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Synthetic silk production has undergone significant technological and commercial advances over the past 5 years, with fibers from most labs and companies now regularly matching the properties of natural silk by one metric or another. Yet the fundamental links between silk protein processing and performance remain largely unresolved and fiber optimization is commonly achieved through non‐natural methods. In an effort to address this challenge, data that closes this loop of processing and performance is presented by spinning a native silk feedstock ex vivo into a near‐native fiber using just two naturally occurring parameters; pH activation and extensional flow (i.e., spinning rate). This allows us to link previous experimental and modelling hypothesis surrounding silk's pH responsiveness directly to multiscale hierarchical structure development during spinning. Finally, fibers that match, and then exceed, natural silk's mechanical properties are spun and understood by rate of work input. This approach not only provides energetic insights into natural silk spinning and controlled protein denaturation, but is believed will help interpret and improve synthetic silk processing. Ultimately, it is hoped that these results will contribute towards novel bioinspired energy‐efficient processing strategies that are driven by work input optimization and where excellent mechanical properties are self‐emergent. [ABSTRACT FROM AUTHOR]

Abstract The Filippi's gland, also called the Lyonet's gland, is in truth a pair of tiny glands that are unique to lepidopteran insects. Although the ultrastructure of the Filippi's gland has been well-understood, the specific biological function of this gland in silk spinning is still unclear. Previous studies proposed a hypothesis that this gland might synthesize and secrete some substances into the anterior silk gland (ASG) to help silk spinning. In order to identify these metabolites, a GC/MS-based metabolomics technique was introduced. A total of 59 metabolites, including fatty acids, amino acids, and sugars, were identified in glands from silkworm larvae in the feeding and silk spinning stages. Abundance and pathway analyses revealed that these metabolites had different abundances during gland development and silk spinning, which may facilitate the transport of small molecules and ions. The most interesting result is that the Filippi's gland has a very active fatty acid biosynthesis process during spinning, suggesting that it may synthesize lipids or waxes and secrete them into the ASG to promote silk spinning. This data provides instructive insight into the biological functions of Filippi's gland from both silkworms and other lepidoptera. Graphical abstract Image 1 Highlights • GC/MS-based metabolomics identified 59 metabolites in the Filippi's glands of the silkworm at various stages. • Most of the metabolites are involved in metabolic pathways, transport, and mineral absorption. • Fatty acids are significantly enriched during spinning. • There is an active ester synthesis in the Filippi's glands. [ABSTRACT FROM AUTHOR]

Straining Flow Spinning is a versatile and robust spinning technique for the production of regenerated silkworm silk fibers using mild chemistries. However, reaching high values of tensile strength and strain at breaking requires a step of wet-stretching in water, which limits scalability and the practical usage of the technique. Here, we show that adding a post-spinning drawing step to the procedure improves the performance of the fibers, and allows the development of a scalable process. It is also shown that the properties of the fiber can be tuned by varying the parameters of the post-spinning step. Finally, equivalence is established between the discrete wet-stretching process and the continuous post-spinning drawing step. [ABSTRACT FROM AUTHOR]

Biomimetic spinning of artificial spider silk requires that the terminal domains of designed minispidroins undergo specific structural changes in concert with the β-sheet conversion of the repetitive region. Herein, we combine solution and solid-state NMR methods to probe domain-specific structural changes in the NT2RepCT minispidroin, which allows us to assess the degree of biomimicry of artificial silk spinning. In addition, we show that the structural effects of post-spinning procedures can be examined. By studying the impact of NT2RepCT fiber drying, we observed a reversible beta-to-alpha conversion. We think that this approach will be useful for guiding the optimization of artificial spider silk fibers. [ABSTRACT FROM AUTHOR]

Natural silk spinning offers several advantages over the synthetic fiber spinning, although the underlying mechanisms of this process are yet to be fully elucidated. Silkworm silks, specifically B. mori, comprise two main proteins: fibroin, which forms the fiber, and sericin, a coextruded coating that acts as a matrix in the resulting nonwoven composite cocoon. To date, most studies have focused on fibroin's self-assembly and gelation, with the influence of sericin during spinning receiving little to no attention. This study investigates sericin's effects on the self-assembly of fibroin via their natural phase-separation. Through changes in sample opacity, FTIR, and XRD, we report that increasing sericin concentration retards the time to gelation and β-sheet formation of fibroin, causing it to adopt a Silk I conformation. Such findings have important implications for both the natural silk spinning process and any future industrial applications, suggesting that sericin may be able to induce long-range conformational and stability control in silk fibroin, while being in a separate phase, a factor that would facilitate long-term storage or silk feedstocks. [ABSTRACT FROM AUTHOR]

