Helicoidal Structure Research Articles

A Soft, Fatigue‐free, and Self‐healable Ionic Elastomer via the Synergy of Skin‐like Assembly and Bouligand Structure

AbstractSoft ionic elastomers that are self‐healable, fatigue‐free, and environment‐tolerant are ideal structural and sensing materials for artificial prosthetics, soft electronics, and robotics to survive unpredictable service conditions. However, most synthetic strategies failed to unite rapid healing, fatigue resistance, and environmental robustness, limited by their singular compositional/structural designs. Here, we present a soft, tough, fatigue‐resistant, and self‐healable ionic elastomer (STFSI elastomer), which fuses skin‐like binary assembly and Bouligand helicoidal structure into a composite of thermoplastic polyurethane (TPU) fibers and a supramolecular ionic biopolymer. The interlocked binary assembly enables skin‐like softness, high stretchability, and strain‐adaptive stiffening through a matrix‐to‐scaffold stress transfer. The Bouligand structure contributes to superhigh fracture toughness (101.6 kJ m−2) and fatigue resistance (4937 J m−2) via mechanical toughening by interlayer slipping and twisted crack propagation path. Besides, the STFSI elastomer is self‐healable through a “bridging” method and environment‐tolerant (−20 °C, strong acid/alkali, saltwater). To demonstrate the versatile structural and sensing applications, we showcase a safety cushion with efficient damping and suppressed rebounding, and a robotic sensor with excellent fatigue crack tolerance and instant sensation recovery upon cutting‐off damage. Our presented synthetic strategy is generalizable to other fiber‐reinforced tough polymers for applications involving demanding mechanical/environmental conditions.

A Soft, Fatigue-free, and Self-healable Ionic Elastomer via the Synergy of Skin-like Assembly and Bouligand Structure.

Soft ionic elastomers that are self-healable, fatigue-free, and environment-tolerant are ideal structural and sensing materials for artificial prosthetics, soft electronics, and robotics to survive unpredictable service conditions. However, most synthetic strategies failed to unite rapid healing, fatigue resistance, and environmental robustness, limited by their singular compositional/structural designs. Here, we present a soft, tough, fatigue-resistant, and self-healable ionic elastomer (STFSI elastomer), which fuses skin-like binary assembly and Bouligand helicoidal structure into a composite of thermoplastic polyurethane (TPU) fibers and a supramolecular ionic biopolymer. The interlocked binary assembly enables skin-like softness, high stretchability, and strain-adaptive stiffening through a matrix-to-scaffold stress transfer. The Bouligand structure contributes to superhigh fracture toughness (101.6 kJ m-2) and fatigue resistance (4937 J m-2) via mechanical toughening by interlayer slipping and twisted crack propagation path. Besides, the STFSI elastomer is self-healable through a "bridging" method and environment-tolerant (-20 °C, strong acid/alkali, saltwater). To demonstrate the versatile structural and sensing applications, we showcase a safety cushion with efficient damping and suppressed rebounding, and a robotic sensor with excellent fatigue crack tolerance and instant sensation recovery upon cutting-off damage. Our presented synthetic strategy is generalizable to other fiber-reinforced tough polymers for applications involving demanding mechanical/environmental conditions.

Influence of lay‐up sequences on cylindrical parts drawability of CFRP laminates

AbstractCarbon Fiber Reinforced Polymers (CFRP) is one of the ideal materials in the field of automotive lightweight. As one of the traditional manufacturing processes of CFRP, autoclave process has long production time, high cost and complicated operation. To overcome these shortcomings, deep drawing can be used for CFRP forming. It has the advantages of stable product quality, good repeatability, low cost, simple operation and can produce parts with complex shapes. In this paper, the influence of lay‐up sequences on the drawability of cylindrical parts was studied by using self‐made deep drawing device. The results showed that among the four lay‐up sequences [0]°12, [0/90]°6, [0/90/45/‐45/90/0]°S and [15/30/……/180]°, the [15/30/……/180]° lay‐up parts had excellent deformation coordination ability due to less angular variation in the fiber direction, and the maximum depth of 21.99 mm could be obtained. Due to the influence of wrinkles, the thickness of [15/30/……/180]° parts increased at the die corner and side wall. The thickness decreased at the flange, punch corner and bottom due to the compressive pressure. In addition, [15/30/……/180]° lay‐up parts benefited from the high level of in‐plane isotropy of the helicoidal structure, it had the fewest forming defects. The resin poor areas and resin rich areas were less and no fiber cracks were found.Highlights Investigated the influence of lay‐up sequences on the drawability of CFRP. The forming depth of [15/30/……/180]° parts was 21.99 mm. [15/30/……/180]° lay‐up parts had the best drawability. No cracks were found on the [15/30/……/180]° part.

