Twisted Filaments Research Articles

Unveiling the microstructural evolution and interaction mechanisms for twisted structures

Twisting plays an important role in fabricating twisted actuators and energy harvesters, which require excellent microstructural deformation and interaction properties between different layers. However, the cross-layer microstructural evolution and interaction mechanism of helical structures under twisting and stretching are still unclear. Herein, a multi-layer model is established to theoretically investigate the response of the filaments under twisting and stretching. The results quantitatively indicate that the filaments with a higher twist have more structural evolution and less elongation deformation in the tensile process, which contributes to the increase of ductility. The evolution of the helical angle is also verified by in-situ experiments and finite element simulations. Besides, a theoretical method is provided for investigating the mechanical behavior of anisotropic twisted fibers, and the contact pressure is also promoted to understand the twisting-induced densification. The interlayer extrusion reveals that appropriate stretching of twisted fiber is an effective way to densify the loose fibers, and it also provides the theoretical reason for twisting and stretching simultaneously when wringing out a wet towel. We believe that this work would shed light on the interaction mechanism of twisted filaments and provide mechanistic insights into the twisting design of multi-layer helical structures.

2D and 3D PVA electrospun scaffold evaluation for ligament implant replacement: A mechanical testing, modelling and experimental biomechanics approach

The gold standard to characterise anterior cruciate ligament (ACL) implants is through the evaluation of mechanical properties such as Young's modulus or ultimate tensile stress. Currently, no studies have been performed to relate the in-vivo hyper-elastic behaviour of the ACL with the design of tissue engineered ligaments. The aim of this work is to determine the most comparable 2D/3D polyvinyl alcohol (PVA) electrospun structure to the in-vivo mechanical behaviour of the natural ligament. Biomechanics of 12 young participants were captured while daily and high impact activities were performed. A musculoskeletal knee model and kinematic data were used to estimate the in-vivo ACL length and strain. The in-vivo ACL tensile forces were determined with a non-linear force/strain relationship. 2D scaffolds, 1 twisted filament scaffolds, 3 twisted filaments scaffolds and 3 twisted/braided filaments scaffolds were fabricated using electrospinning and characterised morphologically and mechanically using scanning electron microscopy and tensile testing respectively. Cyclic tensile and shear tests were performed in dry and wet conditions to crosslinked and non-crosslinked samples. The hyper-elastic behaviour of our PVA scaffolds was characterised with the Mooney Rivlin model and a non-linear string-based model, and both models compared with the in-vivo mechanical behaviour of the native ACL. Crosslinked 3 twisted/braided filaments scaffolds faithfully mimicked the morphology and the hyper-elastic behaviour of the natural ACL, showed a good resistance to shear loading and remained undegraded in phosphate-buffer saline solution. This study demonstrated, for the first time, that 3 twisted/braided filaments PVA electrospun scaffolds have an excellent potential for ACL replacements.

Mechanics and topology of twisted hyperelastic filaments under prescribed elongations: Experiment, theory, and simulation

Soft filaments can be stretched, bent, and twisted, exhibiting complex configurations. When a filament undergoes large torsional deformation, it can display instabilities, and its post-buckling behavior and configuration evolution differs significantly from that observed under small deformation. We study the mechanics and topologically complex morphologies of twisted rubber filaments under prescribed elongation by combining experiment and finite strain theory. Based on the Mooney-Rivlin model, a finite strain theory of the hyperelastic filament under combined tension, bending, and torsion has been established, accounting for both geometrical and material nonlinearities. An experimental and theoretical morphological phase diagram is constructed as a function of the twist density and the initial elongation. The buckling and post-buckling behaviors of the twisted rubber filaments under prescribed elongation are well captured by the theory that considers geometrical nonlinearity and self-contact. By tracking the interconversion of link, twist, and writhe, we accurately determine the configuration and the critical points of phase transitions. The theoretical predictions agree closely with the measurements. This work sheds light on understanding the morphological complexity of the loaded hyperelastic rod.

Structure of the nonhelical filament of the Alzheimer's disease tau core.