Spiders and silkworms spin silks that outcompete the toughness of all natural and manmade fibers. Herein, we compare and contrast the spinning of silk in silkworms and spiders, with the aim of identifying features that are important for fiber formation. Although spiders and silkworms are very distantly related, some features of spinning silk seem to be universal. Both spiders and silkworms produce large silk proteins that are highly repetitive and extremely soluble at high pH, likely due to the globular terminal domains that flank an intermediate repetitive region. The silk proteins are produced and stored at a very high concentration in glands, and then transported along a narrowing tube in which they change conformation in response primarily to a pH gradient generated by carbonic anhydrase and proton pumps, as well as to ions and shear forces. The silk proteins thereby convert from random coil and alpha helical soluble conformations to beta sheet fibers. We suggest that factors that need to be optimized for successful production of artificial silk proteins capable of forming tough fibers include protein solubility, pH sensitivity, and preservation of natively folded proteins throughout the purification and initial spinning processes. [ABSTRACT FROM AUTHOR]

The exceptional strength and extensibility of spider dragline silk have been thought to be facilitated by two spidroins, major ampullate spidroin 1 (MaSp1) and major ampullate spidroin 2 (MaSp2), under the assumption that protein secondary structures are coupled with the expressed spidroins. We tested this assumption for the dragline silk of three co-existing Australian spiders, Argiope keyserlingi, Latrodectus hasselti and Nephila plumipes. We found that silk amino acid compositions did not differ among spiders collected in May. We extended these analyses temporally and found the amino acid compositions of A. keyserlingi silks to differ when collected in May compared to November, while those of L. hasselti did not. To ascertain whether their secondary structures were decoupled from spidroin expression, we performed solid-state nuclear magnetic resonance spectroscopy (NMR) analysis on the silks of all spiders collected in May. We found the distribution of alanine toward β-sheet and 3,10helix/random coil conformations differed between species, as did their relative crystallinities, with A. keyserlingi having the greatest 3,10helix/random coil composition and N. plumipes the greatest crystallinity. The protein secondary structures correlated with the mechanical properties for each of the silks better than the amino acid compositions. Our findings suggested that a differential distribution of alanine during spinning could decouple secondary structures from spidroin expression ensuring that silks of desirable mechanical properties are consistently produced. Alternative explanations include the possibility that other spidroins were incorporated into some silks. [ABSTRACT FROM AUTHOR]

For centuries silkworm filaments have been the focus of R&D innovation centred on textile manufacture with high added value. Most recently, silk research has focused on more fundamental issues concerning bio-polymer structure-property-function relationships. This essay outlines the complexity and fundamentals of silk spinning, and presents arguments for establishing this substance as an interesting and important subject at the interface of systems biology (discovery) and synthetic biology (translation). It is argued that silk is a generic class of materials where each type of silk presents a different embodiment of emergent properties that combine genetically determined (anticipatory) and environmentally responsive components. In spiders' webs the various silks have evolved to form the interactive components of an intricate fabric that provides an extended phenotype to the spider's body morphology. [ABSTRACT FROM AUTHOR]

Silk spinning defines the morphologically constrained embiopterans. All individuals spin for protection, including immatures, adult males and the wingless females. Enlarged front tarsi are packed with silk glands and clothed with ejectors. They spin by stepping with their front feet and releasing silk against substrates and onto pre-existing silk, often cloth-like. Spinning is stereotypical and appears to differ between species in frequency and probability of transition between two spin-step positions. This spinning choreography was assessed using thousands of spin-steps scored in the laboratory for 22 species to test: (1) the body size hypothesis predicting that spinning would be more complex for larger species; and (2) the phylogeny hypothesis which predicted that spinning would display phylogenetic signal. Tests relied on published phylogenies for the order Embioptera. Independent contrast analysis revealed relationships between five spin characteristics and body size, whereby, for example, larger webspinners invested in relatively larger prothoracic tarsi used for spinning and in spin-steps that would yield expansive silk coverings. Spin-step dynamics displayed a phylogenetic signal for the frequency of six spin-steps and for 16 spin-step transitions. Discussion focuses on patterns revealed by analysis of phylogenetic signal and the relationship to life style and to recently discovered chemical characteristics of silk. [ABSTRACT FROM AUTHOR]

