Biodegradable ferroelectric molecular crystal with large piezoelectric response

Ultrasound-triggered lysosomal alkalinization to block autophagy in tumor therapy

Lysosomes play a crucial role in regulating cancer progression and drug resistance. However, there is a pressing need for the development of drugs that can safely and effectively modulate the pH of cancerous lysosomes in a controlled manner. In this study, we propose a novel strategy for lysosomal alkalinization triggered by piezoelectricity. Our findings indicate that the electrons generated by (BaTiO3/Zr/Ca) BCZT under sonication effectively alkalinize the lysosomes. Molecular dynamics simulations further demonstrate that alterations in lysosomal pH lead to modifications in the conformation of V-ATPase (proton pump), enhancing its interaction with sodium ions while partially excluding hydrogen ions from entering the lysosomes. This mechanism helps maintain lysosomal alkalization, resulting in reduced hydrolase activity and preventing the degradation of proteins and damaged organelles. The accumulation of nanoparticles within the lysosomes causes swelling and gradual destruction of the lysosomal membrane. Consequently, this lysosomal dysfunction hampers the fusion with autophagosomes, inhibiting autophagy in tumor cells and promoting apoptosis in various tumor types. Our strategy significantly inhibited tumor volume growth in mice during animal studies. In conclusion, our piezoelectric-triggered lysosomal alkalinization strategy holds promise for innovative breakthroughs in the treatment of multiple cancers.

Unlocking ferroelectricity in a metal-free adamantane derivative via targeted symmetry reduction

By introducing a symmetry-reduction design strategy in adamantane derivatives, overcoming the inherent high symmetry of globular molecules that typically hinders long-range electrical ordering, we report a metal-free ferroelectric 2-adamantylammonium bromide (2-ADAB) with a high Curie temperature of 383 K and robust polarization switching.

Electrotherapy and health monitoring with piezoelectric and triboelectric technologies

The growing need for advanced therapeutic and diagnostic technologies has spurred interest in self-powered systems for electrotherapy and health monitoring. Traditional battery-dependent medical devices (MDs) face limitations, including short operational lifespans and patient discomfort, underscoring the importance of sustainable alternatives. Mechanical energy harvesting technologies, such as piezoelectric and triboelectric nanogenerators (PENGs and TENGs), have emerged as promising solutions, enabling real-time health monitoring and non-invasive electrotherapy by converting biomechanical energy into electricity. This review explores the latest advancements in PENG and TENG technologies, emphasizing their applications in wound healing, neural regeneration, and real-time physiological monitoring. Strategies to overcome hurdles are discussed, demonstrating the transformative potential of PENG and TENG systems in next-generation MDs. By integrating energy harvesting with therapeutic and monitoring functionalities, piezoelectric and triboelectric systems offer a path toward non-invasive, efficient, and patient-centric medical solutions.

Inflammatory targeted nanoplatform incorporated with antioxidative nano iron oxide to attenuate ulcerative colitis progression

Antioxidative nanomaterials with reactive oxygen species (ROS) scavenging capabilities hold promise for the treatment of ulcerative colitis (UC). However, their clinical application is limited by rapid diffusion, susceptibility to inactivation, and insufficient targeting of inflammatory sites. This study focuses on developing a nanoplatform by integrating iron oxide nanoparticles (IONPs) into zeolitic imidazolate frameworks-8 (ZIF-8), termed as ZIF-8@IONPs. ZIF-8@IONPs exhibited good biocompatibility and effective ROS scavenging capabilities in RAW 264.7 cells. To enhance inflammatory targeting, HA@ZIF-8@IONPs were generated through hyaluronic acid (HA) surface modification. HA@ZIF-8@IONPs effectively reduced damage to intestinal tissues in the UC mouse model. Mechanistic revealed that HA@ZIF-8@IONPs exhibited antioxidant and anti-inflammatory activities by eliminating endogenous ROS, activating the Nrf2 signaling pathway, and inhibiting the NF-κB signaling pathway. This study highlights the nanoplatform's potential as a promising candidate for UC treatment due to its great targeting of inflammatory microenvironments and efficient ROS scavenging.

Enantiomeric Ferroelectric Chiral Domains

Chiral ferroelectric crystals with inherent chirality and spontaneous polarization have recently gained considerable interest. However, the chiral topological texture, which provides a promising platform for exploring exotic functionalities, has never been found in enantiomeric ferroelectric crystals. Here, we report a pair of enantiomeric molecular ferroelectrics, [RFAO][ReO4] and [SFAO][ReO4] (RFAO/SFAO = (4R,5R/4S,5S)-4-fluoro-1-azabicyclo[3.2.1]octane). The enantiomers crystallize in the chiral-polar point group 2 at room temperature and undergo two ferroelectric phase transitions with an Aizu notation of 222F2 at 350 K and 432F2 at 463 K, respectively. Such phase transitions enable them to show a multistep switchable second-harmonic generation circular dichroism (SHG-CD) effect from high to low to off (inactive) SHG-CD states. More importantly, we observed spiral chiral ferroelectric domains in the enantiomers. To the best of our knowledge, this is the first discovery of chiral domains in enantiomeric ferroelectric crystals. Our breakthrough findings give new sights into the interplay between polarization and chirality and will greatly stimulate further exploration of chiral ferroelectric crystals with switchable SHG-CD and chiral domains for next-generation electronic-photonic devices.

Spiro-Driven Ferroelectric Coordination Polymer Exhibiting Distinct Phase Transitions Under Thermal and Pressure Stimuli

Controllable strategies for the design of molecular ferroelectrics have been actively pursued in recent years due to their promising applications in modern electronic devices. In this work, we present a spiro-driven approach for the design of a new class of molecular ferroelectrics. Using 2-morpholinoethanol (MEO) as a bidentate chelating ligand and the SCN⁻ anion as a bridging co-ligand, we obtained a neutral chain-like ferroelectric coordination polymer, [Cd(MEO)(SCN)₂]. Interestingly, it undergoes both a thermal-induced phase transition, driven by ring-conformational flipping of the spiro-like [Cd(MEO)] fragment, and a pressure-induced transition, triggered by significant deformation of the spring-like [Cd(SCN)₂]∞ helical chain. Unlike most previously reported ferroelectric coordination polymers, which often rely on organic cationic guests, this work introduces a new avenue for designing neutral ferroelectric coordination polymers. Overall, the spiro-driven strategy provides valuable insights and a novel structural motif for the development of advanced molecular ferroelectrics.