The microtubule-associated protein tau aggregates into neurofibrillary tangles in Alzheimer's disease (AD). The main type of aggregates, the paired helical filaments (PHF), incorporate about 20% of the full-length protein into the rigid core. Recently, cryo-electron microscopy data showed that a protease-resistant fragment of tau (residues 297-391) self-assembles in vitro in the presence of divalent cations to form twisted filaments whose molecular structure resembles that of AD PHF tau [S. Lövestam et al., Elife 11, e76494 (2022)]. To investigate whether this tau construct is uniquely predisposed to this morphology and structure, we fibrillized tau (297-391) under the reported conditions and determined its structure using solid-state NMR spectroscopy. Unexpectedly, the protein assembled predominantly into nontwisting ribbons whose rigid core spans residues 305-357. This rigid core forms a β-arch that turns at residues 322CGS324. Two protofilaments stack together via a long interface that stretches from G323 to I354. Together, these two protofilaments form a four-layered β-sheet core whose sidechains are stabilized by numerous polar and hydrophobic interactions. This structure gives insight into the fibril morphologies and molecular conformations that can be adopted by this protease-resistant core of AD tau under different pH and ionic conditions.

Micromorphology of hesperidin crystals and ultrastructure of crystal-bearing cells in Metrodorea nigra, a neotropical Rutaceae species

Researches on the developmental and morphological features of organic crystals in plants are relatively scarce. Hesperidin is a flavanone glycoside found abundantly in Rutaceae, mainly in Citrus fruits. Due to the variety of biological activities, hesperidin is one of the most promising bioflavonoids. We investigated the distribution, micromorphology and intracellular localization of hesperidin crystals in the vegetative organs of Metrodorea nigra, a neotropical Rutaceae tree. Additionally, we analyzed the ultrastructural organization of crystal-bearing cells. Bright field, epifluorescence and polarized-light microscopy, scanning (SEM) and transmission electron microscopy (TEM) analysis were performed. Hesperidin crystals appeared as needle-shaped crystals forming plumose clusters under SEM, and as acicular solitary crystal or aggregate yellow/brown twisted filaments inside cells under light microscope. Hesperidin and calcium oxalate crystals often occurred together in the epidermis and mesophyll tissues. Hesperidin crystals were abundant inside the phloem, while calcium oxalate crystals were absent in the vascular tissues. Phenolic substances occurred in all tissues, but they were abundant within vascular tissues. Flavonoid autofluorescence in blue color was associated with crystals in the cell walls and cytoplasm. The crystal-bearing cells exhibited extensive rough endoplasmic reticulum (RER) and associated vesicles filled with electron-dense materials, proliferation of the tonoplast and abundance of multilamellar bodies containing electron-dense or crystalline materials close to irregular plasmalemma. Our ultrastructural observations allow us to speculate that the RER and tonoplast membranes and associated vesicles appeared to be involved in the packaging and channeling of the materials toward the cell walls. Crystals of hesperidin and calcium oxalate occurred on the surface of common epidermal cells and glandular trichomes. The mechanisms of condensation, crystallization and extrusion of hesperidin crystal through the cell walls remain to be investigate, and could be an interesting subject for future studies.

Tychonema sp. BBK16 Characterisation: Lifestyle, Phylogeny and Related Phages.

Cyanobacterial expansion is harmful to the environment, the ecology of Lake Baikal and the economy of nearby regions and can be dangerous to people and animals. Since 2011, the process of colonisation of the lake with potentially toxic cyanobacteria belonging to the genus Tychonema has continued. An understanding of the mechanism of successful expansion of Tychonema requires scrutiny of biological and genomic features. Tychonema sp. BBK16 was isolated from the coastal zone of Lake Baikal. The morphology of BBK16 biofilm was studied with light, scanning electron and confocal microscopy. The biofilm is based on filaments of cyanobacteria, which are intertwined like felt; there are also dense fascicles of rope-like twisted filaments that impart heterogeneity to the surface of the biofilm. Genome sequencing, intergenomic comparisons and phylogenetic analyses indicated that Tychonema sp. BBK16 represent a new species related to planktic cyanobacterium Tychonema bourrellyi, isolated from Alpine lentic freshwater. Genome investigation revealed the genes possibly responsible for the mixotrophic lifestyle. The presence of CRISPR-Cas and restriction modification defence mechanisms allowed to suggest the existence of phages infecting Tychonema sp. BBK16. Analysis of CRISPR spacers and prophage-derived regions allowed to suggest related cyanophages. Genomic analysis supported the assumption that mobile elements and horizontal transfer participate in shaping the Tychonema sp. BBK16 genome. The findings of the current research suggest that the aptitude of Tychonema sp. BBK16 for biofilm formation and, possibly, its mixotrophic lifestyle provide adaptation advantages that lead to the successful expansion of this cyanobacterium in the Baikal's conditions of freshwater lake environments.