Quartinia canariensis was recorded from three semidesertic sand habitats in Fuerteventura. All localities were sparsely covered by halophytic vegetation and characterized by large patches of flowering plants of Frankenia laevis (Frankeniaceae). Males and females were exclusively observed to visit flowers of Frankenia laevis. During flower visits the imagines often switched between nectar and pollen uptake. Pollen was consumed directly from the anthers or pollen uptake was indirect with pollen grains gathering on the frons being brushed towards the mouthparts with the fore legs. During nectar uptake the wasps protruded their long proboscis into the nectariferous pockets between the claws of the petals of the Frankenia flowers. Brood cell provisions consisted mainly of pollen from Frankenia but to a small amount also from Polycarpaea (Caryophyllaceae) suggesting that Quartinia canariensis is polylectic with strong preference. Males regularly stood on the ground in the vicinity of Frankenia plants and frequently performed patrol flights along the flowers. Flower visiting females avoided contact with the males and mainly offered resistance against the insertion of the male genitalia. The behavioural sequence during copulation of a species of Quartinia is described for the first time. The nest was a multicellular sub-vertical burrow surmounted by a short turret. The burrow was excavated by the female in friable sandy soil. The walls of the nest were stabilized by silk produced by the nest building female and applied with the mouthparts. Inconsistencies concerning the host-parasite-relationship between Quartinia canariensis and Chrysis atrocomitata established by Gusenleitner 1990 are discussed. [ABSTRACT FROM AUTHOR]

Spider silk is one of the best illustrations of biomimetism. Thanks to a complex hierarchical structure, this fibre exhibits remarkable characteristics, especially renowned tensile properties. Silk filaments result from a complex spinning process that occurs in mild conditions of pressure and temperature, in aqueous solution and under optimised physicochemical conditions, so that minimal energy is required to form the thread. Spiders can spin different types of silks that exhibit various physical and biological features. Understanding the relationship between structure and function may soon lead to high performance and tailored materials and devices. Besides silk's performances and spinning process efficiency, silk proteins (spidroins) may become a renewable and biodegradable source of materials that exhibit attractive biocompatibility properties. Considering striking recent scientific advances, spider silk inspired materials maybe beneficial to humans and help to reduce the ecological footprint of societies. Nevertheless, designing truly green and efficient functional materials is complex, and much remains to be carried out to reach this objective. Producing spider silk inspired materials at industrial scale also raises fundamental sustainability questions, including those related to the supply of the raw material, the appropriateness of using spidroins and broader issues related to technology, economics and governance. This paper first summarises the characteristics of natural silk that may lead to innovative applications and may facilitate green technologies. Then, some challenges are presented in a context where societies urgently need to reduce the environmental impact of their activities. Finally, we address global sustainability challenges for spider inspired silk and material engineering. [ABSTRACT FROM PUBLISHER]

The natural process of silk spinning covers a fascinating versatility of aggregate states, ranging from colloidal solutions through hydrogels to solid systems. The transition among these states is controlled by a carefully orchestrated process in vivo . Major players within the natural process include the control of spatial pH throughout passage of the silk dope, the composition and type of ions, and fluid flow mechanics within the duct, respectively. The function of these input parameters on the spinning process is reviewed before detailing their impact on the design and manufacture of silk based drug delivery systems (DDS). Examples are reported including the control of hydrogel formation during storage or significant parameters controlling precipitation in the presence of appropriate salts, respectively. The review details the use of silk fibroin (SF) to develop liquid, semiliquid or solid DDS with a focus on the control of SF crystallization, particle formation, and drug–SF interaction for tailored drug load. [ABSTRACT FROM AUTHOR]

Spider silk fibers have a sophisticated hierarchical structure composed of proteins with highly repetitive sequences. Their extraordinary mechanical properties, defined by a unique combination of strength and extensibility, are superior to most man-made fibers. Therefore, spider silk has fascinated mankind for thousands of years. However, due to their aggressive territorial behavior, farming of spiders is not feasible on a large scale. For this reason, biotechnological approaches were recently developed for the production of recombinant spider silk proteins. These recombinant proteins can be assembled into a variety of morphologies with a great range of properties for technical and medical applications. Here, the different approaches of biotechnological production and the advances in material processing toward various applications will be reviewed. [ABSTRACT FROM AUTHOR]

Understanding the interactions between fibroin and sericin is crucial in solving the mechanism of silk spinning. In this study, various commercially available dyes were used to monitor the interface between fibroin and sericin during the gelation of fibroin. The phase separation between fibroin and sericin could be observed by the addition of azo dyes over a certain molecular weight. Furthermore, the addition of the dyes to the sericin layer showed vivid phase separation over addition to the fibroin layer. [ABSTRACT FROM AUTHOR]

