A Strong, Tough, and Stable Composite with Nacre-Inspired Sandwich Structure.

Improving the fracture resistance of nacre-inspired composites is crucial in addressing the strength-toughness trade-off. However, most previously proposed strategies for enhancing fracture resistance in these composites have been limited to interfacial modification by polymer, which restricts mechanical enhancement. Here, a composite material consisting of graphene oxide (GO) lamellae and nanocrystalline reinforced amorphous alumina nanowires (NAANs) has been developed. The structure of the composite is inspired by nacre and is composed of stacked GO nanosheets with NAANs in between, forming a sandwich-like structure. This design enhances the fracture resistance of the composite through the pull-out of GO nanosheets at the nanoscale and GO/NAANs sandwich-like coupling at the micro-scale, while also providing stiff ceramic support. This composite simultaneously possesses high strength (887.8 MPa), toughness (31.6 MJ m-3), superior cyclic stability (1600 cycles), and long-term (2 years) immersion stability, which outperform previously reported GO-based lamellar composites. The hierarchical fracture design provides a new path to design next-generation strong, tough, and stable materials for advanced engineering applications.

Stabilizing Single-Atomic Pt by Forming PtFe Bonds for Efficient Diboration of Alkynes.

Precisely tailoring the oxidation state of single-atomic metal in heterogeneous catalysis is an efficient way to stabilize the single-atomic site and promote their activity, but realizing this approach remains a grand challenge to date. Herein, a class of stable single-atomic catalysts with well-tuned oxidation state of Pt by forming PtFe atomic bonds is reported, which are supported by defective Fe2 O3  nanosheets on reduced graphene oxide (PFARFNs). These as-synthesized materials can greatly enhance the catalytic activity, stability, and selectivity for the diboration of alkynes. The PFARFNs exhibit high conversion of 99% at 100 °C with an outstanding turnover frequency (TOF) of 545 h-1 , and a relatively high conversion of 58% at room temperature (25 °C) with a TOF of 310 h-1 , which has been hardly achieved previously. Through both experimental and theoretical investigation, it is demonstrated that the fast electron transfer from Fe to Pt in Fe-Pt-O atomic sites in PFARFNs can not only stabilize the single-atomic Pt, but also significantly improve their catalytic activity.

Interference of EFNA4 suppresses cell proliferation, invasion and angiogenesis in hepatocellular carcinoma by downregulating PYGO2.

Hepatocellular carcinoma (HCC) is the most common type of liver cancer. Ephrin A4 (EFNA4) acts as an oncogene in multiple cancers but is little known in HCC. It is revealed that EFNA4 is highly expressed in patients with HCC and influences the proliferation of HCC cells; however, detailed regulatory mechanism of EFNA4 in HCC needs to be unveiled. Here, we discovered that EFNA4 was highly expressed in HCC cell lines. EFNA4 knockdown greatly suppressed cell proliferation, migration and invasion, as well as inhibiting angiogenesis in Huh7 cells. EFNA4 was demonstrated to interact with pygopus-2 (PYGO2) and positively regulate PYGO2 expression. Gene gain- and loss-of-function experiments revealed that the anti-tumor effect of EFNA4 knockdown was partly abolished by PYGO2 overexpression. Furthermore, EFNA4 knockdown blocked wnt/ß-catenin signaling in Huh7 cells, which was then abolished by PYGO2. In conclusion, this study further ensured the oncogenic role of EFNA4 in HCC, and disclosed that EFNA4 knockdown suppressed cell proliferation, invasion, angiogenesis, and wnt/ß-catenin signaling in HCC by downregulating PYGO2.

Role of Inorganic Amorphous Constituents in Highly Mineralized Biomaterials and Their Imitations.

