Natural Hierarchical Structure Research Articles

Bioinspired Hierarchical Porous Architecture for Enhanced Kinetics and Mechanical Integrity in Thick Cathode.

Increasing the thickness of the electrodes is considered the primary strategy to elevate battery energy density. However, as the thickness increases, rate performance, cycling performance, and mechanical stability are affected due to the sluggish ion transfer kinetics and compromised structural integrity. Inspired by the natural hierarchical porous structure of trees, electrodes with bioinspired architecture are fabricated to address these challenges. Specifically, electrodes with aligned columns consist of tree-inspired vertical channels, and hierarchical pores are constructed by screen printing and ice-templating, imparting enhanced electrochemical and mechanical performance. Employing an aqueous-based binder, the LiNi0.8Mn0.1Co0.1O2 cathode achieves a high areal energy density of 15.1 mWh cm-2 at a rate of 1C at mass loading of 26.0mg cm-2,benefitting from the multiscale pores that elevated charge transfer kinetics in the thick electrode. The electrodes demonstrate capacity retention of 90% at the 100th cycle at a high current density of 5.2mA cm-2. To understand the mechanisms that promote electrode performance, simplified electro-chemo-mechanical models are developed,the drying process and the charge-discharge process are simulated. The simulation results suggested that the improved performance of the designed electrode benefits from the lower ohmic overpotential and less strain gradient and stress concentration due to the hierarchical porous architecture.

Deep hyperbolic convolutional model for knowledge graph embedding

Recent advancements in knowledge graph embedding have enabled the representation of entities and relations in continuous vector spaces. Performing link prediction on incomplete knowledge graphs using these embeddings has emerged as a challenging task, drawing considerable research interest. Knowledge graphs in the real world typically exhibit a natural hierarchical structure. Hyperbolic embedding methods have shown promising results in modeling hierarchical data, especially in low-dimensional representations. However, existing hyperbolic models for knowledge graph embedding are generally shallow, resulting in limited expressiveness. Additionally, some deep hyperbolic models exist but are often constrained to fixed curvature spaces, which may not optimally capture varying hierarchical structures. In this work, we propose DeER, a novel multi-layer hyperbolic model that leverages a trainable curvature space, marking an advancement in the depth and adaptability of hyperbolic modeling for knowledge graph embeddings. We specifically design a hyperbolic convolutional neural network to learn the heterogeneous interactions between entities and relations within this adaptable hyperbolic space. Additionally, we introduce a hyperbolic feedforward neural network to transform hyperbolic features across multiple layers, enhancing the model’s ability to capture complex hierarchical relationships. Experimental results on three benchmark datasets demonstrate that DeER significantly enhances expressiveness and hierarchical modeling performance when compared to both shallow and other deep baseline approaches.

Activating Adsorption Sites of Waste Crayfish Shells via Chemical Decalcification for Efficient Capturing of Nanoplastics.

The property of being stubborn and degradation resistant makes nanoplastic (NP) pollution a long-standing remaining challenge. Here, we apply a designed top-down strategy to leverage the natural hierarchical structure of waste crayfish shells with exposed functional groups for efficient NP capture. The crayfish shell-based organic skeleton with improved flexibility, strength (14.37 to 60.13 MPa), and toughness (24.61 to 278.98 MJ m-3) was prepared by purposefully removing the inorganic components of crayfish shells through a simple two-step acid-alkali treatment. Due to the activated functional groups (e.g., -NH2, -CONH-, and -OH) and ordered architectures with macropores and nanofibers, this porous crayfish shell exhibited effective removal capability of NPs (72.92 mg g-1) by physical interception and hydrogen bond/electrostatic interactions. Moreover, the sustainability and stability of this porous crayfish shell were demonstrated by the maintained high-capture performance after five cycles. Finally, we provided a postprocessing approach that could convert both porous crayfish shell and NPs into a tough flat sheet. Thus, our feasible top-down engineering strategy combined with promising posttreatment is a powerful contender for a recycling approach with broad application scenarios and clear economic advantages for simultaneously addressing both waste biomass and NP pollutants.