Customizing Room-Temperature Perovskite Ferroelectrics toward the Multichannel Domain Manipulation

Manipulating domain structure in ferroelectrics by external stimuli presents a fascinating avenue for new-generation electronic devices. However, multichannel controlling of ferroelectric domains is still a challenge, due to the lack of knowledge on their bistability to diverse physical stimuli. Herein, we have customized a series of perovskite ferroelectrics, (CnH2n+1NH3)2(CH3NH3)2Pb3Br10 (n = 2-7), of which the Curie temperatures are modulated in a wide temperature range (ΔT = 74 K) by tailoring chain length of organic spacers. Strikingly, the n = 7 member is a room-temperature ferroelectric with bistable characteristics, thus endowing the manipulation of domains via four channels (i.e., thermal, stress, light, and electric fields). Such a non-volatile memory behavior of the stress-switching domain is unprecedented in hybrid perovskite ferroelectrics. This manipulation of domains reveals the unique bistability of its ferroelectric orders, which sheds light on the future advance of customizing electric-ordered materials toward smart device applications.

From Flexible Crystals to Piezoelectrics: The Advent of a New Class of Flexible Functional Molecular Materials

The recent discoveries of mechanically flexible molecular crystals have fuelled a resurgence of research interest in molecular piezoelectrics. This has raised the quest to explore structure-property relations in molecular piezoelectric crystals, which remain largely obscure. Here, the fundamental structural features associated with organic molecular piezoelectric crystals are explored in relation to their mechanical and supramolecular flexibility. Along with the electrostatic properties such as molecular dipole moments and spontaneous crystal polarization, possible correlations of piezoelectric coefficients with intermolecular interaction topologies and their anisotropy point toward their link with mechanical flexibility in molecular crystals. In addition, the possible roles of crystal packing efficiency, lattice cohesive energies, Young's moduli, and its anisotropy from elastic tensors have been examined. This quantitative overview suggests that piezoelectric response in molecular materials is a complex interplay of several structural and electrostatic factors. Based on these analyses and the fundamental aspects of electromechanical coupling, it becomes apparent that combining mechanical flexibility and supramolecular chirality/polarity can be a promising approach to discovering soft molecular piezoelectrics for novel actuators and energy-harvesting materials.

Facile Access to Piezoelectric Polyamides by Polyamidation of Carboxylic Acids and Ynamides for Potent Tumor Immunotherapy

Polyamides are a fascinating group of piezoelectric materials that are largely synthesized by the polycondesation of dicarboxylic acids with diamines or the ring-opening polymerization of special lactams. However, developing a green polymerization approach for the facile synthesis of piezoelectric polyamides is highly desirable but also challenging. Here, a simple polyamidation of carboxylic acids and ynamides is successfully established to synthesize versatile piezoelectric polyamides. This polymerization also possesses the merits of 100% atom economy, no waste generation, and additive-free as well as catalyst-free system. A range of polyamides are synthesized in moderate to good yields with satisfactory molecular weights. Importantly, piezoelectric polyamides containing tetraphenylethene (P1e/2b) can generate a bundant reactive oxygen species under ultrasound (US) exposure, thereby eliciting robust immunogenic cell death induction for augmented piezoelectric immunotherapy. Furthermore, P1e/2b exhibits distinctive aggregation-induced emission property that allows fluorescence imaging. In vivo evaluation using a bilateral tumor-bearing mouse model manifested that P1e/2b administration reinforced systemic immunity and triggered immune memory under US exposure, thereby leading to primary tumor eradication and distant tumor suppression. Therefore, this work represents a transition-metal-free and waste-free polymerization paradigm for the construction of piezoelectric polyamides, providing a distinct strategy to designing new piezoelectric polymers for effective tumor immunotherapy.

High-performance elastic ferroelectrics via low-temperature carbene crosslinking and high-temperature annealing

With the increasing demand for wearable electronics, elastic ferroelectrics with high polarization intensity and Curie temperature have become essential. However, balancing high ferroelectric performance with elasticity in polymeric ferroelectrics remains a challenge, as higher crosslinking density to improve elasticity often compromises Curie temperature and remnant polarization. To address this trade-off, we introduce unsaturated bonds into commercial P(VDF-TrFE), forming P(VDF-TrFE-DB) with enhanced crosslinking reactivity while retaining its inherent ferroelectric properties. A novel two-step LT-HT processing strategy is developed to achieve this balance. The low-temperature (LT) step leverages carbene-mediated crosslinking with diazirine-based crosslinkers below the polymer's Curie temperature, preventing premature crystallization and forming amorphous regions essential for mechanical flexibility. The high-temperature (HT) annealing step promotes the formation and alignment of well-ordered ferroelectric crystalline structures, optimizing remnant polarization and Curie temperature while preserving the crosslinked amorphous regions critical for elasticity. This approach enables high elasticity with minimal crosslinker content while maintaining excellent ferroelectric performance. The resulting elastic P(VDF-TrFE-DB) polymer exhibits a significantly elevated Curie temperature (∼140 °C) and high remnant polarization (7.63 μC cm-2), comparable to commercial P(VDF-TrFE). This method offers a versatile pathway for advanced flexible electronics, soft actuators, and wearable devices requiring robust mechanical and ferroelectric properties.

Advancements in Wearable and Implantable BioMEMS Devices: Transforming Healthcare Through Technology

Wearable and implantable BioMEMSs (biomedical microelectromechanical systems) have transformed modern healthcare by enabling continuous, personalized, and minimally invasive monitoring, diagnostics, and therapy. Wearable BioMEMSs have advanced rapidly, encompassing a diverse range of biosensors, bioelectronic systems, drug delivery platforms, and motion tracking technologies. These devices enable non-invasive, real-time monitoring of biochemical, electrophysiological, and biomechanical signals, offering personalized and proactive healthcare solutions. In parallel, implantable BioMEMS have significantly enhanced long-term diagnostics, targeted drug delivery, and neurostimulation. From continuous glucose and intraocular pressure monitoring to programmable drug delivery and bioelectric implants for neuromodulation, these devices are improving precision treatment by continuous monitoring and localized therapy. This review explores the materials and technologies driving advancements in wearable and implantable BioMEMSs, focusing on their impact on chronic disease management, cardiology, respiratory care, and glaucoma treatment. We also highlight their integration with artificial intelligence (AI) and the Internet of Things (IoT), paving the way for smarter, data-driven healthcare solutions. Despite their potential, BioMEMSs face challenges such as regulatory complexities, global standardization, and societal determinants. Looking ahead, we explore emerging directions like multifunctional systems, biodegradable power sources, and next-generation point-of-care diagnostics. Collectively, these advancements position BioMEMS as pivotal enablers of future patient-centric healthcare systems.

Alkali Metal Substitution for Modulating Three-Dimensional Halide Double Perovskite Ferroelectric

Organic-inorganic hybrid halide double perovskites have garnered significant attention because of their broad utility in data storage, transducers, and signal processing. However, halide double perovskites incorporating alkali metal components with ferroelectricity are still relatively scarce. Herein, we utilize the alkali metal substitution strategy to fabricate a new homochiral K/Bi-based halide double perovskite ferroelectric, (S-3-hydroxypyrrolidinium)2KBiBr6 (1). Compound 1 forms a three-dimensional (3D) inorganic framework and features a lon topology characterized by a Schläfli symbol of 66. The sp3 O atoms from the organic cations coordinate with the alkali metal K atoms, forming the twist dodecahedron and creating a large distortion in the inorganic framework. Structural analysis reveals 1 undergoes two phase transitions at 357 and 420 K. Symmetry-breaking with the 2F1 structural species leads to the emergence of ferroelasticity and ferroelectricity. 1 possesses clear ferroelectricity with a remnant polarization (Pr) value of 1.86 μC cm-2 and a low coercive field (Ec) value of 1.4 kV cm-1. Interestingly, the Pr value remains nearly unchanged, while the Ec value decreases by 17.6% after the alkali metal substitution. This work enlarges the family of hybrid bimetal halides containing alkali metals and provides new insights for exploring stable multifunctional ferroelectric materials.