A highly mineralized biomaterial is one kind of biomaterial that usually possesses a high content of crystal minerals and hierarchical microstructure, exhibiting excellent mechanical properties to support the living body. Recent studies have revealed the presence of inorganic amorphous constituents (IAC) either during the biomineralization process or in some mature bodies, which heavily affects the formation and performance of highly mineralized biomaterials. These results are surprising given the preceding intensive research into the microstructure design of these materials. Herein, we highlight the role of IAC in highly mineralized biomaterials. We focused on summarizing works demonstrating the presence or phase transformation of IAC and discussed in detail how IAC affects the formation and performance of highly mineralized biomaterials. Furthermore, we described some imitations of highly mineralized biomaterials that use IAC as the synthetic precursor or final strengthening phase. Finally, we briefly summarized the role of IAC in biomaterials and provided an outlook on the challenges and opportunities for future IAC and IAC-containing bioinspired materials researches.

Multiscale engineered artificial tooth enamel.

Tooth enamel, renowned for its high stiffness, hardness, and viscoelasticity, is an ideal model for designing biomimetic materials, but accurate replication of complex hierarchical organization of high-performance biomaterials in scalable abiological composites is challenging. We engineered an enamel analog with the essential hierarchical structure at multiple scales through assembly of amorphous intergranular phase (AIP)-coated hydroxyapatite nanowires intertwined with polyvinyl alcohol. The nanocomposite simultaneously exhibited high stiffness, hardness, strength, viscoelasticity, and toughness, exceeding the properties of enamel and previously manufactured bulk enamel-inspired materials. The presence of AIP, polymer confinement, and strong interfacial adhesion are all needed for high mechanical performance. This multiscale design is suitable for scalable production of high-performance materials.

Manipulation on Two-Dimensional Amorphous Nanomaterials for Enhanced Electrochemical Energy Storage and Conversion.

Low-carbon society is calling for advanced electrochemical energy storage and conversion systems and techniques, in which functional electrode materials are a core factor. As a new member of the material family, two-dimensional amorphous nanomaterials (2D ANMs) are booming gradually and show promising application prospects in electrochemical fields for extended specific surface area, abundant active sites, tunable electron states, and faster ion transport capacity. Specifically, their flexible structures provide significant adjustment room that allows readily and desirable modification. Recent advances have witnessed omnifarious manipulation means on 2D ANMs for enhanced electrochemical performance. Here, this review is devoted to collecting and summarizing the manipulation strategies of 2D ANMs in terms of component interaction and geometric configuration design, expecting to promote the controllable development of such a new class of nanomaterial. Our view covers the 2D ANMs applied in electrochemical fields, including battery, supercapacitor, and electrocatalysis, meanwhile we also clarify the relationship between manipulation manner and beneficial effect on electrochemical properties. Finally, we conclude the review with our personal insights and provide an outlook for more effective manipulation ways on functional and practical 2D ANMs.

An Amorphous Peri-Implant Ligament with Combined Osteointegration and Energy-Dissipation.

Progress toward developing metal implants as permanent hard-tissue substitutes requires both osteointegration to achieve load-bearing support, and energy-dissipation to prevent overload-induced bone resorption. However, in existing implants these two properties can only be achieved separately. Optimized by natural evolution, tooth-periodontal-ligaments with fiber-bundle structures can efficiently orchestrate load-bearing and energy dissipation, which make tooth-bone complexes survive extremely high occlusion loads (>300 N) for prolonged lifetimes. Here, a bioinspired peri-implant ligament with simultaneously enhanced osteointegration and energy-dissipation is presented, which is based on the periodontium-mimetic architecture of a polymer-infiltrated, amorphous, titania nanotube array. The artificial ligament not only provides exceptional osteoinductivity owing to its nanotopography and beneficial ingredients, but also produces periodontium-similar energy dissipation due to the complexity of the force transmission modes and interface sliding. The ligament increases bone-implant contact by more than 18% and simultaneously reduces the effective stress transfer from implant to peri-implant bone by ≈30% as compared to titanium implants, which as far as is known has not previously been achieved. It is anticipated that the concept of an artificial ligament will open new possibilities for developing high-performance implanted materials with increased lifespans.

Enamel Repair with Amorphous Ceramics.