Twist response of actin filaments

Actin cytoskeleton force generation, sensing, and adaptation are dictated by the bending and twisting mechanics of filaments. Here, we use magnetic tweezers and microfluidics to twist and pull individual actin filaments and evaluate their response to applied loads. Twisted filaments bend and dissipate torsional strain by adopting a supercoiled plectoneme. Pulling prevents plectoneme formation, which causes twisted filaments to sever. Analysis over a range of twisting and pulling forces and direct visualization of filament and single subunit twisting fluctuations yield an actin filament torsional persistence length of ~10 µm, similar to the bending persistence length. Filament severing by cofilin is driven by local twist strain at boundaries between bare and decorated segments and is accelerated by low pN pulling forces. This work explains how contractile forces generated by myosin motors accelerate filament severing by cofilin and establishes a role for filament twisting in the regulation of actin filament stability and assembly dynamics.

Three-dimensional coordination of cell-division site positioning in a filamentous cyanobacterium.

Bacterial cells mostly divide symmetrically. In the filamentous, multicellular cyanobacterium Anabaena, cell-division planes are aligned vertically relative to the long axis of every single cell. This observation suggests that both the placement and the angle of the division planes are controlled in every single cell so that the filament can grow in one single dimension along the long axis. In this study, we showed that inactivation of patU3 encoding a cell-division inhibitor led cells to divide asymmetrically in two dimensions leading to twisted filaments, indicating that PatU3 controls not only the position but also the angle of the division planes. Deletion of the conserved minC and minD genes affected cell division symmetry, but not the angle of the division planes. Remarkably, when both patU3 and minCD were inactivated, cells could divide asymmetrically over 360° angles in three dimensions across different cellular sections, producing not only cells with irregular sizes, but also branching filaments. This study demonstrated the existence of a system operating in a three-dimensional manner for the control of cell division in Anabaena. Such a regulation may have been evolved to accommodate multicellular behaviors, a hallmark in evolution.

OmpR and Prc contribute to switch the Salmonella morphogenetic program in response to phagosome cues.

Salmonella enterica serovar Typhimurium infects eukaryotic cells residing within membrane-bound phagosomes. In this compartment, the pathogen replaces the morphogenetic penicillin-binding proteins 2 and 3 (PBP2/PBP3) with PBP2SAL /PBP3SAL , two proteins absent in Escherichia coli. The basis for this switch is unknown. Here, we show that PBP3 protein levels drop drastically when S. Typhimurium senses acidity, high osmolarity and nutrient scarcity, cues that activate virulence functions required for intra-phagosomal survival and proliferation. The protease Prc and the transcriptional regulator OmpR contribute to lower PBP3 levels whereas OmpR stimulates PBP2SAL /PBP3SAL production. Surprisingly, despite being essential for division in E. coli, PBP3 levels also drop in non-pathogenic and pathogenic E. coli exposed to phagosome cues. Such exposure alters E. coli morphology resulting in very long bent and twisted filaments indicative of failure in the cell division and elongation machineries. None of these aberrant shapes are detected in S. Typhimurium. Expression of PBP3SAL restores cell division in E. coli exposed to phagosome cues although the cells retain elongation defects in the longitudinal axis. By switching the morphogenetic program, OmpR and Prc allow S. Typhimurium to properly divide and elongate inside acidic phagosomes maintaining its cellular dimensions and the rod shape.

