2 across 10 MΩ resistance when repeatedly hammered by the human hand. The nanogenerator is further employed to light up several LEDs and to charge capacitors with a small active area demonstrating significant promise for prospective wearables and portable devices and paving the way for high-performance nanogenerators using lead-free halide perovskites. Density functional theory calculations were performed to understand the interaction of the electroactive phase of the PVDF with different perovskite surface terminations to unravel the various interaction mechanisms and their ensuing charge transfer properties.

Utilizing Strain-Engineered Stable Halide Perovskite for Interfacial Interaction with Molecular Dipoles To Enhance Ferroelectric Switching and Piezoresponse in Polymer Composite Nanofibers

Mechanical and solar to electrical energy conversion using piezo- and ferroelectric and photovoltaic effects may be a practical answer to the rising energy demand. In this quest, piezoelectric polymer poly(vinylidene fluoride-hexafluoroproylene) (P(VDF-HFP)) has gained interest due to its superior piezo- and ferroelectricity. In photovoltaic applications, inorganic halide perovskite (IHP) of CsPbI₃ is considered a prime model compound. However, its application is limited because of the photoactive perovskite phase instability at ambient conditions. Here, we report the in situ synthesis of the stable perovskite γ-CsPbI₃ through an electrospinning process at room temperature, encapsulated within a ferroelectric copolymer poly(vinylidene fluoride-hexafluoroproylene) (P(VDF-HFP)) as a composite nanofiber. Computational calculation using density functional theory (DFT) reveals that tensile strain plays a critical role in the dynamical stabilization of γ-CsPbI₃. This tensile strain is triggered by the electrospinning process, which aids in the formation and growth of γ-CsPbI₃. In the CsPbI₃-P(VDF-HFP) composite nanofiber, γ-CsPbI₃ nucleates the polar β-crystalline phase in P(VDF-HFP), which results in the intrinsic piezo- and ferroelectric characteristics. The γ-CsPbI₃ aids in preferable molecular dipole orientation, resulting in improved nanoscale piezo- and ferroelectric properties. The composite nanofiber features a higher piezoelectric d₃₃ magnitude (∼30 pm/V) and lower decay constant for polarized domains (τ_composite ≈ 17). The composite was utilized as a piezoelectric nanogenerator to demonstrate human physiological motion monitoring in self-power mode. The relevant pressure sensitivities of 81 and 40 mV/kPa for the low-pressure (<0.6 kPa) and high-pressure (>0.6 to 12 kPa) ranges, respectively, promise its suitability in the health care sector.