Influence of chalcopyrite nanoplatelets on nematic phases of bend-shaped dimeric molecules: Phase diagram, birefringence, and reorientation transition

We investigated the influence of chalcopyrite (CuFeS2) nanoplatelets on the ordering of uniform and twist-bend nematic phases of achiral bend-shaped dimers, employing polarized optical microscopy, optical and electro-optical measurements. Specifically, aliphatic amine surface-functionalized hydrophobic chalcopyrite nanoplatelets were synthesized and characterized by XRD, TEM, and IR-vis-UV spectroscopy. Nanocomposites of the liquid crystal compound 1”,9”-bis(4-cyanobiphenyl-4'-yl)nonane (CB9CB) with the nanoplatelets were prepared. The study encompasses an assessment of the thermodynamic stability of the nanocomposites, constructing the corresponding phase diagram as a function of temperature and nanoplatelet mass fraction. Large phase temperature shifts were observed for minute mass fractions of NPs. Birefringence measurements were performed to investigate the orientational order parameter and the conical tilt angle's dependence on the mass fraction of the nanoplatelets and the temperature. Additionally, we measured a Fréedericksz-like reorientation transition voltage threshold and switching times as functions of the mass fraction and temperature. A huge increase of the voltage threshold was measured in the twist-bend nematic phase. The dependence of the viscoelastic coefficient ζ on NPls' mass fraction was investigated. The splay elastic constant of the helicoidal structure was estimated, using a coarse grain approximation, to be two orders of magnitude higher than in the uniform nematic phase. Finally, in the twist-bend nematic phase, the impact of temperature and nanoplatelets mass fraction on the hysteresis loop of the reorientation transition was investigated.

On the isogeometric analysis of vibration and buckling of bioinspired composite plates using inverse hyperbolic shear deformation theory

Inspired by the remarkable energy absorption and damage tolerance capabilities observed in mantis shrimp crustaceans, this study delves into the intricate realm of biological composites with helicoidal structures. However, the effect of the relative orientation of fibers within the helicoidal structure matrix on the buckling and vibration characteristics still warrants comprehensive investigation for the better design of the bioinspired structures. For the first time, a Non-Uniform Rational B-Splines (NURBS)-based isogeometric analysis (IGA) framework termed NURBio is proposed to investigate the vibration and buckling characteristics of bioinspired laminated composite structures. The framework employs NURBS basis functions for exact complex geometric representation and field approximation and offers superior computational accuracy and efficiency as compared to conventional finite element method (FEM). The present analysis is underpinned by an inverse hyperbolic shear deformation theory (IHSDT) capable of accurately capturing the interlaminar stress distribution. This research investigates the performance of various bioinspired layup configurations encompassing recursive, exponential, semicircular, and Fibonacci helicoidal designs and compares them with those of unidirectional, and cross-ply laminates. A series of numerical examples on the buckling and vibration response of bioinspired composite plates are presented to demonstrate the versatility and efficacy of the proposed isogeometric framework. The influence of different layups, loading and boundary conditions, and geometric properties on the response of different bioinspired plate structures are meticulously examined. The study offers valuable insights into the design and optimization of high-performance bioinspired structures.

