Showing papers in "Npg Asia Materials in 2020"

Material aspects of triboelectric energy generation and sensors

Abstract: The triboelectric nanogenerator (TENG) is a new type of energy generator first demonstrated in 2012. TENGs have shown potential as power sources for electronic devices and as sensors for detecting mechanical and chemical stimuli. To date, studies on TENGs have focused primarily on optimizing the systems and circuit designs or exploring possible applications. Even though triboelectricity is highly related to the material properties, studies on materials and material designs have been relatively less investigated. This review article introduces recent progress in TENGs, by focusing on materials and material designs to improve the electrical output and sensing performance. This article discusses the current technological issues and the future challenges in materials for TENG. The development of materials for a technology that uses the movement of the human body to provide power has been reviewed by scientists in South Korea. A triboelectric nanogenerator converts mechanical energy into electricity by harnessing the fact that two surfaces rubbing against one another can become electrically charged. This is known as the triboelectric effect. One exciting use for these nanogenerators is in wearable electronics, where the motion of the body provides the power. Unyong Jeong and colleagues from Pohang University of Science and Technology have reviewed recent progress in material advances in the four main elements of a triboelectric nanogenerator: the charge-generating layer, the charge-trapping layer, the charge-collecting layer, and the charge-storage layer. These improvements all aim to increase the electrical output of such devices. Over the last decade, triboelectric nanogenerator (TENG) has been verified to be an effective way of converting daily mechanical energy into electric power or detecting various stimuli in the external environment. To promote the material researches in TENG, we introduce recent progresses in materials and material designs to improve the power generation and sensing performance. Also, we discuss on the future challenges and suggest possible approaches to solve the challenges.

Lanthanide doping in metal halide perovskite nanocrystals: spectral shifting, quantum cutting and optoelectronic applications

Abstract: Lanthanides have been widely explored as optically active dopants in inorganic crystal lattices, which are often insulating in nature. Doping trivalent lanthanide (Ln3+) into traditional semiconductor nanocrystals, such as CdSe, is challenging because of their tetrahedral coordination. Interestingly, CsPbX3 (X = Cl, Br, I) perovskite nanocrystals provide the octahedral coordination suitable for Ln3+ doping. Over the last two years, tremendous success has been achieved in doping Ln3+ into CsPbX3 nanocrystals, combining the excellent optoelectronic properties of the host with the f-f electronic transitions of the dopants. For example, the efficient quantum cutting phenomenon in Yb3+-doped CsPb(Cl,Br)3 nanocrystals yields a photoluminescence quantum yield close to 200%. Other approaches of Ln3+ doping and codoping have enabled promising proof-of-principle demonstration of solid-state lighting and solar photovoltaics. In this perspective article, we highlight the salient features of the material design (including doping in Pb-free perovskites), optical properties and potential optoelectronic applications of lanthanide-doped metal halide perovskite nanocrystals. While review articles on doping different metal ions into perovskite nanocrystals are present, the present review-type article is solely dedicated to lanthanide-doped metal halide perovskite nanocrystals. Methods for integrating lanthanide materials into light-emitting devices to improve their performance have been reviewed by scientists from India and China. Semiconductors create light when the energy of a high-energy electron is converted to a single photon. Conventionally, the minimum energy of this photon is determined by an intrinsic material property known as the bandgap. Wasim Mir from the Indian Institute of Science Education and Research Pune, and colleagues, summarize developments in using lanthanide ions to enable the generation of lower-energy light. Lanthanide ions provide an energy “step” within the bandgap that means the electron is converted to two low energy photons rather than a single high energy one. The authors review how embedding lanthanum ions within nanoparticles made from so-called metal-halide perovskites makes them easier to integrate into common optoelectronic semiconductors such as silicon. Metal halide perovskites are extraordinary defect-tolerant semiconductors. A unique structural aspect of perovskites is the octahedral coordination for (B-site) metal ions, unlike other semiconductors that exhibit tetrahedral coordination. This octahedral coordination helped to achieve lanthanide doping in halide perovskite nanocrystals in 2017. Fundamental understanding of material design, luminescence and quantum cutting phenomena in lanthanides (with focus on Yb3+) doped in CsPbX3 (X = Cl, Br, I) and Cs2AgInCl6 nanocrystals are reported. Subsequently, these doped systems are applied for solar energy harvesting and lighting in both visible and near infrared region. This perspective article summarizes everything important that has happened so far in field and discusses about the future research directions.

Electret formation in transition metal oxides by electrochemical amorphization

Abstract: Transition metal oxides (TMOs) are an important class of materials that show a wide range of functionalities involving spin, charge, and lattice degrees of freedom. The strong correlation between electrons in d-orbitals and the multivalence nature give rise to a variety of exotic electronic states ranging from insulator to superconductor and cause intriguing phase competition phenomena. Despite a burst of research on the multifarious functionalities in TMOs, little attention has been paid to the formation and integration of an electret—a type of quasi-permanent electric field generator useful for nanoscale functional devices as an electric counterpart to permanent magnets. Here, we find that an electret can be created in LaMnO3 thin films by tip-induced electric fields, with a considerable surface height change, via solid-state electrochemical amorphization. The surface charge density of the formed electret area reaches ~400 nC cm−2 and persists without significant charge reduction for more than a year. The temporal evolution of the surface height, charge density, and electric potential are systematically examined by scanning probe microscopy. The underlying mechanism is theoretically analyzed based on a drift-diffusion-reaction model, suggesting that positively charged particles, which are likely protons produced by the dissociation of water, play crucial roles as trapped charges and a catalysis to trigger amorphization. Our finding opens a new horizon for multifunctional TMOs. A material that generates its own electric field has been developed by scientists in South Korea. An electret is the electrical equivalent of a magnet in that it is formed of two electric poles rather than two magnetic poles. Just as magnetic dipoles give rise to permanent magnets, electret materials create a quasi-permanent electric field. They are useful for microphones, photocopiers and many other electrical devices. Yong-Jin Kim and Chan-Ho Yang from the Korea Advanced Institute of Science and Technology, Daejeon, have created an electret using transition metal oxides. The researchers used a sharp tip of platinum-coated silicon to “write” a charged pattern with a density similar to that of commercially available electrets into a thin film of lanthanum manganite. These patterns persisted for more than a year. An electret can be created in a complex transition metal oxide LaMnO3 by tip-induced electric fields with a considerable surface height change via solid-state electrochemical amorphization. The surface charge density of the formed electret area reaches ~400 nC cm−2 and persists without significant charge reduction for more than a year. Our finding opens a new horizon for multifunctional transition metal oxides by providing an electric counterpart to permanent magnets.

Pursuit of reversible Zn electrochemistry: a time-honored challenge towards low-cost and green energy storage

Abstract: The world’s mounting demands for environmentally benign and efficient resource utilization have spurred investigations into intrinsically green and safe energy storage systems. As one of the most promising types of batteries, the Zn battery family, with a long research history in the human electrochemical power supply, has been revived and reevaluated in recent years. Although Zn anodes still lack mature and reliable solutions to support the satisfactory cyclability required for the current versatile applications, many new concepts with optimized Zn/Zn2+ redox processes have inspired new hopes for rechargeable Zn batteries. In this review, we present a critical overview of the latest advances that could have a pivotal role in addressing the bottlenecks (e.g., nonuniform deposition, parasitic side reactions) encountered with Zn anodes, especially at the electrolyte-electrode interface. The focus is on research activities towards electrolyte modulation, artificial interphase engineering, and electrode structure design. Moreover, challenges and perspectives of rechargeable Zn batteries for further development in electrochemical energy storage applications are discussed. The reviewed surface/interface issues also provide lessons for the research of other multivalent battery chemistries with low-efficiency plating and stripping of the metal. Using novel functional electrolytes to stabilize zinc batteries could help power technology including wearable electronics without the costs and hazards of lithium-ion devices. Jingwen Zhao and Guanglei Cui from the Chinese Academy of Sciences in Qingdao review how the performance of zinc batteries, which have high energy storage but unsatisfactory cyclability, can be improved through modified electrolytes that limit unwanted (electro)chemical processes. Especially, a shift from water-based electrolytes towards polymers can tremendously extend zinc battery lifetimes, while simultaneously enabling packaging into devices. Other approaches include coating electrodes with polymers or inorganic materials to encourage uniform zinc deposition during recharging. Electrodes that combine zinc with carbon fibers, or form the metal into 3D sponges, can also ensure reliable recharging. Zn battery family with a long research history in the human electrochemical power supply has been revived and reevaluated in recent years. However, Zn anode in rechargeable batteries still lacks mature and reliable solutions to support the satisfactory cyclability required for the current versatile applications. In this paper, novel functional electrolytes, modified electrode-electrolyte interfaces and advanced electrode structures for addressing the bottlenecks encountered in rechargeable Zn anodes are reviewed, highlighting the mechanisms and open questions in practical applications.