Composite demineralized bone matrix nanofiber scaffolds with hierarchical interconnected networks via eruptive inorganic catalytic decomposition for osteoporotic bone regeneration

Demineralized bone matrix (DBM) is one of the standard biomaterials used to fill surgical bone defects in general orthopedic procedures. However, current DBM products come in the form of powder or viscous solutions that fail to mimic the natural hierarchical structure of bone while also using large amounts of valuable material. To overcome this, compact fibrous DBM/polymer (fDBM) composites were prepared via electrospinning. Then, by exploiting the catalytic decomposition of hydrogen peroxide, oxygen pockets are formed in the scaffold imparting it with a hierarchical porous structure similar to bone (Op-fDBM). These pockets created by bubbles of oxygen help give the scaffold a mechanically stable shape while the incorporated DBM supports cell adhesion and growth. In vivo evaluations reveal that fDBM increased bone volume by 41.7 % while Op-fDBM increased bone volume by 68.6 %. Significant increases in regenerated bone volume with the use of minimal amounts of DBM in fiber form go to show the great potential of this work in the field of bone regeneration.

Environmentally-friendly preparation of natural hollow carbon spheres derived from a biomass puffball for in situ upgrading of lignin-derived vanillin

Biomass appears to be a potential candidate for the preparation of porous carbon materials with wide applications for catalytic fields due to its low price, green sustainability and natural hierarchical porous structure.

Revisiting hemodynamics and blood oxygenation in a microfluidic microvasculature replica

The complexity of microvascular circulation has led to the development of advanced imaging techniques and biomimetic models. This study developed a multifaceted microfluidic-based microdevice as an in vitro model of microvasculature to replicate important geometric and functional features of in vivo perfusion in mice. The microfluidic device consisted of a microchannel for blood perfusion, mirroring the natural hierarchical branching vascular structures found in mice. Additionally, the device incorporated a steady gradient of oxygen (O2) which diffused through the polydimethylsiloxane (PDMS) layer, allowing for dynamic blood oxygenation. The assembled multi-layered microdevice was accompanied by a dual-modal imaging system that combined laser speckle contrast imaging (LSCI) and intrinsic signal optical imaging (ISOI) to visualize full-field blood flow distributions and blood O2 profiles. By closely reproducing in vivo blood perfusion and oxygenation conditions, this microvasculature model, in conjunction with numerical simulation results, can provide quantitative information on physiologically relevant hemodynamics and key O2 transport parameters that are not directly measurable in traditional animal studies.

Bio-inspired dual-responsive photonic crystal with smart responsive hydrogel for pH and temperature detection

Responsive photonic crystals (PCs) with bio-inspired microstructures and tailorable functionalities are of critical importance for their potential applications in diverse fields such as biological detection, sensing, decoration, anti-counterfeiting, etc. However, limited by preparation technologies and design theories, it is still a challenge to accurately and uniformly deposit smart responsive materials on natural PC structures and achieve dual stimulus response. Herein, a simple and rapid in situ polymerization method is presented for preparing dual-responsive PCs with ultra-precise micro-/nanoscale hierarchical structures. Exposure of the reaction site by deacetylation of Morpho butterfly wings allows in situ polymerisation of poly (N-isopropylacrylamide-co-acrylic acid) (P(NIPAAM-co-AAc)) on the surface of the natural photonic structure. The obtained P(NIPAAM-co-AAc) photonic crystals (P(NIPAAM-co-AAc)-PCs) exhibited a dual response to pH and temperature reversibility. In addition, the synergistic effect of the structures and materials on the optical response of the natural PCs is revealed. This work allows the combination of natural hierarchical PC structures with smart hydrogel to achieve an optical response to pH and temperature, thus opening up the channels for responsive PC to multiple stimulus responses.