Applications of Piezoelectric Materials in Biomedical Engineering

Piezoelectric materials are unique biomedical materials whose asymmetric crystal structures enable them to convert various forms of mechanical energy from the environment, including ultrasound, into electrical or chemical energy. These materials have wide applications in the biomedical field and are gradually becoming a research hotspot in applications such as energy harvesters, biosensors, and tissue engineering. This article first provides a systematic review of the research progress on piezoelectric materials, then outlines frontier strategies for achieving high-performance electrical materials and devices. This article discusses the highly oriented nature of piezoelectric materials mediated by intermolecular forces and explores the applications of piezoelectric implants in biomedicine, including biosensing, energy harvesting, tissue engineering, and disease treatment. Finally, the challenges faced by piezoelectric devices in future research are elaborated.

Advancements in Carbon-Based Piezoelectric Materials: Mechanism, Classification, and Applications in Energy Science

The piezoelectric phenomenon has garnered considerable interest due to its distinctive physical properties associated with the materials involved. Piezoelectric materials, which are inherently non-centrosymmetric, can generate an internal electric field under mechanical stress, enhancing carrier separation and transfer due to electric dipole moments. While inorganic piezoelectric materials are often investigated for their high piezoelectric coefficients, they come with potential drawbacks such as toxicity and high production cost, which hinder their practical applications. Consequently, carbon-based piezoelectric materials have emerged as an alternative to inorganic materials, boasting advantages such as a large specific surface area, high conductivity, flexibility, and eco-friendliness. Research into the applications of carbon-based piezoelectric materials spans environmental remediation, energy conversion, and biomedical treatments, indicating a promising future. This review marks the first comprehensive attempt to discuss and summarize the various types of carbon-based piezoelectric materials. It delves into the underlying mechanisms by which piezoelectricity influences catalysis, biomedical applications, nanogenerators, and sensors. Additionally, various potential techniques are presented to enhance the piezoelectric performance. The design principles of representative fabrication strategies for carbon-based piezoelectric materials are analyzed, emphasizing their current limitations and potential improvements for future development. It is believed that recent advances in carbon-based piezoelectric materials will make a significant impact.

The First Kleinman-type Second-Harmonic Generation Circular Dichroism On/Off Switchable Ferroelectrics

Chiral ferroelectrics have recently received considerable interest due to their unique chiroptical properties. They can adopt Kleinman symmetry second-harmonic generation (SHG)-active chiral-polar point groups in the ferroelectric phase while Kleinman symmetry SHG-inactive chiral-nonpolar point groups in the paraelectric phase, providing a great opportunity to realize on/off switching of SHG circular dichroism (SHG-CD) response. However, the SHG-CD effect was rarely explored in chiral ferroelectrics, and the on/off switchable SHG-CD has never been reported. Herein, we report the first crown ether-based chiral ferroelectrics (R/S-CS)Ca(18-crown-6) (CS=camphor-10-sulfonic acid), which undergo a 422F2 type ferroelectric phase transition at around 336 K from Kleinman symmetry SHG-active point group 2 to Kleinman symmetry SHG-inactive point group 422. Notably, they exhibit obvious SHG-CD responses with an anisotropy factor of up to 0.31. More importantly, the SHG-CD response can be switched between SHG-CD active (SHG-CD on) and inactive (SHG-CD off) states during the ferroelectric phase transition, which is unprecedented. To the best of our knowledge, this is the first example of Kleinman-type SHG-CD on/off switchable ferroelectric. Our findings open up a new way to switch SHG-CD response based on chiral ferroelectrics, which would greatly inspire the further exploration of switchable SHG-CD effects in chiral ferroelectrics.

Molecular Engineering of Amino Acid Crystals with Enhanced Piezoelectric Performance for Biodegradable Sensors

Amino acid crystals have emerged as promising piezoelectric materials for biodegradable and biocompatible sensors; however, their relatively low piezoelectric coefficients constrain practical applications. Here, we introduce a fluoro-substitution strategy to overcome this limitation and enhance the piezoelectric performance of amino acid crystals. Specifically, we substituted hydrogen atoms on the aromatic rings of L-tryptophan, L-phenylalanine, and N-Cbz-L-phenylalanine with fluorine, resulting in significantly elevated piezoelectric coefficients. Density functional theory calculations further indicate that fluorination strengthens polarization by modifying molecular dipole moments. Consequently, these fluoro-substituted crystals achieve piezoelectric coefficients of up to 50.36 pm/V, surpassing those of other organic piezoelectric materials such as polyvinylidene fluoride (PVDF), poly(L-lactic acid) (PLLA), and gelatin. When integrated into flexible, biodegradable force sensors, the fluoro-substituted crystals exhibit a broad sensing range, high sensitivity, and stable in vivo operation over extended periods. This work establishes a versatile route for boosting piezoelectricity in biomaterials, thereby broadening their scope in biomedical applications.

Organomolecular Ferroelectric Nanocatalyst Augments Tumor Immunotherapy by Inducing Apoptosis and Ferroptosis

Immunogenic programmed cell death effectively triggers acute inflammatory responses, thereby enhancing antitumor immunity. The advancement of biodegradable nonmetallic dual inducers represents a promising strategy. Herein, a biodegradable organomolecular ferroelectric nanoplatform (C60-TCNQ, CT) is designed to facilitate effective ferroelectric catalysis, thereby augmenting tumor immunotherapy through apoptosis and ferroptosis. CT-mediated ultrasound-triggered ferroelectric catalysis promotes ferroelectric polarization and significantly increases the production of reactive oxygen species, leading to substantial tumor cell apoptosis. Moreover, the polycyano group of CT nanoparticles selectively reacts with cysteine under mild conditions, resulting in redox imbalances and the accumulation of lipid peroxides, which contribute to the induction of ferroptosis in tumor cells. Additionally, the apoptosis and ferroptosis induced by CT stimulate immunogenic cell death progression, eliciting robust immune responses. In vivo evaluation using a bilateral tumor model demonstrates the capacity of CT to sensitize anti-PD-L1 therapy under ultrasound irradiation, achieving an impressive antitumor response rate of 96.2% against malignant melanoma and an 80% inhibition of tumor metastasis. RNA sequencing analysis revealed that treatment with CT resulted in a downregulation of gene signatures associated with the immune-related Jak-Stat signaling pathway. This study opens a novel avenue to developing organomolecular ferroelectric nanomedicines for effective tumor immunotherapy.