Benzodithiophenedione-based polymers: recent advances in organic photovoltaics

Abstract: Over the past 20 years, significant progress has been made in organic photovoltaics (OPVs) due to its advantages of being cost-effective, being lightweight, and having flexible manufacturability. The optical-active layer of OPVs consists of a p-type polymer as the donor and an n-type small molecule as the acceptor. An efficient design strategy of a polymer donor is based on an alternating electron-donating unit (D) and an electron-accepting unit (A). Among numerous electron-accepting units, an emerging annelated thiophene of benzodithiophenedione (BDD) has exhibited a distinguished photovoltaic performance because of its planar molecular structure, low-lying highest occupied molecular orbit (HOMO) level and good self-assembly property. In this review article, we summarize the most recent developments in BDD-based photovoltaic materials. Special attention is paid to the chemical structure-property relationships, such as the absorption, bandgap, energy levels, mobilities, and photovoltaic performances. The empirical regularities and perspectives on the future development of BDD-based photovoltaic materials are included. Development of a polymer that has exciting potential for solar-energy conversion has been reviewed by researchers in China. Traditional solar cells are made using silicon, but their efficiency has not yet reached a level where they can compete with fossil fuels. In the last few decades, organic solar cells have emerged as an alternative, offering simpler fabrication and lighter, cost-effective and flexible devices. Lijun Huo from Beihang University, Beijing, and colleagues summarise recent progress in organic photovoltaic cells made using benzodithiophenedione (BDD) based polymeric donors. The authors review the properties of this kind of material that are key to optimising photovoltaic performance such as optical absorption, the electron energy levels, the charge mobility, the crystallinity and morphology. Careful control of these properties has enabled BDD-based devices to achieve power conversion efficiencies of over 15%. An emerging annelated thiophene of benzodithiophenedione (BDD) has exhibited its distinguished photovoltaic performance since its planar molecular structure, low-lying highest occupied molecular orbit (HOMO) level and well self-assembly property. In recent 7 years, BDD-based polymer donor have shown a rapid and incredible advancement by utilizing different acceptor materials. Considering the potentials of BDD-based materials, we summarize the most recent advances in the BDD-based photovoltaic materials and highlight the relations between BDD-based molecular structures and photovoltaic properties.

Downsizing metal–organic frameworks by bottom-up and top-down methods

Abstract: Downsizing metal–organic framework (MOF) crystals into the nanoregime offers a promising approach to further benefit from their inherent versatile pore structures and surface reactivity. In this article, downsizing is referred to as the deliberate production of typical large MOF crystals into their nanosized versions. Here, we discuss various strategies towards the formation of crystals below 100 nm and their impact on the nano-MOF crystal properties. Strategies include an adjustment of the synthesis parameters (e.g., time, temperature, and heating rate), surface modification, ligand modulation, control of solvation during crystal growth and physical grinding methods. These approaches, which are categorized into bottom-up and top-down methods, are also critically discussed and linked to the kinetics of MOF formation as well as to the homogeneity of their size distribution and crystallinity. This collection of downsizing routes allows one to tailor features of MOFs, such as the morphology, size distribution, and pore accessibility, for a particular application. This review provides an outlook on the enhanced performance of downsized MOFs along with their potential use for both existing and novel applications in a variety of disciplines, such as medical, energy, and agricultural research. Methods for enhancing the properties of porous materials known as metal–organic frameworks (MOFs) by making the crystals smaller have been reviewed by scientists in Australia and the Philippines. MOF crystals have an open atomic structure which includes large voids. MOFs are highly crystalline materials, typically generated in powder form, useful for applications such as hydrogen storage and carbon capture. Reducing the crystal sizes to nanometer scales significantly enhances the material’s physical and chemical properties. Ken Usman, Ludovic Dumee and Joselito Razal from Deakin University, Geelong, Australia, and co-workers have reviewed the latest methods for synthesizing MOF crystals smaller than a hundred nanometers. Synthesis strategies include altering a wide range of parameters such as time, temperature and heating rate. The authors show how these different approaches allow the properties of nano-sized MOF, including morphology and size distribution, to be controlled to suit a specific application. Metal organic frameworks are typically synthesized at the macroscale, into powders, films or as coatings generated across appropriate supporting materials. The downsizing of metal–organic frameworks offers opportunities to not only benefit from their properties at the nanoscale but also to enhance surface interactions and reactivities. The potential and challenges with current downsizing techniques are discussed in this review in light of materials properties and application performance.

Synthesis of highly dispersed Pt nanoparticles into carbon supports by fluidized bed reactor atomic layer deposition to boost PEMFC performance

Abstract: The performance of proton exchange membrane fuel cells (PEMFCs) depends on the controlled size, dispersion and density of Pt nanoparticles (NPs) on carbon supports, which are strongly affected by the carbon characteristics and fabrication methods. Here, we demonstrated a high-performance Pt/carbon catalyst for PEMFCs using fluidized bed reactor atomic layer deposition (FBR-ALD) that was realized by an effective matching of the carbon supports for the FBR-ALD process and an optimization of the ionomer content during the preparation of the membrane electrode assembly (MEA). For this, the synthesis of Pt NPs was conducted on two porous supports (Vulcan XC-72R and functionalized carbon) by FBR-ALD. The functionalized carbon possessed a higher surface area with a large pore volume, abundant defects in a disordered structure and a large number of oxygen functional groups compared to those of the well-known Vulcan carbon. The favorable surface characteristics of the functionalized carbon for nucleation produced Pt particles with an increased uniformity and density and a narrow size range, which led to a higher electrochemical surface area (ECSA) than that of Pt/Vulcan carbon and commercial Pt/carbon. The PEMFC test of the respective Pt/carbon samples was investigated, and highly dense and uniform Pt/functionalized-carbon showed the highest performance through optimization of the higher ionomer content compared to that for the ALD Pt growth on Vulcan carbon and commercial Pt/carbon. In addition, the Pt catalyst using ALD demonstrated a significant long-term stability for the PEMFC. This finding demonstrates the remarkable advantages of FBR-ALD for the fabrication of Pt/carbon and the ability of functionalized carbon supports to achieve a high PEMFC efficiency and an enhanced durability. Small tweaks to techniques used to manufacture platinum catalysts can have a big impact on the long-term stability of fuel cells. Platinum nanoparticle catalysts help fuel cells turn hydrogen and oxygen into water and electricity, but their small size makes them tricky to manipulate. Se-Hun Kwon from Pusan National University in Busan, South Korea, and colleagues have now optimized a high-tech procedure for attaching these tiny nanocatalysts to large, porous materials known as carbon supports. Their process coats various supports with platinum nanoparticles, less than one monolayer at a time, until the desired thicknesses are reached. Various factors including the physical textures of the supports and leftover chemical impurities were shown to significantly affect coating uniformity. Adjusting these factors enabled the team to generate supports with greater durability than commercial platinum–carbon composites. Very efficient, fast and scalable Fluidized Bed Reactor Atomic Layer Deposition (FBR-ALD) of highly dense and uniform Pt nanoparticles (NPs) on the functionalized carbon were successfully demonstrated for the proton exchange membrane fuel cell (PEMFC) application. The textural properties, functional groups and structural defects of the carbon supports significantly influenced Pt NPs deposition. A proper carbon supporter matching for FBR-ALD of Pt resulted in excellent electrochemical properties, long-term durability and fuel cell performance.

Premature failure of an additively manufactured material

Abstract: Additively manufactured metallic materials exhibit excellent mechanical strength. However, they often fail prematurely owing to external defects (pores and unmelted particles) that act as sites for crack initiation. Cracks then propagate through grain boundaries and/or cellular boundaries that contain continuous brittle second phases. In this work, the premature failure mechanisms in selective laser melted (SLM) materials were studied. A submicron structure was introduced in a SLM Ag–Cu–Ge alloy that showed semicoherent precipitates distributed in a discontinuous but periodic fashion along the cellular boundaries. This structure led to a remarkable strength of 410 ± 3 MPa with 16 ± 0.5% uniform elongation, well surpassing the strength-ductility combination of their cast and annealed counterparts. The hierarchical SLM microstructure with a periodic arrangement of precipitates and a high density of internal defects led to a high strain hardening rate and strong strengthening, as evidenced by the fact that the precipitates were twinned and encircled by a high density of internal defects, such as dislocations, stacking faults and twins. However, the samples fractured before necking owing to the crack acceleration along the external defects. This work provides an approach for additively manufacturing materials with an ultrahigh strength combined with a high ductility provided that premature failure is alleviated. An analysis of metallic alloys fabricated through layer-by-layer deposition processes has revealed critical factors in preventing these materials from unexpectedly breaking. In selective laser melting (SLM) technology, thin layers of metal powders are assembled into three-dimensional objects using rapid heating and cooling steps. Zhi Wang from the South China University of Technology in Guangzhou and colleagues now show that the microstructure of a silver-copper-germanium alloy formed through SLM can affect the material’s strength. Using optical and X-ray microscopy, the team found that regularly spaced precipitates formed inside the 3D-printed alloy prevented abrupt atomic sliding movements, giving the material a higher natural strength and good ductility. Fractures that occurred at lower than expected stress levels were identified as arising from errors in the printing process, such as pores and unmelted powder particles. A submicron structure strategy was introduced in a selective laser melted (SLM) Ag-Cu-Ge alloy, showing semi-coherent precipitates distributed in a discontinuous but periodic fashion along the cellular boundaries. It leads to a remarkable strength of ~410 MPa with ~16% ductility, well surpassing the strength-ductility combination of their cast counterparts. The hierarchal SLM microstructure and high density of internal defects leading to a high strain hardening rate and strong strengthening. Premature failure occurred due to the external defects, such as pores and unmelted particles. This work paves a way for additively manufacturing materials towards high strength–ductility synergy.