Developing high-performance materials in physiological conditions to clinically repair stiff tissue for long lifespan remains a great challenge. Here, an enamel repair strategy is reported by efficiently growing a biocompatible ZrO2 ceramic layer on defective enamel through controllable hydrolysis of Zr4+ in oral-tolerable conditions. Detailed analysis of the grown layer indicates that the grown ZrO2 ceramic is amorphous without grain boundary and dislocation, which endows the repaired enamel with natural enamel comparable mechanical performance (modulus ≈82.5 GPa and hardness ≈5.2 GPa). Besides, the strong chemical connection between unsaturated coordinated Zr4+ in amorphous structure and PO4 3- greatly strengthen the crystalline-amorphous interface of the repaired enamel to endure the long-time mastication damage. Moreover, these ZrO2 ceramics provide hydrophilic, electronegative, and smooth surfaces to resist the adhesion and proliferation of cariogenic bacteria. The hybrid amorphous-crystalline interface design with advantages in biomechanical compatibility would promote the evolution of a variety of cutting-edge functional materials for medical and engineering application.

Two-Dimensional Amorphous TiO2 Nanosheets Enabling High-Efficiency Photoinduced Charge Transfer for Excellent SERS Activity.

Substrate-molecule vibronic coupling enhancement, especially the efficient photoinduced charge transfer (PICT), is pivotal to the performance of nonmetal surface-enhanced Raman scattering (SERS) technology. Here, through developing novel two-dimensional (2D) amorphous TiO2 nanosheets (a-TiO2 NSs), we successfully obtained an ultrahigh enhancement factor of 1.86 × 106. Utilizing the Kelvin probe force microscopy (KPFM) technology, we found that these 2D a-TiO2 NSs possessed more positive surface potential than their 2D crystalline counterpart (c-TiO2 NSs). First-principles density functional theory (DFT) was used to further reveal that the low coordination number of surface Ti atoms and the large amount of surface oxygen defects endowed the 2D a-TiO2 with high electrostatic potential, which allowed significant charge transfer from the adsorbed molecule to the 2D a-TiO2 and facilitated the formation of a stable surface charge-transfer (CT) complex. Significantly, comparing with the 2D c-TiO2, the smaller band gap and higher electronic density of states (DOS) of the 2D a-TiO2 effectively enhanced the vibronic coupling of resonances in the substrate-molecule system. The strong vibronic coupling within the CT complex obviously enhanced the PICT resonance and lead to the remarkable SERS activity of a-TiO2 NSs. To the best of our knowledge, this is the first report on the remarkable SERS activity of 2D amorphous semiconductor nanomaterials, which may bring the cutting edge of development of stable and highly sensitive nonmetal SERS technology.

Dual-Phase Super-Strong and Elastic Ceramic.

Ceramic materials exhibit very high stiffness and extraordinary strength, but they typically suffer from brittleness. Amorphization and size confinement are commonly used to reinforce materials. However, the inverse Hall-Petch effect and the shear-band softening effect usually limit further improvement of their performance under a critical size. With an optimum structure design, we demonstrate that dual-phase zirconia nanowires (DP-ZrO2 NWs) with nanocrystals embedded in an amorphous matrix as a strengthening phase can overcome these problems simultaneously. As a result of this structure, in situ tensile tests demonstrate that the mechanical properties have been enormously improved in a way that does not follow both the inverse Hall-Petch effect and the shear band softening effect. The elastic strain approaches ∼7%, and the ultimate strength is 3.52 GPa, accompanied by a high toughness of ∼151 MJ m-3, making the DP-ZrO2 NW composite the strongest and toughest ZrO2 ever achieved. The findings provide a way to improve the mechanical properties of ceramics in a controllable manner, which may serve as a pervasive approach to be broadly applied to a variety of materials.

Application of 3D hierarchical monoclinic-type structural Sb-doped WO3 towards NO2 gas detection at low temperature.

