Design Of Hierarchical Structures Research Articles

A Dry Patch with In Situ Solid-to-Gel Transformation for All-in-One Skin Wound Care.

Hydrogel-based dressing materials offer significant potential in expediting skin wound healing. Nevertheless, they face several challenges: poor adhesion to wound tissues, difficulties in preservation under ambient conditions, and limited multifunctionality to support all wound healing stages. In this work, a dry patch is designed to address these persistent issues by featuring an in situ solid-to-gel transformation and Janus wet tissue adhesiveness. The HGP patch integrates a wet adhesive layer combining dopamine-conjugated hyaluronic acid (HD) and poly(acrylic acid) (PAA), a drug-loading layer comprising gelatin (Gel), and a nonadhesive gelation layer of poly(vinyl alcohol) (PVA) and sodium alginate (SA). This hierarchical structural design confers exceptional wound adhesion, hemostatic capabilities, and antibacterial and antioxidant activities, as well as immune regulatory properties. These attributes collectively support accelerated skin wound healing, particularly in cases complicated by bacterial infections. This research charts an approach to engineer hydrogel-based wound dressings through on-site hydrogel formation, thus advancing the treatment of wounds afflicted with complex infections.

3D printed feathers with embedded aerodynamic sensing

Bird flight is often characterized by outstanding aerodynamic efficiency, agility and adaptivity in dynamic conditions. Feathers play an integral role in facilitating these aspects of performance, and the benefits feathers provide largely derive from their intricate and hierarchical structures. Although research has been attempted on developing membrane-type artificial feathers for bio-inspired aircraft and micro air vehicles (MAVs), fabricating anatomically accurate artificial feathers to fully exploit the advantages of feathers has not been achieved. Here, we present our 3D printed artificial feathers consisting of hierarchical vane structures with feature dimensions spanning from 10-2to 102mm, which have remarkable structural, mechanical and aerodynamic resemblance to natural feathers. The multi-step, multi-scale 3D printing process used in this work can provide scalability for the fabrication of artificial feathers tailored to the specific size requirements of aircraft wings. Moreover, we provide the printed feathers with embedded aerodynamic sensing ability through the integration of customized piezoresistive and piezoelectric transducers for strain and vibration measurements, respectively. Hence, the 3D printed feather transducers combine the aerodynamic advantages from the hierarchical feather structure design with additional aerodynamic sensing capabilities, which can be utilized in future biomechanical studies on birds and can contribute to advancements in high-performance adaptive MAVs.

Hierarchical Ordered Mesoporous Sr2Bi4Ti5O18 Microflowers with Rich Oxygen Vacancies In Situ Assembled by Nanosheets for Piezo-Photocatalysis.

The Aurivillius phase layered perovskite ferroelectric material Sr2Bi4Ti5O18 (SBTO) exhibits spontaneous polarization and piezoelectric properties, which confer significant potential for piezo-photocatalysis. Its ability to enhance electron-hole separation while providing excellent fatigue resistance positions it as a promising candidate in this field. Defects were introduced to improve the structural polarization and photoelectrochemical properties of SBTO. SBTO nanocrystals, featuring a mixed structure of hierarchically ordered mesoporous microflowers and nanosheets, were successfully synthesized via the hydrothermal method. The SBTO sample synthesized at a lower hydrothermal temperature displayed optimal oxygen vacancy concentration and exhibited superior piezoelectric-photo synergistic degradation activity for organic pollutants. Additionally, corona polarization increases the macroscopic polarization of the SBTO photocatalyst, promoting the separation of photogenerated carriers. Finite element simulations confirmed that a single flower-like SBTO structure generates a higher piezoelectric potential compared to a sheet-like morphology. In conclusion, integrating self-assembled hierarchical structure design, ferroelectric polarization, and defect engineering forms an effective strategy for achieving high-performance SBTO-based layered perovskite piezo-photocatalysts.