Phenol-soluble modulins PSMα3 and PSMβ2 form nanotubes that are cross-α amyloids

Phenol-soluble modulins (PSMs) are peptide-based virulence factors that play significant roles in the pathogenesis of staphylococcal strains in community-associated and hospital-associated infections. In addition to cytotoxicity, PSMs display the propensity to self-assemble into fibrillar species, which may be mediated through the formation of amphipathic conformations. Here, we analyze the self-assembly behavior of two PSMs, PSMα3 and PSMβ2, which are derived from peptides expressed by methicillin-resistant Staphylococcus aureus (MRSA), a significant human pathogen. In both cases, we observed the formation of a mixture of self-assembled species including twisted filaments, helical ribbons, and nanotubes, which can reversibly interconvert in vitro. Cryo–electron microscopy structural analysis of three PSM nanotubes, two derived from PSMα3 and one from PSMβ2, revealed that the assemblies displayed remarkably similar structures based on lateral association of cross-α amyloid protofilaments. The amphipathic helical conformations of PSMα3 and PSMβ2 enforced a bilayer arrangement within the protofilaments that defined the structures of the respective PSMα3 and PSMβ2 nanotubes. We demonstrate that, similar to amyloids based on cross-β protofilaments, cross-α amyloids derived from these PSMs display polymorphism, not only in terms of the global morphology (e.g., twisted filament, helical ribbon, and nanotube) but also with respect to the number of protofilaments within a given peptide assembly. These results suggest that the folding landscape of PSM derivatives may be more complex than originally anticipated and that the assemblies are able to sample a wide range of supramolecular structural space.

Instability of Soft Elastic Filaments Under Torsion: Experiment and Analysis

Abstract Twist insertion in soft filaments is an efficient way to produce the twisted and coiled polymer (TCP) muscles. The study on the formation process of highly twisted filaments is significant for understanding the mechanics of filament-based artificial muscles. A novel in situ torsion tester is developed for measuring the torsional behavior of monofilaments under an array of axial forces. The torque transducer consists of a flexural pivot attached by a mirror, the rotation angle of which is measured by an electronic autocollimator. The calibration results demonstrate perfect linearity between the torque and the angular displacement. The torsion tester combines a vast torque capacity of about 8.59 × 10−3 Nm with a resolution of about 1.02 × 10−8 Nm. Torsion experiments are performed on nylon 6 monofilaments under various axial forces. The critical torques for the first and the secondary instability of monofilaments under different axial forces are obtained. Three stability criteria of filaments subjected to torsion and tension, due to Timoshenko, to Ross, and to Dwivedi and co-workers, are accessed within the context of measurement data. The critical torque for the first instability predicted by the Timoshenko model agrees with the experimental results. The critical torques for the secondary instability can be well predicted by both the Ross and the Dwivedi et al.'s models, although the latter model gives a more reliable prediction.

Effects of chirality and inhomogeneous growth on the morphology of plant tendril

By controlling the growth rate, biomaterials with chiral microstructure can produce nonuniform prestress and then form chiral morphologies, such as twisted biological filaments, while it is not clear how the chiral microstructure of biomaterials affects the formation and movement of its macro chiral morphologies under the action of uneven prestresses. In this work, a double-layered composite beam model considering the chiral microstructure of biological materials based on experimental observations is established. The influences of inhomogeneous growth and chiral microstructure on the formation of the chiral morphologies of tendrils are considered as a typical example and discussed in detail. The results show that the macro chiral phases of plant tendrils provide a remarkable dependence on their chiral microstructures.