FeO-CeO 2 nanocomposites: an efficient and highly selective catalyst system for photothermal CO 2 reduction to CO

Abstract: Solar-driven catalysis is a promising strategy for transforming CO2 into fuels and valuable chemical feedstocks, with current research focusing primarily on increasing CO2 conversion efficiency and product selectivity. Herein, a series of FeO–CeO2 nanocomposite catalysts were successfully prepared by H2 reduction of Fe(OH)3-Ce(OH)3 precursors at temperatures (x) ranging from 200 to 600 °C (the obtained catalysts are denoted as FeCe-x). An FeCe-300 catalyst with an Fe:Ce molar ratio of 2:1 demonstrated outstanding performance for photothermal CO2 conversion to CO in the presence of H2 under Xe lamp irradiation (CO2 conversion, 43.63%; CO selectivity, 99.87%; CO production rate, 19.61 mmol h−1 gcat−1; stable operation over 50 h). Characterization studies using powder X-ray diffraction and high-resolution transmission electron microscopy determined that the active catalyst comprises FeO and CeO2 nanoparticles. The selectivity to CO of the FeCe-x catalysts decreased as the reduction temperature (x) increased in the range of 300–500 °C due to the appearance of metallic Fe0, which introduced an additional reaction pathway for the production of CH4. In situ diffuse reflectance infrared Fourier transform spectroscopy identified formate, bicarbonate and methanol as important reaction intermediates during light-driven CO2 hydrogenation over the FeCe-x catalysts, providing key mechanistic information needed to explain the product distributions of CO2 hydrogenation on the different catalysts. A nanomaterial that helps convert carbon dioxide to more useful chemicals has been developed by researchers in China. One potential method is to convert the carbon dioxide into carbon monoxide using a reaction known as reverse water-gas shift, and then use further reactions to convert this into fuel, or produce useful chemicals such as methanol or methane. This reaction normally requires high temperatures, and a catalyst is required to make the conversion efficient at lower, more practical temperatures. Tierui Zhang from the Technical Institute of Physics and Chemistry in Beijing and co-workers developed a nanocomposite based on iron and cerium with excellent performance in converting carbon dioxide into carbon monoxide with hydrogen only under light irradiation. This result indicates the potential of solar-driven catalysis for transforming carbon dioxide into fuels. A series of FeO-CeO2 nanocomposite catalysts (FeCe-x) were successfully fabricated by hydrogen reduction of hydroxide precursors at temperatures (x) between 200–600 °C. A FeCe-300 catalyst with a Fe:Ce ratio of 2-1 exhibited excellent performance for photothermal CO2 hydrogenation to CO (CO selectivity = 99.87%, CO production rate 19.61 mmol h−1 gcat−1, excellent stability). The FeO phase was effective in promoting the reverse water-gas shift (RWGS, CO2 + H2 → CO + H2O). Catalysts prepared at higher reduction temperatures contained both Fe0 and FeO, with the Fe0 catalyzing the Sabatier reaction (CO2 + 4H2 → CH4 + 2H2O) and thus lowering FeCe-x catalyst selectivity to CO.

Machine-learning-guided discovery of the gigantic magnetocaloric effect in HoB2 near the hydrogen liquefaction temperature

Abstract: Magnetic refrigeration exploits the magnetocaloric effect, which is the entropy change upon the application and removal of magnetic fields in materials, providing an alternate path for refrigeration other than conventional gas cycles. While intensive research has uncovered a vast number of magnetic materials that exhibit a large magnetocaloric effect, these properties remain unknown for a substantial number of compounds. To explore new functional materials in this unknown space, machine learning is used as a guide for selecting materials that could exhibit a large magnetocaloric effect. By this approach, HoB2 is singled out and synthesized, and its magnetocaloric properties are evaluated, leading to the experimental discovery of a gigantic magnetic entropy change of 40.1 J kg−1 K−1 (0.35 J cm−3 K−1) for a field change of 5 T in the vicinity of a ferromagnetic second-order phase transition with a Curie temperature of 15 K. This is the highest value reported so far, to the best of our knowledge, near the hydrogen liquefaction temperature; thus, HoB2 is a highly suitable material for hydrogen liquefaction and low-temperature magnetic cooling applications. A material for magnetically cooling hydrogen to its liquid form has been identified by a data-driven approach. Some materials get colder when they are exposed to an alternating magnetic field. This so-called magnetocaloric effect enables refrigeration to within one thousandth of a degree of absolute zero. Trial and error have uncovered many magnetocaloric materials, but Pedro Baptista de Castro, from the National Institute for Materials Science in Tsukuba, Japan, and co-workers have instead approached material discovery in a more systematic way using machine learning. They trained their algorithm to screen prospective compounds using data from the scientific literature. In this way they identified, and then experimentally confirmed, that holmium boride, HoB2, has a giant magnetocaloric effect at temperatures around 15 Kelvin (–258 °C), near the liquefaction point of hydrogen. Magnetic refrigeration, which is based on the magnetocaloric effect (MCE), is an emerging pathway for environment-friendly refrigeration. In this work, we performed a machine learning based approach to discover experimentally that HoB2 exhibits |ΔSM| = 40.1 J/kg K (0.35 J/cm−3 K) for μ0ΔΗ = 5 Τ at second order transition of TC ~ 15 K, having the largest |ΔSM| around this temperature region. Thus, HoB2 is a highly suitable material for hydrogen liquefaction and low-temperature magnetic cooling applications. Our study also sheds light on the machine learning approach as an effective method for searching functional materials characterized by complex physical properties.

An injectable photopolymerized hydrogel with antimicrobial and biocompatible properties for infected skin regeneration

Abstract: Currently, wound infection is an important health problem for the public. Wound infection can not only hinder healing but it can also lead to serious complications. Injectable wound dressings with biocompatible and antibacterial properties can promote wound healing during skin infections and reduce antibiotic use. Here, we used glycidyl methacrylate (GMA) to modify e-polylysine (e-PL) and γ-poly(glutamic acid) (γ-PGA) to produce e-polylysine-glycidyl methacrylate (e-PL-GMA) and γ-poly(glutamic acid)-glycidyl methacrylate (γ-PGA-GMA). Subsequently, e-PL-GMA- and γ-PGA-GMA-based hydrogels were developed through photopolymerization using visible light. The hydrogels were injectable, could rapidly gelatinize, were biocompatible, and showed a wide spectrum of antibacterial activity. The hydrogels also promoted wound healing. The results show that these hydrogels inhibit bacterial infection and shorten the wound healing time of skin defects in Staphylococcus aureus models. This demonstrates that the hydrogels hold potential for clinical antimicrobial and wound healing therapy. A biocompatible material with natural resistance to E. coli and Staphylococcus bacteria shows promise for healing damaged skin. Hydrogels that trap water molecules inside three-dimensional polymer networks have recently been used to keep skin wounds hydrated during recuperation. Zhiyong Qian from Sichuan University in Chengdu, China, and colleagues have now developed a hydrogel based on polylysine, a peptide complex with broad-spectrum antimicrobial activity. Using mice with skin wounds infected with Staphylococcus, the team injected aqueous polysine precursors directly into the wound surface. The injuries were then exposed to visible light to polymerize the peptides into a hydrogel. Experiments demonstrated that hydrogel-containing wounds completely closed over after 12 days, while untreated injuries remained open. The antibacterial hydrogel even stimulated growth of new tissue including hair follicles. In this study, we designed an injectable antibacterial hydrogel that was photopolymerized by visible light for the treatment of skin infections. The hydrogel consists of γ-poly(glutamic acid)-glycidyl methacrylate (γ-PGA-GMA) and e-polylysine-glycidyl methacrylate (e-PL-GMA). The hydrogels showed the characteristics of injectable and rapid gels, and were easy to use. Importantly, the hydrogels demonstrated high levels of antibacterial activity and biocompatibility. In in vivo infection models, the hydrogels reduced inflammation, promoted wound healing, and shortened the healing time. This highlights the hydrogels as promising candidates for anti-infection and wound healing.