Magneto-Dielectric Synergy and Multiscale Hierarchical Structure Design Enable Flexible Multipurpose Microwave Absorption and Infrared Stealth Compatibility

HighlightsA multiscale hierarchical structure design, integrating wrinkled MXene radar-infrared shielding layer and flexible Fe3O4@C/PDMS microwave absorption layerThe assembled stealth devices realize a near-perfect stealth capability in both X-band (8-12 GHz) and long-wave infrared (8-14 µm) wavelength ranges.The optimal device demonstrates exceptional curved surface conformability, self-cleaning capability (contact angle ≈ 129°), and abrasion resistance (recovery time ≈ 5 s).

Jellyfish-Inspired Polyurea Ionogel with Mechanical Robustness, Self-Healing, and Fluorescence Enabled by Hyperbranched Cluster Aggregates.

Ionogels are promising for soft iontronics, with their network structure playing a pivotal role in determining their performance and potential applications. However, simultaneously achieving mechanical toughness, low hysteresis, self-healing, and fluorescence using existing network structures is challenging. Drawing inspiration from jellyfish, we propose a novel hierarchical crosslinking network structure design for in situ formation of hyperbranched cluster aggregates (HCA) to fabricate polyurea ionogels to overcome these challenges. Leveraging the disparate reactivity of isocyanate groups, we induce the in situ formation of HCA through competing reactions, enhancing toughness and imparting the clustering-triggered emission of ionogel. This synergy between supramolecular interactions in the network and plasticizing effect in ionic liquid leads to reduced hysteresis of the ionogel. Furthermore, the incorporation of NCO-terminated prepolymer with dynamic oxime-urethane bonds (NPU) enables self-healing and enhances stretchability. Our investigations highlight the significant influence of HCA on ionogel performance, showcasing mechanical robustness including high strength (3.5 MPa), exceptional toughness (5.5 MJ m-3), resistance to puncture, and low hysteresis, self-healing, as well as fluorescence, surpassing conventional dynamic crosslinking approaches. This network design strategy is versatile and can meet the various demands of flexible electronics applications.

Co-crosslinking and anchoring strategy: One-step preparation of N-doped porous carbon for supercapacitors and zinc ion hybrid capacitors

Porous carbon has been widely used in aqueous capacitors due to its wide source, high stability, and controllable preparation. However, the two-step preparation strategy of carbonization and activation with complex operation and serious energy consumption severely limits its further application. In this paper, resorcinol/urea-furfural resin was successfully prepared by using cleaner and greener furfural as raw material and co-crosslinking with resorcinol and urea under the action of catalyst. It is noteworthy that during the curing process, KOH is uniformly anchored inside the resin, so the system only needs one-step high-temperature pyrolysis to obtain a N-doped ant-nest-like three-dimensional interconnected porous carbon material. Consequently, the porous carbon exhibited an impressive specific capacitance of 283F g−1. The assembled symmetrical device shows a capacitance retention of 92 % after 50 000 cycles, showing excellent cycle stability. In addition, the assembled zinc ion hybrid capacitor exhibits a capacitance of 138 mAh g−1 and an energy density of 111 Wh kg−1. The one-step carbonization-doping-activation strategy of this bottom-up in-situ anchoring activator will provide further insights into the hierarchical pore structure design of porous carbon and facilitate the simple and efficient preparation of carbon materials.

Structural design and characterization of hybrid hierarchical lattice structures based on sheet-network Triply periodic Minimal surface topology

The ability to adjust topological features of lattice structures offers a great potential to finely calibrate their physical and mechanical response to precisely meet specific requirements. This study explores a new topological design that leverages the internal porosity of Triply Periodic Minimal Surfaces (TPMS) unit cells to optimize and control their mechanical properties. A smaller-scale TPMS lattice structure was integrated within the internal volume of the sheet-network Schwarz Primitive TPMS cell, culminating in a hybrid hierarchical architecture. Various TPMS topologies with distinct mechanical behavior and varying relative density combinations were examined. Experimental and numerical approaches were developed to reveal the structure’s deformation behaviour and quantify stiffness, anisotropy, quasi-static uniaxial compressive strength, and energy absorption capacity. The topological design of the internal lattice was found to play a key role in defining the mechanical performance of the integrated structures, leading to enhanced energy absorption up to 4 times that of the reference structure. Moreover, all the studied hierarchical topologies exhibited a lower Emax/Emin ratio in comparison to the reference topology, indicating more isotropic performance of the hybrid designs (upto 40% reduction of anisotropy). The findings underscore the significant promise of hybrid hierarchical design methodologies in attaining lattice structures with tailored properties.