High-Entropy High-Temperature High-Piezoelectricity Ceramics

High-temperature piezoelectric materials are essential components of transducers and accelerometers applied in the fields of aircraft engines, automobiles, nuclear power units, etc., yet how to achieve large piezoelectricity accompanied by high Curie temperature and superior resistivity is still a big challenge. Here, the high-entropy strategy is utilized to design bismuth-layer high-temperature piezoelectric ceramics, resulting in an excellent comprehensive piezoelectric performance with a record-high figure of merit (d33 *TC) and a high electrical DC resistivity of 1.0 × 106 Ω cm at 750 °C. High-energy synchrotron X-ray diffraction and transmission electron microscopy results suggest that there is no significant change in long-range average orthorhombic structure through high-entropy engineering, providing a structural basis for retaining a high TC. Encouragingly, highly dense bismuth-layer vacancies occupied by alien atoms trigger extra unique out-of-plane polarization in perovskite layers around these 2D amorphous defects, as confirmed by quantitative analysis of local polarization configurations and density functional theory calculations. Together with the decreased polarization reversal energy barrier, the high entropy strategy benefits polarization flexibility under external stimulation and offers breakthroughs in electrical properties. This work provides new insight into the improvement of comprehensive functional properties through the cocktail effect and structure mechanism for designing novel high-entropy materials.

Cholesterol Cocrystal Ferroelectrics Modulated by Solvent Effect

Cholesterol (CHOL) is an inherently biodegradable material with multiple chiral centers, being an essential component for cell membranes. Considering the close relationship between chirality and ferroelectric feature, this compound with chiral-polar structure is an intrinsic polar material. However, the ferroelectricity of CHOL crystals has never been found to date. Herein, a series of ferroelectric cocrystals of CHOL methanol (CHOL-MeOH) and CHOL ethanol (CHOL-EtOH) have been constructed through the solvent effect. It is found that the introduction of some solvent molecules containing hydroxyls such as methanol and ethanol can reduce the acceptor···donor length and thus form a 1D electroactive channel and further induce ferroelectricity in CHOL. Based on the density functional theory (DFT) calculation analyses represented by CHOL-EtOH, the largely decreased maximum energy barrier for the polarization reversal of ≈50% suggests that the electric polarization of the cocrystal is much easier to be reoriented under the external electric field through the solvent effect. These ferroelectric materials show good biocompatibility and biodegradability through in vitro and in vivo evaluation. These attributes make these CHOL cocrystals good candidates for the application of next-generation smart implantable electronic devices. This work sheds light on the chemical design of biodegradable ferroelectrics in biomaterials.

Zero-Dimensional Plastic Phase Transition Iron-Based Compounds with High Tc and Switchable SHG Responses

Organic-inorganic hybrid materials have garnered significant interest due to their unique combination of phase transition characteristics, substantial entropy changes, simple preparation methods, and structural flexibility, making them promising candidates for applications in sensor technologies and data storage systems. In the present research, two plastic organic-inorganic hybrid phase transition materials: [C7H17NF]FeCl4 (1) and [C7H17NF]FeBr4 (2) were successfully synthesized by the H/F substitution strategy. Significant step-like dielectric changes were observed during the reversible phase transitions of 1 (401 K) and 2 (406 K). At the same time, 1 and 2 have flexible switchable SHG effects and show the characteristics of band gap semiconductors with band gaps of 2.44 and 2.08 eV, respectively. This research presents an efficacious approach for devising the structures and modulating the properties of organic-inorganic hybrid materials.

Precise Design of Organic-Inorganic Hybrid Indium Molecular Ferroelectrics Based on Halogen Substitution

Low-dimensional hybrid organic-inorganic ferroelectric materials have attracted significant interest due to their outstanding optical and electrical properties. Nevertheless, many of the most extensively studied organic-inorganic hybrids incorporate lead or tin, which raises concerns related to long-term stability and environmental sustainability. Here, by using the quasi-spherical strategy, we have designed and obtained a series of zero-dimensional organic-inorganic hybrid indium metal ferroelectric compounds: [Me2CH2X(i-Pr)N][InBr4] (X = H, 1; F, 2; Cl, 3; Br, 4, respectively), based on halogen-substituted quaternary amines. The differential scanning calorimetry (DSC), dielectric, and second harmonic generation (SHG) measurement results show that these four compounds have high-temperature phase transitions (above room temperature). The ferroelectric properties of the compounds were confirmed through piezoresponse force microscopy (PFM) and electric hysteresis loop (P-E) measurements. This research offers new ideas for the advancement of ferroelectric materials and the innovation of future smart materials and optoelectronic devices.

Mechanically deformable organic ferroelectric crystal with plasticity optimized by fluorination

The ability of plastic deformation exerts in bulk crystals would offer great promise for ferroelectrics to achieve emerging and exciting applications. However, conventional ferroelectric crystals generally suffer from inherent brittleness and are easy to fracture. Here, by implementing fluorination on anion, we successfully design a flexible organic ferroelectric phenylethylammonium trifluoromethanesulfonate (PEA-TFMS) with interesting plasticity in its bulk crystals. To our knowledge, it is the first observation since the discovery of organic ferroelectric crystal triglycine sulfate in 1956. Compared to parent PEA-MS (phenylethylammonium mesylate), fluorination subtly alters ionic orientation and interactions to reorganize dipole arrangement, which not only brings switchable spontaneous polarization but also endows PEA-TFMS crystal with macroscopical bending and spiral deformability, making it a competitive candidate for flexible and wearable devices. Our work will bring inspiration for obtaining mechanically deformable organic ferroelectric crystals toward flexible electronics.

Spatial Symmetry Operation Breaking Sulfur-Chiral Photoswitchable Ferroelectrics

Ferroelectrics with switchable spontaneous polarization have gained enormous attention for a century. However, the structural phase transitions of conventional ferroelectrics have been mainly limited to the ones with crystallographic point group changes accompanied by the breaking of spatial symmetry elements. Moreover, although chiral and photoswitchable ferroelectrics have both been of great interest in recent years, heteroatomic chiral photoswitchable ferroelectrics have never been reported. Herein, for the first time, we designed a pair of sulfur-chiral photoswitchable ferroelectrics (Rs and Ss)-N-(3-bromo-5-chloro-2-hydroxybenzylidene)-2-methylpropane-2-sulfinamide (1-Rs and 1-Ss). Notably, they undergo a structural phase transition from the chiral polar C2 to P21 space group of point group 2 at around 142 K, accompanied by the symmetry operation breaking from 2-fold rotation and screw rotation in C2 to only 2-fold screw rotation in P21. Such a structural phase transition with the same point group, while different space groups with the breaking of symmetry operations, is significantly distinct from the structural phase transition with different point groups and space groups in conventional ferroelectrics. Furthermore,1-Rs exhibits the highest piezoelectric d33 value of 10 pC/N among organic photoswitchable ferroelectrics and shows optical control of ferroelectric polarization. To our knowledge, this is the first report of sulfur-chiral photoswitchable ferroelectrics showing phase transitions with only the space group change. This work enriches the family of chiral ferroelectrics and provides great inspiration for the exploitation of heteroatomic chiral photoswitchable ferroelectrics.