Lynds Bright Nebulae: sites of possible twisted filaments and ongoing star formation

ABSTRACT The paper presents an analysis of multiwavelength data of two Lynds Bright Nebulae (LBNs), LBN 140.07+01.64 and LBN 140.77−1.42. The 1420-MHz continuum map reveals an extended Y-shaped feature (linear extent ∼3.7°), which consists of a linear part and a V-like structure. The sites LBN 140.07+01.64 and AFGL 437 are located towards the opposite sides of the V-like structure, and LBN 140.77−1.42 is spatially seen towards the linear part. Infrared-excess sources are traced towards the entire Y-feature, suggesting star formation activities. Infrared and submillimetre images show the presence of at least two large-scale dust filaments extended towards the LBN sources. The Herschel maps, which are available only towards the northern and central parts of the Y-feature, display the presence of higher column density (≥2.4 × 1021 cm−2) of materials towards the filaments. Using the 12CO(1–0) line data, the distribution of molecular gas at [−42.7, −34.4] km s−1 traces the cloud associated with the Y-feature, and confirms the existence of filaments. The large-scale filaments appear to be possibly spatially twisted. There is a hint of an oscillatory-like velocity pattern along both the filaments, favouring their proposed twisted nature. It is the first study showing the possible twisting of filaments, which is more prominent in the northern and central parts of the Y-feature. This possible twisting/coupling of the large-scale filaments appears to be responsible for the observed star formation (including known OB stars). The proposed physical process and the energetics of OB stars together seem to explain the origin of the ionized Y-feature.

Нові знахідки Bambusina borreri (Ralfs) Cleve (Charophyta) – виду з Червоної книги України

he article presents information about new finds of desmid Bambusina borreri (= B. brebissonii Kütz. ex Kütz.) in Ukraine and analysis of its distribution in the country. Peculiar features of the genus are cylindrical or barrel-shaped cells arranged in slightly twisted non-mucous filaments. Bambusina borreri is cosmopolitan with a disjunctive rangeж its distribution is limited by pH and trophic level of water bodies. Environmental selectivity determines its low frequency of occurrence. The species was included in the third edition of the Red Data Book of Ukraine. The authors first discovered B. borreri in the swamp protected by the Chornolisky Landscape Reserve of National Importance (Kirovohrad Region, Ukraine).In the Maliovanka Regional Landscape Park (Khmelnytsky Region, Ukraine) this species was confirmed to inhabit Rusalchyne Lake and first found in three more lakes. In all cases B. borreri occurred in typical habitats: oligotrophic reservoirs with low pH. A list of locations and a map of the distribution of B. borreri in Ukraine has been compiled. Among 22 localities cited for this species five sites are currently dissappeared. Most of the B. borreri localities are situated in the Pripyat-Desna Algofloristic Subprovince and only two belong to the Middle Dnieper and Carpathian-Danube algofloristic subprovinces; this is due to ecological preferences of the species. It is important to note that 10 of the 17 still existing habitats of B. borreri are located within the objects of the Nature Preservation Fund of Ukraine, which is an important aspect of its conservation.

Collagen-Inspired Self-Assembly of Twisted Filaments.

Collagen consists of three peptides twisted together through a periodic array of hydrogen bonds. Here we use this as inspiration to find design rules for programmed specific interactions for self-assembling synthetic collagenlike triple helices, starting from disordered configurations. The assembly generically nucleates defects in the triple helix, the characteristics of which can be manipulated by spatially varying the enthalpy of helix formation. Defect formation slows assembly, evoking kinetic pathologies that have been observed to mutations in the primary collagen amino acid sequence. The controlled formation and interaction between defects gives a route for hierarchical self-assembly of bundles of twisted filaments.

Bean’s critical-state model as a consequence of the circuit model of non-linear resistance

Bean’s critical-state model has served as the foundation for computing the heat generated by the time-varying magnetic field or current in type-II superconductors. Two key features of the Bean model are (i) the current density is either zero or at the critical value Jc and (ii) the change in the current distribution begins at the surface. In this work, we apply the circuit model to simulate the process of charging a type-II superconductor. In addition to the self and mutual inductances among the basic units, we introduce a current-dependent longitudinal resistance to describe the critical current density, above which the conductor becomes resistive. By identifying the inductance values, we are able to reproduce the characteristic behavior of the Bean model. Specifically, we consider a superconducting slab and a superconducting wire composed of straight or twisted filaments and recover the established analytical results for these geometries. In terms of the circuit model, the behavior of the Bean model is a consequence of the geometry-specific structure of inductances and the non-linear resistances. Besides offering an intuitive explanation of the Bean model, our circuit-model calculations provide concrete examples to show that they can be used to simulate the complete charging process of multi-filament superconducting wires.

