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.     

Raman and surface enhanced Raman scattering of a black dyed silk

The Raman and surface enhanced Raman scattering (SERS) spectra of a black dyed silk sample (BDS) were registered. The spectral analysis was performed on the basis of Raman and SERS spectral data of isolated samples of Bombyx mori silk fibroin, its motif peptide component (GAGAGS) and the synthetic reactive black 5 dye (RB5). The macro FT‐Raman spectrum of the silk sample is consistent with a silk II‐Cp crystalline fraction of Bombyx mori silk fibroin; the SERS spectrum is highly consistent with conformational modifications of the fibroin due to the interactions with the Ag nanoparticles. The GAGAGS peptide sequence dominates the Raman spectrum of the silk. The SERS spectrum of the peptide suggests a random coil conformation imposed by the surface interaction; the serine residue in the new conformation is exposed to the surface. Quantum chemical calculations for a model of the GAGAGS–Ag surface predict a nearly extended conformation at the Ag surface. The Raman spectrum of the dye was analysed, and a complete band assignment was proposed; it was not possible to propose a preferential orientation or organization of the molecule on the metal surface. Quantum chemical calculations for a model of the dye interacting with a silver surface predict a rather coplanar orientation of the RB5 on the Ag metal surface. The Raman spectrum of the BDS sample is dominated by signals from the dye; the general spectral behaviour indicates that the dye mainly interacts with the silk through the sulphone (–SO₂–) and sulphonate (–SO₂–O–) groups. Besides the presence of dye signals, mainly ascribed to the sulphone and sulphonate bands, the SERS spectrum of the BDS sample also displays bands belonging to the amino acids alanine, glycine, serine and particularly tyrosine. Copyright © 2013 John Wiley & Sons, Ltd.     

Stability toward alkaline hydrolysis of B. mori silk fibroin grafted with methacrylamide

Bombyx mori silk fibroin fibers were grafted with methacrylamide (MAA) and characterized by Raman and infrared (IR) vibrational spectroscopy before and after hydrolysis in NaOH 5% to elucidate the possible interactions between the two components and the stability of the fibers toward alkaline hydrolysis. Upon grafting, the fibers underwent conformational rearrangements toward a more unordered state and lost orientation at weight gains higher than 60%. Vibrational spectroscopy disclosed the occurrence of intermolecular interactions (mainly hydrogen bonds) between B. mori silk fibroin and polyMAA in the grafted fibers, and the formation of covalent bonds has been explored. These strong interactions made the grafted fibers as a whole more stable toward alkaline hydrolysis because they prevented the solubilization of the polymer upon hydrolysis and made slower the transformation of its CONH₂ groups into COOH and COO⁻ groups. Upon hydrolysis, silk fibroin underwent an enrichment in the β‐sheet crystalline domains, because of the preferential removal of the unordered domains, which were more prone to the OH⁻ attack. IR and Raman spectroscopy proved valid techniques to investigate the degradation mechanism and kinetics of grafted silk fibroin fibers and so for designing high‐performing silk‐based materials. The A₇₃₁/A₁₀₀₄ Raman intensity ratio was proposed to spectroscopically evaluate the composition of the grafted samples; its value was found to linearly increase with weight gain (R² = 0.998), envisaging the possibility of using Raman spectroscopy as a routine analytical technique for qualitative and quantitative characterization of grafted industrial samples. Copyright © 2016 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.     

Origin of the variability of the mechanical properties of silk fibres: 2 The nanomechanics of single silkworm and spider fibres

The variability in mechanical stress–strain behaviour of various silks obtained from Bombyx mori silkworm and Nephila madagascarensis spider fibres has been studied by high resolution Raman analysis using the Raman shift induced by application of a controlled strain on the νN–H mode as a probe. Silk fibres exhibiting typical 1, 2, 3 and 4 Types have been selected from their characteristic tensile stress–strain behaviour. A perfect relationship between the nanomechanic (at the scale of the chemical bond) and macroscopic (silk single fibre) behaviour is observed as in the case of other polyamide fibres (natural keratin and synthetic PA66). Copyright © 2012 John Wiley & Sons, Ltd.     

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.     

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.     

Comparative Raman spectroscopic analysis of orientation in fibers and regenerated films of Bombyx mori silk fibroin

