Origin of the variability of the mechanical properties of silk fibres: 3. Order and macromolecule orientation in Bombyx mori bave,hand‐stretched strings and Nephila madagascarensis spider fibres

The comparison of the low wavenumber of polarized Raman spectra (50–300 cm^–1) from Bombyx mori (fresh cocoons fibres, hand‐stretched ‘Crins de Florence’ strings from the gland content, dried gland, regenerated silk films) and Nephila madagascarensis silks reveals the high polarisation of fibre modes and the absence of polarisation for dried gland and regenerated silk films. This is consistent with X‐ray diffraction measurements. The orientation of the fibroin/spidroin chains is due to the stretching during production, as for advanced synthetic fibres. The bandwidth of the ‘ordered chains’ signature is almost the same for the different fibres. However, the degree of polarisation seems to be higher in the case of spider fibre. The huge bandwidth of low wavenumber components of regenerated films indicates high disorder. Measurements along the fibre point out conformation changes with a periodicity (~20 mm) related to the silkworm head motion during the fabrication of the cocoon. Copyright © 2012 John Wiley & Sons, Ltd.     

Origin of the variability of the mechanical properties of silk fibres: 1 ‐ The relationship between disorder,hydration and stress/strain behaviour

The causes of the variability in mechanical behaviour of various silks obtained from silkworms (Bombyx mori, Antheraea/Tussah) and spiders (Nephila madagascarensis) have been studied by tensile uniaxial tests, differential scanning calorimetry and Raman microspectrometry. Analyses of tensile stress–strain curves recorded for different silkworm and spider baves and single fibres, undergoing different histories (age, degumming, thermal/chemical treatments), allow the behaviour to be classified into five groups and correlated with the fibroin/spidroin structural status: (1) Type I exhibits linear elastic behaviour and then a quasi plateau, (2) Type II has a two‐step linear elastic behaviour with kinks then a quasi plateau, (3) Type III exhibits a smooth transition from a linear behaviour to a plateau, (4) Type IV has a behaviour rather similar to that of Type I but above ~8–12% hardening occurs, and (5) Type V results in the breakage of fibres during the first elastic stage. Unambiguously, Type IV is more frequent for degummed, very dried fibres and Type III for water‐saturated fibres. The most striking Raman signature differences are observed in the Raman intensity of the amorphous/‘ordered’ νN–H and H₂O band components and correlated to the water content and disorder degree according to the calorimetry study. Types I and II are frequently observed for fresh (largely amorphous) spun fibres/baves. Type V is characteristic of degraded fibres. Type IV represents the most ordered state. The similar stress–strain types for dried silkworm and spider fibres show that the general difference in amino acid contents is not the most pertinent parameter for the mechanical behaviour. Copyright © 2011 John Wiley & Sons, Ltd.     

Origin of the variability of the mechanical properties of silk fibers: 4. Order/crystallinity along silkworm and spider fibers

The poor crystallinity of proteic fibers has fuelled an ongoing debate over their exact organization. We present a full‐range Raman comparison of Nephila madagascariensis spider and Bombyx mori silkworm silks that sheds some new light on that matter. On the one hand, a large variability is observed along the fibers in the −200 to 200 cm⁻¹ spectral window, which is sensitive to the long‐range order signature of polyamide chains. This questions the validity of previous literature data considering silk fiber as a homogeneous material. On the other hand, the ‘amide I’ band is almost independent of the targeted point, which sets a limit to this widely used structure probe. In‐line mapping of the fibers showed that the extension of the ordered zones ranges between 1 and 3 µm. The correlation between the macromechanical behavior (the stress–strain curves) and the nanomechanics (Raman low wavenumber signatures) under controlled tensile strain demonstrates a Prevorsek's type microstructure: the macromolecular chains belong to both ordered and amorphous ‘regions’. Copyright © 2014 John Wiley & Sons, Ltd.     

