3D-Printed Piezoelectric Stents for Electricity Generation Driven by Pressure Fluctuation.

Vascular stenting is a common procedure used to treat diseased blood vessels by opening the narrowed vessel lumen and restoring blood flow to ischemic tissues in the heart and other organs. In this work, we report a novel piezoelectric stent featuring a zigzag shape fabricated by fused deposition modeling three-dimensional (3D) printing with a built-in electric field. The piezoelectric composite was made of potassium sodium niobite microparticles and poly(vinylidene fluoride-co-hexafluoropropylene), complementing each other with good piezoelectric performance and mechanical resilience. The in situ poling yielded an appreciable piezoelectricity (d33 ∼ 4.2 pC N-1) of the as-printed stents. In vitro testing revealed that materials are nontoxic to vascular cells and have low thrombotic potential. Under stimulated blood pressure fluctuation, the as-printed piezoelectric stent was able to generate peak-to-peak voltage from 0.07 to 0.15 V corresponding to pressure changes from 20 to 120 Psi, giving a sensitivity of 7.02 × 10-4 V Psi-1. Biocompatible piezoelectric stents bring potential opportunities for the real-time monitoring of blood vessels or enabling therapeutic functions.

Active Dendrite Suppression by Ferroelectric Membrane Separators in Rechargeable Batteries.

Anodic dendrite formation is a critical issue in rechargeable batteries and often leads to poor cycling stability and quick capacity loss. Prevailing strategies for dendrite suppression aim at slowing down the growth rate kinetically but still leaving possibilities for dendrite evolution over time. Herein, we report a complete dendrite elimination strategy using a mesoporous ferroelectric polymer membrane as the battery separator. The dendrite suppression is realized by spontaneously reversing the surface energetics for metal ion reduction at the protrusion front, where a positive piezoelectric polarization is generated and superimposed as the protrusion compresses the separator. This effect is demonstrated first in a Zn electroplating process, and further in Zn-Zn symmetric cells and Zn-NaV3O8·1.5H2O full cells, where the dendritic Zn anode surfaces are completely turned into featureless flat surfaces. Consequently, a substantially longer charging/discharging cycle is achieved. This study provides a promising pathway toward high-performance dendrite-free rechargeable batteries.

Development of Ferroelectric P(VDF-TrFE) Microparticles for Ultrasound-Driven Cancer Cell Killing.

Current breast cancer treatments involve aggressive and invasive methods, leaving room for new therapeutic approaches to emerge. In this work, we explore the possibility of using piezoelectric [P(VDF-TrFE)] microparticles (MPs) as a source of inducing irreversible electroporation (IRE) of 4T1 breast cancer cells. We detail the MP formation mechanism and size control and subsequent characterizations of the as-synthesized MPs which confirms the presence of piezoelectric ß-phase. Production of the necessary piezoelectric output of the MPs is achieved by ultrasound agitation. We confirm the primary factor of the IRE effect on 4T1 breast cancer cells to be the local electric field produced from the MPs by using confocal imaging and an alamarBlue assay. The results show a 52.6% reduction in cell viability, indicating that the MP treatment can contribute to a reduction of live cancer cells. The proposed method of ultrasound-stimulated P(VDF-TrFE) MPs may offer a more benign cancer treatment approach.

Strong Room-Temperature Ferromagnetism in Ultrathin NiOOH Nanosheets through Surfactant Manipulation.

Two-dimensional (2D) ferromagnetic (FM) materials with nanoscale thickness and spontaneous net magnetization have emerged as a promising class of functional materials for applications in next-generation spintronics, quantum processing, and data storage devices. However, most 2D materials exhibit weak FM even at low temperatures, limiting their potential applications in many technological fields. The fabrication of strong room-temperature FM 2D materials is highly desirable for the development of practical applications. Here, we demonstrate an ionic layer epitaxy strategy to synthesize few-layered NiOOH nanosheets with strong room-temperature FM and a saturation magnetization up to 409.86 emu cm-3 at 300 K. The results are consistent with the ab initio predictions of a stable FM NiOOH nanolayer structure with an FM configuration. The FM strength of the NiOOH nanosheets can be tuned by controlling the surfactant monolayer density and annealing. This work offers a promising strategy for achieving strong high-temperature FM in 2D materials for spintronic applications.