High performance aqueous asymmetric supercapacitors developed by interfacial engineering wood-derived nanostructured electrodes

Supercapacitors (SCs) are becoming new candidates in the field of sustainable energy supply. Nevertheless, the unsatisfactory energy density due to the narrow voltage window of the supercapacitor is the main barrier to its practical application. Developing appropriate electrode materials to improve the electrochemical performance of SCs and broaden the operating voltage of supercapacitors are imperative. Herein, compatible interfacial engineering wood-derived nanostructured electrodes for aqueous asymmetric supercapacitors (AASCs) are demonstrated. The 3D carbonized wood matrix serves as a high specific surface area current collector and a porous host for the high capacitive active substance, which is composed of manganese dioxide (MnO2) nanowires and polyaniline (PANI) nanoparticles grown uniformly on the porous wall of aligned microchannels (CW@MnO2 and CW@PANI). The resulting electrochemical exchange reactive sites enable the positive electrode to deliver a high areal capacitance of 729 mF cm−2 at 1 mA cm−2 (369 F g−1 at 0.5 A g−1). The negative electrode delivers a high areal capacitance of 1721 mF cm−2 at 1 mA cm−2 (848 F g−1 at 0.5 A g−1). The areal capacitance of two electrodes is superior to most reported supercapacitor electrodes. Additionally, the assembled CW@MnO2//CW@PANI AASC achieves a desirable energy density (170.84 μWh cm−2 at a power density of 0.5 mW cm−2) because a considerable work function difference between electrodes achieved a 2 V wide voltage window. The results of this study provide a critical benchmark and optimistic incentives to adopt natural hierarchical structures to enhance the performance of new-generation energy-related systems.

A Versatile 2D Cellulose Platform Strategy from Natural Wood Scaffold.

A wood cell wall with cellulose as the key scaffold is a natural hierarchical lamellar structure. This wood-derived cellulose scaffold has recently attracted enormous attention and interest, but almost all efforts have been devoted to its whole tissue functionalization. Here, we report the short ultrasonic processing of a wood cellulose scaffold to directly generate 2D cellulose materials. The obtained 2D cellulose nanosheets consist of many highly oriented fibrils densely arranged and can be further converted to ultrathin 2D carbon nanosheets. The nanoparticles, nickel-iron layer double hydroxide nanoflowers, manganese dioxide nanorods, and zinc oxide nanostars, are successfully loaded in the 2D nanosheet, providing a versatile 2D platform strategy for excellent 2D hybrid nanomaterials.

Robust, Fire-Retardant, and Water-Resistant Wood/Polyimide Composite Aerogels with a Hierarchical Pore Structure for Thermal Insulation.

The use of energy-saving materials is an effective strategy for decreasing energy consumption and carbon emission. Wood is a type of biomass material with a natural hierarchical structure, which results in its high thermal insulation. It has been widely used in construction. However, developing wood-based materials without flammability and dimensional instability is still a challenge. Herein, we developed a wood/polyimide composite aerogel with a well-preserved hierarchical pore structure and dense hydrogen bonds inside, resulting in its excellent chemical compatibility and strong interfacial interactions between its two components. This novel wood-based composite was fabricated by removing most hemicellulose and lignin from natural wood, followed by the fast impregnation using an 'in situ gel' process. The introduction of polyimide into delignified wood substantially improved its mechanical properties, with the compression resistance being improved by over five times. Notably, the thermal conductivity coefficient of the developed composite was approximately half that of natural wood. Furthermore, the composite exhibited excellent fire-retardancy, hydrophobicity, thermal insulation, and mechanical properties. This study provides a novel method for wood modification, which not only aids interfacial compatibility between wood and polyimide but also retains the properties of the two components. The developed composite can effectively reduce energy consumption, making it promising for practical and complex thermal insulation applications.