Nanomechanics of single silkworm and spider fibres: a Raman and micro‐mechanical in situ study of the conformation change with stress

The combination of micro‐Raman spectroscopy and an advanced universal fibre tester (UFT) made it possible to probe at the nanoscale (through monitoring the modification of chemical bonds) the change in conformation (α‐helix, β‐sheet, etc.), macromolecular fibroin chain orientation and coupling during the application of stress, quantitatively. Different single fibres of silkworms (Bombyx mori, Gonometa rufobrunea, Gonometa postica) and a spider (Nephila madagascariensis) were tested in a dry environment and compared with the behaviour of keratin fibre. As observed previously for single keratin fibres, a direct relationship is observed between nano‐ and micro‐mechanical tensile behaviour. The phase transition plateau, well defined for some pristine B. mori fibres, disappears in degummed fibres, which indicates a structural modification and increasing disorder with chemical treatments. Stress‐controlled micro‐Raman analysis shows that a few modes involving CH₂ and/or amide groups of β‐conformation chains undergo a wavenumber softening during the elastic behaviour (∼0–3%), although most of the modes are not affected. A different behaviour is observed for modes associated with ‘ordered’ and ‘disordered’ β‐sheets and helical chains. Larger softening is observed for lattice modes with increasing stress/strain, as expected. Structural changes and relationships with mechanical behaviour are discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Affinity of protein fibres towards sulfation

Wool, Bombyx mori and Antheraea pernyi (Tussah) silk fibres were treated with chlorosulfonic acid in pyridine and investigated by FT‐IR and FT‐Raman spectroscopies as well as mechanical measurements. The reactivity towards sulfation was found to decrease along the series: wool > Bombyx mori silk fibroin > Tussah silk fibroin, in agreement with weight gain which decreased along the same series. Accordingly, Tussah silk maintained its intrinsic tensile properties essentially unchanged upon the treatment, while for Bombyx mori silk fibroin, the tensile performance decreased sharply especially at longer reaction times. Sulfated wool was characterized by an increased fibre extensibility. New IR and Raman bands attributable to various vibrations of sulfated groups were detected in sulfated wool and to a lower extent in Bombyx mori silk fibroin fibres; all the fibres underwent conformational rearrangements upon sulfation, independent of the sulfation yield. Wool fibres treated with chlorosulfonic acid in pyridine bound considerable amounts of sulfate mainly through the hydroxyl groups of serine, threonine and tyrosine. Also, tryptophan and basic amino acids were found to participate to the reaction. B. mori silk fibroin fibres appeared to bind a minor amount of sulfate groups mainly trough the hydroxyl groups of Ser. Weight gain, spectroscopic and mechanical data are discussed in relation to the difference in fibre morphology, structure and crystallinity, as well as to the amount and accessibility of potentially reactive amino acids. Copyright © 2012 John Wiley & Sons, Ltd.     

Preparation and mechanical properties of layers made of recombinant spider silk proteins and silk from silk worm

Layers of recombinant spider silks and native silks from silk worms were prepared by spin-coating and casting of various solutions. FT-IR spectra were recorded to investigate the influence of the different mechanical stress occurring during the preparation of the silk layers. The solubility of the recombinant spider silk proteins SO1-ELP, C16, AQ24NR3, and of the silk fibroin from Bombyx mori were investigated in hexafluorisopropanol, ionic liquids and concentrated salt solutions. The morphology and thickness of the layers were determined by Atomic Force Microscopy (AFM) or with a profilometer. The mechanical behaviour was investigated by acoustic impedance analysis by using a quartz crystal microbalance (QCMB) as well as by microindentation. The density of silk layers (d<300 nm) was determined based on AFM and QCMB measurements. At silk layers thicker than 300 nm significant changes of the half-band-half width can be correlated with increasing energy dissipation. Microhardness measurements demonstrate that recombinant spider silk and sericine-free Bombyx mori silk layers achieve higher elastic penetration modules E_EP and Martens hardness values H_M than those of polyethylenterephthalate (PET) and polyetherimide (PEI) foils.     