Precise Tailoring of Unprecedent Layered Perovskite-Type Heterostructure Ferroelectric via Chemical Molecular Scissor

Precise stacking of distinct two-dimensional (2D) rigid slabs to build heterostructures has renewed the portfolio of 2D materials, e.g., magic-angle graphene, due to the emergence of exotic physical properties. Recently, single-crystal heterostructures of layered perovskites have emerged as an exciting branch, while it remains scarce to achieve strong ferroelectricity in this new heterostructure family. Here, we present the first ferroelectric of 2D perovskite heterostructures as single crystal, (EA3Pb2Br7)EA4Pb3Br10 (1, EA=ethylamine), by precisely tailoring inorganic sheets via a chemical molecular scissor. It has notable ferroelectricity of large spontaneous polarization (Ps~5.0 μC/cm2) and high Curie temperature (Tc~375 K). Structurally, its inorganic framework adopts a unique 2D heterostructure that contains two different rigid slabs of {EA3Pb2Br7}n and {EA4Pb3Br10}n. This motif is self-assembled by layer-by-layer clipping of rigid prototype sheets, using extra neopentylamine as a molecular chemical scissor. Unlike epitaxial growth, such a molecule-level stacking facilitates the growth of heterostructure single crystals. Combining its strong ferroelectricity and inherent anisotropy, crystal-based device of 1 exhibits an ultrahigh polarized-light sensitivity up to ~37 in self-powered mode, being the highest level of 2D perovskite ferroelectric family. Our work will facilitate the further development of ferroelectric materials for optoelectronic device applications.

A Lithium Complex Ferroelectric with High Curie Temperature: [Li(1,10-Phenanthroline)2]I

Paraelectric-ferroelectric phase transitions have been mainly acknowledged by the order-disorder type in most molecular ferroelectrics or the displacive type in inorganic ferroelectrics. However, reports regarding symmetry-breaking ferroelectric phase transitions induced by distortion in the coordination geometry have been scarce. In this study, we present a lithium complex molecular ferroelectric [Li(1,10-phenanthroline)2]I, which undergoes an Aizu mmmFmm2 type symmetry-breaking ferroelectric phase transition at 371 K. Its ferroelectricity has been identified by the geometric distortion of the lithium ions coordination environment and the concomitant directional movement of iodide ions. Besides, the ferroelectric loop of [Li(1,10-phenanthroline)2]I can be readily obtained from a polarized polycrystalline pellet at room temperature; in addition, its nonlinear optical signal is comparable to that of KH2PO4 (KDP). To the best of our knowledge, [Li(1,10-phenanthroline)2]I represents the first lithium-based organic complex ferroelectric exhibiting a coordination geometry-triggered symmetry-breaking ferroelectric phase transition. This work will provide significant inspiration for the design of novel molecular ferroelectrics.

Wearable Resistive-Type Stretchable Strain Sensors: Materials and Applications

The rapid advancement of wearable electronics over recent decades has led to the development of stretchable strain sensors, which are essential for accurately detecting and monitoring mechanical deformations. These sensors have widespread applications, including movement detection, structural health monitoring, and human-machine interfaces. Resistive-type sensors have gained significant attention due to their simple design, ease of fabrication, and adaptability to different materials. Their performance, evaluated by metrics like stretchability and sensitivity, is influenced by the choice of strain-sensitive materials. This review offers a comprehensive comparison and evaluation of different materials used in resistive strain sensors, including metal and semiconductor films, low-dimensional materials, intrinsically conductive polymers, and gels. The review also highlights the latest applications of resistive strain sensors in motion detection, healthcare monitoring, and human-machine interfaces by examining device physics and material characteristics. This comparative analysis aims to support the selection, application, and development of resistive strain sensors tailored to specific applications.

Advances in Symbiotic Bioabsorbable Devices

Symbiotic bioabsorbable devices are ideal for temporary treatment. This eliminates the boundaries between the device and organism and develops a symbiotic relationship by degrading nutrients that directly enter the cells, tissues, and body to avoid the hazards of device retention. Symbiotic bioresorbable electronics show great promise for sensing, diagnostics, therapy, and rehabilitation, as underpinned by innovations in materials, devices, and systems. This review focuses on recent advances in bioabsorbable devices. Innovation is focused on the material, device, and system levels. Significant advances in biomedical applications are reviewed, including integrated diagnostics, tissue repair, cardiac pacing, and neurostimulation. In addition to the material, device, and system issues, the challenges and trends in symbiotic bioresorbable electronics are discussed.

Advanced Piezoelectric Materials, Devices, and Systems for Orthopedic Medicine

Harnessing the robust electromechanical couplings, piezoelectric materials not only enable efficient bio-energy harvesting, physiological sensing and actuating but also open enormous opportunities for therapeutic treatments through surface polarization directly interacting with electroactive cells, tissues, and organs. Known for its highly oriented and hierarchical structure, collagen in natural bones produces local electrical signals to stimulate osteoblasts and promote bone formation, inspiring the application of piezoelectric materials in orthopedic medicine. Recent studies showed that piezoelectricity can impact microenvironments by regulating molecular sensors including ion channels, cytoskeletal elements, cell adhesion proteins, and other signaling pathways. This review thus focuses on discussing the pioneering applications of piezoelectricity in the diagnosis and treatment of orthopedic diseases, aiming to offer valuable insights for advancing next-generation medical technologies. Beginning with an introduction to the principles of piezoelectricity and various piezoelectric materials, this review paper delves into the mechanisms through which piezoelectric materials accelerated osteogenesis. A comprehensive overview of piezoelectric materials, devices, and systems enhancing bone tissue repair, alleviating inflammation at infection sites, and monitoring bone health is then provided, respectively. Finally, the major challenges faced by applications of piezoelectricity in orthopedic conditions are thoroughly discussed, along with a critical outlook on future development trends.

Isolation Transformer Based Very Low Frequency Antenna with Enhanced Radiation Characteristics

Very low frequency electromagnetic waves adeptly propagate in harsh cross-medium environments, surmounting the rapid attenuation that impedes high-frequency counterparts. Traditional low frequency antennas, however, encounter challenges concerning size, efficiency, and power. Here, an isolation transformer based very low frequency loop antenna with compact size and well impedance matching is proposed to enhance radiation characteristics for long-distance communication. By utilizing the high magnetic permeability amorphous/nanocrystalline alloy Fe73.5Cu1Nb3B9Si13.5, the isolation transformer enables efficient and stable high-current input. This design surpasses the current limitation of the conventional loop antennas, thereby improving its electromagnetic performance. Consequently, the radiation intensity of proposed antenna can be effectively increased over 30 times compared to traditional loop antennas. According to the experimental measurements, the transmission distance is over 340 m at 15 kHz using a single proposed antenna with a diameter of 2 m. Its robust performance, such as high radiation efficiency, low power consumption, and long-distance transmission capacity, suggests significant potential for applications in underground communications and underwater information transmission.