Importance of tailoring lattice strain in halide perovskite crystals

Abstract: In this review paper, the residual strain of a polycrystalline halide perovskite film is systematically studied based on its structural inhomogeneity, which is closely correlated to the local carrier dynamics caused by a modulated electronic band structure. Long-range collective strain ordering is responsible for the overall structural properties, consequently determining the optoelectronic properties of the perovskite film. Notably, the perovskite phase stability is strongly affected by the internal strain, favoring a lower energy state. The important parameters affecting the residual strain in a real perovskite film, ranging from thermal stress to lattice mismatch and compositional inhomogeneity, are subsequently introduced along with their impacts on the optoelectronic properties and/or the stability of the crystals. Methods for using strain to improve the performance of a promising solar cell material have been reviewed by researchers in South Korea. A family of hybrid organic-inorganic semiconductors known as halide perovskites have emerged as a rival to silicon for the production of solar cells. Atomic-level physical forces, for example, the strain induced when a material is compressed, can improve the semiconductor’s optoelectronic properties. Hui-Seon Kim from Inha University in Incheon, and Nam-Gyu Park from Sungkyunkwan University in Suwon have summarized how this strain arises in perovskite thin films and the ways in which it modifies the dynamics of the material’s electrical charge carriers. The researchers used this understanding to suggest methods for strain engineering these materials to improve the performance of solar cell devices. The structural inhomogeneity is inherited by residual strain in perovskite crystals. The residual strain affects an electronic band structure of the perovskite film and thus determines its optoelectronic properties. Therefore, the strain engineering can be a powerful tool to not only govern structural defects but also derive demanding properties with an ensured phase stability. In this review, the effect of lattice strain is broadly explored, coupled with relevant affecting parameters.

Extremely fast electrochromic supercapacitors based on mesoporous WO 3 prepared by an evaporation-induced self-assembly

Abstract: Mesoporous metal oxides consisting of fully interconnected network structures with small pores (20–50 nm) have high surface areas and decreased ion intercalation distances, making them ideal for use in high-performance electrochromic supercapacitors (ECSs). Evaporation-induced self-assembly (EISA), which combines sol–gel chemistry and molecular self-assembly, is a powerful method for the fabrication of mesoporous metal oxides through a solution phase synthesis. Herein, we introduce ultrafast sub-1 s ECSs based on an amorphous mesoporous tungsten trioxide (WO3) that is prepared by EISA. Compared to that of a compact-WO3 film-based device, the performances of an ECS with mesoporous WO3 exhibits a large optical modulation (76% at 700 nm), ultrafast switching speeds (0.8 s for coloration and 0.4 s for bleaching), and a high areal capacitance (2.57 mF/cm2), even at a high current density (1.0 mA/cm2). In addition, the excellent device stability during the coloration/bleaching and charging/discharging cycles is observed under fast response conditions. Moreover, we fabricated a patterned mesoporous WO3 for ECS displays (ECSDs) via printing-assisted EISA (PEISA). The resulting ECSDs can be used as portable energy-storage devices, and their electrochromic reflective displays change color according to their stored energy level. The ECSDs in this work have enormous potential for use in next-generation smart windows for buildings and as portable energy storage displays. Networks of tiny holes improve the energy storage properties of materials that can also be used for smart windows. In electrochromic materials, the fraction of light passing through the material can be controlled using an electrical voltage. This is useful for smart windows which electrically switch from being transparent to opaque. This change is associated with the storage or release of energy, so the same materials are being investigated for energy storage. Keon-Woo Kim from Pohang University of Science and Technology, South Korea, and co-workers have developed an improved electrochromic supercapacitor made from tungsten trioxide. They used an evaporation-induced self-assembly process to deposit a film of tungsten trioxide containing pores approximately 30 nanometers across. This porous structure increased the material’s switching speed and capacitance compared to a conventional tungsten trioxide thin film. Ultra-fast electrochromic supercapacitors (ECSs) are demonstrated based on mesoporous WO3 prepared by evaporation-induced self-assembly (EISA). Mesoporous WO3 based ECSs show excellent electrochromic and supercapacitor performances under fast operating condition. Furthermore, printing assisted EISA is introduced to produce patterned mesoporous WO3 for ECS displays (ECSDs). The resulting ECSDs have great potential as next-generation smart electrochemical components.

Quasi-2D halide perovskites for resistive switching devices with ON/OFF ratios above 10 9

Abstract: Resistive random-access memory (ReRAM) devices based on halide perovskites have recently emerged as a new class of data storage devices, where the switching materials used in these devices have attracted extensive attention in recent years. Thus far, three-dimensional (3D) halide perovskites have been the most investigated materials for resistive switching memory devices. However, 3D-based memory devices display ON/OFF ratios comparable to those of oxide or chalcogenide ReRAM devices. In addition, perovskite materials are susceptible to exposure to air. Herein, we compare the resistive switching characteristics of ReRAM devices based on a quasi-two-dimensional (2D) halide perovskite, (PEA)2Cs3Pb4I13, to those based on 3D CsPbI3. Astonishingly, the ON/OFF ratio of the (PEA)2Cs3Pb4I13-based memory devices (109) is three orders of magnitude higher than that of the CsPbI3 device, which is attributed to a decrease in the high-resistance state (HRS) current of the former. This device also retained a high ON/OFF current ratio for 2 weeks under ambient conditions, whereas the CsPbI3 device degraded rapidly and showed unreliable memory properties after 5 days. These results strongly suggest that quasi-2D halide perovskites have potential in resistive switching memory based on their desirable ON/OFF ratio and long-term stability. A type of computer memory that stores data by changing the resistance of insulating crystals can be made more durable with organic chemical additives. Resistive memory devices constructed from inorganic crystals known as halide perovskites are inexpensive and have minimal power requirements. However, they can degrade quickly in humid conditions. Hyojung Kim from Seoul National University in South Korea and colleagues now report that these stability issues can be improved by sandwiching thin layers of aromatic hydrocarbons between halide perovskite crystals. The water-repelling nature of the organic molecules helps double the lifespan of the new hybrid compared to an unmodified halide perovskite device. In addition, the organic layers augment the differences between ‘ON’ and ‘OFF’ resistive memory states, making device operation more reliable. ReRAM devices based on halide perovskites have recently emerged as a new class of data storage device, where the switching materials used in these devices have attracted huge attention in recent years. In this study, we compare the resistive switching characteristics of ReRAM devices based on a quasi-2D halide perovskite, (PEA)2Cs3Pb4I13, to those based on 3D CsPbI3. Astonishingly, the ON/OFF ratio of the (PEA)2Cs3Pb4I13-based memory devices was much higher than that of the CsPbI3 device. Also this device retained a high ON/OFF current ratio for two weeks under ambient conditions, whereas the CsPbI3 device degraded rapidly and showed unreliable memory properties after five days. We strongly believe that quasi-2D halide perovskites have potential in resistive switching memory based on their high ON/OFF ratio and long-term stability.

Multifunctional load-bearing hybrid hydrogel with combined drug release and photothermal conversion functions

Abstract: The inability of damaged load-bearing cartilage to regenerate and self-repair remains a long-standing challenge in clinical settings. In the past, the use of PVA hydrogels as cartilage replacements has been explored; however, both pristine and annealed PVA are not ideal for load-bearing cartilage applications, and new materials with improved properties are highly desirable. In this work, we developed a novel hybrid hydrogel system consisting of glycerol-modified PVA hydrogel reinforced by a 3D printed PCL-graphene composite scaffold. The composition of the hydrogel within the hybrid material was optimized to achieve high water retention and enhanced stiffness. The hybrid hydrogel formed by reinforcement with a 3D printed PCL-graphene scaffold with optimized architecture demonstrated desirable mechanical properties (stiffness, toughness, and tribological properties) matching those of natural load-bearing cartilage. Our novel hydrogel system has also been designed to provide drug release and on-demand photothermal conversion functions and at the same time offers excellent biocompatibility with low cell adhesion. These promising properties may allow our unique hybrid hydrogel system to be used for potential applications, such as load-bearing cartilage repair/replacement, as well as targeting certain challenging clinical conditions, such as the treatment of severe arthritis. A hybrid hydrogel for replacing damaged cartilage has been developed by researchers in China and the UK. Fibrocartilage - the toughest type of cartilage found between the intervertebrae discs and the knee joints, is able to withstand heavy weights. The damage of such cartilage is difficult to repair and scientists have begun to investigate hydrogels as an artificial cartilage replacement. A hydrogel is a soft spongy material made from interconnected polymers; however, conventional hydrogels are not well-suited to load-bearing applications. Dan Sun from Queen’s University Belfast, Li Zhang from Sichuan University, Chengdu, and co-workers have reinforced a poly (vinyl alcohol) hydrogel with a scaffold made from a composite of graphene and another polymer called polycaprolactone. This scaffold increases the stiffness and toughness of the hydrogel, and has the added benefit of on-demand drug release. In this work, we developed a novel hybrid hydrogel system consisting of glycerol-modified PVA hydrogel reinforced by a 3D printed PCL-graphene composite scaffold. The biocompatible hybrid hydrogel shows desirable mechanical properties matching those of natural load-bearing cartilage, while providing drug release and on-demand photothermal conversion functions. These promising properties may allow their potential applications in load-bearing cartilage repair/replacement and treatment of severe arthritis.