Predicting the mechanical properties of spider silk as a model nanostructured polymer

Spider silk is attractive because it is strong and tough. Moreover, an enormous range of mechanical properties can be achieved with only small changes in chemical structure. Our research shows that the full range of thermo-mechanical properties of silk fibres can be predicted from mean field theory for polymers in terms of chemical composition and the degree of order in the polymer structure. Thus, we can demonstrate an inherent simplicity at a macromolecular level in the design principles of natural materials. This surprising observation allows in depth comparison of natural with man-made materials.     

Tubuliform silk protein: A protein with unique molecular characteristics and mechanical properties in the spider silk fibroin family

Orb–web weavers can produce up to six different types of silk and a glue for various functions. Tubuliform silk is unique among them due to its distinct amino acid composition, specific time of production, and atypical mechanical properties. To study the protein composing this silk, tubuliform gland cDNA libraries were constructed from three orb–weaving spiders Argiope aurantia, Araneus gemmoides, and Nephila clavipes. Amino acid composition comparison between the predicted tubuliform silk protein sequence (TuSp1) and the corresponding gland protein confirms that TuSp1 is the major component in tubuliform gland in three spiders. Sequence analysis suggests that TuSp1 shares no significant similarity with its paralogues, while it has conserved sequence motifs with the most primitive spider, Euagrus chisoseus silk protein. The presence of large side-chain amino acids in TuSp1 sequence is consistent with the frustrated β-sheet crystalline structure of tubuliform silk observed in transmission electron microscopy. Repeat unit comparison within species as well as among three spiders exhibits high sequence conservation. Parsimony analysis based on carboxy terminal sequence shows that Argiope and Araneus are more closely related than either is to Nephila which is consistent with phylogenetic analysis based on morphological evidence. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users. PACS 61.41; 87.14 Ee; 87.15 Cc     

Non-linear mechanical behaviour and bio-composite modelling of oil palm mesocarp fibres

Understanding the non-linear mechanical behaviour of oil palm mesocarp fibres (OPMF) is important for bio-composite application. The mechanical characterisation of this fibre is challenging due to the microstructure of the fibres consisting of silica bodies on the surface and cellular structures within the cross section. In this work, we proposed a constitutive material model for OPMF by including a stress-softening function into the large strain viscoelastic model. The model shows agreement with loading–unloading and stress relaxation tensile tests. The model was then used for micro-scale finite element modelling of the fibre–silica body–matrix (resin) interface to simulate sliding of a bio-composite material. A multi-particles model was also developed to check the effect of the constitutive model towards the mechanics of a bio-composite system. Modelling results suggested that under the micro-scale level (~50 μm), silica body plays a major role in improving the mechanical behaviour of the bio-composite system. On the other hand, under the macro-scale level (~0.18 mm), a single fibre model is sufficient to simulate a bio-composite multi-fibres material.     

The structure and mechanical properties of Fe2AlMn single crystals

The microstructure and mechanical properties of off-stoichiometric single-crystal Fe₂AlMn have been investigated. After casting, the alloy contained two sets of thermal antiphase boundaries, (a/4)?111? and (a/2)?100?, which are attributed to the fact that the compound solidifies into a bcc structure and subsequently orders to a B2 structure and then a L2₁ structure respectively upon further cooling. Crystals strained under tension at room temperature in air at 1s^?1 showed 6% elongation, whereas specimens strained at 1?×?10^?5?s^?1 showed no elongation, indicating that the compound is sensitive to the testing environment. Fracture occurred on {100} in both cases. Compression tests showed that a yield anomaly was present at intermediate temperatures, with the peak yield strength occurring at about 800?K, which is slightly below the L2₁–B2 transition temperature of 898?K. The slip systems were found to be ?111?{110} at room temperature and 800?K. Transmission electron microscopy observations showed fourfold-dissociated ?111? dislocations in specimens strained at room temperature but only paired ?111? dislocations in specimens strained at the peak temperature. The room-temperature yield strength of quenched specimens increased with increasing quench temperatures from 700 to 1100?K.     

