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An artificial spinning system using regenerated silk fibroin solutions is adopted to produce high-performance silk fibers. In previous studies, alcohol-based agents, such as methanol or ethanol, were used to coagulate silk dope solutions, producing silk fiber with poor mechanical properties compared with those of native silk fibers. The alcohol-based coagulation agents induce rapid β-sheet crystallization of the silk molecules, which inhibits subsequent alignment of the β-sheet crystals. Here, we induce gradual β-sheet formation to afford adequate β-sheet alignment similar to that of native silk fiber. To this aim, we developed an amorphous silk fiber spinning process that prevents fast β-sheet formation in silk molecules by using tetrahydrofuran (THF) as a coagulation solvent. In addition, we apply postdrawing to the predominantly amorphous silk fibers to induce β-sheet formation and orientation. The resultant silk fibers showed a 2.5-fold higher extensibility, resulting in 1.5-fold tougher silk fibers compared with native Bombyx mori silk fiber. The amorphous silk fiber spinning process developed here will pave the way to the production of silk fibers with desired mechanical properties. [ABSTRACT FROM AUTHOR]

Conspectus Electrospinning is a simple and versatile technique that relies on the electrostatic repulsion between surface charges to continuously draw nanofibers from a viscoelastic fluid. It has been applied to successfully produce nanofibers, with diameters down to tens of nanometers, from a rich variety of materials, including polymers, ceramics, small molecules, and their combinations. In addition to solid nanofibers with a smooth surface, electrospinning has also been adapted to generate nanofibers with a number of secondary structures, including those characterized by a porous, hollow, or core-sheath structure. The surface and/or interior of such nanofibers can be further functionalized with molecular species or nanoparticles during or after an electrospinning process. In addition, electrospun nanofibers can be assembled into ordered arrays or hierarchical structures by manipulation of their alignment, stacking, and/or folding. All of these attributes make electrospun nanofibers well-suited for a broad spectrum of applications, including those related to air filtration, water purification, heterogeneous catalysis, environmental protection, smart textiles, surface coating, energy harvesting/conversion/storage, encapsulation of bioactive species, drug delivery, tissue engineering, and regenerative medicine. Over the past 15 years, our group has extensively explored the use of electrospun nanofibers for a range of applications. Here we mainly focus on two examples: (i) use of ceramic nanofibers as catalytic supports for noble-metal nanoparticles and (ii) exploration of polymeric nanofibers as scaffolding materials for tissue regeneration. Because of their high porosity, high surface area to volume ratio, well-controlled composition, and good thermal stability, nonwoven membranes made of ceramic nanofibers are terrific supports for catalysts based on noble-metal nanoparticles. We have investigated the use of ceramic nanofibers made of various oxides, including SiO2, TiO2, SnO2, CeO2, and ZrO2, as supports for heterogeneous catalysts based on noble metals such as Au, Pt, Pd, and Rh. On the other hand, the diameter, composition, alignment, porosity, and surface properties of polymeric nanofibers can be engineered in a controllable fashion to mimic the hierarchical architecture of an extracellular matrix and help manipulate cell behaviors for tissue engineering and regenerative medicine. To this end, we can mimic the native structure and morphology of the extracellular matrix in tendon using uniaxially aligned nanofibers; we can use radially aligned nanofibers to direct the migration of cells from the periphery to the center in an effort to speed up wound healing; and we can also use uniaxially aligned nanofibers to guide and expedite the extension of neurites for peripheral nerve repair. Furthermore, we can replicate the anatomic structures at the tendon-to-bone insertion using nanofiber scaffolds with graded mineral coatings. In this Account, we aim to demonstrate the unique capabilities of electrospun nanofibers as porous supports for heterogeneous catalysis and as functional scaffolds for tissue regeneration by concentrating on some of the recent results. [ABSTRACT FROM AUTHOR]

