Complex Hierarchical Structure Research Articles

Identification of pennaceous barbule cell factor (PBCF), a novel gene with spatiotemporal expression in barbule cells during feather development.

Bird contour feathers exhibit a complex hierarchical structure composed of a rachis, barbs, and barbules, with barbules playing a crucial role in maintaining feather structure and function. Understanding the molecular mechanisms underlying barbule formation is essential for advancing our knowledge of avian biology and evolution. In this study, we identified a novel gene, pennaceous barbule cell factor (PBCF), using microarray analysis, RT-PCR, and in situ hybridization. PBCF is expressed in barbule cells adjacent to the ramus during pennaceous barbule formation, where these cells fuse with the ramus to establish the feather's branching structure. PBCF expression occurs transiently after melanin pigmentation of the barbule plates but before the expression of barbule-specific keratin 1 (BlSK1). Orthologues of PBCF, predicted to be secreted proteins, are conserved across avian species, with potential homologues detected in reptiles, suggesting an evolutionary lineage-specific adaptation. Additionally, PBCF is expressed in non-vacuolated notochord cells and the extra-embryonic ectoderm of the yolk sac, hinting at its broader developmental significance. The PBCF gene produces two mRNA isoforms via alternative splicing, encoding a secreted protein and a glycophosphatidylinositol (GPI)-anchored membrane-bound protein, indicating functional versatility. These findings suggest that PBCF may be involved as an avian-specific extracellular matrix component in cell adhesion and/or communication, potentially contributing to both feather development and embryogenesis. Further investigation of PBCF's role in feather evolution and its potential functions in other vertebrates could provide new insights into the interplay between development and evolution.

Inverse design of copolymers including stoichiometry and chain architecture.

The demand for innovative synthetic polymers with improved properties is high, but their structural complexity and vast design space hinder rapid discovery. Machine learning-guided molecular design is a promising approach to accelerate polymer discovery. However, the scarcity of labeled polymer data and the complex hierarchical structure of synthetic polymers make generative design particularly challenging. We advance the current state-of-the-art approaches to generate not only repeating units, but monomer ensembles including their stoichiometry and chain architecture. We build upon a recent polymer representation that includes stoichiometries and chain architectures of monomer ensembles and develop a novel variational autoencoder (VAE) architecture encoding a graph and decoding a string. Using a semi-supervised setup, we enable the handling of partly labelled datasets which can be beneficial for domains with a small corpus of labelled data. Our model learns a continuous, well organized latent space (LS) that enables de novo generation of copolymer structures including different monomer stoichiometries and chain architectures. In an inverse design case study, we demonstrate our model for in silico discovery of novel conjugated copolymer photocatalysts for hydrogen production using optimization of the polymer's electron affinity and ionization potential in the latent space.

Programmable Self‐Assembly from Two‐Dimensional Nanosheets to Spiral, Twisted and Branched Nanostructures

AbstractSelf‐assembly of nanomaterials into hierarchical structure is of great interest to fabricate functional materials. However, programmable design of the assembled structures remains a great challenge. Herein, we reported a programmable self‐assembly strategy to customize the assembled structure. The self‐assembly strategy is designed to orderly transform the two‐dimensional (2D) Ca ions assembled F127 nanosheets (Ca‐F127 NSs) into spiral nanosheet structures (S‐Ca‐F127 NSs), branched nanosheet structures (B‐Ca‐F127 NSs), branched‐spiral nanosheet structures (B‐S‐Ca‐F127 NSs), and twisted‐branched structures (T‐Ca‐F127 NBs). Wide‐angle X‐ray scattering (WAXS) and X‐ray absorption spectroscopy (XAS) indicate that these different structures maintain the same orthorhombic phase and Ca‐O octahedral coordination structure. Selected area electron diffraction (SAED) in the double‐tilt liquid nitrogen cooling holder identifies the Eshelby twist in the twisted structures, demonstrating the spiral structure are formed by screw dislocation growth. Cryo‐electron microscopy (cryo‐EM) proves the oriented epitaxial growth in the B‐Ca‐F127 NSs. Furthermore, the formation mechanisms of spiral structure and branched structure can be recombined to form complex hierarchical structures. The epitaxial growth along screw dislocation can lead to the formation of B‐S‐Ca‐F127 NSs, while the twisted epitaxial growth in the screw dislocation can lead to the formation of T‐Ca F127 NBs.