Electrically tunable total reflection of light by oblique helicoidal cholesteric

An oblique helicoidal state of a cholesteric liquid crystal (ChOH) is capable of continuous change of the pitch P\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$P$$\\end{document} in response to an applied electric field. Such a structure reflects 50% of the unpolarized light incident along the ChOH axis in the electrically tunable band determined by P\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$P$$\\end{document}/2. Here, we demonstrate that at an oblique incidence of light, ChOH reflects 100% of light of any polarization. This singlet band of total reflection is associated with the full pitch P\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$P$$\\end{document}. We also describe the satellite P/2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$P/2$$\\end{document}, P/3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$P/3$$\\end{document}, and P/4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$P/4$$\\end{document} bands. The P/2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$P/2$$\\end{document} and P/4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$P/4$$\\end{document} bands are triplets, whereas P/3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$P/3$$\\end{document} band is a singlet caused by multiple scatterings at P\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$P$$\\end{document} and P/2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$P/2$$\\end{document}. A single ChOH cell acted upon by an electric field tunes all these bands in a very broad spectral range, from ultraviolet to infrared and beyond, thus representing a structural color device with enormous potential for optical and photonic applications.Impact statementPigments, inks, and dyes produce colors by partially consuming the energy of light. In contrast, structural colors caused by interference and diffraction of light scattered at submicrometer length scales do not involve energy losses, which explains their widespread in Nature and the interest of researchers to develop mimicking materials. The grand challenge is to produce materials in which the structural colors could be dynamically tuned. Among the oldest known materials producing structural colors are cholesteric liquid crystals. Light causes coloration by selective Bragg reflection at the periodic helicoidal structure formed by cholesteric molecules. The cholesteric pitch and thus the color can be altered by chemical composition or by temperature, but, unfortunately, dynamic tuning by electromagnetic field has been elusive. Here, we demonstrate that a cholesteric material in a new oblique helicoidal ChOH state could produce total reflection of an obliquely incident light of any polarization. The material reflects 100% of light within a band that is continuously tunable by the electric field through the entire visible spectrum while preserving its maximum efficiency. Broad electric tunability of total reflection makes the ChOH material suitable for applications in energy-saving smart windows, transparent displays, communications, lasers, multispectral imaging, and virtual and augmented reality.Graphical

Bragg diffraction of higher orders on oblique helicoidal liquid crystal structures

ABSTRACT For the oblique helicoidal (ChOH) structure of the chiral twist-bend nematic-forming mixture of CB7CB/CB6OCB/5CB doped by light-sensitive chiral compound based on azo-fragment, at oblique incidence of light two consequent states of Bragg reflection in the visible spectral range from 400 to 750 nm were experimentally observed in the course of decreasing the applied electric field. These states were assigned to different orders of Bragg’s diffraction occurring at ChOH layers with full pitch periodicity P. While the second and third orders of Bragg’s diffraction can be easily observed in conditions of standard electrooptic cell, the first order could be revealed only at very high electric field near the ‘red’ edge of the visible spectral range. For the second and third orders of diffraction there is a narrow range of electric field where both diffraction orders are observed (so-called hybrid state), with transmittance spectra of the ChOH structure showing two peaks at the short-wavelength and the long-wavelength edges of the visible spectral range. Model calculations of Bragg’s reflection of light were carried out using literature values of elasticity constants and dielectric permittivity, and the calculated plots of the selective reflection maximum vs. voltage were in good agreement with experimental data.

Nature-Inspired Helicoidal Nanocellulose-Based Multi-Compartment Assemblies with Tunable Chiroptical Properties.

Cellulose-based nanocomposites are highly appealing for the development of next-generation sustainable functional materials. Although many advances have been made in this direction, the true potential of fibrillar nanocomposites has yet to be realized because available fabrication approaches are inadequate for achieving precise structural control at the sub-micrometer scale. Here a spray-assisted alignment methodology of cellulose nanofibrils is combined with the layer-by-layer assembly into an additive manufacturing process in which the alignment direction of each cellulose layer is rationally selected to achieve thin films with a helicoidal arrangement of the nanofibrils. The helicoidal structure of the films is verified by measuring the circular dichroism (CD) of the samples. The sign and position of the structural CD peak show that the handedness and the pitch of the chiral structures can be easily tuned by deliberately selecting simple parameters, such as the number of consecutive cellulose layers sprayed in the same direction, and the angle of rotation between successive stacks of layers. To the authors' knowledge, this approach is unique as it offers the possibility to prepare complex nanocomposite architectures with various nanoscale-controlled sub-structures from different anisometric objects, which is enabling novel designs of composite films with damage-resistant and/or optical filtering functionalities.

Tunable and Switchable Thermochromism in Cholesteric Liquid Crystalline Elastomers.