Magnetic hierarchically porous biomass carbon for realizing broadband and strong absorption of electromagnetic wave

Hierarchically porous carbon materials provide favorable conditions for electromagnetic wave loss enhancement due to the superimposed positive influence of multilevel pores. However, high production costs and complex preparation limit their large-scale production. Biomass carbon with a natural hierarchically porous structure offers an alternative; however, the impedance mismatch and single-loss mechanism prevent biomass carbon from being an ideal absorbent for broadband and strong absorption. In this study, a series of magnetic hierarchically porous biomass carbons were prepared using a facile adsorption-inert calcination method. The natural hierarchical porous structure of the loofah sponge provides numerous adsorption sites for ferric ions, which are transformed in situ into Fe3O4 during calcination to regulate the conductivity. The impedance matching and electromagnetic loss properties of the biomass carbon/Fe3O4 composites were adjusted by varying the amount of ferric nitrate. Optimal performance occurs when ferric nitrate weighs 0.8 g, and the calcination temperature is 600 °C. Under these conditions, the effective absorption bandwidth reaches 5.28 GHz (11.84–17.12 GHz, 2.5 mm), and the minimum reflection loss (RLmin) is as low as −52.54 dB (4.5 mm), which is achieved by superior impedance matching and strong conduction loss together with polarization loss due heterogeneous interfaces and carbon defects. Our work provides a new perspective and a simple method for the large-scale production of high-efficiency biomass-based electromagnetic wave absorbents.

Nitrogen-rich Graphite Flake from Hemp as Anode Material for High Performance Lithium-ion Batteries.

Biomass-derived carbon (BC) has attracted extensive attention as anode material for lithium ion batteries (LiBs) due to its natural hierarchical porous structure and rich heteroatoms that can adsorb Li+ . However, the specific surface area of pure biomass carbon is generally small, so we can help NH3 and inorganic acid produced by urea decomposition to strip biomass, improve its specific surface area and enrich nitrogen elements. The nitrogen-rich graphite flake obtained by the above treatment of hemp is named NGF. The product that has a high nitrogen content of 10.12% has a high specific surface area of 1151.1 m2 g-1 . In the lithium ion battery test, the capacity of NGF is 806.6 mAh g-1 at 30 mA g-1 , which is twice than that of BC. NGF also showed excellent performance that is 429.2 mAh g-1 under high current testing at 2000 mA g-1 . The reaction process kinetics is analyzed and we found that the outstanding rate performance is attributed to the large-scale capacitance control. In addition, the results of the constant current intermittent titration test indicate that the diffusion coefficient of NGF is greater than that of BC. This work proposes a simple method of nitrogen-rich activated carbon, which has a significantly commercial prospect.

The structure evolution from intrinsic micro-nano skeleton of natural wood to hierarchical porous carbon

The natural hierarchical pore structure existing in biomass provides favorable foundation for the design and preparation of carbon materials with 3D structure. However, it remains a challenge to understand the structure evolution from intrinsic micro-nano skeleton of natural wood to hierarchical porous carbon. In this study, a unique delignification process was used to remove lignin and hemicellulose without damaging the bulk structure of cellulose. The effects of the delignification process on pore structure during carbonization and activation were examined. It was found that biochar with fine micropores and hierarchical pores could be prepared through controlled dissolution of lignin, resulting in an SBET and Vtotal of 880 m2/g and 0.36 cm3/g respectively. The developed micropores then contributed to improved gas diffusion during the activation process, leading to mesoporous carbon materials with an SBET of 1310 m2/g and Vtotal of 1.08 cm3/g after 30 min. This research shed light on understanding how natural wood can be converted into hierarchical porous carbon by removing lignin followed by CO2 activation, significantly improving its potential for use as a porous material.

Nanosilk Template-Guided/Induced Construction of Brush-/Flower-like 3D Nanostructures.