Stretchable piezoelectric biocrystal thin films.

Stretchability is an essential property for wearable devices to match varying strains when interfacing with soft tissues or organs. While piezoelectricity has broad application potentials as tactile sensors, artificial skins, or nanogenerators, enabling tissue-comparable stretchability is a main roadblock due to the intrinsic rigidity and hardness of the crystalline phase. Here, an amino acid-based piezoelectric biocrystal thin film that offers tissue-compatible omnidirectional stretchability with unimpaired piezoelectricity is reported. The stretchability was enabled by a truss-like microstructure that was self-assembled under controlled molecule-solvent interaction and interface tension. Through the open and close of truss meshes, this large scale biocrystal microstructure was able to endure up to 40% tensile strain along different directions while retained both structural integrity and piezoelectric performance. Built on this structure, a tissue-compatible stretchable piezoelectric nanogenerator was developed, which could conform to various tissue surfaces, and exhibited stable functions under multidimensional large strains. In this work, we presented a promising solution that integrates piezoelectricity, stretchability and biocompatibility in one material system, a critical step toward tissue-compatible biomedical devices.

Surface Ligand Modification on Ultrathin Ni(OH)2 Nanosheets Enabling Enhanced Alkaline Ethanol Oxidation Kinetics.

The ethanol oxidation reaction (EOR) is an economical pathway in many electrochemical systems for clean energy, such as ethanol fuel cells and the anodic reaction in hydrogen generation. Noble metals, such as platinum, are benchmark catalysts for EOR owing to their superb electrochemical capability. To improve sustainability and product selectivity, nickel (Ni)-based electrocatalysts are considered promising alternatives to noble-metal EOR. Although Ni-based electrocatalysts are relieved from intermediate poisoning, their performances are largely limited by their relatively high onset potential. Therefore, the EOR usually competes with the oxygen evolution reaction (OER) at working potentials, resulting in a low EOR efficiency. Here, we demonstrate a strategy to modify the surface ligands on ultrathin Ni(OH)2 nanosheets, which substantially improved their catalytic properties for the alkaline EOR. Chemisorbed octadecylamine ligands could create an alcoholophilic layer at the nanosheet surface to promote alcohol diffusion and adsorption, resulting in outstanding EOR activity and selectivity over the OER at higher potential. These non-noble-metal-based 2D electrocatalysts and surface ligand engineering showcase a promising strategy for achieving high-efficiency electrocatalysis of EOR in many practical electrochemical processes.

Strain-Correlated Piezoelectricity in Quasi-Two-Dimensional Zinc Oxide Nanosheets.

Two-dimensional (2D) piezoelectric materials have recently drawn intense interest in studying the nanoscale electromechanical coupling phenomenon and device development. A critical knowledge gap exists to correlate the nanoscale piezoelectric property with the static strains often found in 2D materials. Here, we present a study of the out-of-plane piezoelectric property of nanometer-thick 2D ZnO-nanosheets (NS) in correlation to in-plane strains, using in situ via strain-correlated piezoresponse force microscopy (PFM). We show that the strain configuration (either tensile or compressive) can dramatically influence the measured piezoelectric coefficient (d33) of 2D ZnO-NS. A comparison of the out-of-plane piezoresponse is made for in-plane tensile and compressive strains approaching 0.50%, where the measured d33 varies between 2.1 and 20.3 pm V-1 resulting in an order-of-magnitude change in the piezoelectric property. These results highlight the important role of in-plane strain in the quantification and application of 2D piezoelectric materials.

Substantial lifetime enhancement for Si-based photoanodes enabled by amorphous TiO2 coating with improved stoichiometry.

Amorphous titanium dioxide (TiO2) film coating by atomic layer deposition (ALD) is a promising strategy to extend the photoelectrode lifetime to meet the industrial standard for solar fuel generation. To realize this promise, the essential structure-property relationship that dictates the protection lifetime needs to be uncovered. In this work, we reveal that in addition to the imbedded crystalline phase, the presence of residual chlorine (Cl) ligands is detrimental to the silicon (Si) photoanode lifetime. We further demonstrate that post-ALD in-situ water treatment can effectively decouple the ALD reaction completeness from crystallization. The as-processed TiO2 film has a much lower residual Cl concentration and thus an improved film stoichiometry, while its uniform amorphous phase is well preserved. As a result, the protected Si photoanode exhibits a substantially improved lifetime to ~600 h at a photocurrent density of more than 30 mA/cm2. This study demonstrates a significant advancement toward sustainable hydrogen generation.