Spinning of cellulose nanofibrils (CNF) offers promising opportunities to develop renewable fibers and filaments with strong, aligned structure. This review introduces recent findings on the relationship between the properties of CNF hydrogels, the spinning conditions and the performance of filaments obtained by dry- and wet-spinning. For example, the filament Young's modulus correlates with CNF structural factors, such as slenderness and crystallinity. Furthermore, high shear rates and extensional flow strengthen the filament, mainly by improving structural uniformity and partly by effectively orienting the fibrils. However, other less obvious factors, such as those associated with coagulation and drying, play critical roles in filament performance. These and other details related to this timely application of CNF are presented here for the benefit of researchers and users of fibers and filaments for composites, textiles and others. [ABSTRACT FROM AUTHOR]

Graphene macroscopic materials have attracted tremendous attention for their fascinating performance and rich functionalities. Here, we provide an elaborate description of techniques in the fabrication of graphene macroscopic materials, focusing on the wet-spinning of 1D fibers and wet-spinning of continuous 2D films and 3D ultraflyweight aerogels. The thread of the research concepts is discussed to offer an overview of graphene macroscopic assembly. We summarize the fabrication system of wet-spinning of fiber and films, which extends to the chemistry of solvated graphene, the formation of graphene LCs, and the chemical/thermal reduction of graphene materials. The experimental details of graphene ultraflyweight aerogel are also been described. We hope that this paper can act as an experimental guidance for researchers, and become suggestive for forthcoming advances in graphene macroscopic materials. [ABSTRACT FROM AUTHOR]

We herein report the influences of chain orientation and packing on the photoluminescent (PL) and photothermal properties of polybenzimidazole fibers with meta-linkage under different excitation wavelengths (λex) and powers of laser sources. For the purpose, poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole] (PmBI) was synthesized and then processed into fibers via solution spinning and heat treatment. The chain orientation and packing of the as-spun PmBI fiber decreased and increased owing to the heat treatment, respectively, which resulted from the nonlinear chain conformation of PmBI with meta-linkage. It was found that the visible PL intensity under λex = 325 nm, which is associated with an efficient interchain photorelaxation between benzimidazole rings, was much higher for the as-spun fiber with higher chain orientation, while the infrared PL intensity under λex = 514 nm, which is dominated by an intrachain photorelaxation, was far higher for the heat-treated fiber with higher chain packing. Accordingly, the heat-treated PmBI fiber exhibited excellent photothermal heating behavior by attaining maximum temperature increments (ΔTmax) of ~31.7 °C under λex = 405 nm and 18.4 mW, which was even higher than the as-spun fibers (ΔTmax ~ 27.5 °C). For the PmBI fibers, the ΔTmax values were also found to increase with the decrease of λex. [ABSTRACT FROM AUTHOR]

The present study describes a uniqueway of integrating substrateless electrospinning process with textiletechnology. We developed a new collector design that provided a pressure-driven,localized cotton-wool structure in free space from which continuoushigh strength yarns were drawn. An advantage of this integration wasthat the textile could be drug/dye loaded and be developed into acore–sheath architecture with greater functionality. This methodcould produce potential nanotextiles for various biomedical applications. [ABSTRACT FROM AUTHOR]

Dragline silk has been proposed tocontain two main protein constituents,MaSp1 and MaSp2. However, the mechanical properties of synthetic spidersilks spun from recombinant MaSp1 and MaSp2 proteins have yet to approachnatural fibers, implying the natural spinning dope is missing criticalfactors. Here we report the discovery of novel molecular constituentswithin the spinning dope that are extruded into dragline silk. Proteinstudies of the liquid spinning dope from the major ampullate gland,coupled with the analysis of dragline silk fibers using mass spectrometry,demonstrate the presence of a new family of low-molecular-weight cysteine-richproteins (CRPs) that colocalize with the MA fibroins. Expression ofthe CRP family members is linked to dragline silk production, specificallyMaSp1 and MaSp2 mRNA synthesis. Biochemical data support that CRPmolecules are secreted into the spinning dope and assembled into macromolecularcomplexes via disulfide bond linkages. Sequence analysis supportsthat CRP molecules share similarities to members that belong to thecystine slipknot superfamily, suggesting that these factors may haveevolved to increase fiber toughness by serving as molecular hubs thatdissipate large amounts of energy under stress. Collectively, ourfindings provide molecular details about the components of draglinesilk, providing new insight that will advance materials developmentof synthetic spider silk for industrial applications. [ABSTRACT FROM AUTHOR]