Programmable Self-Assembly from Two-Dimensional Nanosheets to Spiral, Twisted and Branched Nanostructures.

Self-assembly of nanomaterials into hierarchical structure is of great interest to fabricate functional materials. However, programmable design of the assembled structures remains a great challenge. Herein, we reported a programmable self-assembly strategy to customize the assembled structure. The self-assembly strategy is designed to orderly transform the two-dimensional (2D) Ca ions assembled F127 nanosheets (Ca-F127 NSs) into spiral nanosheet structures (S-Ca-F127 NSs), branched nanosheet structures (B-Ca-F127 NSs), branched-spiral nanosheet structures (B-S-Ca-F127 NSs), and twisted-branched structures (T-Ca-F127 NBs). Wide-angle X-ray scattering (WAXS) and X-ray absorption spectroscopy (XAS) indicate that these different structures maintain the same orthorhombic phase and Ca-O octahedral coordination structure. Selected area electron diffraction (SAED) in the double-tilt liquid nitrogen cooling holder identifies the Eshelby twist in the twisted structures, demonstrating the spiral structure are formed by screw dislocation growth. Cryo-electron microscopy (cryo-EM) proves the oriented epitaxial growth in the B-Ca-F127 NSs. Furthermore, the formation mechanisms of spiral structure and branched structure can be recombined to form complex hierarchical structures. The epitaxial growth along screw dislocation can lead to the formation of B-S-Ca-F127 NSs, while the twisted epitaxial growth in the screw dislocation can lead to the formation of T-Ca F127 NBs.

Extraction of Natural-Based Raw Materials Towards the Production of Sustainable Man-Made Organic Fibres.

Bioresources have been gaining popularity due to their abundance, renewability, and recyclability. Nevertheless, given their diverse composition and complex hierarchical structures, these bio-based sources must be carefully processed to effectively extract valuable raw polymeric materials suitable for producing man-made organic fibres. This review will first highlight the most relevant bio-based sources, with a particular focus on promising unconventional biomass sources (terrestrial vegetables, aquatic vegetables, fungi, and insects), as well as agroforestry and industrial biowaste (food, paper/wood, and textile). For each source, typical applications and the biopolymers usually extracted will also be outlined. Furthermore, acknowledging the challenging lignocellulosic structure and composition of these sources, an overview of conventional and emerging pre-treatments and extraction methods, namely physical, chemical, physicochemical, and biological methodologies, will also be presented. Additionally, this review aims to explore the applications of the compounds obtained in the production of man-made organic fibres (MMOFs). A brief description of their evolution and their distinct properties will be described, as well as the most prominent commercial MMOFs currently available. Ultimately, this review concludes with future perspectives concerning the pursuit of greener and sustainable polymeric sources, as well as effective extraction processes. The potential and main challenges of implementing these sources in the production of alternative man-made organic fibres for diverse applications will also be highlighted.

Facile synthesis and microwave absorption capabilities of hierarchical porous BN@C composites

With the rapid advancement of electronic information technology, the issue of electromagnetic radiation has become increasingly severe. It is urgent to develop high efficiency microwave absorber with excellent microwave absorbing performance. The construction of complex and diversified hierarchical porous structure is regarded as a promising way to enhance electromagnetic wave absorption. In this study, leveraging the porous architecture of melamine foam, a BN@C composite material featuring a hierarchical pore structure comprising larger and smaller pores, both residing in the micrometer regime, was synthesized via a high-temperature-assisted sol-gel method, using polyvinyl alcohol as the carbon precursor and boron nitride (BN) as the filler. By optimizing the molar ratio of raw materials, BN@C composites exhibiting superior microwave absorption performance were successfully obtained. When the matching thickness was set at 2.5 mm and 1.5 mm, respectively, the minimum reflection loss (RLmin) reached −29.12 dB, and the maximum effective absorption bandwidth (EAB) was 5.44 GHz, demonstrating a broad application prospect in the realm of microwave absorption. This research not only provides novel insights into enhancing the microwave absorption capabilities of carbon-based materials but also lays a material foundation for the development of electromagnetic radiation protection and stealth technologies.