Abstract: Nature's high performance material, spider silk, is formed during the passage of a protein solution through a spinning duct. Herein we present a microfluidic device with dual laminar mobile phases where silk formation can be mimicked and investigated. Recombinant miniature spidroins, with or without the pH-switching N-terminal domain, were used to investigate spinning conditions into silk-like fibers using this setup. [Copyright &y& Elsevier]

Spidermajor ampullate (MA) silk varies in mechanical propertieswhen spun in different environments. Amino acid compositional changesinduced by variations in MaSp1 and MaSp2 expression, and various biochemicaland physiological glandular processes induce silk property variability.Quantifying the contributions of these mechanisms on silk variabilitymay facilitate the development of silk biomimetics. Wind is a mediumthat induces variations in MA silk mechanics. We exposed the spider Cyclosa mulmeinensisto wind and measured the aminoacid composition, tensile mechanics, and crystalline structure ofits MA silk using HPLC, tensile tests, and X-ray diffraction. We foundthe mechanical properties of MA silks from spiders exposed to windto differ from unexposed spiders. The amino acid compositions didnot differ, but X-ray diffraction found a lower crystal density andgreater β-sheet alignment relative to the fiber axis in thesilks of spiders exposed to wind. We found no evidence that the mechanicalproperty variations were a product of profound changes to the alignmentof the protein within the amorphous region. We conclude that variationsin the density and alignment of the crystalline β-sheets, probablyaccompanied by some alignment change in the amorphous region as aresult of “stretching” during spinning of the silk,probably explains the mechanical property variations that we foundacross treatment subgroups. As C. mulmeinensisMA silk increases both in strength and elasticity when the spidersare exposed to wind, bioengineers may consider it as a model for thedevelopment of high-performance silk biomimetics. [ABSTRACT FROM AUTHOR]

Theaccurate 1H positions of alanine-glycine alternating copolypeptide,(AG)15with Silk I structure were determined. For the purpose,the geometry optimization was performed starting with the atomic coordinatesof the hetero atoms reported previously (Macromolecules2005, 38, 7397−7403) and applied only for protons under periodic boundaryconditions. The agreement between the calculated and observed chemicalshifts of all 1H,13C and 15N nucleiwas excellent, indicating strongly that the determination of all theatomic-coordinate including 1H nuclei was performed withhigh accuracy. Here the 1H chemical shift was obtainedby using both 1 mm microcoil MAS NMR probe-head for mass-limited solid-statesamples developed by us and ultrahigh field NMR at 920 MHz. The DQcorrelations in the 1H DQMAS NMR spectra were also usedto confirm the intra- and intermolecular structures obtained here.The characteristic structure of Silk I which can be easily convertedto Silk II by external forces was discussed together with the generationof Silk I structure from the aqueous solution of the silk fibroin. [ABSTRACT FROM AUTHOR]

Abstract: In silk-spinning arthropods, silk can be used for web building, protection, and communication. Silk is an informative material about the presence of conspecifics. It can therefore inform on habitat suitability and hence assist in habitat choice. In this context, we investigated the influence of silk on microhabitat choice by the two-spotted spider mite, Tetranychus urticae. Three factors that could potentially influence habitat choice were manipulated: the strain, number, and the stage of mites. Our study showed that these factors all influence the choice of microhabitat. The tendency of whether to settle on a silk-covered area was influenced by the origin of mites (strain effect). Adult females showed a higher tendency to settle on an area covered with the silk laid by numerous congeners (number effect). Moreover, larvae seemed to be more responsive to the presence of silk than adults (stage effect). This suggests that individuals use silk as a social cue in selecting their microhabitat and that the spatial organization and group behaviour seem to be shaped by the individuals’ response to social cues, such as the amount of silk already present. [Copyright &y& Elsevier]

Although natural silk fibers have excellent strengthand flexibility,the regenerated silk materials generally become brittle in the drystate. How to reconstruct the flexibility for silk fibroin has bewilderedscientists for many years. In the present study, the flexible regeneratedsilk fibroin films were achieved by simulating the natural formingand spinning process. Silk fibroin films composed of silk I structurewere first prepared by slow drying process. Then, the silk fibroinfilms were stretched in the wet state, following the structural transitionfrom silk I to silk II. The difference between the flexible film anddifferent brittle regenerated films was investigated to reveal thecritical factors in regulating the flexibility of regenerated silkmaterials. Compared with the methanol-treated silk films, althoughhaving similar silk II structure and water content, the flexible silkfilms contained more bound water rather than free water, implyingthe great influence of bound water on the flexibility. Then, furtherstudies revealed that the distribution of bound water was also a criticalfactor in improving silk flexibility in the dry state, which couldbe regulated by the nanoassembly of silk fibroin. Importantly, theresults further elucidate the relation between mechanical propertiesand silk fibroin structures, pointing to a new mode of generatingnew types of silk materials with enhanced mechanical properties inthe dry state, which would facilitate the fabrication and applicationof regenerated silk fibroin materials in different fields. [ABSTRACT FROM AUTHOR]