Biomaterials with natural hierarchical structures typically exhibit extraordinary properties because of their multilevel structural designs. They offer many templates and models as well as inspiration for material design, particularly for fabricating structure-regulated, performance-enhanced, and function-enriched materials. Biopolymer-based nanocomposites with ingenious nanostructures constructed through ecofriendly and sustainable approaches are highly desirable to meet the multifunctional requirements of developing bioinspired materials. Herein, an all-silk fibroin-based nanocomposite with a brush-like nanostructure was constructed for the first time using a nanotemplate-guided assembly approach in which dissolved silk assembled directly on a silk nanowhisker (SNW) backbone to form peculiar nanobrushes based on the classical micelle model. Three-dimensional spider-like or centipede-like silk nanobrushes (SNBs) were fabricated by varying the SNW backbone length from 0.16 to 6 μm. The branches with average lengths of 32-290 nm were also adjustable. SNBs were further designed to regulate and induce biomineralization of hydroxyapatite (HAP) to form interesting flower-like nanostructures, in which the HAP nanosphere (diameters ∼16 nm) "core" was covered by SNBs with branches extending to form a "shell" (∼101 nm in length). Based on such protein nanotemplate-guided formation of nanoscale structures, practical hollow conduits with remarkable mechanical properties, biocompatibility, shape memory behavior, and bone engineering potential were fabricated. This study inspires the design of polymorphous biopolymer-based nanostructures with enhanced performance at multiple length scales where the weaknesses of individual building blocks are offset.

Design of experiments as a tool to guide the preparation of tailor-made activated carbons

Activated carbon produced from biomass exhibits a high specific surface area due to the natural hierarchical porous structure of the precursor material. To reduce production costs of activated carbon, bio-waste materials receive more and more attention, which has led to a steep increase in the number of publications over the past decade. However, the characteristics of activated carbon are highly dependent on the properties of the precursor material used, making it difficult to draw assumptions about activation conditions for new precursor materials based on published work. Here, we introduce a Design of Experiment methodology with a Central Composite Design to better predict the properties of activated carbons from biomass. As a model precursor, we employ well-defined regenerated cellulose-based fibers which contain 25 wt.% chitosan as intrinsic dehydration catalyst and nitrogen donor. The use of the DoE methodology opens up the possibility to better identify the crucial dependencies between activation temperature and impregnation ratio on the yield, surface morphology, porosity and chemical composition of the activated carbon, independent of the used biomass. The use of DoE yields contour plots, which allows for more facile analysis on correlations between activation conditions and activated carbon properties, thus enabling its tailor-made manufacturing.

Spatio-temporal hierarchical MLP network for traffic forecasting

Traffic forecasting is an indispensable part of intelligent transportation systems. However, existing methods suffer from limited capability in capturing hierarchical temporal characteristics of the traffic time series. To be specific, they neglect the property that the time series is composed of trend-cyclical and seasonal parts. On the other hand, prior methods ignore the natural hierarchical structure of traffic road networks and thus fail to capture the macro spatial dependence of region networks. To address these issues, we propose a novel spatio-temporal hierarchical MLP network (STHMLP) for traffic forecasting. By adopting a decomposition architecture in the STHMLP, trend-cyclical and seasonal features are gradually grasped from multi-scale local compositions of traffic time series. For each scale of traffic time series, we design a fine module and a coarse module to extract spatio-temporal information from roads and regions, respectively. Specifically, the fine module utilizes spatial filters on the frequency domain features of traffic time series to efficiently capture fine-grained spatial dependencies. The coarse module adaptively coarsens road networks to region networks and captures coarse-grained spatial dependencies from region networks. Experiments on four real-world traffic datasets demonstrate the STHMLP outperforms state-of-the-art baselines on traffic forecasting.

Molecular insights on the crystalline cellulose-water interfaces via three-dimensional atomic force microscopy.

Cellulose, a renewable structural biopolymer, is ubiquitous in nature and is the basic reinforcement component of the natural hierarchical structures of living plants, bacteria, and tunicates. However, a detailed picture of the crystalline cellulose surface at the molecular level is still unavailable. Here, using atomic force microscopy (AFM) and molecular dynamics (MD) simulations, we revealed the molecular details of the cellulose chain arrangements on the surfaces of individual cellulose nanocrystals (CNCs) in water. Furthermore, we visualized the three-dimensional (3D) local arrangement of water molecules near the CNC surface using 3D AFM. AFM experiments and MD simulations showed anisotropic water structuring, as determined by the surface topologies and exposed chemical moieties. These findings provide important insights into our understanding of the interfacial interactions between CNCs and water at the molecular level. This may allow the establishment of the structure-property relationship of CNCs extracted from various biomass sources.