Multiscale interstitial fluid computation modeling of cortical bone to characterize the hydromechanical stimulation of lacunar-canalicular network.

Bone tissue is a biological composite material with a complex hierarchical structure that could continuously adjust its internal structure to adapt to the alterations in the external load environment. The fluid flow within bone is the main route of osteocyte metabolism, and the pore pressure as well as the fluid shear stress generated by it are important mechanical stimuli perceived by osteocytes. Owing to the irregular multiscale structure of bone tissue, the fluid stimulation that lacunar-canalicular network (LCN) in different regions of the tissue underwent remained unclear. In this study, we constructed a multiscale conduction model of fluid flow stimulus signals in bone tissue based on the poroelasticity theory. We analyzed the fluid flow behaviors at the macro-scale (whole bone tissue), macro-meso scale (periosteum, interstitial bone, osteon and endosteum), and micro-scale (lacunar-osteocyte-canalicular) levels. We explored how fluid stimulation at the tissue level correlated with that at the cellular level in cortical bone and characterized the distributions of the pore pressure, fluid velocity and fluid shear stress that the osteocytes experienced across the entire tissue structure. The results showed that the initial conditions of intramedullary pressure had a significant impact on the pore pressure of Haversian systems, but had a relatively small influence on the fluid velocity. The osteocyte which were located at different positions in the bone tissue received very distinct fluid stimuli. Osteocytes in the vicinity of the Haversian Canals experienced higher fluid shear stress stimulation. When the permeability of the LCN was within the range from 10-21m2 to 10-18m2, the distribution of pressure, fluid velocity and fluid shear stress within the osteon near the periosteum and endosteum was significantly different from that in other parts of the bone. However, when the permeability was less than 10-22m2, such a difference did not exist. Particularly, the flow velocity at the lacunae was markedly higher than that in the canaliculi. Meanwhile, the pore pressure and fluid shear stress were conspicuously lower than those in the canaliculi. In this study, we considered the interconnections of different biofunctional units at different scales of bone tissue, construct a more complete multiscale model of bone tissue, and propose that osteocytes at different locations receive different fluid stimuli, which provides a reference for a deeper understanding of bone mechanotransduction.

Container Management System in Batumi Port

Currently, the maritime economy of Georgia is developing quite rapidly. The special geopolitical position of our country in the Eurasian region, in the neighborhood of countries on the path of market reforms, forces the Georgian government to restore the infrastructure of the national economy to effectively use our territorial traditional advantages: mineral resources, free agricultural areas, a large coast, to create convenient port complexes. All this contributes to the development of modern marine transport, cargo, passenger, as well as mixed cargo-passenger complexes. Sea transport is used to transport goods between the country's ports, as well as to develop and ensure Georgia's foreign economic relations with foreign countries. As of 2015, maritime transport accounted for more than 86% of the country's export-import traffic. In 2021, sea vessels entered the ports of Georgia 370 times from 65 foreign countries, which provided more than 86% of the country's needs in foreign trade transportation. In recent years, major technical retooling of seaports has been carried out, tonnage has significantly increased, and the capacity of ships has increased. The capacity of the ships' power plants has increased, automation of several production processes on ships has been introduced, and new transport technologies have been introduced, which ensure safer and more trouble-free navigation of the fleet. The modern port system is a complex hierarchical structure that combines ship companies and fleets, navigation and information support systems, computer systems, and computer-related means of land transportation of goods. Keywords: Container management system, Batumi port, container platform, computer system.

Engineered Protein Fibers with Reinforced Mechanical Properties Via β-Sheet High-Order Assembly.