Experimentally informed structure optimization of amorphous TiO2 films grown by atomic layer deposition.

Amorphous titanium dioxide TiO2 (a-TiO2) has been widely studied, particularly as a protective coating layer on semiconductors to prevent corrosion and promote electron-hole conduction in photoelectrochemical reactions. The stability and longevity of a-TiO2 is strongly affected by the thickness and structural heterogeneity, implying that understanding the structure properties of a-TiO2 is crucial for improving the performance. This study characterized the structural and electronic properties of a-TiO2 thin films (∼17 nm) grown on Si by atomic layer deposition (ALD). Fluctuation spectra V(k) and angular correlation functions were determined with 4-dimensional scanning transmission electron microscopy (4D-STEM), which revealed the distinctive medium-range ordering in the a-TiO2 film. A realistic atomic model of a-TiO2 was established guided by the medium-range ordering and the previously reported short-range ordering of a-TiO2 film, as well as the interatomic potential. The structure was optimized by the StructOpt code using a genetic algorithm that simultaneously minimizes energy and maximizes the match to experimental short- and medium-range ordering. The StructOpt a-TiO2 model presents improved agreements with the medium-range ordering and the k-space location of the dominant 2-fold angular correlations compared with a traditional melt-quenched model. The electronic structure of the StructOpt a-TiO2 model was studied by ab initio calculations and compared to the crystalline phases and experimental results. This work uncovered the medium-range ordering in a-TiO2 thin films and provided a realistic a-TiO2 structure model for further investigation of structure-property relationships and materials design. In addition, the improved multi-objective optimization package StructOpt was provided for structure determination of complex materials guided by experiments and simulations.

Nucleation Kinetics and Structure Evolution of Quasi-Two-Dimensional ZnO at the Air-Water Interface: An In Situ Time-Resolved Grazing Incidence X-ray Scattering Study.

The design and synthesis of high-quality two-dimensional (2D) materials with desired morphology are essential for property control. One critical challenge that impedes the understanding and control of 2D crystal nucleation and growth is the inability of direct observation of the nanocrystal evolution process with high enough time resolution. Here, we demonstrated an in situ X-ray scattering approach that directly reveals 2D wurtzite ZnO nanosheet growth at the air-water interface. The time-resolved grazing incidence X-ray diffraction (GID) and grazing incidence X-ray off-specular scattering (GIXOS) results uncovered a lateral to vertical growth kinetics switch phenomenon in the ZnO nanosheet growth. This switch represents the 2D to three-dimensional (3D) crystal structure evolution, which governs the size and thickness of nanosheets, respectively. This phenomenon can guide 2D nanocrystal synthesis with rationally controlled size and thickness. Our work opens a new pathway toward the understanding of 2D nanomaterial growth kinetics based on time-resolved liquid surface grazing incidence X-ray techniques.

Thickness-Dependent Piezoelectric Property from Quasi-Two-Dimensional Zinc Oxide Nanosheets with Unit Cell Resolution.

A quantitative understanding of the nanoscale piezoelectric property will unlock many application potentials of the electromechanical coupling phenomenon under quantum confinement. In this work, we present an atomic force microscopy- (AFM-) based approach to the quantification of the nanometer-scale piezoelectric property from single-crystalline zinc oxide nanosheets (NSs) with thicknesses ranging from 1 to 4 nm. By identifying the appropriate driving potential, we minimized the influences from electrostatic interactions and tip-sample coupling, and extrapolated the thickness-dependent piezoelectric coefficient (d 33). By averaging the measured d 33 from NSs with the same number of unit cells in thickness, an intriguing tri-unit-cell relationship was observed. From NSs with 3n unit cell thickness (n = 1, 2, 3), a bulk-like d 33 at a value of ~9 pm/V was obtained, whereas NSs with other thickness showed a ~30% higher d 33 of ~12 pm/V. Quantification of d 33 as a function of ZnO unit cell numbers offers a new experimental discovery toward nanoscale piezoelectricity from nonlayered materials that are piezoelectric in bulk.