Abstract: In this study, silk sericin nanofibers from sericin hope-silkworm, whose cocoons consist almost exclusively of sericin were successfully prepared by electrospinning method. Scanning electron microscopy (SEM) was used to observe the morphology of the fibers. The effect of spinning conditions, including the concentration of sericin cocoon solution, acceleration voltage, spinning distance and flow rate on the fiber morphologies and the size distribution of sericin nanofibers were examined. The structure and physical properties were also observed by Fourier transform infrared (FT-IR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TG). The optimum conditions for producing finely thinner fibrous sericin nanofibers without beads were the concentration of sericin solution above 6–8wt%, acceleration voltage ranging from 25 to 32kV, spinning distance above 9cm, and flow rate above 0.06cmmin−1. The mean diameter of as spun sericin fibers varied from 114 to 430nm at the different spinning conditions. In the as-spun fibers, silk sericin was present in a random coil conformation, while after methanol treatment, the molecular structure of silk sericin was transformed into a β-sheet containing structure. Sericin hope nanofiber demonstrated thermal degradation at lower temperature than the sericin hope cocoon, which probably due to the randomly coiled rich structure of the sericin hope nanofiber. [Copyright &y& Elsevier]

Although the basic taxonomic characteristics usually remain unchanged, some spinning apparatuses undergo consistent adaptive variations. As the presence of additional protuberances known as nubbins and tartipores have caused disagreements regarding some Araneidae spiders, more detailed definitions on the cuticular structures have recently been proposed. Reflecting this definition, microstructural organization of silk spinning apparatuses in the orb web spider Argiope bruennichi were reconsidered using field emission scanning electron microscopy. Among the seven kinds of functional spigots in females, it was revealed that two types (major ampullates and pyrifoms) are located on anterior spinnerets and another five types are distributed on median (minor ampullates, tubuliforms and aciniforms) or posterior (tubuliforms, flagelliforms, aggregates and aciniforms) spinnerets, respectively. In addition to functional spigots, cuticular remnants of the nubbins and the tartipores were found on the spinning fields, but the number of tartipores on each spinneret varied among individuals based on maturity. Nevertheless, three kinds of cuticular protuberances of ampullate silk glands were clearly visible at both the anterior and median spinnerets. [ABSTRACT FROM AUTHOR]

Abstract: The regenerated silk fibers with high strength and high biodegradability were prepared from the aqueous solution of Bombyx mori silk fibroin from cocoons with wet spinning method. Although the tensile strength of the regenerated silk fibroin fiber, 210MPa is still half of the strength of native silk fiber, the diameter of the fiber is about 100μm which is suitable for monofilament of suture together with high biodegradability. The high concentration (30%, w/v) of the aqueous solution of the silk fibroin which corresponds to the high concentration in the middle silkgland of silkworm was obtained. This was performed by adjusting the pH of the aqueous solution to 10.4 which corresponds to pK a value of the OH group of Tyr residues in the silk fibroin. The mixed solvent, methanol/acetic acid (7:3 in volume ratio) was used as coagulant solvent for preparing the regenerated fiber. The structural change of silk fibroin fiber by stretching was monitored with both 13C solid state NMR and X-ray diffraction methods, indicating that the high strength of the fiber is related with the long-range orientation of the silk fibroin chain with β-sheet structure. [Copyright &y& Elsevier]

Abstract: Although silk sericin (SS) occupies 25% of silk protein, its importance has often been overlooked in the natural silk spinning process and in the formation of the crystalline structure of silk fibroin (SF). In this study, we elucidated the role of SS in the crystallization process of SF under shear using SF/SS blend solutions. In order to apply shear stress to the blend solution, a rotating glass rod was inserted into a glass tube filled with the solution and the shear rate was determined to be in the range of 598–724s−1. After shearing, SF aggregates were formed and the amount of the aggregates increased with shearing time. Additionally, it was observed that the aggregate formation and β-sheet transition of SF were enhanced when a proper amount of SS was in the blend solution. Consequently, the SS considerably contributes to the structural transition of SF under shear. The SS can improve the shear-induced β-sheet transition and crystallization of SF. [Copyright &y& Elsevier]