Bonding Optimization Strategies for Flexibly Preparing Multi-Component Piezoelectric Crystals

Flexible films with optimal piezoelectric performance and water-triggered dissolution behavior are fabricated using the co-dissolution-evaporation method by mixing trimethylchloromethyl ammonium chloride (TMCM-Cl), CdCl2, and polyethylene oxide (PEO, a water-soluble polymer). The resultant TMCM trichlorocadmium (TMCM-CdCl3) crystal/PEO film exhibited the highest piezoelectric coefficient (d33) compared to the films employing other polymers because PEO lacks electrophilic or nucleophilic side-chain groups and therefore exhibits relatively weaker and fewer bonding interactions with the crystal components. Furthermore, upon slightly increasing the amount of one precursor of TMCM-CdCl3 during co-dissolution, this component gained an advantage in the competition against PEO for bonding with the other precursor. This in turn improved the co-crystallization yield of TMCM-CdCl3 and further enhanced d33 to ≈71 pC/N, exceeding that of polyvinylidene fluoride (a commercial flexible piezoelectric) and most other molecular ferroelectric crystal-based flexible films. This study presents an important innovation and progress in the methodology and theory for maintaining a high piezoelectric performance during the preparation of flexible multi-component piezoelectric crystal films.

Ferroelectric Perovskite/MoS2 Channel Heterojunctions for Wide-Window Nonvolatile Memory and Neuromorphic Computing

Ferroelectric materials commonly serve as gate insulators in typical field-effect transistors, where their polarization reversal enables effective modulation of the conductivity state of the channel material, thereby realizing non-volatile memory. Currently, novel 2D ferroelectrics unlock new prospects in next-generation electronics and neuromorphic computation. However, the advancement of these materials is impeded by limited selectivity and narrow memory windows. Here, new concepts of 2D ferroelectric perovskite/MoS2 channel heterostructures field-effect transistors are presented, in which 2D ferroelectric perovskite features customizable band structure, few-layered ferroelectricity, and submillimeter-size monolayer wafers. Further studies reveal that these devices exhibit unique charge polarity modulation (from n- to p-type channel) and remarkable nonvolatile memory behavior, especially record-wide hysteresis windows up to 177 V, which enables efficient imitation of biological synapses and achieves high recognition accuracy for electrocardiogram patterns. This result provides a device paradigm for future nonvolatile memory and artificial synaptic applications.

Flexible mechano-optical dual-responsive perovskite molecular ferroelectric composites for advanced anticounterfeiting and encryption

Hybrid organic-inorganic molecular ferroelectrics have emerged as promising materials for multifunctional piezoelectric devices. However, they present challenges in practical applications because of their inherent brittleness and poor ductility. Herein, we present a flexible mechano-optical dual-responsive molecular ferroelectric composite by incorporating trimethylchloromethyl ammonium (TMCM)-MnCl3 into styrene ethylene butylene styrene (SEBS) matrix. The SEBS/TMCM-MnCl3 exhibits excellent stretchable mechanical properties (tensile strain >1300%, thickness of 30 μm), piezoelectricity, and photoluminescence, enabling advanced visual-tactile-fused anticounterfeiting and encryption applications. Anticounterfeiting and antitampering tags are developed to judge whether the valued items are true or tampered with based on pattern recognition and piezoelectric response, respectively. Additionally, high-security password keyboards featuring triple-layer encryption are designed, offering more password combinations (524,288 times greater than those of traditional password devices relying solely on digital encryption) and enhanced security reliability against cracking attempts. This work can inspire designs of multifunctional optoelectronic materials and enable visual-tactile-fused intelligent applications in human-machine interfaces, information security, and advanced robotics.

Noncollinear ferroelectric and screw-type antiferroelectric phases in a metal-free hybrid molecular crystal

Noncollinear dipole textures greatly extend the scientific merits and application perspective of ferroic materials. In fact, noncollinear spin textures have been well recognized as one of the core issues of condensed matter, e.g. cycloidal/conical magnets with multiferroicity and magnetic skyrmions with topological properties. However, the counterparts in electrical polarized materials are less studied and thus urgently needed, since electric dipoles are usually aligned collinearly in most ferroelectrics/antiferroelectrics. Molecular crystals with electric dipoles provide a rich ore to explore the noncollinear polarity. Here we report an organic salt (H2Dabco)BrClO4 (H2Dabco = N,N'-1,4-diazabicyclo[2.2.2]octonium) that shows a transition between the ferroelectric and antiferroelectric phases. Based on experimental characterizations and ab initio calculations, it is found that its electric dipoles present nontrivial noncollinear textures with 60o-twisting angle between the neighbors. Then the ferroelectric-antiferroelectric transition can be understood as the coding of twisting angle sequence. Our study reveals the unique science of noncollinear electric polarity.

Biodegradable and Implantable Triboelectric Nanogenerator Improved by β-Lactoglobulin Fibrils-Assisted Flexible PVA Porous Film

Triboelectric nanogenerators (TENGs) are highly promising as implantable, degradable energy sources and self-powered sensors. However, the degradable triboelectric materials are often limited in terms of contact electrification and mechanical properties. Here, a bio-macromolecule-assisted toughening strategy for PVA aerogel-based triboelectric materials is proposed. By introducing β-lactoglobulin fibrils (BF) into the PVA aerogel network, the material's mechanical properties while preserving its swelling resistance is significantly enhanced. Compared to pure PVA porous film, the BF-PVA porous film exhibits an eightfold increase in fracture strength (from 1.92 to 15.48 J) and a fourfold increase in flexibility (from 10.956 to 39.36 MPa). Additionally, the electrical output of BF-PVA in triboelectric performance tests increased nearly fivefold (from 45 to 203 V). Leveraging these enhanced properties, a biodegradable TENG (bi-TENG) for implantable muscle activity sensing is developed, achieving real-time monitoring of neuromuscular processes. This innovation holds significant potential for advancing implantable medical devices and promoting new applications in bio-integrated electronics.

Large Local Internal Stress in an Elastically Bent Molecular Crystal Revealed by Raman Shifts

The structural dynamics involved in the mechanical flexibility of molecular crystals and the internal stress in such flexible materials remain obscure. Here, the study reports an elastically bending lipidated molecular crystal that shows systematic shifts in characteristic vibrational frequencies across the bent crystal region - revealing the nature of structural changes during bending and the local internal stress distribution. The blueshifts in the bond stretching modes (such as C═O and C-H modes) in the inner arc region and redshifts in the outer arc region of the bent crystals observed via micro-Raman mapping are counterintuitive to the bending models based on intermolecular hydrogen bonds. Correlating these shifts with the trends observed from high-pressure Raman studies on the crystal reveals the local stress difference between the inner arc and outer arc regions of the bent crystal to be ≈2 GPa, more than an order of magnitude higher than the previously proposed value in elastically bending crystals. High local internal stress can have direct ramifications on the properties of molecular piezoelectric energy harvesters, actuators, semiconductors, and flexible optoelectronic materials.