High-Performance Poly(vinylidene difluoride)/Dopamine Core/Shell Piezoelectric Nanofiber and Its Application for Biomedical Sensors.

Fabrication of soft piezoelectric nanomaterials is essential for the development of wearable and implantable biomedical devices. However, a big challenge in this soft functional material development is to achieve a high piezoelectric property with long-term stability in a biological environment. Here, a one-step strategy for fabricating core/shell poly(vinylidene difluoride) (PVDF)/dopamine (DA) nanofibers (NFs) with a very high ß-phase content and self-aligned polarization is reported. The self-assembled core/shell structure is believed essential for the formation and alignment of ß-phase PVDF, where strong intermolecular interaction between the NH2 groups on DA and the CF2 groups on PVDF is responsible for aligning the PVDF chains and promoting ß-phase nucleation. The as-received PVDF/DA NFs exhibit significantly enhanced piezoelectric performance and excellent stability and biocompatibility. An all-fiber-based soft sensor is fabricated and tested on human skin and in vivo in mice. The devices show a high sensitivity and accuracy for detecting weak physiological mechanical stimulation from diaphragm motions and blood pulsation. This sensing capability offers great diagnostic potential for the early assessment and prevention of cardiovascular diseases and respiratory disorders.

Prevention of Hepatic Ischemia-Reperfusion Injury by Carbohydrate-Derived Nanoantioxidants.

Hepatic ischemia-reperfusion injury (IRI), which mainly results from excessive reactive oxygen species (ROS) generated by a reperfusion burst of oxygen, has long been a major cause of liver dysfunction and failure after surgical procedures. Here, a monodispersed hydrophilic carbohydrate-derived nanoparticle (C-NP) was synthesized as a nanoantioxidant that could effectively prevent hepatic IRI. The spherical C-NPs had a size of ∼78 ± 11.3 nm covered with polar surface groups. They were well dispersible in water with good colloidal stability, nontoxicity, and good ROS scavenging capability. The C-NPs also exhibited good circulation lifetime, effective delivery to liver, and gradual degradability with an ability to assist the IRI group maintaining a normal and healthy liver status. The pathology mechanism of C-NPs in hepatic IRI was confirmed to be scavenging of excessive ROS by C-NPs. The effective therapeutic treatment of C-NPs in living animals revealed a great potential in clinical prevention for hepatic IRI.

Piezoelectric Nanocellulose Thin Film with Large-Scale Vertical Crystal Alignment.

Cellulosic materials are attractive candidates for nature piezoelectrics. Vertically aligned cellulose nanocrystal (CNC) films are expected to show strong piezoelectricity as the largest dipole moment in CNCs exists along the cellulose chain. In this work, we adapted the confinement cell technology that was used to fabricate colloidal opal structures to align CNC rods vertically on a large scale. The high interfacial energy between the CNC-poly(tetrafluoroethylene) (PTFE) surface and torque induced by the shear force led to a large degree to the vertical alignment of CNC rods. An external DC electric field was added to further align the dipole moment of each CNC to the same direction. The as-obtained CNC film displayed excellent piezoelectric performance, and the piezoelectric coefficient was found to be 19.3 ± 2.9 pm/V, comparable to the piezoelectric coefficient d33 of poly(vinylidene difluoride) (PVDF) (20-30 pm/V). This work presents a new class of high-performance piezoelectric polymeric materials from renewable and biocompatible natural resources.

Nanoparticle-Decorated Ultrathin La2O3 Nanosheets as an Efficient Electrocatalysis for Oxygen Evolution Reactions.