Protein fibers are ideal alternatives to synthetic polymers due to their unique mechanical properties, biocompatibility, and sustainability. However, engineering biomimetic protein fibers with high mechanical properties remains challenging, particularly in mimicking the high molecular weight of natural proteins and regulating their complex hierarchical structures. Here, a modular design and multi-scale assembly strategy is developed to manufacture robust protein fibers using low- or medium-molecular-weight proteins. The distinct functional and structural properties of flexible, rigid, and cross-linked domains in modular proteins are skillfully harnessed. By regulating the ratio of rigid to flexible domains, the formation of high-order β-sheet crystals aligned along the fiber axis is promoted, enhancing both strength and toughness. Furthermore, the dynamic imine cross-linking network, formed by the aldehyde-amine condensation reaction of the cross-linked domains, further reinforces the protein fibers. Remarkably, fibers spun from modular proteins significantly smaller than natural spidroin exhibit outstanding mechanical properties, surpassing those of protein fibers with same or even higher molecular weights. This strategy offers a promising pathway for fabricating protein fibers suitable for diverse applications.

Effects of tree species pore structure characteristics and CO2 activation on the performance of their derived carbon electrode for supercapacitors

Herein, we investigated the effects of tree species selection on the specific surface area and electrochemical properties of wood-derived carbon electrodes. The SEM, Raman spectra and aperture distribution test results showed that compared with BCW and ZCW, CW had a more complex hierarchical porous structure and more defects. The N2 adsorption/desorption isotherms and electrochemical test results showed that CW had the largest specific surface area and the best electrochemical performance, with a specific surface area of 495.3 m2g−1 and an areal capacitance of 3079 mF cm−2 at 5 mA cm−2. The specific surface area and electrochemical properties of ACW, ABCW and AZCW electrodes obtained by CO2 activation were significantly improved compared with CW, BCW and ZCW electrodes. Among the activated electrodes, the ACW electrode had the highest specific surface area (558.4 m2g−1) and the highest areal capacitance (3727 mF cm−2 at 5 mA cm−2).

Anti-icing and de-icing properties of composite superhydrophobic coating with microwave heating performance on asphalt pavement

Severe icing on asphalt pavements significantly impacts traffic safety and efficiency. Superhydrophobic coatings exhibit excellent hydrophobic and anti-icing properties, making them suitable for asphalt pavements. However, the formation of dense and hard ice limits their anti-icing effectiveness in cold regions. Within this paper, we have developed a novel composite superhydrophobic coating (CSC) with microwave heating performance by constructing a hierarchical structure using carbon nanotubes and incorporating micron-sized iron powder as a primary microwave-absorbing material. Scanning electron microscopy, 3D confocal microscopy, and contact angle tests reveal that the optimally mixed CSC possesses a complex micro-nano hierarchical structure, superhydrophobic properties (contact angle of 155.4°), and excellent anti-icing properties. Microwave heating results show that the CSC achieves a maximum heating rate of 1.108 ℃/s and an energy utilization efficiency of 47 %, representing improvements of 118.1 % and 18.3 % compared to uncoated specimens. Durability tests indicate that after wear, the CSC's contact angle decreases by 6.2 %, and the microwave heating rate drops by 13.7 %. Despite these reductions, the coating still maintains high hydrophobicity and microwave heating performance. While the friction coefficient of CSC-coated pavement decreases to μ=0.63, it still meets regulatory requirements. Overall, the application of CSC can effectively increase de-icing efficiency and mitigate the adverse effects of ice and snow on pavements.

Controlled Fabrication of Distinct Nanostructures from Discrete Oligourethanes via Thermal Annealing.