Thermochromic materials have found widespread commercial use in packaging as temperature indicators. Often, these products utilize leuco dyes that are mixed into conventional polymeric resins to prepare coatings or films that exhibit temperature-dependent color change. Here, we consider a distinctive approach to thermochromism via the selective reflection of liquid crystalline elastomers that retain the helicoidal structure of the cholesteric phase (CLCEs). Upon heating, the order of the CLCEs reduces and approaches zero, resulting in a change in birefringence as well as material thickness, both of which manifest as changes in the selective reflection to heating. This examination systematically prepares CLCEs capable of reversible thermochromic response as a function of cross-link density and liquid crystalline composition. A particular focus of this examination is the preparation of CLCEs composed of chiral and achiral liquid crystalline monomers that reduce the strength of the mesogen-mesogen interaction and accordingly reduce the nematic-isotropic transition temperature. The low birefringence of some of the CLCE compositions facilitates thermochromic reflection tuning, followed by switching.

Dual tunability of selective reflection by light and electric field for self-organizing materials

The oblique helicoidal structure is formed in right-angle cholesterics under the applied electric field. The electric field changes the pitch and cone angle but preserves the single-harmonic modulation of the refractive index. As a result, in such a supramolecular system, we can tune the selective reflection of light in a broad range. Here, we report that structural colors can be tuned by simultaneously illuminating the structure with UV light and the action of an electric field. The cholesterics with the oblique helicoidal structure were doped with newly designed rod-like, chiral, and bent-shaped azo-photosensitive materials characterized by a very low rate of thermal back cis (Z) – trans (E) isomerization. The E-Z isomerization of the photo-active compounds under UV light causes the red shift of the selective light reflection in the cholesteric mixtures. We found that the molecular structure of the photosensitive materials used affects the reflection coefficient, bandwidth, response time to UV irradiation, and tuning range. The effect was explained by considering the effect of molecular matching, cis–trans isomerization, and electric field action. We investigated the dynamics of molecular changes in the oblique helicoidal structure under the influence of external factors. The designed supramolecular system has the potential application in soft matter UV detectors.

Multiscale study of the chiral self-assembly of cellulose nanocrystals during the frontal ultrafiltration process.

The structural organization of cellulose nanocrystal (CNC) suspensions at the membrane surface during frontal ultrafiltration has been characterized, for the first time, at the nano- and microscale by in situ small-angle X-ray and light scattering (SAXS and SALS, respectively). During filtration, the particles assembled at the membrane surface and formed the so-called concentration polarization layer (CPL), which contains CNCs arranged in a chiral nematic (cholesteric) helicoidal structure, with the long axis of the CNCs oriented parallel to the membrane surface, and the helical axis of the cholesteric structure oriented perpendicular to the membrane surface. The self-organization of CNCs in the form of oriented cholesteric structures was further characterized by a pitch gradient in the CPL. The structure of the CPL was also investigated upon release of the transmembrane pressure. SAXS data revealed a relaxation process associated with a diffusion of the CNCs from the membrane surface towards the bulk, while SALS measurements revealed a re-organization of the cholesteric phase that was preserved all along the deposit. The preservation of the observed structure after 14 days of continuous filtration followed by air-drying was confirmed using scanning electron microscopy and wide-angle X-ray diffraction, demonstrating the feasibility of the process scale-up.

Angle-resolved optical spectroscopy of photonic cellulose nanocrystal films reveals the influence of additives on the mechanism of kinetic arrest.

Cellulose nanocrystals (CNCs) are rod-like nanoparticles whose chiral self-assembly into photonic films has been promoted as a sustainable source of colouration. Upon drying, an aqueous CNC suspension passes through two regimes: first, a liquid phase, where the CNCs self-organise into a cholesteric liquid crystal, followed by a kinetically-arrested phase, where the helicoidal structure compresses upon loss of solvent, resulting in a solid film with vibrant structural colour. The transition between these two regimes plays an important role in the visual appearance of photonic CNC films, but details on when and how kinetic arrest occurs have remained elusive. In this work, we combine angle-resolved optical spectroscopy of photonic films (approx. 100 vol% CNC) with a model for compressed helicoidal structures to retrieve the suspension conditions during kinetic arrest (approx. 10 vol% CNC). This analysis indicates a shift in the mechanism of kinetic arrest from a glass transition at lower ionic strength to gelation at higher ionic strength, explaining the trends in domain size and film colour. In contrast, neutral additives (glucose, poly(ethylene glycol)) appear to primarily reduce the compression upon drying without affecting cholesteric behaviour, as supported by a general analytical model. These findings deepen our understanding of CNC co-assembly with various commonly-used additives, enabling better control over the production of multifunctional structurally coloured materials.