Interaction of 2D materials with liquids: wettability, electrochemical properties, friction, and emerging directions

Abstract: The emergence of two-dimensional (2D) materials as functional surfaces for sensing, electronics, mechanics, and other myriad applications underscores the importance of understanding 2D material–liquid interactions. The thinness and environmental sensitivity of 2D materials induce novel surface forces that drive liquid interactions. This complexity makes fundamental 2D material–liquid interactions variable. In this review, we discuss the (1) wettability, (2) electrical double layer (EDL) structure, and (3) frictional interactions originating from 2D material–liquid interactions. While many 2D materials are inherently hydrophilic, their wettability is perturbed by their substrate and contaminants, which can shift the contact angle. This modulation of the wetting behavior enables templating, filtration, and actuation. Similarly, the inherent EDL at 2D material–liquid interfaces is easily perturbed. This EDL modulation partially explains the wettability modulation and enables distinctive electrofluidic systems, including supercapacitors, energy harvesters, microfluidic sensors, and nanojunction gating devices. Furthermore, nanoconfinement of liquid molecules at 2D material surfaces arising from a perturbed liquid structure results in distinctive hydrofrictional behavior, influencing the use of 2D materials in microchannels. We expect 2D material–liquid interactions to inform future fields of study, including modulation of the chemical reactivity of 2D materials via tuning 2D material–liquid interactions. Overall, 2D material–liquid interactions are a rich area for research that enables the unique tuning of surface properties, electrical and mechanical interactions, and chemistry. Materials made from single layers of atoms have unique interactions with liquids that can unlock new chemical and biological applications. Peter Snapp and SungWoo Nam from the University of Illinois at Urbana-Champaign in the United States review how studies of water on graphene films have revealed methods to control how tightly droplets make contact with two-dimensional (2D) materials. For example, by using chemical modifications to make 2D surfaces more or less water-repelling, researchers can direct cellular and crystal growth, or produce nanoscale membranes capable of separating oil from water. Combining surface engineering with external electric fields enables droplets to form into charged layers capable of storing energy like a capacitor. The charged layers have been applied for biomolecular sensing, and to modify nanoscale frictional behavior in fluid channels. 2D materials’ thinness and environmental sensitivity induce novel surface forces which render fundamental 2D material–liquid interactions variable. 2D material wettability is perturbed by substrates and contaminants enabling templating, filtration, and actuation. Fluid structure at 2D material–liquid interfaces is similarly perturbed, partially explaining wettability modulation and enabling distinctive electro-fluidics applications including supercapacitors, energy harvesters, and sensors. Finally, nanoconfinement of molecules arising from perturbed liquid structure modified hydro-frictional behavior, influencing 2D materials’ use in microchannels. 2D material–liquid interactions will inform future fields of study, including modulation of 2D materials’ chemical reactivity, offering a rich area for research on tuned surface fluid interactions.

Triple-synergistic 2D material-based dual-delivery antibiotic platform

Abstract: Two-dimensional (2D) nanomaterials have raised significant interest in not only energy and environmental fields but also biomedical areas. Among these materials, one type that has many interesting properties and possesses numerous exciting applications is graphene oxide (GO)-based 2D materials. However, their poor stability in aqueous solutions and weak bioactivities limit their use in biomedical applications, especially antimicrobial fields. In this study, GO was functionalized with hydrophilic polymers and used as a vector for silver nanoparticles (Ag NPs) and sulfadiazine (SD). The stability of the material in aqueous solutions was greatly improved. The antibacterial activity of the novel hybrid antibacterial system (HAS) was enhanced by over 3 times compared to that of the system lacking SD. The antibacterial performance of the HAS was due to the triple synergy: bacterial capping, puncture, and inhibition. This study provides new insights into the design and fabrication of surface-modified GO and carbon materials and their 2D hybrid multifunctional materials for advanced applications including biomedical and especially antibacterial applications, broadening the design and application scope of carbon and 2D materials. An efficient method for harnessing the antibacterial properties of silver nanoparticles has been developed by researchers in China and the USA. Silver is frequently used in bandages because of its antibacterial effects. Recent studies have suggested that silver nanoparticles are even more effective; however, a way to prevent them clumping together is needed. Fengqi Han from the Henan Provincial People’s Hospital, Zhengzhou, and co-workers achieved this using two-dimensional graphene oxide combined with a hydrophilic polymer. While graphene oxide has already found numerous applications, its use in medicine has been limited because it is unstable in water and other aqueous solutions. The researchers increased this stability by adding the hydrophilic polymer. When loaded with silver sulfadiazine nanoparticles, the hybrid material exhibited antibacterial activity three times higher than silver sulfadiazine on its own. In this study, a novel hybrid antibacterial system (HAS) based on graphene oxide (GO) 2D materials for co-delivery of silver nanoparticles (Ag NPs) and sulfadiazine (SD) was fabricated. The antibacterial activity of HAS was enhanced over 3 times due to triple synergy: capping effect of GO, puncture effect of Ag NPs, and inhibitory effect of SD. This study provides new insights into the design and fabrication of antibiosis systems and multifunctional materials and broadens the biomedical applications of 2D materials.

Multifunctional electrochromic energy storage devices by chemical cross-linking: impact of a WO 3 ·H 2 O nanoparticle-embedded chitosan thin film on amorphous WO 3 films

Abstract: With the advent of multifunctional devices with electrochromic (EC) behavior and electrochemical energy storage, complementary design of film structures using inorganic–organic materials has shown great potential for developing EC energy storage devices. Herein, hybrid films consisting of WO3·H2O nanoparticle (WHNP)-embedded chitosan thin films on amorphous WO3 (a-WO3) films were designed. By exploiting the hybrid effect of chitosan and WHNPs to generate unique chemical cross-linking between them, the designed films exhibited attractive EC behaviors compared to bare a-WO3 films. These included fast switching speeds (4.0 s for coloration and 0.8 s for bleaching) due to enhanced electrical conductivity and Li-ion diffusivity, high coloration efficiency (62.4 cm2/C) as a result of increased electrochemical activity, and superb long-cycling retention (91.5%) after 1000 cycles due to improved electrochemical stability. In addition, hybrid films exhibited a noticeable energy storage performance with a high specific capacitance (154.0 F/g at a current density of 2 A/g) and a stable rate capability as a result of improved electrochemical activity and fast electrical conductivity, respectively. This resulted in brighter illumination intensity for the 1.5-V white-light-emitting diode due to improved energy density compared to a bare a-WO3 film. Therefore, the results suggest a new design strategy for materials to realize the coincident application of multifunctional devices with EC energy storage performance. A material that can both store energy and block the transmission of light has been developed by scientists in South Korea. Electrochromic materials change their color when a voltage is applied, and have been used in smart-glass applications, where windows can be electrically switched between transparency and opaqueness. They are now also being developed for energy applications as whenever the material cycles from transparent to opaque, a charge is electrochemically stored just as in a capacitor. Hyo-Jin Ahn and colleagues from the Seoul National University of Science and Technology have now improved the properties of an electrochromic material specifically with energy storage in mind. They showed that a thin film of chitosan containing WO3·H2O nanoparticles has better switching speed, electrical conductivity, and energy storage than a film made only of WO3. Hybrid films with WO3·H2O nanoparticles-embedded chitosan on amorphous WO3 films are newly designed for multi-functional devices with electrochromic energy storage performances.

Structure and properties of densified silica glass: characterizing the order within disorder

Abstract: The broken symmetry in the atomic-scale ordering of glassy versus crystalline solids leads to a daunting challenge to provide suitable metrics for describing the order within disorder, especially on length scales beyond the nearest neighbor that are characterized by rich structural complexity. Here, we address this challenge for silica, a canonical network-forming glass, by using hot versus cold compression to (i) systematically increase the structural ordering after densification and (ii) prepare two glasses with the same high-density but contrasting structures. The structure was measured by high-energy X-ray and neutron diffraction, and atomistic models were generated that reproduce the experimental results. The vibrational and thermodynamic properties of the glasses were probed by using inelastic neutron scattering and calorimetry, respectively. Traditional measures of amorphous structures show relatively subtle changes upon compacting the glass. The method of persistent homology identifies, however, distinct features in the network topology that change as the initially open structure of the glass is collapsed. The results for the same high-density glasses show that the nature of structural disorder does impact the heat capacity and boson peak in the low-frequency dynamical spectra. Densification is discussed in terms of the loss of locally favored tetrahedral structures comprising oxygen-decorated SiSi4 tetrahedra. A method for characterizing order in disordered materials such as glass has been developed by an international team of scientists. The atoms in most solid materials are arranged in a regular pattern. Other materials are amorphous, with the positions of each atom more random. However, even these amorphous materials can exhibit some level of ordering over short distances. Shinji Kohara from the National Institute for Materials Science in Ibaraki, Japan, Philip Salmon from the University of Bath, UK, and their colleagues have devised a way of characterizing order within disordered silica glass. The team increased the temperature of silica while keeping it under constant pressure, thereby inducing a transition from a low- to high-density state. Their description of a structural collapse with increasing density could provide a clear structural signature for defining amorphous materials. There is a fundamental divide in symmetry between crystalline and glassy materials, where the structural disorder in glass leads to unique material properties and a myriad of applications. The provision of metrics for describing the order within disorder remains, however, an open challenge, especially on length scales beyond the nearest neighbor that are characterized by rich structural complexity. Here, we address this challenge by applying the method of persistent homology to characterize the structure of silica glass. The structural disorder is systematically engineered by preparing the glass under different high-pressure and temperature conditions, which impacts on the low-frequency vibrational and thermodynamic properties.