Metal-free small molecule-based piezoelectric energy harvesters

Organic and metal-free molecules with piezoelectric and ferroelectric properties have gained wide interest for their applications in the domain of mechanical energy harvesting due to their desirable properties such as light weight, thermal stability, mechanical flexibility, feasibility to achieve high Curie temperatures, and ease of synthesis. However, the understanding and design of these materials for piezoelectric energy harvesting applications is still in its early stages. This review paper presents a comprehensive overview of the fundamental characterization of piezoelectricity for a range of organic ferro- and piezoelectric materials and their composites. It also discusses the limitations of traditional piezoelectric materials and highlights the advantages of organic materials in this area in the introduction part. In addition, the paper provides a detailed description of peptide-based and other biomolecular piezoelectric materials as a bio-friendly alternative to current materials. This perspective aims to guide researchers in designing functional organic materials and composites for practical mechanical energy harvesting applications and to highlight current limitations and future perspectives in this emerging area of research.

Organic Ferroelastic with Dual-Channel Manipulation Obtained by H/F Substitution

Ferroelastic materials with high phase transition temperature have broad application prospects in information conversion and storage, shape memory, energy conversion, hyperelasticity, etc. However, most of the current reports focus on inorganic ferroelastic materials. Inorganic ferroelastic materials have the disadvantages of high energy consumption and harmful metals, which limit their application in practical work. In contrast, organic ferroelastic materials have the advantages of structural adjustability, environmental protection, easy processing, low cost, mechanical flexibility, and so on, which have great development potential in new ferroelastic materials. Here, we have successfully designed and synthesized a pair of homochiral enantiomers [(R/S)-4-fluorobenzoic acid-2-amino-2-phenylethanol] (R- and S-F) using the chemical design strategy of H/F substitution. Compared with the non-F substitution [(R/S)-benzoic acid-2-amino-2-phenylethanol] (R- and S-H), they undergo 2F1-type ferroelastic phase transitions at 370 K. Notably, the ferroelastic domains of R/S-F can be controlled through two physical channels that are temperature and stress, showing great potential in dual-channel switches.

Graphene-Doped Piezoelectric Transducers by Kriging Optimal Model for Detecting Various Types of Laryngeal Movements

This study fabricated piezoelectric fibers of polyvinylidene fluoride (PVDF) with graphene using near-field electrospinning (NFES) technology. A uniform experimental design table U*774 was applied, considering weight percentage (1-13 wt%), the distance between needle and disk collector (2.1-3.9 mm), and applied voltage (14.5-17.5 kV). We optimized the parameters using electrical property measurements and the Kriging response surface method. Adding 13 wt% graphene significantly improved electrical conductivity, increasing from 17.7 µS/cm for pure PVDF to 187.5 µS/cm. The fiber diameter decreased from 21.4 µm in PVDF/1% graphene to 9.1 µm in PVDF/13% graphene. Adding 5 wt% graphene increased the β-phase content by 6.9%, reaching 65.4% compared to pure PVDF fibers. Material characteristics were investigated using scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), contact angle measurements, and tensile testing. Optimal parameters included 3.47 wt% graphene, yielding 15.82 mV voltage at 5 Hz and 5 N force (2.04 times pure PVDF). Force testing showed a sensitivity (S) of 7.67 log(mV/N). Fibers were attached to electrodes for piezoelectric sensor applications. The results affirmed enhanced electrical conductivity, piezoelectric performance, and mechanical strength. The optimized piezoelectric sensor could be applied to measure physiological signals, such as attaching it to the throat under different conditions to measure the output voltage. The force-to-voltage conversion facilitated subsequent analysis.

High-Performance Piezoelectric Two-Dimensional Covalent Organic Frameworks

Organic piezoelectric nanogenerators (PENGs) are attractive in harvesting mechanical energy for various self-powering systems. However, their practical applications are severely restricted by their low output open circuit voltage. To address this issue, herein, we prepared two two-dimensional (2D) covalent organic frameworks (COFs, CityU-13 and CityU-14), functionalized with fluorinated alkyl chains for PENGs. The piezoelectricity of both COFs was evidenced by switchable polarization, characteristic butterfly amplitude loops, phase hysteresis loops, conspicuous surface potentials and high piezoelectric coefficient value (d33). The PENGs fabricated with COFs displayed highest output open circuit voltages (60 V for CityU-13 and 50 V for CityU-14) and delivered satisfactory short circuit current with an excellent stability of over 600 seconds. The superior open circuit voltages of CityU-13 and CityU-14 rank in top 1 and 2 among all reported organic materials-based PENGs.

The H/F substitution strategy can achieve large spontaneous polarization in 1D hybrid perovskite ferroelectrics

Hybrid organic-inorganic perovskite (HOIP) ferroelectrics exhibit polarization reversibility and have a wide range of applications in the fields of smart switches, memorizers, sensors, etc. However, the inherent limitations of small spontaneous polarization (P s) and large coercive field (E c) in ferroelectrics have impeded their broader utilization in electronics and data storage. Molecular ferroelectrics, as a powerful supplement to inorganic ferroelectrics, have shown great potential in the new generation of flexible wearable electronic devices. The important research responsibility is to greatly improve progressiveness and overcome the above limitations. Here, a novel one-dimensional (1D) HOIP ferroelectric, (3-F-BTAB)PbBr3 (3-F-BTAB = 3-fluorobenzyltrimethylammonium), was successfully synthesized by employing the H/F substitution strategy to modify parent compound (BTAB)PbBr3 (BTAB = benzyltrimethylammonium), which undergoes a ferroelectric phase transition with Aizu notation 2/mF2 at 420 K. Notably, (3-F-BTAB)PbBr3 demonstrates exceptional ferroelectric properties with a large P s of 7.18 μC cm-2 and a low E c of 1.78 kV cm-1. As far as we know, (3-F-BTAB)PbBr3 features the largest P s among those reported for 1D lead-based HOIP ferroelectrics. This work enriches the 1D lead-based ferroelectric family and provides guidance for applying ferroelectrics in low-voltage polar memories.

Research progress of piezoelectric materials in protecting oral health and treating oral diseases: a mini-review

Piezoelectric materials, as a class of materials capable of generating electrical charges under mechanical vibration, have special piezoelectric effects and have been widely applied in various disease treatment fields. People generate vibrations in the oral cavity during daily activities such as brushing teeth, using electric toothbrushes, chewing, and speaking. These natural vibrations (or external ultrasound) provide ideal conditions for activating piezoelectric materials, leading to their high potential applications in protecting oral health and treating oral diseases. Based on this, this review reports on the research progress and trends of piezoelectric materials in the protection of oral health and the treatment of oral diseases in the past 5 years, and discusses its treatment mechanism, challenges and shortcomings, aiming to provide theoretical basis and new ideas for the future application of piezoelectric materials in the field of oral cavity. Finally, a brief outlook is provided, suggesting that the potential of piezoelectric materials may enable them to quickly move towards real clinical applications.