Structure Investigation of Mesogenic Homo- and Copolymers Based on Chiral and Achiral Acrylates

The X-ray diffraction method was used to study the structure of mesogenic homo- and copolymers based on chiral and achiral acrylates (disubstituted biphenyl and phenylbenzoate) under the orienting influence of magnetic and (in some cases) electric fields. The analysis of diffraction patterns was carried out in terms of the Hosemann model of a paracrystal using structural modeling and diffraction calculations on models. It was established that chiral and achiral homopolymers form smectic bilayer polar structures, but the structure of the achiral homopolymer possesses weak polarization due to small value of total dipole moment of C=O groups in the side chains. The copolymers (as the chiral homopolymer) form smectic bilayer polar helicoidal structures. The distribution of chiral and achiral components in the layers of the common bilayer depends on their ratios in the copolymer. In turn, this distribution affects both the step of helicoidal structure and the nature of structural-phase transformations in the copolymers. A comparative evaluation of the orientational effects of magnetic and electric fields on the structure of the chiral homopolymer and the copolymers has been carried out. The analysis of the temperature dependences of diffraction and structural parameters of the investigated polymers allowed us to explain some features of their behaviour within seemingly similar (by the type of X-ray patterns) smectic phases.

Enhanced Dynamic Impact Resistance of 3D-Printed Continuous Optical Fiber-Reinforced Helicoidal Polylactic Acid Composites.

Characterized by light weight and high strength, composites are widely used as protective materials in dynamic impact loading under extreme conditions, such as high strain rates. Therefore, based on the excellent tensile properties of continuous fiber and the good flexibility and toughness of the bionic spiral structure, this study uses a multi-material 3D printer to incorporate continuous fiber, and then modifies the G-CODE file to control the printing path to achieve the production of a continuous fiber-reinforced Polylactic Acid composite helicoidal (spiral angle 60°) structure (COF-HP). Dynamic behavior under high-strain-rate impact experiments have been conducted using the Split Hopkinson Pressure Bar (SHPB). Stress-strain curves, impact energy curves and high-speed camera photographs with different strain rates at 680 s-1 and 890 s-1 have been analyzed to explore the dynamic process and illustrate the damage evolution. In addition, some detailed simulation models considering the incorporation of continuous optical fiber (COF) and different strain rates have been established and verified for deeper investigations. The results show that the COF does enhance the impact resistance of the laminates. When the porosity is reduced, the maximum stress of the continuous fiber-reinforced composite material is 4~7% higher than that of the pure PLA material. Our findings here expand the application of COF and provide a new method for designing protective materials, which have broad application prospects in the aerospace and automotive industries.

Laser additive manufactured NiTi-based bioinspired helicoidal structure with excellent pseudoelasticity and energy absorption capacity

Functionality-driven biomimetic additive manufacturing (AM), as a research hotspot of 3D printing field, is providing unprecedented opportunities for developing next-generation functional materials in mechanical, electrical, optical and biomedical engineering. In this work, we developed a laser AM-ed NiTi-based helicoidal structure with excellent pseudoelasticity and energy absorption capacity, inspired by the biological architecture in the exoskeleton of the crab's claw. The rotation angle θ corresponding to the misorientation of rods in adjacent layers, as the key structure parameter, was involved into the investigations on the forming quality, pseudoelastic response and fracture behavior of the laser AM-ed helicoidal structures. The results showed that an increase in θ could improve the forming accuracy of rods but decrease the porosity due to the formation of more closed pores filled with unmelted powder particles. These pores formed by the helically stacked rods had sharp edges that could trigger earlier stress concentration and phase transformation or even strain hardening during the loading process. In views of more uniform stress distribution, the helicoidal structure with θ = 36° exhibited the largest recoverable strain of 4.32 %. Regarding the deformation and fracture behavior, it was found that the helicoidal structures with small θ were inclined to exhibit an auxetic deformation behavior and a sluggish fracture process, while the ones with larger θ were prone to a buckling deformation mode and a sudden failure. Furthermore, all helicoidal structures presented excellent energy absorption properties in terms of both unit volume and unit mass values, which could be attributed to the cross-scale hierarchical structures.