Influence of grafting with acrylate compounds on the conformational rearrangements of silk fibroin upon electrospinning and treatment with aqueous methanol

Silk fabrics from Bombyx mori silkworm were grafted with 2‐hydroxyethyl methacrylate (HEMA) as well as a binary system of HEMA and 4‐hydroxybutyl acrylate (HBA) and then analysed by Raman and infrared (IR) spectroscopy to elucidate the interactions between the components and their possible conformational changes. The samples were then dissolved in trifluoroacetic acid and electrospun; the influence of the grafted polymers on the silk fibroin rearrangements upon these treatments was investigated by vibrational spectroscopy. Upon grafting, the fabrics underwent conformational rearrangements towards a more unordered state, although they kept their prevailing β‐sheet conformation; also the polymeric component underwent hydrogen bonding and backbone rearrangements upon interaction with silk fibroin and the occurrence of strong covalent bonds cannot be excluded. By immersing the as‐electrospun grafted and pure fibroin nanofibres (prevalently unordered) in aqueous methanol, they partially recovered the β‐sheet content observed in the corresponding starting fabrics; the percentage of recovery decreased along the series: pure silk > HEMA‐grafted silk > HEMA and HBA‐grafted silk. This trend suggests that the presence of the polyHEMA grafted component hinders the silk fibroin recrystallization into β‐sheet upon aqueous methanol treatment; moreover, the addition of the more sterically hindered HBA monomer in the grafting system further prevented this process. Copyright © 2016 John Wiley & Sons, Ltd.     

Determination of the refractive index of fibres using the modified area method: I. Homogeneous fibres

The mathematical formulae for determining the mean refractive indices and birefringence of homogeneous fibres are modified. This modification depends on calculating the area under the fringe shift and cross-sectional area of homogeneous fibres having nearly circular cross-sectional area taking the refraction of the incident light beam by the fibre into consideration. The mathematical analysis for two-beam and multiple-beam interferometric techniques is dealt with. These formulae are applied to polypropylene fibres with draw ratios of 3.5 and 4 using the two techniques. A comparison between the results when using the new formulae and when neglecting the refraction has been studied. The diffraction of a He–Ne laser beam is used for determining the shape of the cross-sectional area of these fibres. Microinterferograms are given for illustration.     

The Electrodynamic 2-Body Problem and the Origin of Quantum Mechanics

We numerically solve the functional differential equations (FDEs) of 2-particle electrodynamics, using the full electrodynamic force obtained from the retarded Lienard–Wiechert potentials and the Lorentz force law. In contrast, the usual formulation uses only the Coulomb force (scalar potential), reducing the electrodynamic 2-body problem to a system of ordinary differential equations (ODEs). The ODE formulation is mathematically suspect since FDEs and ODEs are known to be incompatible; however, the Coulomb approximation to the full electrodynamic force has been believed to be adequate for physics. We can now test this long-standing belief by comparing the FDE solution with the ODE solution, in the historically interesting case of the classical hydrogen atom. The solutions differ. A key qualitative difference is that the full force involves a delay torque. Our existing code is inadequate to calculate the detailed interaction of the delay torque with radiative damping. However, a symbolic calculation provides conditions under which the delay torque approximately balances (3rd order) radiative damping. Thus, further investigations are required, and it was prematurely concluded that radiative damping makes the classical hydrogen atom unstable. Solutions of FDEs naturally exhibit an infinite spectrum of discrete frequencies. The conclusion is that (a) the Coulomb force is not a valid approximation to the full electrodynamic force, so that (b) the n-body interaction needs to be reformulated in various current contexts such as molecular dynamics.     