Bioinspired Bouligand-Structured Cellulose Nanocrystals/Poly(vinyl alcohol) Composite Hydrogel for Enhanced Impact Resistance.

Impact-protective materials are gaining importance because of the widespread occurrence of impact damage. Hydrogels have emerged as promising candidates owing to their lightweight and flexible nature. However, achieving soft impact-resistant hydrogels with exceptional stiffness, strength, and toughness remains a challenge. Inspired by the Bouligand structure found in the smasher dactyl club of stomatopods, we propose a straightforward multiscale hierarchical structural design strategy. This strategy integrates self-assembly and salting-out techniques to enhance the impact resistance of soft hydrogels. Rigid cellulose nanocrystals (CNCs) self-assemble into Bouligand-like structures within soft poly(vinyl alcohol) (PVA) matrix via supramolecular interactions. This rational structural design combines the CNC Bouligand structure with a cross-linked network of soft PVA crystalline domains, resulting in a composite hydrogel with impressive mechanical properties: high tensile fracture strength (30.2 MPa), elastic modulus (62.7 MPa), and fracture energy (75.6 kJ m-2), surpassing those of other tough hydrogels. Moreover, the multiscale hierarchical structure facilitates various energy dissipation mechanisms, including crack twisting, tortuous crack paths, and PVA chain orientation, resulting in notable force attenuation (80.4%) in the composite hydrogel. This biomimetic design strategy opens new avenues for developing soft and lightweight impact-resistant materials.

Jellyfish‐Inspired Polyurea Ionogel with Mechanical Robustness, Self‐Healing, and Fluorescence Enabled by Hyperbranched Cluster Aggregates

AbstractIonogels are promising for soft iontronics, with their network structure playing a pivotal role in determining their performance and potential applications. However, simultaneously achieving mechanical toughness, low hysteresis, self‐healing, and fluorescence using existing network structures is challenging. Drawing inspiration from jellyfish, we propose a novel hierarchical crosslinking network structure design for in situ formation of hyperbranched cluster aggregates (HCA) to fabricate polyurea ionogels to overcome these challenges. Leveraging the disparate reactivity of isocyanate groups, we induce the in situ formation of HCA through competing reactions, enhancing toughness and imparting the clustering‐triggered emission of ionogel. This synergy between supramolecular interactions in the network and plasticizing effect in ionic liquid leads to reduced hysteresis of the ionogel. Furthermore, the incorporation of NCO‐terminated prepolymer with dynamic oxime–urethane bonds (NPU) enables self‐healing and enhances stretchability. Our investigations highlight the significant influence of HCA on ionogel performance, showcasing mechanical robustness including high strength (3.5 MPa), exceptional toughness (5.5 MJ m−3), resistance to puncture, and low hysteresis, self‐healing, as well as fluorescence, surpassing conventional dynamic crosslinking approaches. This network design strategy is versatile and can meet the various demands of flexible electronics applications.