Structural insights on the nucleoprotein C-terminal domain of Měnglà virus.

Filoviruses depend on the nucleoprotein (NP) to accomplish multiple functions during the viral life cycle. NP is the most abundantly expressed viral protein in infected cells and the main component of the viral nucleocapsid. It can be structurally divided into amino- and carboxy- terminal domains (NTD and CTD). The NTD can homo-oligomerize to interact and protect the (-) ssRNA genome, forming long helical structures. The flexible CTD is responsible for the binding of other nucleocapsid proteins and is involved in the formation of inclusion bodies (IBs)-the cytoplasmic sites of nucleocapsid formation and genome replication. The CTD ends in a ~100-residue globular tail. Měnglà virus (MLAV) is the only member of the new Dianlovirus genus within the Filoviridae family. Their differential characteristics and the possibility of becoming a threat for human health justify the interest in better understanding of its structure and function. In this work, we present the structure of the globular tail of the MLAV NP CTD, showing an overall conformation closely related to that previously reported for the equivalent NP region in MARV. Moreover, analyses of the CTD-CTD interactions in the crystal asymmetric unit revealed a higher-order helicoidal structure. Mutational studies underscore the crucial role of a number of residues, located at the CTD-CTD contact interface, for IB formation. Site-directed mutagenesis of amino acids L653 and F687, involved in the formation of these helicoidal assemblies, abrogate the growth of IBs when the full-length MLAV NP was ectopically expressed in cells. Our findings confirm the role of NP CTD in IB formation, also for MLAV, and focus the attention on particular residues as starting point for further analysis.IMPORTANCEFiloviruses are the causative agents of severe and often fatal hemorrhagic disease in humans. Měnglà virus (MLAV) is a recently reported filovirus, isolated from fruit bats that is capable to replicate in human cells, representing a potential risk for human health. An in-depth structural and functional knowledge of MLAV proteins is an essential step for antiviral research on this virus that can also be extended to other emerging filoviruses. In this study, we determined the first crystal structures of the C-terminal domain (CTD) of the MLAV nucleoprotein (NP), showing important similarities to the equivalent domain in MARV. The structural data also show that the NP CTD has the ability to form large helical oligomers that may participate in the control of cytoplasmic inclusion body formation during viral replication.

Highly efficient separation of water-in-oil emulsion using electrospun helicoidal polymer strips

Rationally designed electrospun membranes are commonly used to efficiently separate water-in-oil emulsions. However, obtaining high separation efficiency without sacrificing separation flux cannot be readily attained. Herein, we propose a strategy for controlling the overall geometry of the electrospun product to simultaneously achieve high water-in-oil emulsion separation flux and efficiency. Polycaprolactone (PCL)/polyvinylpyrrolidone (PVP) strips with multi-scale helicoidal structures were readily prepared by using immersion electrospinning. The multi-scale helicoidal structure of the strip could be precisely regulated by controlling the PCL/PVP weight ratio and the applied voltage. The desired helicoidal structure of the immersion electrospun strip provided preferred membrane porosity and thickness, as well as multifaceted wettability, leading to a high water-in-oil emulsion separation flux of 2350 L/m2h and a high separation efficiency of over 99 %. After 10 cycles, the separation flux of the immersion electrospun membrane was still around 60 % higher than that of the non-recycled conventional electrospun membrane without sacrificing separation efficiency. Moreover, the mechanisms responsible for the excellent performance of immersion electrospun membranes are discussed in depth. This work offers new insight into the rational preparation of advanced electrospun membranes for oil/water separation applications.

A study of a bio-inspired impact resistant carbon fiber laminate with a sinusoidal helicoidal structure in the mandibles of trap-jaw ants.