The self-assembly of sequence-defined polymers (SDPs) enables the formation of a diverse array of nanostructures; however, the construction of complex hierarchical structures via thermal annealing from SDPs remains relatively unexplored. In this study, two series of oligourethanes, 2Cit-pBn-OH and 2Cit-mBn-OH, were synthesized to investigate their thermal annealing behaviors. Nanorod clusters were generated from 2Cit-pB6-OH in a mixture of 1,4-dioxane and toluene, whereas 2Cit-pB8-OH formed nanosheets after thermal annealing. Upon modifying the structure of the repeating units, 2Cit-mB6-OH self-assembled into ultrathin nanosheets, transitioning from nanospheres after thermal annealing in a mixture of isopropanol and cyclohexane, while "flower" micelles were produced from 2Cit-mB8-OH. Interestingly, when isopropanol was replaced with a mixture of isopropanol and tetrahydrofuran (THF), uniform nanotubes were generated by 2Cit-mB6-OH under the same thermal annealing conditions. Additionally, a discrete amphiphile (2Cit-mB4-(S)DPEG) was synthesized, leading to the formation of uniform nanosheets in aqueous solution after thermal annealing. This work highlights the significant effects of sequence and repeating unit structure of SDPs on their self-assembly behaviors and presents a novel strategy for the controlled fabrication of unique nanostructures from SDPs.

Nonuniversal Dynamics of Hyperbranched Metallo-Supramolecular Polymer Networks by the Spontaneous Formation of Nanoparticles.

Various transient and permanent bonds are commonly combined in increasingly complex hierarchical structures to achieve biomimetic functions, along with high mechanical properties. However, there is a traditional trade-off between mechanical strength and biological functions like self-healing. To fill this gap, we develop a metallo-supramolecular polymer hydrogel based on the hyperbranched poly(ethylene imine) (PEI) backbone and phenanthroline ligands, which have unexpectedly high plateau modulus at low concentrations. Rheological measurements demonstrate nonuniversal metal-ion-specific dynamics, with significantly larger plateau moduli, longer relaxation times, and stronger temperature dependencies, compared to equivalent networks based on model-type telechelic precursors, which cannot be explained by the theory of linear viscoelasticity. TEM images reveal the in situ mineralization of metal ions, which nucleate by the ligand complexation and grow thanks to the spontaneous reducing effect of the PEI backbone. Evidently, the complex lifetime works against Ostwald ripening, resulting in the formation of thermodynamically stable smaller particles. This trend is followed by time-dependent network buildup measurements and is confirmed by a kinetic model for particle formation and aggregation. The spontaneous formation of particles with complex lifetime-dependent sizes can explain the nonuniversal dynamics through the interaction of polymer segments and particles at the nanoscale. This work describes how the polymer backbone can affect the strength and stability of supramolecular bonds, promising for combining high mechanical properties and self-healing comparable to natural tissues.

Atomic force microscopy-based nanoindentation technique for characterizing the transverse and shear moduli of flax fibers

Experimentally evaluating the elastic properties of flax fibers is challenging due to their complex hierarchical structure, and a standard test procedure for measuring their transverse and shear moduli is currently not reported in the literature. Hence, this study presents an atomic force microscopy (AFM) based nanoindentation technique to evaluate the transverse and shear moduli of flax fiber. A high-precision focused ion beam (FIB)-milling process was used to fabricate a flat surface for indentation along the longitudinal fiber cross-section of the fiber and transverse fiber cross-section by polishing the unidirectional (UD) lamina in order to evaluate the indentation modulus. Further, Swanson's numerical contour approach was adopted to evaluate the elastic properties of the fiber from the measured indentation modulus. The accuracy of the experimentally obtained fiber properties is verified by using it in a micromechanics model for predicting the elastic properties of the UD lamina and comparing it with experimental results reported in the literature.

Multichannel Carbon Nanofibers: Pioneering the Future of Energy Storage.