The effect of mechanical drawing on optical and structural properties of nylon 6 fibres

The Pluta polarizing double-refracting interference microscope was attached to a mechanical drawing device to study the effect of cold drawing on the optical and structural properties of nylon 6 fibres. The microscope was used in its two positions for determining the refractive indices and birefringence of fibres. Different applied stresses and strain rates were obtained using the mechanical-drawing device. The effect of the applied stresses on the optical and physical parameters was investigated. The resulting optical parameters were utilized to investigate the polarizability per unit volume, the optical orientation factor, the orientation angle and the average work per chain. The refractive index and birefringence profiles were measured. Relationships between the average work per chain and optical parameters at different strains rates were determined. An empirical formula was deduced for these fibres. Micro-interferograms are given for illustration.     

光子晶体光纤的导波模式与色散特性

利用有效折射率方法基于标量近似理论对光子晶体光纤的传播模式和色散特性进行了数值模 拟，发现通过调节光纤包层的空气填充率或包层空气穴节距及其有效芯径可以在很宽的波长 范围实现单模传播，可以设计零色散波长小于1.27μm的光子晶体光纤和在较宽的波段接近 于零色散的色散平坦光纤，以及具有较大的正常色散值的色散补偿光纤. 关键词： 光子晶体光纤 有效折射率 标量近似 导波模式     

Interferometric determination of the refractive indices and birefringence of some highly oriented fibres

Variable wavelength interferometric technique (VAWI) is a direct method for determining the refractive indices and birefringence of highly oriented fibres. This method uses the polarizing interference Pluta microscope with a monochromatic light from wedge interference filter that provides a continuously variable wavelength. The standard calibration process of the Pluta polarizing interference microscope is carried out and a calibration graph is obtained. The refractive indices and birefringence of PEN, CONEX and TECHNORA were measured over the visible range of the spectrum and the constants for the Cauchy's dispersion formula were determined. The oscillation and dispersion energies were calculated from the measurements of the refractive index.     

Canonical symmetry properties of the constrained singular generalized mechanical system

Based on generalized Apell－Chetaev constraint conditions and to take the inherent constrains for singular Lagrangian into account, the generalized canonical equations for a general mechanical system with a singular higher-order Lagrangian and subsidiary constrains are formulated. The canonical symmetries in phase space for such a system are studied and Noether theorem and its inversion theorem in the generalized canonical formalism have been established.     

Comparative experimental studies on the mechanical and degradation properties of natural fibers reinforced polypropylene composites

Coir/silk fiber-reinforced polypropylene (PP) based unidirectional composites (40 wt.%) were manufactured by compression molding. Coir/silk fibers and PP sheets were treated with ultraviolet radiation at different intensities and then composites were fabricated. It was found that mechanical properties of irradiated silk/irradiated PP composites were found to increase significantly compared to the untreated ones and even higher than that of irradiated coir/irradiated PP composites. Soil degradation tests indicated that irradiated coir/irradiated PP composites significantly lost much of its mechanical properties, but irradiated silk/irradiated PP composites retained their strength of its original integrity. Scanning electron microscopy and water uptake of both types of composites were also investigated.     

Molecular characterization of the brain secretory peptides,prothoracicotropic hormone (PTTH) and bombyxin,of the silkmoth Bombyx mori

Molecular characterization of the brain secretory peptides, PTTH and bombyxin, of Bombyx mori is reviewed. PTTH is a 30-kDa homodimeric glycoprotein, the monomer of which consists of 109 amino acids. Two monomers are held together by a disulfide bond. cDNA and gene coding for PTTH were cloned and the precursor protein for PTTH monomer was deduced. A novel 5-kD brain secretory peptide named bombyxin has been discovered from Bombyx brain. Bombyxin is highly homologous to vertebrate insulin-family peptides and possesses the prothoracicotropic activity when injected into brain-removed pupae of a heterologous moth, Samia cynthia ricini, though inactive to Bombyx from which it was derived. cDNA and gene coding for bombyxin were cloned, preprobombyxin protein was deduced, and posttranslational processing to generate mature bombyxin was suggested. The Bombyx genome contains highly multiple copies of the gene coding for bombyxins. Immunohistochemically, PTTH- and bombyxin-producing brain neurosecretory cells were identified.