Wereport knitted fabrics made from highly conductive stretchablefibers. The maximum initial conductivity of fibers synthesized bywet spinning was 17460 S cm–1with a rupture tensilestrain of 50%. The maximum strain could be increased to 490% by decreasingthe conductivity to 236 S cm–1. The knitted fabricwas mechanically and electrically reversible up to 100% tensile strainwhen coated by poly(dimethylsiloxane). The normalized resistance ofthe poly(dimethylsiloxane)-coated fabric decreased to 0.65 at 100%strain. [ABSTRACT FROM AUTHOR]

Vanillinseparation was efficiently enhanced when vanillin-imprintedpolymer particles were embedded in hollow fiber membranes. Vanillin-imprintedpoly(ethersulfone) hollow fiber membranes were prepared using a dry-wetspinning method. In the preparation process of the imprinted hollowfiber membranes, the vanillin-imprinted polymer particles composedof vanillin methacrylate and methacrylic acid in divinylbenzene segmentswere used and embedded in poly(ethersulfone) hollow fiber membraneswith different contents of the vanillin-imprinted particles at 0,2.5, 5.0, 10, and 15 wt %. Permeability of 100 mM aqueous solutionscontaining each vanillin and its analog toward the imprinted membranewas examined in permeation flux and separation factor. The value ofthe separation factor was 32 for 10 wt % loading with 93 L/(m2h) flux, while for 2.5 wt %, the values of separation factorand the permeation flux were 9.5 and 22 L/(m2h), respectively.This experimental evidence indicated the importance of an alternativetailormade separation of vanillin mixture. [ABSTRACT FROM AUTHOR]

Controlledreeling is a powerful tool to investigate the detailsof silk processing. However, consistent forced reeling of silkwormsis hindered by the significant degree of behaviorally induced variationcaused by the animal. This paper proposes silkworm paralysis as anovel method to control the animal and thus in vivo spinning conditions.Using these methods, we achieve low and consistent reeling forcesduring the collection of over 500 m of individual silk fiber whilemonitoring filament variability, morphology, and properties. Noveltechniques to measure the irregular silk cross-sectional areas leadto the more accurate calculation of the true engineering values andmechanical property variation of individual silk fibers. Combiningcontrolled reeling and accurate thread measurement techniques allowsus to present the relative contributions of processing and behaviorin the performance envelope of Bombyx morisilk. [ABSTRACT FROM AUTHOR]

This paper presents the volume fractions of n-heptaneand watermeasured in a rotor-stator spinning disc reactor. The volume fractionswere measured using γ-ray tomography and photographic imageanalysis. The volume fractions were determined as a function of rotationaldisc speed, flow ratio, position in the reactor, and rotor material.In addition, the effect of the density difference between water andn-heptane was determined by dissolving potassium iodide in the waterphase. Below a rotational disc speed of 75 rpm the volume fractionmeasured by tomography and photographic image analysis are within10% deviation. For low rotational disc speeds, the n-heptane volumefraction decreases slightly with increasing rotational disc speed:the centrifugal force accelerates the larger n-heptane droplets tothe center. At higher rotational disc speeds the droplets become smalleraccordingly, the friction between the phases determines the flow,and the n-heptane volume fraction becomes equal to the n-heptane tototal flow ratio. An increase in density difference from 0.31 to 0.79kg dm–3did not influence the volume fractions. [ABSTRACT FROM AUTHOR]