Based on the phase diagram constructed for water-silk fibroin-LiBr using the osmotic stress method, wet-spinning of osmotically stressed, regenerated Bombyx morisilk fibroin was performed, without the necessity of using expensive or toxic organic solvents. The osmotic stress was applied to prestructure the regenerated silk fibroin molecule from its original random coil state to a more oriented state, manipulating the phase of the silk solution in the phase diagram before the start of spinning. Various starting points for spinning were selected from the phase diagram to evaluate the spinning performance and also physical properties of fibers produced. Monofilament fiber with a diameter of 20 μm was produced. It was found that the fibers whose starting point in the phase diagram were around the phase boundary between silk I and silk II, at very low LiBr concentrations, showed the best spinning process stability and physical properties. This underpins the prediction that the enhanced control over structure and phase behavior using the osmotic stress method helps improve the physical properties of wet-spun regenerated silk fibroin fibers. [ABSTRACT FROM AUTHOR]

Spiders and silkworms employ the complex flow of highly concentrated silk solution as part of silk fiber spinning. To understand the role of fluidic forces in this process, the flow of silk solution in the spider major ampullate and silkworm silk glands was investigated using numerical simulation. Our simulations demonstrate significant differences between flow in the spider and silkworm silk glands. In particular, shear flow effects are shown to be much greater in the spider than the silkworm, the silkworm gland exhibits a much different flow extension profile than the spider gland, and the residence time within the spider gland is eight times greater than in the silkworm gland. Lastly, simulations on the effect of spinning speed on the flow of silk solution suggest that a critical extension rate is the initiating factor for fiber formation from silk solution. These results provide new insight into silk spinning processes and will guide the future development of novel fiber spinning technologies. [ABSTRACT FROM AUTHOR]

We have characterized the steps involved in silk assembly from the protein solution into β-type fibers by a combination of small-angle and wide-angle X-ray scattering and Raman spectroscopy. The aggregation process was studied in a concentric flow microfluidic cell, which allows mimicking the spinning duct. The fibroin molecule in solution shows an elongated shape with a maximum diameter of 38 nm. During the pH-driven initial assembly step, large-scale aggregates of fibroin molecules with a maximum diameter of about 260 nm are formed. Raman spectroscopy on the dried, fibrous material shows a principally a-helical silk I secondary structure, which is transformed gradually into β-type silk II by increasing immersion times in water. The formation of crystalline β-sheet domains within the fiber is confirmed by wide-angle X-ray scattering. The assembly process resembles the peptide condensation-ordering model proposed for amyloid cross-β formation. [ABSTRACT FROM AUTHOR]

Abstract: Silkworms have been developed over thousands years to optimize folding and crystallization of fibroin under highly controlled conditions which have resulted in their efficient fiber formation. In this paper, we reconstructed the three-dimensional architecture of the spinneret of a wild silkworm Samia cynthia ricini from approximately 1000 optical micrographs of the semi-thin cross sections. The chitin plates and muscles were observed in the silk press part together with large change in the diameter of the spinneret lumen at the press part by large shear stress. This is similar to the case of the spinneret of Bombyx mori silkworm, indicating that the structural change in the silk fibroin of S.c. ricini silkworm occurs exclusively at the silk press part due to large shear stresses. Molecular dynamics (MD) calculations were then performed to study the structural change that occurs in the crystalline region of S.c. ricini silk fibroin under shear stress. Namely, using the peptide AGGAGG(A)12GGAGAG as a model of the crystalline part of the silk fibroin under different shear stresses in the presence of water molecules and followed by molecular mechanics (MM) calculation after removal of water molecules. The simulation indicates that the Ala residues in the model peptides adopt a predominantly β-sheet structure under shear stresses of above 1.0GPa. [Copyright &y& Elsevier]

Silkworm silk has outstanding mechanical properties despite being spun at room temperature and from aqueous solution. Although it has been proposed that fiber formation is mainly induced by shearing and extensional flow in the spinneret, the detailed structure and function of the spinning apparatus of Bombyx morisilkworms are still not fully elucidated. In this paper we describe three aspects of the functional microanatomy of the spinning apparatus:  changes in the diameter of the silk gland duct with distance along the duct, how the birefringence of the fibroin changes as it flows down the duct, and the detailed three-dimensional structure of the silk press and related structures. The existence of a double escaped nematic liquid crystal texture in the fibroin in a region of the duct is described. After this region the birefringence suddenly disappeared until the start of an internal draw down taper which commenced just before the silk press. In the internal draw down taper the birefringence increased dramatically to an asymptotic value as a thread was drawn from the fibroin gel. The structure of the silk press suggests that it acts as a restriction die whose diameter can be regulated. [ABSTRACT FROM AUTHOR]