Power to Detect Moderated Effects in Studies with Three-Level Partially Nested Data

Comprehensive evaluation of treatment effects is aided by considerations for moderated effects. In educational research, the combination of natural hierarchical structures and prevalence of group-administered or shared facilitator treatments often produces three-level partially nested data structures. Literature details planning strategies for a variety of experimental designs when moderation effects are of interest but has yet to establish power formulas for detecting moderation effects in three-level partially nested designs. To address this gap, we derive and assess the accuracy of power formulas for detecting the different types of moderation effects possible in these designs. Using Monte Carlo simulation studies, we probe power rates and adequate sample sizes for detecting the different moderation effects while varying common influential factors including variance in the outcome explained by covariates, magnitude of the moderation effect, and sample sizes. The power formulas developed improve the planning of experimental studies with partial nesting and encourage the inclusion of moderator variables to capture for whom and under what conditions a treatment is effective. Educational researchers also have some initial guidance regarding adequate sample sizes and the factors that influence detecting moderation effects in three-level partially nested designs.

Lightweight, stiff and Heat-Resistant Bamboo-Derived carbon scaffolds with gradient aligned microchannels for highly efficient EMI shielding

Advanced multifunctional electromagnetic interference (EMI) shielding materials with lightweight, stiff, heat-resistant and superb shielding performance features are highly desired to eliminate the increasingly serious EM pollution. Herein, a series of bamboo-derived carbon scaffolds with naturally optimized anisotropic, hierarchical gradient and aligned microchannels are successfully fabricated as shielding materials through pyrolysis. The 3-mm thick pyrolyzed bamboo charcoal exhibits an ultrahigh shielding effectiveness (SE) of 81.52 dB, which can be significantly improved to a superb level of 95.67 dB, with the SEA value accounting for 93.71%, by endowing the charcoal with a more porous structure and an extra magnetic loss. The specific SE reaches 1823–2676 dB cm2 g−1, and the normalized SE achieves 75.55 dB/mm, which is higher than those of other carbon scaffolds produced to date. Such excellent shielding performance is mainly attributed to the ingenious combination of dielectric loss, the natural hierarchical gradient structure, the anisotropic pore effect, and magnetic loss. More importantly, the bamboo-derived carbon scaffold features robust compressive strength (35.97 MPa), ultralow thermal conductivity (0.161 W m−1 K−1), and high thermal structural stability (500 °C in air). This study paves the way for the utilization of natural green bamboo-based porous carbon scaffolds as multifunctional high-performance shielding materials.

A feather-inspired interleaf for enhanced interlaminar fracture toughness of carbon fiber reinforced polymer composites

Carbon fiber reinforced polymer (CFRP) composites with lightweight, high-strength and high-modulus properties are in high demand across the fields of aerospace engineering , urban mass transit, new energy and architectural design . However, most CFRP composites suffer from delamination owing to the weak interlayer which plays an important role to transfer perpendicular load to plies. Here, inspired by natural hierarchical structures of feathers, a novel interleaf towards conventional CFRP composites was rationally designed and experimentally proved to be effective for significant enhancement of anti-delamination performance. Interestingly, ZnO nanorods grown on the electrospun nanofibrous mats and carbon fiber bundles formed a kind of cross-scale structure system. It was very similar to the natural hierarchical structures of feathers with rachis, barbs and barbules. Experimental results verified that the introduced hierarchical structures assuredly enhanced the interlayer toughening performance via substantial energy dissipation . When compared with original CFRP composites, the obtained CFRP composites with a feather-inspired interleaf exhibited significantly improved mechanical performance in Mode I and Mode II interlaminar fracture toughness . The proposed bio-inspired design philosophy and feasible fabrication method are anticipated to provide an industry-friendly way to effectively improve the mechanical performance of traditional CFRP composites and promote potential large-scale applications of bio-inspired CFRP composites in the broad engineering field. TOC: Inspired by natural hierarchical structure of feathers, a novel interleaf was designed and fabricated to enhance the mechanical performance of CFRP laminates, which provides a promising and versatile design strategy for the effective mechanical improvement of laminated composites.