Electrospinning has been widely used to prepare polymerfiberswith diameters ranging from a few nanometers to micrometers. Whilemost studies focus on controlling the sizes and morphologies of electrospunpolymer fibers by changing electrospinning conditions, the effectof post-treatments such as thermal annealing on the properties ofelectrospun polymer fibers has been less studied. Here, we investigatethe effect of thermal annealing on the morphology changes of electrospunpolystyrene (PS) fibers on substrates. Different from annealing thefibers in a uniform environment, annealing the fibers on substratesresults in a substrate-dependent morphology transformation. When theelectrospun PS fibers are annealed on a glass substrate, wetting ofthe fibers on the glass substrate occurs. When the electrospun PSfibers are annealed on a poly(methyl methacrylate) (PMMA)-coated substrate,a Rayleigh-instability-driven morphology transformation is observed.The polymer fibers transform into hemispherical polymer particlescaused by the lower surface tension of PS than that of PMMA and theinterfacial tension between PS and PMMA. This transformation processis influenced by the annealing time and temperature. The characteristictime of the transformation process is shorter when the sample is annealedat a higher temperature because of the lower polymer viscosity. Thesize of the polymer particles fits well with the theoretical prediction,which is dependent on the initial fiber diameter and is independentof the annealing temperature. [ABSTRACT FROM AUTHOR]

Spider attachment disc silk fibers are spun into a viscous liquid that rapidly solidifies, gluing dragline silk fibers to substrates for locomotion or web construction. Here we report the identification and artificial spinning of a novel attachment disc glue silk fibroin, Pyriform Spidroin 2 (PySp2), from the golden orb weaver Nephila clavipes. MS studies support PySp2 is a constituent of the pyriform gland that is spun into attachment discs. Analysis of the PySp2 protein architecture reveals sequence divergence relative to the other silk family members, including the cob weaver glue silk fibroin PySp1. PySp2 contains internal block repeats that consist of two subrepeat units: one dominated by Ser, Gln, and Ala and the other Pro-rich. Artificial spinning of recombinant PySp2 truncations shows that the Ser-Gln-Ala-rich subrepeat is sufficient for the assembly of polymeric subunits and subsequent fiber formation. These studies support that both orb- and cob-weaving spiders have evolved highly polar block-repeat sequences with the ability to self-assemble into fibers, suggesting a strategy to allow fiber fabrication in the liquid environment of the attachment discs. [ABSTRACT FROM AUTHOR]

Regenerated silk fibroin (RSF) fibers were obtained by extruding a concentrated aqueous silk fibroin solution into an ammonium sulfate coagulation bath. A custom-made simplified industrial-type wet-spinning device with continuous mechanical postdraw was used. The effect of dope concentration, coagulation bath, extrusion rate, and postdraw treatment on the morphology of RSF fiber was examined. The results showed that although RSF fiber could be formed with dope concentration between 13 and 19% (w/w), the ones spun from 15% RSF solution showed the most regular morphology being dense and homogeneous in cross-section with a smooth surface and a uniform cylindrical shape. Though it had little effect on morphology, postdraw treatment especially under steam, significantly improved the mechanical properties of the RSF fibers. [ABSTRACT FROM AUTHOR]

