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Developing advanced sorbents for selective carbon dioxide (CO2) sequestration with minimal energy consumption remains a pivotal challenge. This study presents a novel strategy through transforming 3D bulk zirconium-porphyrin frameworks into the corresponding 2D nanosheet-assembled superstructures for enhanced CO2 capture. The hierarchical frameworks with well-organized nanosheet architectures exhibit significantly increased specific surface area from 600 m2/g to 2400 m2/g while providing kinetic benefits for gas diffusion. Compared to the adsorption behavior of the bulk counterparts, the nanosheet-assembled frameworks demonstrate a 1.5-fold increase in CO2 adsorption capacity without compromising CO2/N2 selectivity. Theoretical calculation reveals that the coordination unsaturated Zr-O clusters, electron delocalized environments both in interlayer gaps and micropores provided binding sites for CO2 capture. Our research demonstrates an adaptable structure-directed approach for the crystal engineering of metal-organic frameworks which would inspire the creation of state-of-the-art crystalline porous materials for broadened applications.

This paper introduces a new type of energy-absorbing hierarchical tapered structure, mimicking the hierarchical architecture of barnacle. The proposed structures are designed by iteratively incorporating sub-tapered tubes at the junctions of primary ribs aiming to enhance the crashworthiness performance. The finite element models of the proposed structures are constructed in Abaqus software and validated using experimental testing. The effects of the geometrical parameters including the number of substructures and the external-to-internal wall thickness ratio on the energy absorption characteristics of the proposed structures are investigated. The results demonstrate that as the number of substructures increases, the specific energy absorption (SEA) and mean crushing force of the proposed design show a significant improvement. Specially, the SEA of the proposed structures with four substructures can reach 32.78 kJ/kg, which is 85.8 % higher than the conventional tapered tube. Additionally, decreasing the ratio of external to internal wall thickness leads to enhanced performance. After optimizing the wall thickness ratio, the maximum SEA can reach 40.87 kJ/kg, which is 26.0 % higher than that before optimization. To complement the findings, a theoretical study is presented, which exhibits excellent agreement with the numerical results, further validating the effectiveness of the proposed design. This study highlights the potential of incorporating hierarchical and tapered features into tapered structures, offering promising prospects for advancements in energy absorption technology across diverse industries.

Skin grafting is a surgical procedure to treat extensive burn injuries, and the design of skin grafts plays an essential role in burn surgery. In skin grafting, parallel incisions are projected onto a small section of healthy skin that has been removed for maximum expansions and coverage of a larger burn area. Currently, in the traditional method, skin graft expansions are insufficient to cover large burn areas. This work studied the hierarchy of alternating slit (AS) shaped and rotating rectangle (RR) shaped auxetic skin graft patterns. The 3D models of hierarchical structures were designed and developed using SolidWorks and additive manufacturing methods, respectively. These moulds were used to fabricate the hierarchical skin graft simulants. Statistical analysis was performed to calculate the significance among the groups. These hierarchical skin graft simulants were tested uniaxially and calculated the effective Poisson's ratio, meshing ratio, and induced stress up to 300% strain. From the results, all the auxetic skin graft simulants showed very high expansion. The first-order AS-shaped skin graft simulant showed the maximum expansion among all the hierarchical models. Till now, skin grafts have not achieved such high expansion experimentally. This research will be useful to the doctors to improve burn surgery outcomes and guide the manufacturers to develop new mesher with higher expansion potential.

Metamaterials are a class of engineered materials that often violate the routine assumptions that apply to ordinary materials. While metamaterials are typically assembled from carefully designed mesoscale units, the intended bulk-scale functionality can be obscured by unintended emergent effects driven by non-additive unit-unit interactions. These interactions are often sensitive to the number of units and their overall arrangement, making them extrinsic to the unit-scale design. As such, the emergence of extrinsic effects adds a significant hurdle for the development of general-purpose metamaterial technologies. Here, we reconceptualize bulk-scale extrinsic properties as a design opportunity and develop an approach that repurposes them in a new class of exponentially reconfigurable origami-inspired mechanical metamaterials. We illustrate the use of extrinsic properties to design a single general-purpose structure that can be transformed into a variety of passive mechanical devices including a waveguide, a wave lens, and a wave cloak. Bench-top experiments validate the core concepts of our approach and show how unintentional extrinsic effects become useful for applications of reconfigurable metamaterials.