Typical spider dragline silk tends to outperform other natural fibres and most man-made filaments. However, even small changes in spinning conditions can have large effects on the mechanical properties of a silk fibre as well as on its water uptake. Absorbed water leads to significant shrinkage in an unrestrained dragline fibre and reversibly converts the material into a rubber. This process is known as supercontraction and may be a functional adaptation for the silk’s role in the spider’s web. Supercontraction is thought to be controlled by specific motifs in the silk proteins and to be induced by the entropy-driven recoiling of molecular chains. In analogy, in man-made fibres thermal shrinkage induces changes in mechanical properties attributable to the entropy-driven disorientation of ‘unfrozen’ molecular chains (as in polyethylene terephthalate) or the ‘broken’ intermolecular hydrogen bonds (as in nylons). Here we show for Nephila major-ampullate silk how in a biological fibre the spinning conditions affect the interplay between shrinkage and mechanical characteristics. This interaction reveals design principles linking the exceptional properties of silk to its molecular orientation. [ABSTRACT FROM AUTHOR]

Much attention has been paid to the natural mechanism of silkworm spinning due to the impressive mechanical properties of the natural fibers. In this work, we studied the effect of Cu(II) ions on the secondary structure of Bombyx mori regenerated silk fibroin (SF) in dilute solution by circular dichroism (CD). The results indicate that a given amount of Cu(II) induces the SF conformational transition from random coil to β-sheet, however, further addition of Cu(II) is unfavorable for this conversion. Meanwhile, the conformational changes induced by Cu(II) follow a nucleation-dependent aggregation mechanism, which is similar to that found in Prion protein (PrP) denaturation and Aβ-peptide aggregations, leading to the neurodegenerative disease. This work would help one understand further the natural spinning process of silkworm. Additionally, it would be significant for the study of the nervous system diseases, because silk fibroin, extracted in large amounts from Bombyx mori silkworm gland, could be a proper model to study PrP denaturation and Aβ-peptide aggregations. [ABSTRACT FROM AUTHOR]

Evidence is presented here that cupric ions play a part in the natural spinning of Bombyx mori silk. Proton induced X-ray emission studies revealed that the copper content increased from the posterior part to the anterior part of silk gland, and then further increased in the silk fiber. Spectrophotometric analysis demonstrated that cupric ions formed coordination complexes with silk fibroin chains while Raman spectroscopy indicated that they induced a conformation transition from random coil/helix to β-sheet. Taken together these findings indicate that copper could play a role in the natural spinning process in silkworms. [Copyright &y& Elsevier]

Spider dragline silk is renowned as one of the toughest materials of its kind. In nature, spider silks are spun out of aqueous solutions under environmental conditions. This is in contrast to production of most synthetic fibres, where hazardous solvents, high temperatures and pressure are used. In order to identify some of the chemical processes involved in spider silk spinning, we have produced a collection of cDNA sequences from specific regions of Nephila senegalensis major ampullate gland. We examined in detail the sequence and expression of a putative Nephila senegalensis peroxidase gene (NsPox) from our EST collection. NsPox encodes a protein with similarity to Drosophila melanogaster and Aedes aegypti peroxidases. Northern analysis and in situ localisation experiments revealed that NsPox is expressed in major and minor ampullate glands of the spider where the main components of the dragline silk are produced. We suggest that NsPox plays a role in dragline silk fibre formation and/or processing. [Copyright &y& Elsevier]

Spider silks are protein-based “biopolymer” filaments or threads secreted by specialized epithelial cells as concentrated soluble precursors of highly repetitive primary sequences. Spider dragline silk is a flexible, lightweight fiber of extraordinary strength and toughness comparable to that of synthetic high-performance fibers. We sought to “biomimic” the process of spider silk production by expressing in mammalian cells the dragline silk genes (ADF-3/MaSpII and MaSpI) of two spider species. We produced soluble recombinant (rc)-dragline silk proteins with molecular masses of 60 to 140 kilodaltons. We demonstrated the wet spinning of silk monofilaments spun from a concentrated aqueous solution of soluble rc-spider silk protein (ADF-3; 60 kilodaltons) under modest shear and coagulation conditions. The spun fibers were water insoluble with a fine diameter (10 to 40 micrometers) and exhibited toughness and modulus values comparable to those of native dragline silks but with lower tenacity. Dope solutions with rc-silk protein concentrations >20% and postspinning draw were necessary to achieve improved mechanical properties of the spun fibers. Fiber properties correlated with finer fiber diameter and increased birefringence. [ABSTRACT FROM AUTHOR]