Multichannel carbon nanofibers (MCNFs), characterized by complex hierarchical structures comprising multiple channels or compartments, have attracted considerable attention owing to their high porosity, large surface area, good directionality, tunable composition, and low density. In recent years, electrospinning (ESP) has emerged as a popular synthetic technique for producing MCNFs with exceptional properties from various polymer blends, driven by phase separation between polymers. These interactions, including van der Waals forces, covalent bonding, and ionic interactions, are crucial for MCNF production. Over time, the applications of MCNFs have expanded, making them one of the most intriguing topics in material research. MCNFs with tailored porous channels, controllable dimensions, confined spaces, high surface areas, designed architectures, and easy electrolyte access to active walls are considered optimal for electrochemical energy storage (EES) technologies. This review provides an exhaustive overview of the working principle, synthesis methods, and structural properties of MCNFs, and examines their advantages, limitations, and potential for producing multichannel architectures. Furthermore, this review explores the relationship between the composition of MCNF electrode materials for EES devices (supercapacitors and batteries) and their electrochemical performance. This review also addresses future directions and challenges in the development and utilization of MCNFs and provides insights into potential research avenues for advancing this exciting field.

Role of prior austenite grain boundary and retained austenite in strain localization of medium-carbon high-strength steels

Exploring the micromechanical behavior of lath-martensitic quenching and tempering (Q&T), as well as quenching and partitioning (Q&P) steels presents a significant challenge due to their complex multi-phase constituents and hierarchical structures. This study conducts a comprehensive comparative analysis using medium-carbon Q&T and Q&P steels with identical chemical compositions. Atom probe tomography (APT) was used to investigate the distribution of chemical elements, while high-resolution digital image correlation (HR-DIC) provided insights into nanoscopic strain localization and partitioning. Both Q&T and Q&P steels exhibit significant strain localization at prior austenite grain boundaries (PAGBs) due to substantial carbon segregation. Strain localization in Q&T steel at PAGBs and packet boundaries strongly depends on preferred geometric orientations, with boundaries inclined 45° to the loading direction experiencing severe deformation. Conversely, in Q&P steel, PAGBs adjacent to large clusters of fine lath martensite, lacking a packet with a longitudinal direction parallel to boundaries and a feasible in-lath slip system, primarily undergo deformation. Carbon partitioning from martensite to retained austenite (RA), along with coexisting carbon and manganese segregation at phase interfaces, stabilizes the RA, resulting in a neighborhood-dependent deformation behavior of RA. The existence of RA not only absorbs carbon, maintaining low strength and high deformability, but also uniformly distributes and induces stable interfaces to hinder the formation of large packets with easily activated in-lath slip transmission.

Characterization of human trabecular bone across multiple length scales using a correlative approach combining X-ray tomography with LaserFIB and plasma FIB-SEM

Three-dimensional correlative multimodal and multiscale imaging is an emerging method for investigating the complex hierarchical structure of biological materials such as bone. This approach synthesizes images acquired across multiple length scales, for the same region of interest, to provide a comprehensive view of the material structure of a sample. Here, we develop a workflow for the structural analysis of human trabecular bone using a femtosecond laser to produce a precise grid to facilitate correlation between imaging modalities and identification of structures of interest, in this case, a single trabecula within a volume of trabecular bone. Through such image registration, high resolution X-ray microscopy imaging revealed fine architectural details, including the cement sheath and bone cell lacunae of the selected bone trabecula. The selected bone volume was exposed with a combination of manual polishing and site-specific femtosecond laser ablation and then examined with plasma focused ion beam-scanning electron microscopy. This reliable and versatile correlation approach has the potential to be applied to a variety of biological tissues and traditional engineered materials. The proposed workflow has the enhanced capability for generating highly resolved and broadly contextualized structural data for a better understanding of the architectural features of a material spanning its macroscopic to nanoscopic levels.

Posttranslational modifications in spider silk influence conformation and dimerization dynamics