Conventional methods of programmed shape change in polymers are one-way and one-time only. We introduce a new method of combining a bioinspired, hierarchical architecture with the pre-strain generated by extrusion-based 3D printing to encode multiple permanent shapes in thermoplastic polymer shell structures. At high temperature, these structures are multistable and can snap repeatedly between all encoded permanent shapes without reprogramming. At low temperature, the structures are monostable with increased stiffness; the multistability can be switched on and off via temperature. Characterization studies are performed to determine how to control the level of pre-strain and the deflection behavior of the structure to enable finite element modeling for analysis and design. This pre-straining technique may be thought of as a virtual mold: printed structures are initially flat but have multiple permanent shapes encoded. Taking advantage of the geometric freedom of 3D printing, complex geometries, and pre-strain fields may be used to create highly tailored snapping structures. Thermoplastic filaments with added particles may be used to impart additional multifunctionality to the structures, such as magnetic responsiveness, to enable remote actuation. These switchable multistable structures have potential applications in fields including robotics, aerospace, and smart buildings.

Commercially available lattices contain various kinds of morphological imperfections which result in great degradation in lattices’ mechanical properties, therefore, to obtain imperfection insensitive lattice structure is obviously a practical research subject. Hierarchical structure materials were found to be a class of promising anti-defect materials. This paper builds hierarchical lattice by adding soft adhesion to lattice’s cell edges and numerical results show that its imperfection sensitivity to missing bars is minor compared with the classic lattice. Soft adhesion with appropriate properties reinforce cell edge’s bending stiffness and thus reduce the bending deformation in lattice caused by missing bars defect, which is confirmed by statistical analysis of normalized node displacements of imperfect lattices under hydrostatic compression and shear loads.

Peptide derivatives and, most specifically, their self-assembled supramolecular structures are being considered in the design of novel biofunctional materials. Although the self-assembly of triphenylalanine homopeptides has been found to be more versatile than that of homopeptides containing an even number of residues (i.e. diphenylalanine and tetraphenylalanine), only uncapped triphenylalanine (FFF) and a highly aromatic analog blocked at both the N- and C-termini with fluorenyl-containing groups (Fmoc-FFF-OFm), have been deeply studied before. In this work, we have examined the self-assembly of a triphenylalanine derivative bearing 9-fluorenylmethyloxycarbonyl and benzyl ester end-capping groups at the N- and C-termini, respectively (Fmoc-FFF-OBzl). The antiparallel arrangement clearly dominates in β-sheets formed by Fmoc-FFF-OBzl, whereas the parallel and antiparallel dispositions are almost isoenergetic in Fmoc-FFF-OFm β-sheets and the parallel one is slightly favored for FFF. The effects of both the peptide concentration and the medium on the self-assembly process have been examined considering Fmoc-FFF-OBzl solutions in a wide variety of solvent:co-solvent mixtures. In addition, Fmoc-FFF-OBzl supramolecular structures have been compared to those obtained for FFF and Fmoc-FFF-OFm under identical experimental conditions. The strength of π-π stacking interactions involving the end-capping groups plays a crucial role in the nucleation and growth of supramolecular structures, which determines the resulting morphology. Finally, the influence of a non-invasive external stimulus, ultrasounds, on the nucleation and growth of supramolecular structures has been examined. Overall, FFF-based peptides provide a wide range of supramolecular structures that can be of interest in the biotechnological field., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Hierarchical interlocking leads to optimal mechanical properties for sutures in nature. Inspired by this, a design method for describing a hierarchal triangular suture joint based on Koch fractal interlocking is developed. The effect of geometrical interlocking was examined by the analysis of the load transmission between joined parts. Samples of hierarchal suture joints were fabricated by using a high-resolution 3D printer and tensile tests were conducted to examine the mechanical behavior of these joints. The surface displacement and strain fields were obtained using the Digital Image Correlation (DIC) technology where the images were taken by a high-resolution microscope camera. Finite element models of the hierarchal suture joints were generated to simulate the tensile responses and to predict the stress distributions and failure modes. The numerical results show good agreement with the experimental data. The results of this study show that the second order suture joint with a sinusoidal center line exhibits not only high strength but also high ductility. Moreover, by increasing the hierarchical order from two to three, the stiffness and strength do not improve while the fracture toughness actually decreases, suggesting that increasing the fractal complexity does not always lead to the improvement of the structure's load-carrying capacity, even with low iterations for the fractal complexity. The results obtained in this study can serve as a guideline to the engineering design of suture joints with fractal interlocks., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The study aimed to obtain the information on the effect of germination temperature on hierarchical structures (granular structure, crystal structure, short-range ordered structure and helical structures) of starch from brown rice and their relation to pasting properties. The results showed that brown rice had gradually elevated germination ability and α-amylase activity as the sprouting temperature rose. And the enhanced enzyme activities during germination promoted the erosion of starch granules, the decrease of relative crystallinity and short-range ordered degree, and the unwinding of double helix structure. In addition, the mathematical correlation and structure-pasting relationship were constructed in this work. These structural disorganizations of germinated rice starch resulted in reduced swelling degree and water-holding capacity, inducing the lower paste viscosity (e.g., peak and final viscosity), breakdown and setback value. Thus, it is concluded that germination can efficiently regulate the pasting properties of starch, which provide a crucial basis for the development and utilization of germinated brown rice products., Competing Interests: Declaration of Competing Interest The authors declare no conflicts of interest., (Copyright © 2019. Published by Elsevier B.V.)