Development of a wearable infrared shield based on a polyurethane–antimony tin oxide composite fiber

Abstract: Here, we investigate a wearable-based IR and thermal stealth structure that effectively blocks IR and thermal radiation from a human body or device using a polyurethane–antimony tin oxide (PU–ATO) composite fiber. The aging time of the ATO sol prepared by a sol–gel method, and the concentration of ATO with respect to that of the PU matrix were optimized to prepare PU–ATO composite fibers that simultaneously have an appropriate mechanical strength (strength of ~4 MPa and strain of ~340%) and IR- and thermal radiation-shielding properties with ~98% IR light, as determined by Fourier transform IR spectroscopic studies. The fabricated PU–ATO composite fiber showed stable IR- and thermal radiation-shielding properties even when exposed to ten cycles of repeated temperature changes of −20 and +80 °C and long-term temperature changes for 30 days. In addition, the surface of the PU–ATO composite fiber was rendered hydrophobic to prevent the distortion of the IR and thermal radiation due to the wetting of the PU–ATO composite fiber with absorbed water. The PU–ATO composite fiber-based textile proposed herein can be applied in wearable IR- and thermal radiation-shielding technologies to shield IR signals generated by objects of diverse and complex shapes. A material that makes us invisible to infrared cameras has been developed by researchers in South Korea. Even in total darkness, the heat that our body produces can give away our position. Clothing that masks this infrared radiation to make the wearer indistinguishable from the background is therefore useful in stealth applications. Sang Yoon Park from Seoul National University, Sanghyun Ju from Kyonggi University, Suwon, and their colleagues have developed a fiber made from a combination of a polymer known as polyurethane and a metal oxide, antimony tin oxide (ATO). The fibers block thermal radiation because the ATO scatters infrared light. The team used a wet-spinning technique to create a number of different composite fiber with varying ATO concentrations so that they could optimize their useful lifetime. The polyurethane–antimony tin oxide (PU–ATO) composite fibers makes infrared (IR) radiations emitted by an object to be as similar as possible to ambient background radiation such that an IR detection sensor fails to distinguish the target object. Hydrophobic surface of the PU–ATO composite fiber prevent the distortion of the IR and thermal radiation caused by the wetting of the PU–ATO composite fiber with water. The PU–ATO composite fiber-based textile can be applied in wearable IR- and thermal radiation-shielding technologies to shield IR signals generated by objects of diverse and complex shapes.

Signature of local stress states in the deformation behavior of metallic glasses

Abstract: The design of ductile heterogeneous metallic glasses (MGs) with enhanced deformability by purposely controlling the shear-band dynamics via modulation of the atomic-scale structures and local stress states remains a significant challenge. Here, we correlate the changes in the local atomic structure when cooling to cryogenic temperature with the observed improved shear stability. The enhanced atomic-level structural and elastic heterogeneities related to the nonaffine thermal contraction of the short-range order (SRO) and medium-range order (MRO) change the characteristics of the activation process of the shear transformation zones (STZs). The experimental observations corroborated by Eshelby inclusion analysis and molecular dynamics simulations disclose the correlation between the structural fluctuations and the change in the stress field around the STZ. The variations in the inclination axes of the STZs alter their percolation mechanism, affect the shear-band dynamics and kinetics, and consequently delay shear failure. These results expand the understanding of the correlation between the atomic-level structure and elementary plastic events in monolithic MGs and thereby pave the way for the design of new ductile metallic alloys. Recent insights into the atomic-scale mechanisms underlying the structural failure of glass-like metals provide strategies for the development of novel materials. Metallic glasses have a disordered atomic structure, unlike the crystalline arrangement of conventional metals. They therefore offer greater flexibility in terms of the shapes they can form. However, so-called shear bands that form when the metallic glass is deformed under stress weaken it, leading to structural failure. G.W. from Shanghai University, China, D.S. from the Erich Schmid Institute of Materials Science in Leoben, Austria, and co-workers used X-ray diffraction to track changes in atomic structure as they cooled a metallic glass to very low temperatures and correlated these changes with local variations in stress. Understanding this correlation will help design metallic glasses with an improved ability to be deformed without structural failure. Understanding the correlation between atomic-scale structural/elastic fluctuations and local plastic rearrangements (shear transformation zone (STZ)) is essential to the widespread use of metallic glasses (MGs). We report a strategy to control the local stress state and enhance the shear stability of MGs. The enhanced degree of structural/elastic heterogeneities relates to the increased nonaffine thermal strain of the short- and medium-range order. We demonstrate that variations in the stress field around STZ affect their dynamics and percolation process, the progressive formation of shear bands, and, consequently, the macroscopic deformability of MGs. This work paves a new way for designing ductile MGs.

Rapidly photocurable silk fibroin sealant for clinical applications

Abstract: Sealants are useful as agents that can prevent the leakage of gas or nonclotting fluids from damaged tissues and of blood from the vascular system following injury or repair Various formulations for sealants have been developed and applied clinically, but problems still remain in terms of biocompatibility issues, long crosslinking times and low adhesive properties Herein, to address these issues, we report a methacrylated silk fibroin sealant (Sil-MAS) with rapidly crosslinkable, highly adhesive and biocompatible properties and demonstrate its versatility as a medical glue The excellent physical properties of Sil-MAS are revealed via in vitro mechanical tests and ex vivo aorta pressure tests In addition, in in vivo biological tests on the skin, liver, and blood vessels of rats, Sil-MAS showed a superb hemostatic and adhesive ability, with high biocompatibility Specifically, Sil-MAS strongly contributed to faster wound healing than commercially available materials Furthermore, we showed a successful proof of concept that Sil-MAS could serve as an ideal photocuring laparoscopic medical glue in a laceration rabbit model of liver and stomach serosa using a homemade endoscopic device These findings on the applicability of rapidly photocurable silk fibroin indicate that Sil-MAS is a suitable material to supplant existing sealants, adhesives, or hemostatic agents An efficient, fast-acting and biocompatible glue for sealing damaged body tissue has been developed by scientists in South Korea and the USA The ability to stop bleeding is crucial in surgery One solution is to use medical glues that can seal tissue and blood vessels These glues need to be biocompatible, fast-acting, long-lasting and low cost Many such sealants are now clinically available, but most do not meet all these requirements Chan Hum Park from Hallym University in Chuncheon, South Korea, and co-workers developed a fast-acting, highly adhesive and biocompatible medical glue using a material derived from a silk protein The team tested their methacrylated silk fibroin sealant on rat skin, liver and blood vessels and observed faster wound healing than that obtained using commercially available materials We report methacrylated silk fibroin sealant (Sil-MAS) with rapid crosslinkable, highly adhesive and biocompatible properties and demonstrate its versatility as medical glue The excellence for physical properties of Sil-MAS is revealed via in vitro mechanical tests and ex vivo aorta pressure test In in vivo biological tests on skin, liver, and blood vessels of rat, Sil-MAS showed a superb hemostatic and adhesive ability with high biocompatibility Specifically, Sil-MAS strongly contributed to fast wound healing Furthermore, we showed that Sil-MAS could be an ideal photocuring laparoscopic medical glue in laceration rabbit model of liver and stomach serosa using self-made endoscopic device

Photoreduced nanocomposites of graphene oxide/N-doped carbon dots toward all-carbon memristive synapses