Currently, the development of semiconducting metal oxide (SMO)-based gas sensors with innovative modification and three-dimensional (3D) structural designs has become a significant scientific interest due to their potential for addressing key technological challenges. Herein, gas sensing devices based on the 3D hierarchical monoclinic-type structural Sb-doped WO3 (HMSW) gas sensing material were successfully constructed by ordered assembly of urchin-like monoclinic-type structural (P2/m) Sb-doped WO2.72 (W18O49) (UMSW) nanocrystals and nanowires. The crystalline microstructure, composition, morphological characteristics, and possible growth mechanisms were systematically investigated. The results of the gas sensor measurements, performed simultaneously on multiple samples, indicated that the 3D HMSW material has superior sensitivity (S = 122) and high selectivity to ppm-level NO2 at 30 °C with a significantly larger response than the best-reported values from other WO3-based gas sensors fabricated so far. All the results clearly demonstrate that the combined effects of abundant structural defects derived from Sb doping modification, reduced band gap, and 3D hierarchical microstructure synergistically play a key role in the NO2 gas sensing performance. Such excellent gas sensing performance foresees the great potential application of 3D hierarchical structural WO3-based sensors for fast and effective detection of toxic gases that can aid in human health and public safety.

Anatomical explanations for acute depressions in radial pattern of axial sap flow in two diffuse-porous mangrove species: implications for water use.

Mangrove species have developed uniquely efficient water-use strategies in order to survive in highly saline and anaerobic environments. Herein, we estimated the stand water use of two diffuse-porous mangrove species of the same age, Sonneratia apetala Buch. Ham and Sonneratia caseolaris (L.) Engl., growing in a similar intertidal environment. Specifically, to investigate the radial patterns of axial sap flow density (Js) and understand the anatomical traits associated with them, we measured axial sap flow density in situ together with micromorphological observations. A significant decrease of Js was observed for both species. This result was accompanied by the corresponding observations of wood structure and blockages in xylem sapwood, which appeared to influence and, hence, explained the acute radial reductions of axial sap flow in the stems of both species. However, higher radial resistance in sapwood of S. caseolaris caused a steeper decline of Js radially when compared with S. apetala, thus explaining the latter's more efficient use of water. Without first considering acute reductions in Js into the sapwood from the outer bark, a total of ~55% and 51% of water use would have been overestimated, corresponding to average discrepancies in stand water use of 5.6 mm day-1 for S. apetala trees and 2.5 mm day-1 for S. caseolaris trees. This suggests that measuring radial pattern of Js is a critical factor in determining whole-tree or stand water use.

Nacre-Inspired Structural Composites: Performance-Enhancement Strategy and Perspective.

For modern material engineering, one of the most ambitious goals is to develop lightweight structural materials with superior strength and toughness. Nacre, a typical biomaterial with high mechanical performance, has always inspired synthesis of high-performance structural composites. Here, the synthesis strategies for further enhancing the strength and toughness of novel nacre-inspired structural composites, including ternary artificial nacre, artificial nacre reinforced by bridges, and those with an ultrahigh content of a hard phase, are reviewed. Also, the challenges and outlook for preparing lighter, stronger, and tougher structural composites are discussed.

A Generalized Strategy for the Synthesis of Large-Size Ultrathin Two-Dimensional Metal Oxide Nanosheets.

Two-dimensional (2D) nanomaterials show unique electrical, mechanical, and catalytic performance owing to their ultrahigh surface-to-volume ratio and quantum confinement effects. However, ways to simply synthesize 2D metal oxide nanosheets through a general and facile method is still a big challenge. Herein, we report a generalized and facile strategy to synthesize large-size ultrathin 2D metal oxide nanosheets by using graphene oxide (GO) as a template in a wet-chemical system. Notably, the novel strategy mainly relies on accurately controlling the balance between heterogeneous growth and nucleation of metal oxides on the surface of GO, which is independent on the individual character of the metal elements. Therefore, ultrathin nanosheets of various metal oxides, including those from both main-group and transition elements, can be synthesized with large size. The ultrathin 2D metal oxide nanosheets also show controllable thickness and unique surface chemical state.