NMR techniques were applied to follow changes in molecular rigidity and diffusion of complexes formed between a humic acid (HA) and either aluminum or calcium ions, added in amounts ranging from 0.05% to 1% of HA carboxylic acidity. Spin-lattice relaxation time in the rotating frame (T1p(H)) and diffusion coefficients (D) of humic-metal complexes were obtained from 13C cross-polarization magic angle spinning (CP-MAS), and ¹H-diffusion order spectroscopy (DOSY) spectra, respectively. Molecular rigidity of humic complexes increased significantly with metal addition throughout the full carbon spectral region, being more pronounced for triple-charged Al than for double-charged Ca. However, T1p(H) values of spectral intervals suggested that molecular rigidity increase was generally in the following order: aliphatic C > aromatic/double bonds C > carboxyl C. Concomitantly, DOSY spectra showed that addition of both Al and Ca decreased substantially the diffusivity of humic alkyl components and increased that of aromatic and hydroxyalkyl components,thereby indicating that complexation induced a molecular-size increase in the former and a decrease in the latter. These results suggest that saturated and unsaturated long-chain alkanoic acids in HA were preferentially involved in metal complexation with Al and Ca, with consequent increase of conformational rigidity and molecular size of humic hydrophobic domains. Conversely, more hydrophilic or mobile humic components appeared relatively less affected bythe molecular and intermolecular rearrangements induced in HA by complexation with metals. Such NMR approach appears thus liable to evaluate the response to metal complexation of specific chemical entities present in the bulk HA and provides a further insight in the molecular architecture of humic-metal complexes. [ABSTRACT FROM AUTHOR]

A recombinant silk-elastin-like protein copolymer SELP-47K containing tandemly repeated amino acid sequence blocks from silk, GAGAGS, and elastin, GVGVP, was fabricated into microdiameter fibers using a wet-spinning technique. Raman spectral analysis revealed the formation of antiparallel β-sheet crystals of the silk-like blocks. Dry SELP-47K fibers display the dependence of mechanical properties such as Young’s modulus on fiber diameter, suggesting more oriented and crystallized molecular chains in small-diameter fibers. Additionally, a brittle fracture mode was identified for dry fibers by SEM analysis of fracture surfaces. Hydration dramatically influenced the mechanical behavior of SELP-47K fibers. In contrast to the high tensile strength and limited strains to failure of dry fibers, fully hydrated SELP-47K fibers possessed strains to failure as high as 700%. Furthermore, upon chemical cross-linking, a tensile mechanical strength up to 20 MPa was achieved in hydrated fibers without compromising their high deformability. By combing the silk- and elastin-derived sequences into a single SELP-47K protein polymer, we demonstrated that protein fibers with high tensile strength and high deformability can be fabricated. [ABSTRACT FROM AUTHOR]

Large, characteristically tear- or finger-shaped voids found in polymer hollow fiber membranes, termed macrovoids, have been known since the early development of asymmetric membranes. These voids are undesirable as they decrease the mechanical integrity of the hollow fiber membrane, limiting the use of high pressure feeds for separations. Moreover, if such macrovoids penetrate the selective layer they become and even more serious problem for membrane performance. With current membrane technology moving toward a mixed-matrix hybrid format with inorganic and carbon molecular sieves embedded in a polymer matrix, additional complications caused by the presence of particulates within the spinning dope toward the formation of macrovoids must be considered. While numerous hypotheses have been suggested regarding the formation of macrovoids formed in polymer-only membranes, no mention so far has been made of such macrovoids initiated in hollow fiber membranes by particles present in the spinning dope. This paper provides evidence for the presence of such macrovoids for such a spinning dope and presents a hypothesis for their formation. This hypothesis is presented in terms of a similar basic mechanism for macrovoid formation in mixed-matrix membranes that benefits from an understanding of macrovoid formation in conventional polymer-only asymmetric membranes. Moreover, decreasing the sieve particle size tends to suppress macrovoid formation tendency, which is consistent with the proposed mechanism. [ABSTRACT FROM AUTHOR]