History of Pick's disease

History of Pick's disease

Preparation and Transmission Characteristics of Hybrid Structure Yarns with Nylon fiber for Smart Wear

Twisted Copper Filaments (TCF) were made by a yarn covering process in order to transmit signals and power for electronic textiles. The 560 denier polyurethane filaments were covered in the S-twist direction by urethane-coated copper wires. Two TCF's twisted in the Z direction were further covered in the S direction by nylon filaments to make final hybrid structure yarns (HSY). The HSY prepared was proportionally increased in apparent resistance and showed resistivity of 1.6210–8Ω·m. The number of ply was critical in terms of resistance variation, showing a linear increase in resistance with ply number. The twist factor, however, was not as significant. Final filaments were found to be changed in resonance frequency mainly due to the change of di-electricity and thus capacitance caused by the nylon covering. It is concluded that while resonance frequency was primarily determined by filament length and dielectric constant of the covering yarns, resonance frequency S11 and S21 were mainly determined by measurement length and ply number.

The CNS in inbred transgenic models of 4-repeat Tauopathy develops consistent tau seeding capacity yet focal and diverse patterns of protein deposition

BackgroundMAPT mutations cause neurodegenerative diseases such as frontotemporal dementia but, strikingly, patients with the same mutation may have different clinical phenotypes.MethodsGiven heterogeneities observed in a transgenic (Tg) mouse line expressing low levels of human (2 N, 4R) P301L Tau, we backcrossed founder stocks of mice to C57BL/6Tac, 129/SvEvTac and FVB/NJ inbred backgrounds to discern the role of genetic versus environmental effects on disease-related phenotypes.ResultsThree inbred derivatives of a TgTauP301L founder line had similar quality and steady-state quantity of Tau production, accumulation of abnormally phosphorylated 64–68 kDa Tau species from 90 days of age onwards and neuronal loss in aged Tg mice. Variegation was not seen in the pattern of transgene expression and seeding properties in a fluorescence-based cellular assay indicated a single “strain” of misfolded Tau. However, in other regards, the aged Tg mice were heterogeneous; there was incomplete penetrance for Tau deposition despite maintained transgene expression in aged animals and, for animals with Tau deposits, distinctions were noted even within each subline. Three classes of rostral deposition in the cortex, hippocampus and striatum accounted for 75% of pathology-positive mice yet the mean ages of mice scored as class I, II or III were not significantly different and, hence, did not fit with a predictable progression from one class to another defined by chronological age. Two other patterns of Tau deposition designated as classes IV and V, occurred in caudal structures. Other pathology-positive Tg mice of similar age not falling within classes I-V presented with focal accumulations in additional caudal neuroanatomical areas including the locus coeruleus. Electron microscopy revealed that brains of Classes I, II and IV animals all exhibit straight filaments, but with coiled filaments and occasional twisted filaments apparent in Class I. Most strikingly, Class I, II and IV animals presented with distinct western blot signatures after trypsin digestion of sarkosyl-insoluble Tau.ConclusionsQualitative variations in the neuroanatomy of Tau deposition in genetically constrained slow models of primary Tauopathy establish that non-synchronous, focal events contribute to the pathogenic process. Phenotypic diversity in these models suggests a potential parallel to the phenotypic variation seen in P301L patients.

A 3-D Numerical Model to Estimate the Critical Current in MgB2 Wire and Cable with Twisted Structure

Due to the low material cost, high critical transition temperature and high-current-carrying capacity, MgB2 round wire with twisted filaments has great potential for applications in engineering. Therefore, it is important to estimate their critical current for optimizing and realizing high-powered wire and cable. A 3-D model is presented to calculate the critical current of wire and cable with twisted filaments. The critical current is estimated based on the Biot-Savart law and self-consistent model. A comparison between 2-D and 3-D models is performed for the wire. We consider the effect of twist pitch on the critical current. Moreover, the critical current of 6-around-1 cable with different twist pitches is analyzed and discussed using the 3-D model. It can be found that twist pitch of filaments plays an important role on the critical current. The model and method may also be useful for other superconducting wires and cables.