Abstract: An all-carbon memristive synapse is highly desirable for hardware implementation in future wearable neuromorphic computing systems. Graphene oxide (GO) can exhibit resistive switching (RS) and may be a feasible candidate to achieve this objective. However, the digital-type RS often occurring in GO-based memristors restricts the biorealistic emulation of synaptic functions. Here, an all-carbon memristive synapse with analog-type RS behavior was demonstrated through photoreduction of GO and N-doped carbon quantum dot (NCQD) nanocomposites. Ultraviolet light irradiation induced the local reduction of GO near the NCQDs, therefore forming multiple weak conductive filaments and demonstrating analog RS with a continuous conductance change. This analog RS enabled the close emulation of several essential synaptic plasticity behaviors; more importantly, the high linearity of the conductance change also facilitated the implementation of pattern recognition with high accuracy. Furthermore, the all-carbon memristive synapse can be transferred onto diverse substrates, showing good flexibility and 3D conformality. Memristive potentiation/depression was stably performed at 450 K, indicating the resistance of the synapse to high temperature. The photoreduction method provides a new path for the fabrication of all-carbon memristive synapses, which supports the development of wearable neuromorphic electronics. A graphene-based device can help computer chips behave more like human brains by transmitting current across thread-like wires. Neural synapses store memories by accessing different types of conductive states. Chinese researchers led by Haiyang Xu at Northeast Normal University in Changchun and Zhenhui Kang at Soochow University in Suzhou now demonstrate that graphene sheets with different conductivity levels—caused by adding or removing oxygen atoms—can also exhibit synapse-like behavior. The team developed a carbon-nitrogen composite to sandwich between two graphene electrodes with high and low levels of conductivity. Exposing the composite to ultraviolet light created numerous tiny filaments between the electrodes that physically restrict electron flow and provide gradual smooth transitions between the graphene electrodes’ two conductive states. The organic framework of this device also provides inherent flexibility for wearable devices. All-carbon memristive synapse is built through photo-reduction of a nanocomposite comprised of graphene oxide and N-doped carbon quantum dots. The analog-type resistive switching was demonstrated, which enabled the emulation of synaptic learning and pattern recognition with high accuracy. The all-carbon devices possess excellent transferability, flexibility and resistance to high temperature, showing the potential for the development of wearable neuromorphic computing system.

Chemically resistant and thermally stable quantum dots prepared by shell encapsulation with cross-linkable block copolymer ligands

Abstract: Endowing quantum dots (QDs) with robustness and durability have been one of the most important issues in this field, since the major limitations of QDs in practical applications are their thermal and oxidative instabilities. In this work, we propose a facile and effective passivation method to enhance the photochemical stability of QDs using polymeric double shell structures from thiol-terminated poly(methyl methacrylate-b-glycidyl methacrylate) (P(MMA-b-GMA)-SH) block copolymer ligands. To generate a densely cross-linked network, the cross-linking reaction of GMA epoxides in the PGMA block was conducted using a Lewis acid catalyst under an ambient environment to avoid affecting the photophysical properties of the pristine QDs. This provides QDs encapsulated with robust double layers consisting of highly transparent PMMA outer-shell and oxidation-protective cross-linked inner shell. Consequently, the resulting QDs exhibited exceptional tolerance to heat and oxidants when dispersed in organic solvents or QD-nanocomposite films, as demonstrated under various harsh conditions with respect to temperature and oxidant species. The present approach not only provides simple yet effective chemical means to enhance the thermochemical stability of QDs, but also offers a promising platform for the hybridization of QDs with polymeric materials for developing robust light-emitting or light-harvesting devices. A treatment that makes nanoparticles robust and thus more useful for optoelectronics has been developed by researchers in South Korea. Quantum dots are semiconductor particles just a few tens of nanometers in diameter. These tiny dimensions restrict the motion of electrons, which gives the dots properties similar to those of an atom. Specifically, they efficiently absorb and emit spectrally pure light, making them useful for displays, photodetectors and solar cells. However, quantum dots are sensitive to heat, moisture and oxidization. Joona Bang, Korea University, Seoul, and colleagues improved the thermochemical stability of quantum dots by surrounding them with a physical barrier to suppress the creation of surface defects. This protective shell was made using a cross-linkable polymer ligand and was shown to reduce the deleterious effects of exposure to high temperatures and an oxidizing agent. Quantum Dot: Shell cross-linking endows stability: Simple and facile cross-linking chemistry was employed to form the robust network shell on the quantum dot (QD) surface without altering the photoluminescence property of pristine QDs. The resulting shell cross-linked QDs exhibited exceptional tolerance against heat or chemical oxidations. And the exterior brush in QDs can be readily tunable and provide the miscibility with host polymer matrix, resulting in well-defined QD-nanocomposite films. This encapsulation strategy can be generally applicable to many other nanoparticles that are vulnerable to various external stimuli.

A hierarchically ordered compacted coil scaffold for tissue regeneration

Abstract: Hierarchically ordered scaffold has a great impact on cell patterning and tissue engineering. The introduction of controllable coils into a scaffold offers an additional unique structural feature compared to conventional linear patterned scaffolds and can greatly increase interior complexity and versatility. In this work, 3D coil compacted scaffolds with hierarchically ordered patterns and tunable coil densities created using speed-programmed melt electrospinning writing (sMEW) successfully led to in vitro cell growth in patterns with tunable cell density. Subcutaneous implantation in mice showed great in vivo biocompatibility, as evidenced by no significant increase in tumor necrosis factor α (TNF-α) and interleukin 6 (IL-6) levels in mouse serum. In addition, a lumbar vertebra was successfully printed for mesenchymal stem cells to grow in the desired pattern. A long-range patterned matrix composed of programmable short-range compacted coils enabled the design of complex structures, e.g., for tailored implants, by readily depositing short-range coil-compacted secondary architectures along with customized primary design. Improvements to a recently developed technique for printing biomaterials could make it easier to fabricate complex scaffolds for tissue regrowth. By shaping biocompatible polymers into thin microfibers and then collecting the strands on a moving platform, researchers can build tissue scaffolds layer-by-layer into 3D structures. Yingchun Su from the Harbin Institute of Technology in Harbin, China, and Aarhus University, Denmark, and colleagues report that materials printed by this ‘speed-programmed melt electrospinning writing’ technique can be composed of coil-shaped microfibers. The team found that the coil-like strands, produced by manipulating platform collection speeds, were effective at introducing pores into 3D scaffolds to better mimic natural tissue. Experiments showed this approach enabled better control over the cell density and growth behavior of stem cells implanted in a scaffold shaped like an artificial lumbar vertebra. Speed-programmed melt electrospinning writing (sMEW) is used to create a hierarchically ordered biomimetic scaffold with long-range patterned and short-range porous architectures for cell growth in patterns with tunable cell density.

One-step synthesis of dandelion-like lanthanum titanate nanostructures for enhanced photocatalytic performance

Abstract: The rational design of nanomaterials with distinct exposed facets is of great importance for improving the physicochemical properties of these materials and for the study of structure–activity relationships. This work describes the first synthesis of lanthanum titanate (La2Ti2O7, LTO) with dandelion-like nanostructures via the molten salt method. The lowest synthesis temperature of 700 °C is at least 200 °C lower than that required by other methods. The dandelion structure consists of well-crystallized LTO nanorods (NRs) with sizes of less than 100 nm in the radial direction and 300–500 nm in the axial direction, which is different from the widely accepted two-dimensional form. LaOCl microplates were formed as an intermediate substrate for LTO NR growth outwards to the basal surfaces of the LaOCl crystallites. DFT calculation results showed that the strong LiCl adsorption on the (100) surface led to distinct growth of the (100) and (020) planes, thus promoting the rod-like growth of LTO along the [010] axis. In addition, the photocatalytic performance of as-prepared LTO was evaluated by determining the degradation of rhodamine B. The results suggested that the as-prepared LTO could markedly enhance the photocatalytic activity as a result of the surface heterojunction of coexposed {100} and {002} facets in LTO NRs. A catalyst that uses light irradiation to decompose organic pollutants can become more active by being fabricated into rod-like nanostructures resembling dandelion seeds. Zhong Huang from the Wuhan University of Science and Technology in China and co-workers have developed a method for synthesizing lanthanum titanate, a ceramic that excels at separating positive and negative photogenerated charges so they can be employed for catalytic reactions. The team’s approach quickly prepares lanthanum titanate nanocrystals using a bath of molten lithium and potassium salts. By optimizing the molten salt concentrations, the researchers isolated tiny aggregates of nanorods that have a high number of exposed crystal facets for charge separation. Experiments showed the nanorods could degrade model pollutants such as rhodamine dyes several times faster than conventional plate-shaped lanthanum titanates. A surface heterojunction is formed in the dandelion-like LTO, resulting in significant enhancement of the photocatalytic performance.