The major problem associated with the production of alginate/chitosan hybridized fibers by wet spinning is the formation of gels due to ionic interactions of the oppositely charged molecules of alginate and chitosan when these two polymers are directly mixed. Here, we proposed a novel method of using chitosan in the form of an emulsion. The emulsion was prepared by adding a primary emulsion of olive oil in a sodium dodecyl sulfate (SDS) aqueous solution into a chitosan−citrate complex. The complexation of chitosan with citric acid is the key of this method. The citrate ions neutralize the positive charges of chitosan, rendering the chitosan−citrate complex to readily penetrate into the core of the SDS/olive oil micelles. The obtained emulsified chitosan−citrate complex (hereafter, the chitosan−citrate emulsion) of varying amount was then added into an alginate aqueous solution to prepare the alginate/chitosan spinning dope suspensions. The alginate/chitosan hybridized fibers showed spotty features of the emulsified chitosan−citrate complex particles locating close to the surface and the inside of the hybridized fibers. At the lowest content of incorporated chitosan (i.e., 0.5% w/w chitosan), both the tenacity and the elongation at break of the obtained chitosan-spotted alginate fibers were the greatest. Further increase in the chitosan content resulted in a monotonous decrease in the property values. Lastly, preliminary studies demonstrated that the obtained chitosan-spotted alginate fibers showed great promises as carriers for drug delivery. [ABSTRACT FROM AUTHOR]

Previously we have demonstrated the use of 1H magic angle spinning (MAS) NMR spectroscopy for the topographical variations in functional metabolic signatures of intact human intestinal biopsy samples. Here we have analyzed a series of MAS 1H NMR spectra (spin-echo, one-dimensional, and diffusion-edited) and 31P-{1H} spectra and focused on analyzing the enhancement of infonnation recovery by use of the statistical total correlation spectroscopy (STOCSY) method. We have applied a heterospectroscopic cross-examination performed on the same samples and between 1H and 31P-{1H} spectra (heteronuclear STOCSY) to recover latent metabolic information. We show that heterospectroscopic correlation can give new information on the molecular compartmentation of metabolites in intact tissues, including the statistical "isolation" of a phosphlipid/triglyceride vesicle pool in intact tissue. The application of 31P-1H HET-STOCSY allowed the cross-assignment of major 31P signals to their equivalent 1H NMR spectra, e.g., for phosphorylcholine and phosphorylethanolainine. We also show pathway correlations, e.g., the ascorbate-glutathione pathway, in the STOCSY analysis of intact tissue spectra. These 31P-1H HFT-STOCSY spectra also showed different topographical regions, particular for minor signals in different tissue microenvironments. This approach could be extended to allow the detection of altered distributions within metabolic subcompartments as well as conventional metabonomics concentration.based diagnostics. [ABSTRACT FROM AUTHOR]

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]

The article describes the development of nitric oxide (NO)-releasing diazeniumdiolated derivatives of poly(acrylonitrile) (PAN) and a variety of related materials that can form the basis of NO-releasing textiles, rubbers and plastics. According to the authors, the polymers are stable at room temperature and represent a broad class of commercially viable materials to be developed as NO donors. The authors add that PAN is easily spun into fibers for fabric production and can form graft copolymers.

In the last years, there has been an increasing interest in bioinspired approaches for different applications, including the spinning of high performance silk fibers. Bioinspired spinning is based on the natural spinning system of spiders and worms and requires combining changes in the chemical environment of the proteins with the application of mechanical stresses. Here we present the novel straining flow spinning (SFS) process and prove its ability to produce high performance fibers under mild, environmentally friendly conditions, from aqueous protein dopes. SFS is shown to be an extremely versatile technique which allows controlling a large number of processing parameters. This ample set of parameters allows fine-tuning the microstructure and mechanical behavior of the fibers, which opens the possibility of adapting the fibers to their intended uses. [ABSTRACT FROM AUTHOR]

The article demonstrates the first synthesis of well-aligned, pearl-line carbon nanotube arrays through a chemical vapor deposition (CVD) process. It is claimed that these carbon nanotubes can be easily spun into macroscopic fibers with excellent mechanical and electrical properties due to the unique morphology. Moreover, it is emphasized that the hollow structure inside the nanotube may open new applications for carbon nanotubes as nanoreactors.