Ca2+ Enhanced Nacre-Inspired Montmorillonite-Alginate Film with Superior Mechanical, Transparent, Fire Retardancy, and Shape Memory Properties.

Inspired by nacre, this is the first time that using the cross-linking of alginate with Ca ions to fabricate organic-inorganic nacre-inspired films we have successfully prepared a new class of Ca2+ ion enhanced montmorillonite (MMT)-alginate (ALG) composites, realizing an optimum combination of high strength (∼280 MPa) and high toughness (∼7.2 MJ m-3) compared with other MMT based artificial nacre. Furthermore, high temperature performance of the composites (with a maximum strength of ∼170 MPa at 100 °C) along with excellent transmittance, fire retardancy, and unique shape memory response to alcohols could greatly expand the application of the mutilfunctional composites, which are believed to show competitive advantages in transportion, construction, and insulations, protection of a flammable biological material, etc.

Cloning Nacre's 3D Interlocking Skeleton in Engineering Composites to Achieve Exceptional Mechanical Properties.

Ceramic/polymer composite equipped with 3D interlocking skeleton (3D IL) is developed through a simple freeze-casting method, exhibiting exceptionally light weight, high strength, toughness, and shock resistance. Long-range crack energy dissipation enabled by 3D interlocking structure is considered as the primary reinforcing mechanism for such superior properties. The smart composite design strategy should hold a place in developing future structural engineering materials.

Strong and Tough Layered Nanocomposites with Buried Interfaces.

In nacre, the excellent mechanical properties of materials are highly dependent on their intricate hierarchical structures. However, strengthening and toughening effects induced by the buried inorganic-organic interfaces actually originate from various minerals/ions with small amounts, and have not drawn enough attention yet. Herein, we present a typical class of artificial nacres, fabricated by graphene oxide (GO) nanosheets, carboxymethylcellulose (CMC) polymer, and multivalent cationic (M(n+)) ions, in which the M(n+) ions cross-linking with plenty of oxygen-containing groups serve as the reinforcing "evocator", working together with other cooperative interactions (e.g., hydrogen (H)-bonding) to strengthen the GO/CMC interfaces. When compared with the pristine GO/CMC paper, the cross-linking strategies dramatically reinforce the mechanical properties of our artificial nacres. This special reinforcing effect opens a promising route to strengthen and toughen materials to be applied in aerospace, tissue engineering, and wearable electronic devices, which also has implication for better understanding of the role of these minerals/ions in natural materials for the mechanical improvement.

Ternary Artificial Nacre Reinforced by Ultrathin Amorphous Alumina with Exceptional Mechanical Properties.

A novel ternary artificial nacre is developed through a vacuum-assisted filtration method, with reinforced ultrathin amorphous alumina that is grown in situ on the surface of GO. This ternary artificial nacre simultaneously shows exceptional strength and toughness, which have, up to now, been considered to be mutually exclusive. This novel material will play a role in the structuring of future materials.

Biomechanics analysis of human walking with load carriage.

BACKGROUND: Comprehensive analysis of the inherent laws and the biomechanic principles of human walking with load carriage and building kinematics, and kinematics model of human walking with load carriage, are very meaningful for the development of devices and apparatus that are related to human walking with load carriage, such as a lower limb exoskeleton. OBJECTIVE: The gait experiment of human walking with load carriage is designed and performed in this paper. METHODS: The obtained video is marked and analyzed by using SIMI motion analytical software. The space motion coordinates at each body's mark point that is needed in the kinematics model of established human walking with load carriage is obtained. Based on inverse kinematics, a dynamic model of human walking with load carriage is established. The SPSS statistical analysis software is used for statistical processing for determining key gait parameters. RESULTS: The influence of load and speed on the walking gait parameters is analyzed systematically. CONCLUSIONS: The method provides a theoretical basis for the design of an exoskeleton.