Strong spin orientation-dependent spin current diffusion and inverse spin Hall effect in a ferromagnetic metal

Abstract: Pure spin current transport has become the central point of the state-of-the-art spintronics. While most spin current phenomena have been extensively explored, aspects of the pure spin current injected into ferromagnetic metals are far from completely understood. The reports on a fundamental problem, i.e. the spin relaxation asymmetry with spin current polarization collinear or transverse to the magnetization of ferromagnetic metals, are quite controversial. By employing a Y3Fe5O12 (YIG)/Cu/Ni80Fe20 (Py)/Ir25Mn75 (IrMn) spin valve heterostructure with the thermal inverse spin Hall effect (ISHE) of a Py well separated from other thermoelectric transport and thermal Hall effects, we find that the ISHE signal amplitude in 10 nm Py increases by 80% when changing the relative orientation of the YIG and Py magnetization from orthogonal (⊥) to collinear (||). Moreover, the spin-diffusion length λsf and effective spin Hall angle $$\theta _{{\mathrm{SH}}}^{{\mathrm{eff}}}$$ of Py are also spin orientation dependent and vary from $$\lambda _{{\mathrm{sf}}}^ \bot$$ = 1.0 ± 0.1 nm to $$\lambda _{{\mathrm{sf}}}^\parallel$$ = 2.8 ± 0.5 nm with $$\theta _{{\mathrm{SH}}}^{{\mathrm{eff}}}\left( \bot \right)/\theta _{{\mathrm{SH}}}^{{\mathrm{eff}}}\left( \parallel \right)$$ = 1.5, respectively. Our results demonstrate magnetization orientation-dependent spin relaxation and spin injection efficiency of a pure spin current, revealing that exchange interactions in ferromagnetic metals strongly affect the transport of the pure spin current. A method for converting quantum spin properties into electricity can be enhanced using magnetic fields. Jian-Wang Cai from the Chinese Academy of Sciences in Beijing, China and colleagues investigated how insulating magnets can transmit information via a phenomenon known as spin current generation. When heat is applied to nanoscale nickel–iron films, information about the magnet’s spin orientation moves through the alloy much like a wave through water. Placing an antiferromagnetic metal on top of the nickel–iron film enables the spin current to be captured and converted into electricity without any spurious effect. The authors’ experiments showed that spin currents could be boosted or diminished by applying external magnetic fields parallel or across the device. Analysis of this orientation dependence revealed how spin movement across interfaces may affect this new type of power generation. The authors demonstrate that the inverse spin Hall effect (ISHE) and pure spin current relaxation in Ni80Fe20 (Py) are strong magnetization orientation dependent through longitudinal spin-Seebeck effect measurement in YIG/Cu/Py/Ir25Mn75 spin valve heterostructure. With the relative orientation of the magnetization of YIG and Py varying from perpendicular (⊥) to collinear (||), it has been found that the detected ISHE amplitude in 10 nm Py increases by 80%. Besides, the spin-diffusion length λsf varies from $$\lambda _{{\mathrm{sf}}}^ \bot$$ = 1.0 ± 0.1 nm to $$\lambda _{{\mathrm{sf}}}^\parallel$$ = 2.8 ± 0.5 nm and the effective spin Hall angle $$\theta _{{\mathrm{SH}}}^{{\mathrm{eff}}}\left( \bot \right)/\theta _{{\mathrm{SH}}}^{{\mathrm{eff}}}\left( \parallel \right) = 1.5$$ .

Regulating the pore structure and oxygen vacancies of cobaltosic oxide hollow dodecahedra for an enhanced oxygen evolution reaction

Abstract: Engineering an electrocatalytic anode material to boost reaction kinetics is highly desirable for the anodic oxygen evolution reaction (OER), which is the major obstacle for high efficiency water electrolysis. Here, we present a novel kind of Zn-doped Co3O4 hollow dodecahedral electrocatalyst. Abundant oxygen vacancy defects are introduced due to the incorporation of Zn2+, which is beneficial for OH− adsorption and the charge transfer reaction during the OER process. Moreover, the increase in surface area caused by the advanced structure of the hollow porous dodecahedra facilitates mass transport by increasing the surface area. The novel strategy proposed in this study provides an efficient way to design high-performance electrocatalysts for water electrolysis. A cheap catalyst that aids water splitting and is made from readily available materials has been developed by researchers in China. Hydrogen releases energy when burned in air, and is therefore a promising source of clean power. Hydrogen can be sourced by splitting water into its constituent atoms, but the chemical reaction separating hydrogen and oxygen, known as the oxygen evolution reaction, is not particularly efficient. Yao Xiao and coworkers from the Changchun Institute of Applied Chemistry developed an oxygen evolution reaction electrocatalyst made from zinc-doped cobalt oxide, Zn-Co3O4. The catalyst has a unique dodecahedral structure, and the team believes it is its large surface area that is responsible for its excellent performance. Unlike many other water-splitting catalysts, the constituent materials of Zn-Co3O4 are cheap and readily available. Cobaltosic oxide hollow dodecahedra with abundant oxygen vacancy defects was synthesized and manifested extraordinary catalytic performance toward the oxygen evolution reaction.

Control of fibroblast shape in sequentially formed 3D hybrid hydrogels regulates cellular responses to microenvironmental cues

Abstract: Cell shape plays important roles in regulating cell behavior; however, independently controlling cell shape in three dimensions is a challenging undertaking, and how cell shape affects cellular responses to mechanical and biochemical cues in three dimensions remains unclear Here, we present a hydrogel-based platform to control cell shape in three dimensions by using sequentially formed hybrid hydrogels consisting of collagen and alginate By adjusting the cross-linking time of the alginate, we fixed the shape of NIH 3T3 fibroblasts at different spreading states Then, we explored the influence of cell shape on the cell responses to microenvironmental cues by using cardiac fibroblasts (CFs) as model cells We found that the spreading state of the CFs influences their responses to both mechanical (ie, matrix stiffness) and biochemical (ie, transforming growth factor-β1 (TGF-β1)) cues in three dimensions Additional experiments revealed that integrin β1 in focal adhesions and Smad2/3 are involved in mediating the cell shape-dependent responses of CFs to matrix stiffness and TGF-β1 cues, respectively This work represents the first step in understanding how cell shape influences cell responses to mechanical and biochemical cues in three dimensions and can be instructive for developing novel approaches to target cell shape regulation for treating fibrosis and other diseases Researchers in China have developed a material-based approach that can control the shape of cells in three dimensions The shape of a cell, which is known to be dependent on its microenvironment, heavily influences its growth, movement and differentiation This dependency has previously been studied mainly using two-dimensional cultures, but it is believed that cell behavior could be significantly different in more realistic three-dimensional cultures To better understand the influence of a cell’s surroundings on its shape and function, Feng Xu, Guoyou Huang and their colleagues from Xi’an Jiaotong University created an artificial cellular microenvironment by developing an approach based on sequentially formed hybrid hydrogels They demonstrated the ability of this microenvironment to control the shape of cardiac fibroblasts in three dimensions and showed how this affected the cells’ responses to mechanical and biochemical stimuli A sequentially formed hybrid hydrogel system consisting of collagen and alginate was designed to control cell shape in 3D The cell with different spreading state had significantly different responses to mechanical (ie, matrix stiffness) and biochemical (ie, transforming growth factor-β1 (TGF-β1)) cues

Enhancement of perpendicular magnetic anisotropy and Dzyaloshinskii–Moriya interaction in thin ferromagnetic films by atomic-scale modulation of interfaces

Abstract: To stabilize nontrivial spin textures, e.g., skyrmions or chiral domain walls in ultrathin magnetic films, an additional degree of freedom, such as the interfacial Dzyaloshinskii–Moriya interaction (IDMI), must be induced by the strong spin-orbit coupling (SOC) of a stacked heavy metal layer. However, advanced approaches to simultaneously control the IDMI and perpendicular magnetic anisotropy (PMA) are needed for future spin-orbitronic device implementations. Here, we show the effect of atomic-scale surface modulation on the magnetic properties and IDMI in ultrathin films composed of 5d heavy metal/ferromagnet/4d(5d) heavy metal or oxide interfaces, such as Pt/CoFeSiB/Ru, Pt/CoFeSiB/Ta, and Pt/CoFeSiB/MgO. The maximum IDMI value corresponds to the correlated roughness of the bottom and top interfaces of the ferromagnetic layer. The proposed approach for significant enhancement of PMA and the IDMI through interface roughness engineering at the atomic scale offers a powerful tool for the development of spin-orbitronic devices with precise and reliable controllability of their functionality. Introducing surface roughness at the atomic scale can improve control of magnetic patterns in thin films, which is potentially useful for very low-power consumption memories. Swirling magnetic-field patterns can form in ultra-thin layers of magnetic materials. Alexander Samardak from the Far Eastern Federal University, Vladivostok, Russia, Young Keun Kim from Korea University, Seoul, Republic of Korea, and their co-workers have identified a method for improving the strength of the so-called interfacial Dzyaloshinskii–Moriya interaction (IDMI), which can influence the dynamics of these magnetic patterns. The team sandwiched a thin film of the ferromagnet cobalt-iron-silicon-boron between two metallic layers and demonstrated the IDMI was correlated with the roughness of the bottom and top interfaces. Using surface roughness, they were able to achieve a 2.5-fold increase in the IDMI. An effect of atomic-scale surface modulation on the magnetic properties and the interfacial Dzyaloshinskii-Moriya interaction (IDMI) is shown in Pt/CoFeSiB/X(MgO, Ta, Ru) ultrathin films sputtered on the epitaxial Pd layers of the different thickness and surface morphology. The correlated roughness of the bottom and top interfaces of CoFeSiB increases IDMI values by up to 2.5 times, with the maximum magnitude Deff = −0.88 erg/cm2. The main reasons for this significant enhancement are the intermixing at interfaces and the correlated interface-roughness variations, which both affect electronic transport across the interface and, as a result, the degree of the electron scattering.