Hierarchical porous structure design and water activation in hydrogels containing hyperbranched peach gum polysaccharide for efficient solar water evaporation

Solar-powered interfacial evaporation is a developing and sustainable technique increasingly utilized in desalination and wastewater purification. This technology involves the creation of cellulose nanofiber (CNF)/polylactic acid (PLA) composite aerogels through the Pickering emulsion approach. Self-floating aero-hydrogel (E-VGP) with a hierarchical porous structure was formed on a viscous mixture containing polyvinyl alcohol (PVA), peach gum polysaccharide (PGP), and polypyrrole (PPy) via an in-situ polymerization process. Furthermore, by modifying the hydrolysis time of PGP with a hyperbranched polyhydroxy structure, VGP hybrid hydrogels of varying microscopic molecular sizes were produced. Additionally, solar vapor generators (SVG) with diverse macroscopic structures were fabricated using molds. The V8G4-12hP0.2 hybrid hydrogel, synthesized using PGP hydrolyzed for 12 h, exhibited an evaporation enthalpy of water at 1204 J g−1. This capacity effectively activates water and enables low enthalpy evaporation. Conversely, the macrostructural design allows the cylindrical rod raised sundial-shaped structure of SVG3 to possess an expanded evaporation area, minimize energy loss, and even harness additional energy from its nonradiative side. Consequently, this micro-macrostructural design enables SVG3 to attain an exceptionally high evaporation rate of 3.13 kg m−2 h−1 under 1 Sun exposure. Moreover, SVG3 demonstrates robust water purification abilities, suggesting significant potential for application in both desalination and industrial wastewater treatment.

Polyphenol-assisted construction of hierarchical microstructure on membrane surface with self-cleaning properties for highly efficient oil/water separation

Rational design of hydrophilic hierarchical structures on the membrane surface is a promising method to improve oil/water separation efficiency. However, oil droplets with intrinsic adhesion tend to accumulate on the membrane surface, which deteriorates membrane performance. In this study, tannic acid-Zn(II) complex was homogeneously anchored on the PVDF membrane surface and further in situ converted to ZIF-8 in the presence of 2-methylimidazole. Subsequently, Cu ion exchange was employed to transfer ZIF-8 layer to gerhardtite (Cu2(OH)3NO3) with a hierarchical structure. Accordingly, the as-prepared PVDF/TA-gerhardtite membrane possessed attractive hydrophilicity and underwater superoleophobicity with oil contact angles above 150°, therefore achieving over 98 % oil rejection towards various surfactant stabilized oil-in-water emulsions. Moreover, self-cleaning properties can be realized by activating peroxymonosulfate, and 97 % of tetracycline hydrochloride, the target pollutant, was degraded within 30 min owing to the generation of sulfate radicals and hydroxyl radicals. Due to the attractive hydrophilicity and catalytic oxidation capacity of the gerhardtite hierarchical structure, degradation and bubble generation induced fouling recovery was accomplished after PMS cleaning, and the irreversible fouling decreased to 2.2 % after consecutive soybean oil fouling. Therefore, this work provides new insights into the construction of hierarchical structures on membrane surfaces and demonstrates their potential applications in oil/water separation and fouling mitigation.

Pushing the Operation Current Density of Alkaline Water Oxidation above 1 A cm2 via Electrocatalyst Engineering

AbstractRapid cost reduction of green hydrogen is essential for the large‐scale deployment of hydrogen‐based energy system. A major component in achieving this is the development of advanced water electrolyzers. Sluggish oxygen evolution reaction (OER) is the bottleneck for water electrolysis, and tremendous efforts have been devoted to develop electrocatalysts that accelerate the OER kinetics. Recent advances have highlighted the potential of precious metal‐free OER electrocatalyst capable of stable operation at current densities above 1 A cm2. This brings an opportunity of constructing new‐generation electrolyzer with lower cost and higher productivity. However, achieving such high operating current densities presents new challenges. This review summarize the recent progress of high‐performance OER catalysts, and identifies key factors that can be leveraged to enhance catalyst activity. These factors include interface/surface engineering, amorphous and crystal phase coupling, hierarchical structure design, structural reconstruction and phase conversion, high entropy catalyst, and defect engineering. Additionally, the pressing challenges that have been largely ignored in previous research is addressed, such as sustaining long‐term stability under crucial conditions, disadvantages of immobilized powder electrocatalysts, electrode scale design, the necessity of designing innovative electrolyzer cell designs and advance characterization techniques.