H/F substitution achieves high piezoelectricity in enantiomeric molecular crystals

Here, we successfully synthesized a pair of enantiomeric molecular piezoelectric materials by H/F substitution strategy. These compounds show a large piezoelectric coefficient d33 value of 25 pC N-1 measured by the quasi-static method. A simple energy harvesting device was fabricated based on this crystal, showing great potential in piezoelectric mechanical energy harvesters.

The First Discovery of Spherical Carborane Molecular Ferroelectric Crystals

Carborane compounds, known for their exceptional thermal stability and non-toxic attributes, have garnered widespread utility in medicine, supramolecular design, coordination/organometallic chemistry, and others. Although there is considerable interest among chemists, the integration of suitable carborane molecules into ferroelectric materials remains a formidable challenge. In this study, we employ the quasi-spherical design strategy to introduce functional groups at the boron vertices of the o-carborane cage, aiming to reduce molecular symmetry. This approach led to the successful synthesis of the pioneering ferroelectric crystals composed of cage-like carboranes: 9-OH-o-carborane (1) and 9-SH-o-carborane (2), which undergo above-room ferroelectric phase transitions (Tc) at approximately 367 K and 347 K. Interestingly, 1 and 2 represent uniaxial and multiaxial ferroelectrics respectively, with 2 exhibiting six polar axes and as many as twelve equivalent polarization directions. As the pioneering instance of carborane ferroelectric crystals, this study introduces a novel structural archetype for molecular ferroelectrics, thereby providing fresh insights into the exploration of molecular ferroelectric crystals with promising applications.

Synthesis, the Reversible Isostructural Phase Transition, and the Dielectric Properties of a Functional Material Based on an Aminobenzimidazole-Iron Thiocyanate Complex

By introducing disordered molecules into a crystal structure, the motion of the disordered molecules easily induces the formation of multidimensional frameworks in functional crystal materials, allowing for structural phase transitions and the realization of various dielectric properties within a certain temperature range. Here, we prepared a novel ionic complex [C7H8N3]3[Fe(NCS)6]·H2O (1) between 2-aminobenzimidazole and ferric isothiocyanate from ferric chloride hexahydrate, ammonium thiocyanate, and 2-aminobenzimidazole using the evaporation of the solvent method. The main components, the single-crystal structure, and the thermal and dielectric properties of the complex were characterized using infrared spectroscopy, elemental analysis, single-crystal X-ray diffraction, powder XRD, thermogravimetric analysis, differential scanning calorimetry, variable-temperature and variable-frequency dielectric constant tests, etc. The analysis results indicated that compound 1 belongs to the P21/n space group. Within the crystal structure, the [Fe(NCS)6]3- anion formed a two-dimensional hydrogen-bonded network with the organic cation through S···S interactions and hydrogen bonding. The disorder-order motion of the anions and cations within the crystal and the deformation of the crystal frameworks lead to a significant reversible isostructural phase transition and multiaxial dielectric anomalies of compound 1 at approximately 240 K.

Discovery of molecular ferroelectric catalytic annulation for quinolines

Ferroelectrics as emerging and attractive catalysts have shown tremendous potential for applications including wastewater treatment, hydrogen production, nitrogen fixation, and organic synthesis, etc. In this study, we demonstrate that molecular ferroelectric crystal TMCM-CdCl3 (TMCM = trimethylchloromethylammonium) with multiaxial ferroelectricity and superior piezoelectricity has an effective catalytic activity on the direct construction of the pharmacologically important substituted quinoline derivatives via one-pot [3 + 2 + 1] annulation of anilines and terminal alkynes by using N,N-dimethylformamide (DMF) as the carbon source. The recrystallized TMCM-CdCl3 crystals from DMF remain well ferroelectricity and piezoelectricity. Upon ultrasonic condition, periodic changes in polarization contribute to the release of free charges from the surface of the ferroelectric domains in nano size, which then quickly interacts with the substrates in the solution to trigger the pivotal redox process. Our work advances the molecular ferroelectric crystal as a catalytic route to organic synthesis, not only providing valuable direction for molecular ferroelectrics but also further enriching the executable range of ferroelectric catalysis.

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.

Computational analysis of electrical stimulation to promote tissue healing for hernia repair at varying mesh placement planes

Development of a tear in the abdominal wall allowing for protrusion of intra-abdominal contents is known as a hernia. This can cause pain, discomfort, and may need surgical repair. Hernias can affect people of any age or demographic. In the USA, over 1 million hernia repair procedures are performed each year. During these surgeries, it is common for a mesh to be utilized to strengthen the repair. Different techniques allow for the mesh to be placed in different anatomical planes depending on hernia location and approach. The locations are onlay, inlay, and sublay, with sublay being split into retromuscular or preperitoneal with sublay being the most commonly used. The use of an electrically active hernia repair mesh is of interest to model as electrical stimulation has been shown to improve soft tissue healing which could reduce recurrence rates. Theoretical 3D COMSOL models were built to evaluate the varying electric fields of an electrically active hernia repair mesh at each of the different anatomical planes. Three voltages were chosen (10, 20, and 30 mV) for the study to simulate a low-level electrical signal and the electric field from a piezoelectric material at the tissue layers surrounding the mesh construct. Based on the model outputs, the optimal mesh placement location was the sublay-retromuscular as this location had the highest electric field values in the connective tissues and rectus abdominis muscle, which are the primary tissues of concern for the healing process and a successful repair.

Molecular orbital breaking in photo-mediated organosilicon Schiff base ferroelectric crystals

Ferroelectric materials, whose electrical polarization can be switched under external stimuli, have been widely used in sensors, data storage, and energy conversion. Molecular orbital breaking can result in switchable structural and physical bistability in ferroelectric materials as traditional spatial symmetry breaking does. Differently, molecular orbital breaking interprets the phase transition mechanism from the perspective of electronics and sheds new light on manipulating the physical properties of ferroelectrics. Here, we synthesize a pair of organosilicon Schiff base ferroelectric crystals, (R)- and (S)-N-(3,5-di-tert-butylbenzylidene)-1-((triphenylsilyl)oxy)ethanamine, which show optically controlled phase transition accompanying the molecular orbital breaking. The molecular orbital breaking is manifested as the breaking and reformation of covalent bonds during the phase transition process, that is, the conversion between C = N and C-O in the enol form and C-N and C = O in the keto form. This process brings about photo-mediated bistability with multiple physical channels such as dielectric, second-harmonic generation, and ferroelectric polarization. This work further explores this newly developed mechanism of ferroelectric phase transition and highlights the significance of photo-mediated ferroelectric materials for photo-controlled smart devices and bio-sensors.