The majority of living organisms demonstrate remarkable attributes and have evolved effective mechanisms for synthesizing impact-resistant and damage-tolerant structures. One exemplary instance is the rapid mandible strikes exhibited by trap-jaw ants, which are a highly aggressive species of terrestrial social organisms. An impact-resistant sinusoidal helicoidal architecture is discovered in the mandibles of trap-jaw ants. The bioinspired laminate with a bi-sinusoidal helicoidal structure was manufactured using unidirectional carbon fiber prepreg by mold press forming. This study examines the impact resistance and damage tolerance of a bionic laminate through low velocity impact, computed tomography, and compression after impact tests. The results demonstrate that bionic laminates effectively limit damage propagation within the plane while enhancing energy dissipation capacity. The sinusoidal helicoidal configuration enhances cushioning capability against impact forces, retards penetration under higher loads, hinders crack propagation, and improves residual strength. Bionic laminates provide a valuable solution for damage tolerance through the resistance to through-the-thickness loads. STATEMENT OF SIGNIFICANCE: Helicoidal and sinusoidal helicoidal microstructures have been identified in the cross-section of the jaws of trap-jaw ants. The multiple waviness ratio parameters are designed for fabricating a sinusoidal helicoidal structure laminate using unidirectional carbon fiber prepreg through the mold press forming technique. This results in a damage-tolerant mechanism characterized by reduced delamination damage, which leads to a stiffer mechanical response. Meanwhile, it enhances resistance to crack propagation, leading to the formation of discontinuous delamination areas and the accumulation of sub-critical failures. Additionally, the sinusoidal helicoidal structure laminate combines the cushioning performance of bi-sinusoidal arrangements with the enhanced impact resistance of helical arrangements. This design delays penetration at higher loads, resulting in increased residual strength.

Investigation of bionic composite laminates inspired by the natural impact-resistant helicoidal structure in the mandibles of trap-jaw ants.

Many living organisms exhibit exceptional capabilities and have evolved effective strategies to synthesize impact-resistant and damage-tolerant structures. One such example can be observed in the rapid mandible strikes ofOdontomachus monticola, a species of trap-jaw ants from the ponerine subfamily. During trap-jaw strikes, the mandibles can achieve peak speeds of 35.42 m s-1, and the maximum acceleration can reach 71 729 g within an average duration of 0.18 ms. The extreme acceleration results in instantaneous mandible strike forces that can exceed 330 times the ant's body weight, withstanding thousands of impacts. A natural impact-resistant fibrous helicoidal structure is found in the mandibles of trap-jaw ants. This microstructure is characterized by periodic modulus oscillations that increase energy absorption and improve stress redistribution, offering added protection against damage from impact loading. A carbon fiber reinforced helicoidal composite is fabricated based on the microstructure of the trap-jaw ant's mandibles. The results show that the helicoidal composite with a 12° helical-fiber exhibits higher residual strength, making it more capable of withstanding strong collisions. The catastrophic propagation of damage along the thickness direction is prevented by in-plane spreading and redirection of cracks. This research provides useful references for fabricating bionic impact-resistant composites.

Mechanical behavior of bio-inspired helicoidal thermoplastic composites

Helicoidal composite has been found naturally existing in many species of crustaceans and it has recently raised a significant amount of interests among researchers due to its great impact performance resulted from unique fiber layup architecture. This work is focused on developing a novel bio-inspired helicoidal thermoplastic composite and studying its mechanical behaviors under different testing conditions. Continuous glass fiber reinforced polypropylene composite preforms were used for compression molding the helicoidal structure with a pitch angle of 16.3° and nonlinear pitch angle. Composites with conventional fiber layups such as 0/90 and quasi-isotropic layup sequences were also prepared and tested for comparison purpose. Various tests at different strain rates, including quasi-static test (flexural test and compression after impact test), low strain rate test (Izod impact test and drop tower impact test), and high strain rate test (Split Hopkinson pressure bar test), were performed to evaluate the mechanical properties of the helicoidal composites and conventional composites. The helicoidal composites showed twisting fracture pattern for deflecting cracks involving more areas for energy absorption in addition to common failure mechanisms in the Izod impact test. It was also found that the helicoidal composite showed considerably higher damage tolerance than the conventional composites in high strain rate scenarios.