Design of hierarchical multi-cell double circular tubes thin-walled structures for energy absorption

This study aims to investigate the crashworthiness performance of a novel hierarchical multi-cell double circular tubes (HMDC) structure under axial impact. Various dual-tube structures of different cross-sections were designed. The effects of hierarchical order, peak number of the core column, and inner circle diameter on the structure were analyzed using Abaqus finite element analysis. The results indicate that in dual-tube structures, replacing the traditional multi-cell structure with a hierarchical multi-cell structure in the interlayer significantly improves energy absorption (EA) characteristics. With the inner circle diameter of the HMDC fixed at 20 mm, the ratio of mean crushing force (MCF) to peak crushing force at the third order increased by 70.70% and 35.68% compared to the first and second orders, respectively. Experimental results and finite element results show that the initial peak value differed by 1.47%, indicating a close match between the experimental and simulation results. The parametric study shows that the inner circle diameter and the peak number of the core column significantly affect EA. The findings of this study provide effective guidance for designing multi-cell dual circular tubes with high EA efficiency.

Dielectric performance improvement of polypropylene film by hierarchical structure design for metallized film capacitors

In this paper, hierarchical structure design method is proposed for improving the dielectric performance of polypropylene (PP) for metallized film capacitors. The results show that the composite film with 0.02 wt% terephthalaldehyde doping and functional layer thickness occupying 25% shows the best dielectric properties. The leakage conductivity declines by 89.0%–94.3%, the DC breakdown strength grows by 15.6%–19.7% and the discharged energy density improves by 50.6%–53.4%. Terephthalaldehyde doping introduces sites that could capture free holes, thereby blocking the carrier migration path. The hierarchical structure design results in the holes accumulating in the functional layer and the reverse electric field formed suppresses the charge injection from the anode. Furthermore, the probability of intrinsic charge excitation due to the band gap width reduction is greatly reduced. The method provides a reference for improving the dielectric performance of PP films from the perspective of regulating the charge transmission behavior.

A High-Performance Passive Radiative Cooling Metafabric with Janus Wettability and Thermal Conduction.

With the development of industry and global warming, passive radiative cooling textiles have recently drawn great interest owing to saving energy consumption and preventing heat-related illnesses. Nevertheless, existing cooling textiles often lack efficient sweat management capacity and wearable comfort under many practical conditions. Herein, a hierarchical cooling metafabric that integrates passive radiation, thermal conduction, sweat evaporation, and excellent wearable comfort is reported through an electrospinning strategy. The metafabric presents excellent solar reflectivity (99.7%, 0.3-2.5µm) and selective infrared radiation (92.4%, 8-13µm), given that the unique optical nature of materials and wettability gradient/micro-nano hierarchical structure design. The strong moisture-wicking effect (water vapor transmission (WVT) of 2985g m-2 d-1 and directional water transport index (R) of 1029.8%) and high heat-conduction capacity can synergistically enhance the radiative cooling efficiency of the metafabric. The outdoor experiment reveals that the metafabric can obtain cooling temperatures of 13.8°C and 19.3°C in the dry and sweating state, respectively. Meanwhile, the metafabric saves ≈19.3% of annual energy consumption compared with the buildings with HAVC systems in Shanghai. The metafabric also demonstrates desirable breathability, mechanical strength, and washability. The cost-effective and high-performance metafabric may offer a novel avenue for developing next-generation personal cooling textiles.

Hierarchical Bilayer Polyelectrolyte Ion Paper Conductor for Moisture-Induced Power Generation.