The development of highly biomimetic scaffolds in terms of composition and structures, to repair or replace damaged bone tissues, is particularly relevant for tissue engineering. This paper investigates a 3D printed porous scaffold containing aligned multi-walled carbon nanotubes (MWCNTs) and nano-hydroxyapatite (nHA), mimicking the natural bone tissue from the nanoscale to macroscale level. MWCNTs with similar dimensions as collagen fibres are coupled with nHA and mixed within a polycaprolactone (PCL) matrix to produce scaffolds using a screw-assisted extrusion-based additive manufacturing system. Scaffolds with different material compositions were extensively characterised from morphological, mechanical and biological points of views. Transmission electron microscopy and polarised Raman spectroscopy confirm the presence of aligned MWCNTs within the printed filaments. The PCL/HA/MWCNTs scaffold are similar to the nanostructure of native bone and shows overall increased mechanical properties, cell proliferation, osteogenic differentiation and scaffold mineralisation, indicating a promising approach for bone tissue regeneration., (Copyright © 2019 Elsevier B.V. All rights reserved.)

This review focuses on the synthesis and chemical sensing characterization of metal oxide heterostructures reported since 2012. Heterostructures exhibit strong interactions between closely packed interfaces, showing superior performances compared to single structures. Surface effects appear thanks to the magnification of nanostructures' surface leading to an enhancement of surface related properties (the base of chemical sensors working mechanism). The combination of different metal oxides to form heterostructures further improves the selectivity and/or other important sensing parameters. A very large number of different morphologies and structures have been proposed, each one exhibiting peculiar sensing properties towards specific chemical compounds. Among the different preparation methodologies, a significant number has been performed by means of hydrothermal method. However, the combination of various fabrication methods seems a very efficient strategy to obtain metal oxide-based heterostructures with different morphologies and dimensions such as core-shell nanostructures, one-dimensional heterostructures, two-dimensional layered heterojunctions, and three-dimensional hierarchical heterostructures. Despite all extraordinary advances in both material science and nanotechnology and the results achieved with heterostructured chemical sensors, there are few points that still deserve further studies and investigations, such as possible diffusion across the junctions, reproducibility of the fabrication process, synergistic or catalytic effects among the materials forming the heterostructures and influence/stability of the contacts. Moreover, perfect control over their growth is mandatory for their application in commercial devices. Only a careful understanding of the growth and the interface properties could fill the existing gap between laboratory studies and real-world exploitation of these heterostructures., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Hierarchical structures on metallic implants can enhance the interaction between cells and implants and thus increase their biocompatibility. However, it is difficult to directly fabricate hierarchical structures on metallic implants. In this study, we used a simple one-step method, ultrasonic nanocrystal surface modification (UNSM), to fabricate hierarchical surface structures on a nickel-titanium (NiTi) alloy. During UNSM, a tungsten carbide ball hits metal surfaces at ultrasonic frequency. The overlapping of the ultrasonic strikes generates hierarchical structures with microscale grooves and embedded nanoscale wrinkles. Cell culture experiments showed that cells adhere better and grow more prolifically on the UNSM-treated samples. Compared with the untreated samples, the UNSM-treated samples have higher corrosion resistance. In addition, the surface hardness increased from 243 Hv to 296 Hv and the scratch hardness increased by 22%. Overall, the improved biocompatibility, higher corrosion resistance, and enhanced mechanical properties demonstrate that UNSM is a simple and effective method to process metallic implant materials., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Improving the site accessibility of molecularly imprinted polymer (MIP) is one of the biggest challenges for application of MIP in solid-phase extraction (SPE). Hierarchically imprinted mesoporous silica polymer was prepared with semicovalently bond imprinting methods based on MCM-41 and SBA-15 mesostructures, aiming to improve the site accessibility of MIP and increase the efficiency of molecularly imprinted-SPE. Characterization and performance tests of the obtained products revealed that molecularly imprinted SBA-15 (MIP-SBA-15) not only retained the mesoporous structure of SBA-15, but also displayed excellent selectivity of MIP to the target molecule. As the MIP-SBA-15 were adopted as the adsorbents of solid-phase extraction for detecting bisphenol A in spiked water samples, the recoveries of spiked samples more than 87%, which reveals that the molecularly imprinted SBA-15 were efficient SPE adsorbents for bisphenol A., (Copyright © 2013 Elsevier B.V. All rights reserved.)