Electrochemical catalysts for oxygen evolution reaction are a critical component for many renewable energy applications. To improve their catalytic kinetics and mass activity are essential for sustainable industrial applications. Here, we report a rare-earth metal-based oxide electrocatalyst comprised of ultrathin amorphous La2O3 nanosheets hybridized with uniform La2O3 nanoparticles (La2O3@NP-NS). Significantly improved OER performance is observed from the nanosheets with a nanometer-scale thickness. The as-synthesized 2.27-nm La2O3@NP-NS exhibits excellent catalytic kinetics with an overpotential of 310 mV at 10 mA cm-2, a small Tafel slope of 43.1 mV dec-1, and electrochemical impedance of 38 Ω. More importantly, due to the ultrasmall thickness, its mass activity, and turnover frequency reach as high as 6666.7 A g-1 and 5.79 s-1, respectively, at an overpotential of 310 mV. Such a high mass activity is more than three orders of magnitude higher than benchmark OER electrocatalysts, such as IrO2 and RuO2. This work presents a sustainable approach toward the development of highly efficient electrocatalysts with largely reduced mass loading of precious elements.

Multifunctional Artificial Artery from Direct 3D Printing with Built-In Ferroelectricity and Tissue-Matching Modulus for Real-Time Sensing and Occlusion Monitoring.

Treating vascular grafts failure requires complex surgery procedures and is associated with high risks. A real-time monitoring vascular system enables quick and reliable identification of complications and initiates safer treatments early. Here, an electric fieldassisted 3D printing technology is developed to fabricate in situ-poled ferroelectric artificial arteries that offer battery-free real-time blood pressure sensing and occlusion monitoring capability. The functional artery architecture is made possible by the development of a ferroelectric biocomposite which can be quickly polarized during printing and reshaped into devised objects. The synergistic effect from the potassium sodium niobite particles and the polyvinylidene fluoride polymer matrix yields a superb piezoelectric performance (bulk-scale d 33 > 12 pC N-1). The sinusoidal architecture brings the mechanical modulus close to the level of blood vessels. The desired piezoelectric and mechanical properties of the artificial artery provide an excellent sensitivity to pressure change (0.306 mV mmHg-1, R 2 > 0.99) within the range of human blood pressure (11.25-225.00 mmHg). The high pressure sensitivity and the ability to detect subtle vessel motion pattern change enable early detection of partial occlusion (e.g., thrombosis), allowing for preventing grafts failure. This work demonstrates a promising strategy of incorporating multifunctionality to artificial biological systems for smart healthcare systems.

Enhanced Ferromagnetism from Organic-Cerium Oxide Hybrid Ultrathin Nanosheets.

Room-temperature ferromagnetism in two-dimensional (2D) oxide materials is an intriguing phenomenon for spintronic applications. Here, we report significantly enhanced room-temperature ferromagnetism observed from ultrathin cerium oxide nanosheets hybridized with organic surfactant molecules. The hybrid nanosheets were synthesized by ionic layer epitaxy over a large area at the water-air interface. The nanosheets exhibited a saturation magnetization of 0.149 emu/g as their thickness reduced to 0.67 nm. This value was 5 times higher than that for CeO2 thin films and more than 20 times higher than that for CeO2 nanoparticles. The magnetization was attributed to the high concentration (15.5%) of oxygen vacancies stabilized by surfactant hybridization as well as electron transfer between organic and oxide layers. This work brings an effective strategy of introducing strong ferromagnetism to functional oxide materials, which leads to a promising route toward exploring new physical properties in 2D hybrid nanomaterials.

Implanted Battery-Free Direct-Current Micro-Power Supply from in Vivo Breath Energy Harvesting.

In vivo biomechanical energy harvesting by implanted nanogenerators (i-NGs) is promising for self-powered implantable medical devices (IMDs). One critical challenge to reach practical applications is the requirement of continuous direct-current (dc) output, while the low-frequency body activities typically generate discrete electrical pulses. Here, we developed an ultrastretchable micrograting i-NG system that could function as a battery-free dc micro-power supply. Packaged by a soft silicone elastomer with a cavity design, the i-NG exhibited an ultralow Young's modulus of ∼45 kPa and a high biocompatibility to soft biological tissues. The i-NG was implanted inside the abdominal cavity of Sprague Dawley adult rats and directly converted the slow diaphragm movement during normal respiration into a high-frequency alternative current electrical output, which was readily transmitted into a continuous ∼2.2 V dc output after being integrated with a basic electrical circuit. A light-emitting diode was constantly operated by the breath-driven i-NG without the aid of any battery component. This solely biomechanical energy-driven dc micro-power supply offers a promising solution for the development of self-powered IMDs.