The spinning mechanism of natural silk has been an open issue. In this study, both the conformation transition from random coil to β sheet and the β sheet aggregation growth of silk fibroin are identified in the B. mori regenerated silk fibroin aqueous solution by circular dichroism (CD) spectroscopy. A nucleation-dependent aggregation mechanism, similar to that found in prion protein, amyloid β (Aβ) protein, and α-synuclein protein with the conformation transition from a soluble protein to a neurotoxic, insoluble β sheet containing aggregate, is a novel suggestion for the silk spinning process. We present evidence that two steps are involved in this mechanism: (a) nucleation, a rate-limiting step involving the conversion of the soluble random coil to insoluble β sheet and subsequently a series of thermodynamically unfavorable association of β sheet unit, i.e. the formation of a nucleus or seed; (b) once the nucleus forms, further growth of the β sheet unit becomes thermodynamically favorable, resulting a rapid extension of β sheet aggregation. The aggregation growth follows a first order kinetic process with respect to the random coil fibroin concentration. The increase of temperature accelerates the β sheet aggregation growth if the β sheet seed is introduced into the random coil fibroin solution. This work enhances our understanding of the natural silk spinning process in vivo. [ABSTRACT FROM AUTHOR]

To understand the spinning process of dragline silk by spiders, the protein conformation before spinning has to be determined. Raman confocal spectromicroscopy has been used to study the conformation of the proteins in situ in the intact abdominal major ampullate gland of Nephila clavipesand Araneus diadematusspiders. The spectra obtained are typical of natively unfolded proteins and are very similar to that of a mixture of recombinant silk proteins. Vibrational circular dichroism reveals that the conformation is composed of random and polyproline II (PPII) segments with some -helices. The -helices seem to be located in the C-terminal part whereas the repetitive sequence is unfolded. The PPII structure can significantly contribute to the efficiency of the spinning process in nature. [ABSTRACT FROM AUTHOR]

In spite of all the efforts towards deciphering the silk spinning process of spiders, the underlying mechanism is yet to be fully revealed. In this research, we designed a novel approach that allowed us to quantitatively evaluate the concentration change of silk dope during the liquid-to-solid spinning process of the orb-weaver Nephila pilipes. As a prior characterization of the optimal silking conditions, we first gauged the influence of silking-rate, ranging from 1.5 to 8.0 m/min, on dragline silk diameters and silk tensile strengths obtained from the spiders. Next, to evaluate the liquid content of the silk dope, the major ampullate gland was dissected and the concentration of the sac portion was measured by thermogravimetric analysis (TGA). The solid content of the dragline fibers leaving the spinneret was investigated by calculating the ratio of collected dried silk to the weight loss of the spider recorded in situ upon spinning. As the results indicate, the tensile strength and diameter of the spun dragline fibers were 800–1100 MPa and 8–11 μm, respectively. The liquid content of silk stored in the major ampullate sac (50.0 wt%) was significantly lower than that of silk leaving the spinnerets (80.9–96.1 wt%), indicating that a liquid supplying mechanism might be involved during the spinning process. This reveals, for the first time, quantitative evidence in support of the lubricative hypothesis proposed formerly, namely that a liquid coating layer is supplemented to compensate for silking resistance during the spinning process of a spider. The spigot, at the exit of the spinneret, is speculated to serve as a valve-like controller that regulates the lubrication process along with fiber formation. Taken together, these findings provide understanding of the physiological functions in the spider spinning process and could further shed some light on the future biomimetic development of silk material fabrication. [ABSTRACT FROM AUTHOR]

Although many researches have revealed that liquid phase of silk in the ampulla is turning into the polymerized dragline silk fibers as the feedstock passes through the long duct, the exact mechanism has still been not fully understood. Spider's strongest silk fiber, dragline, is mainly produced in the large ampullate glands, the biggest silk gland in the abdomen with a distinctive yellow color. Morphologically, the duct of large ampullate gland is in its unique S-shape with 2 loops dividing the entire duct into three limbs. In addition, the diameter of the duct showed radical decrease toward the nozzle of the duct. Therefore, it assumed that the duct is playing a significant role in the entire process of silk production allowing great strength. Here, we present some of the fine structural properties of the large ampullate gland duct in Nephila clavata using various visualizations techniques. [ABSTRACT FROM AUTHOR]

The article provides information pertaining to the silk of the orb web spiders. Araneoid and deinopoid orb weavers are the two lineages of orb weaving that use identical behavioral sequences and spinning apparatuses to develop webs. Spiders silks are composed of protiens combined in an abdominal gland, this gland has three types which produce the fibers that is used in orb-web construction, the major ampullates for frame and radial fibers, minor ampullates for temporary spiral scaffolding and flagelliforms for capture spiral axial fibers.