Spider silk is an archetypal biopolymer material with extreme tensile properties arising from its complex hierarchical assembly. While recent advances in sequencing have yielded abundant insights, relatively little is known concerning post-translational modifications (PTMs) in spider silk. Here, we probe the PTM landscape of dragline silk from the Jorō spider (Trichonephila clavata) using a combination of mass spectroscopy and solid-state nuclear magnetic resonance (NMR). The results reveal a wide array of potential modifications, including hydroxyproline, phosphorylation, and dityrosine cross-links, encompassing the different spidroin constituents. Notably, the MaSp3 repetitive region displayed numerous PTMs, whereas MaSp1 and MaSp2 variants showed distinct phosphorylation patterns in its terminal domains. The N-terminal domain (NTD) phosphorylation sites were found predominantly at the dimer interface, suggesting a modulatory function with respect to its pH-driven dimerization function, a hypothesis supported by studies using phosphomimetic NTD mutants. Possible roles of phosphoserine in limiting β-sheet formation, and hydroxyproline in disrupting β-turns are also discussed.Impact statementSpider silk is an archetypal biomaterial that can outperform our most sophisticated artificial fibers. The secret to its mechanical properties lies in its complex hierarchical structure—encompassing the nano- to macroscales—that forms through a process of molecular self-assembly of the constituent spidroin proteins. While recent advances in "biomateriomics” have given us tremendous insights into the sequence–function relationships that determine spider silk behavior, the picture is still far from complete. One area that has received little attention is posttranslational modifications (PTMs). PTMs are ubiquitous biological phenomena that are crucial for providing dynamic control of the proteome, and effectively expand the structural and functional design space of proteins beyond that provided by the canonical amino acids. Here, we undertook a comprehensive analysis of PTMs from spider dragline silk fiber, which revealed numerous potential sites for a wide array of modifications. The results provide a fascinating window into additional layers of complexity underlying the mechanical behavior of spider silk, and suggest further avenues for creating novel, dynamically tunable, bioinspired materials.Graphical abstract

Hierarchical Biomaterial Scaffolds for Periodontal Tissue Engineering: Recent Progress and Current Challenges.

The periodontium is a complex hierarchical structure composed of alveolar bone, periodontal ligament, cementum, and gingiva. Periodontitis is an inflammatory disease that damages and destroys the periodontal tissues supporting the tooth. Periodontal therapies aim to regenerate the lost tissues, yet current treatments lack the integration of multiple structural/biochemical instructive cues to induce a coordinated regeneration, which leads to limited clinical outcomes. Hierarchical biomaterial scaffolds offer the opportunity to recreate the organization and architecture of the periodontium with distinct compartments, providing structural biomimicry that facilitates periodontal regeneration. Various scaffolds have been fabricated and tested preclinically, showing positive regenerative results. This review provides an overview of the recent research on hierarchical scaffolds for periodontal tissue engineering (TE). First, the hierarchical structure of the periodontium is described, covering the limitations of the current treatments used for periodontal regeneration and presenting alternative therapeutic strategies, including scaffolds and biochemical factors. Recent research regarding hierarchical scaffolds is highlighted and discussed, in particular, the scaffold composition, fabrication methods, and results from in vitro/in vivo studies are summarized. Finally, current challenges associated with the application of hierarchical scaffolds for periodontal TE are debated and future research directions are proposed.

Hierarchical structure and remarkable properties of the CoCrFeNiCu high entropy alloy produced by fast mechanical synthesis and spark plasma sintering

Bulk CoCrFeNiCu-based high entropy alloy was fabricated using a combination of short-term high energy ball milling and rapid spark plasma sintering. Extensive studies by using x-ray diffraction, scanning and transmission electron microscopy, alongside with energy-dispersive and electron energy loss-spectroscopies revealed that the fabricated material possesses a unique hierarchical structure. The structure involves a multicomponent Cu-depleted fcc-solid solution with extremely thin (∼ 1–10 nm) layers of the Cu-based phase, primarily located on the grain boundaries. In addition, Cr2O3 nano-precipitates are uniformly distributed throughout the grain volume. Such complex hierarchical structure contributes to the unique material properties: yield strength 1205±20 MPa, bending strength 1362±62 MPa and Vicker’s micro hardness 4.86 ± 0.63 GPa. Nano-hardness and reduced modulus measured by nano-indentation provided values of 6.3±0.2 GPa and 160±3 GPa, respectively. Furthermore, the alloy was found to exhibit ferromagnetic properties. The results obtained were compared with previously reported data, and the details of the fabrication process and how it impacts the material properties were discussed.