Harvesting energy from air water (atmospheric moisture) promises a sustainable self-powered system without any restrictions from specific environmental requirements (e.g., solar cells, hydroelectric, or thermoelectric devices). However, the present moisture-induced power devices traditionally generate intermittent or bursts of energy, especially for much lower current outputs (generally keeping at nA or μA levels) from the ambient environment, typically suffering from inferior ionic conductivity and poor hierarchical structure design for manipulating sustained air water and ion-charge transport. Here, we demonstrate a universal strategy to design a high-performance bilayer polyelectrolyte ion paper conductor for generating continuous electric power from ambient humidity. The generator can produce a continuous voltage of up to 0.74 V and also an exceptional current of 5.63 mA across a single 1.0 mm-thick ion paper conductor. We discover that the sandwiched LiCl-nanocellulose-engineered paper promises an ion-transport junction between the negatively and positively charged bilayer polyelectrolytes for application in MEGs with both high voltage and high current outputs. Moreover, we demonstrated the universality of this bilayer sandwich nanocellulose-salt engineering strategy with other anions and cations, exhibiting similar power generation ability, indicating that it could be the next generation of sustainable MEGs with low cost, easier operation, and high performance.

Hierarchical structural design towards stretchable strain sensors with ultra-high sensitivity and linearity

Hierarchical structural design towards stretchable strain sensors with ultra-high sensitivity and linearity

Stress-constrained optimization of multiscale structures with parameterized microarchitectures using machine learning

A multiscale topology optimization framework for stress-constrained design is presented. Spatially varying microstructures are distributed in the macroscale where their material properties are estimated using a neural network surrogate model for homogenized constitutive relations. Meanwhile, the local stress state of each microstructure is evaluated with another neural network trained to emulate second-order homogenization. This combination of two surrogate models — one for effective properties, one for local stress evaluation — is shown to accurately and efficiently predict relevant stress values in structures with spatially varying microstructures. An augmented lagrangian approach to stress-constrained optimization is then implemented to minimize the volume of multiscale structures subjected to stress constraints in each microstructure. Several examples show that the approach can produce designs with varied microarchitectures that respect local stress constraints. As expected, the distributed microstructures cannot surpass density-based topology optimization designs in canonical volume minimization problems. Despite this, the stress-constrained design of hierarchical structures remains an important component in the development of multiphysics and multifunctional design. This work presents an effective approach to multiscale optimization where a machine learning approach to local analysis has increased the information exchange between micro- and macroscales.

Directly processing natural cotton into eco-friendly, highly thermal-insulating textiles via hierarchically self-locking structures

Textiles, serving as a second skin for the human body, play a significant role in regulating the microenvironment temperature, and enhancing thermal comfort of the human body during cold weather. However, the most current methods for enhancing the warmth of fabrics involve complex chemical treatment or the application of advanced materials, thus suffering from potential chemical toxicity (especially for infants), complex processing and high cost. Herein, we report a simple strategy for directly processing cotton roving into environmentally friendly and structurally stable thermal-retention cotton textiles by means of hierarchically self-locking structures. The textile not only shows excellent heat-retention properties and mechanical firmness compared with conventional thermal insulation wadding and certain commercial blankets, but is also environmentally friendly and cost effective. This method may provide a new generation of thermal insulation materials with enhanced health and environmental benefits based on hierarchical structure design and natural textile materials.

Efficient dynamic topology optimization of 2D metamaterials based on a complementary energy formulation

The advent of additive manufacturing has revolutionized the design and development of hierarchical structures, with potential applications in compliant, auxetic, and band-gap structures. This paper presents an innovative approach to developing a dynamic Topology Optimization (TO) framework for designing printable lattice structures that exhibit specific dynamic properties. Utilizing parametrically defined filament-based unit cell structures for topology optimization, we achieve desired natural frequency bandgaps in the structures composed of these unit cells. To enhance computational efficiency, we employ a complementary energy-based formulation to (semi)analytically derive the flexibility and stiffness matrices of the unit cell structure, thus, eliminating extensive finite element discretization. Consequently, a wide variety of parametrically defined filament-based meso-structures can be mathematically explored. We apply this innovative framework specifically for band-gap maximization of 2D lattice structures. By tuning the geometry within each cell using TO, we maximize the band gap. Our results show the potential of this approach to create more efficient and effective hierarchical structures with desired band-gap properties.