This study is focused on the Raman spectroscopic analysis of degummed silk fibroin (SF) fibers and regenerated Bombyx mori silk fibroin films: a correlation was found between some spectral features related to the methylene deformation modes and the molecular orientation of the samples. Polarized Raman spectra on SF fibers were used to obtain the orientation distribution function of carbonyl groups along the protein backbone. The variation of the intensity ratio of 1400/1450 cm⁻¹ for the peaks attributed to the wagging and bending deformation modes of CH₂ groups with respect to the angular orientation of the fiber was measured and quantitatively correlated with the orientation distribution function of the carbonyl groups. Unpolarized Raman spectra were measured for regenerated silk fibroin films and lyophilized solutions. The variation of the intensity ratio of 1415/1455 cm⁻¹, which is related to the deformation modes of CH₂ groups in SF regenerated materials, was qualitatively related to the microstructural orientation of the samples observed by scanning electron microscopy (SEM), and to the presence of Silk I phase as suggested by the analysis of samples obtained in different casting conditions and also by the measurements on mechanically deformed films. The results obtained showed the utility of the spectroscopic intensity ratio of 1400/1450 cm⁻¹ for the rapid assessment of molecular orientation in silk fibers, which could be useful for quality and process control of regenerated silk‐based textiles. Moreover, the qualitative dependence of the intensity ratio of 1415/1455 cm⁻¹ was found to be sensitive to both the microstructural orientation and Silk I content of regenerated silk fibroin films, suggesting a possible correlation of this Raman marker of the Silk I phase with the degree of molecular order brought about by this polymorph. Copyright © 2006 John Wiley & Sons, Ltd.     

Formation of silk fibroin nanoparticles in water-miscible organic solvent and their characterization

When Silk fibre derived from Bombyx mori, a native biopolymer, was dissolved in highly concentrated neutral salts such as CaCl₂, the regenerated liquid silk, a gradually degraded peptide mixture of silk fibroin, could be obtained. The silk fibroin nanoparticles were prepared rapidly from the liquid silk by using water-miscible protonic and polar aprotonic organic solvents. The nanoparticles are insoluble but well dispersed and stable in aqueous solution and are globular particles with a range of 35–125 nm in diameter by means of TEM, SEM, AFM and laser sizer. Over one half of the ɛ-amino groups exist around the protein nanoparticles by using a trinitrobenzenesulfonic acid (TNBS) method. Raman spectra shows the tyrosine residues on the surface of the globules are more exposed than those on native silk fibers. The crystalline polymorph and conformation transition of the silk nanoparticles from random-coil and α-helix form (Silk I) into anti-parallel β-sheet form (Silk II) are investigated in detail by using infrared, fluorescence and Raman spectroscopy, DSC, ¹³C CP-MAS NMR and electron diffraction. X-ray diffraction of the silk nanoparticles shows that the nanoparticles crystallinity is about four fifths of the native fiber. Our results indicate that the degraded peptide chains of the regenerated silk is gathered homogeneously or heterogeneously to form a looser globular structure in aqueous solution. When introduced into excessive organic solvent, the looser globules of the liquid silk are rapidly dispersed and simultaneously dehydrated internally and externally, resulting in the further chain–chain contact, arrangement of those hydrophobic domains inside the globules and final formation of crystalline silk nanoparticles with β-sheet configuration. The morphology and size of the nanoparticles are relative to the kinds, properties and even molecular structures of organic solvents, and more significantly to the looser globular substructure of the degraded silk fibroin in aqueous solution. It is possible that the silk protein nanoparticles are potentially useful in biomaterials such as cosmetics, anti-UV skincare products, industrial materials and surface improving materials, especially in enzyme/drug delivery system as vehicle.     

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.     

Application of NMR microscopy to the morphological study of the silkworm,Bombyx mori,during its metamorphosis

Zero (ZQ) and double (DQ) quantum 2D chemical shift selective and spin-echo 3D NMR imaging at microscopy resolution, has been applied to the morphological study of silkworm, Bombyx mori, during its metamorphosis. Attention has been focused on the evolution of the internal structure of the insect during its postembryonal life occurring through the larval, pupal and adult development. A major objective of this work was the characterization of the silk glands, responsible for synthesis and secretion of fibroin and sericin, through the changes of distribution and mobility of water, by imaging the water protons during postembryonal life stages. Moreover, alanine deriving from silk gland proteins was imaged during the last life stage of Bombyx mori.     

In situ detection of flavonoids in weld‐dyed wool and silk textiles by surface‐enhanced Raman scattering

Luteolin and apigenin flavonoid have been detected in silk and wool fibres dyed with weld (Reseda luteola L.) through surface‐enhanced Raman scattering (SERS) measurements carried out ‘on the fibre’. For such purpose, Ag nanoparticles were produced and immobilised in situ via the laser photoreduction of a silver nitrate water solution in contact with the fibre. Control SERS spectra of pure luteolin and apigenin, as well as of mixtures of them, on analogous Ag nanoparticles were also obtained. In this work flavonoids with a similar molecular structure were identified on dyed fibres for the first time without previously hydrolysing the mordant–dye complex. Copyright © 2008 John Wiley & Sons, Ltd.     

Effect of gamma irradiation on synthesis and characterization of bio-nanocomposite SF/Ag nanoparticles

This study describes the synthesis of silver nanoparticles (AgNPs) using aqueous silk fibroin (SF) solution obtained from Bombyx mori silk under gamma radiation environment. The obtained AgNPs were characterized using UV–visible (UV–Vis) spectroscopy, X-ray diffraction (XRD) measurements, dynamic light scattering experiment (DLS) and transmission electron microscope (TEM) images. The UV–Vis absorption spectra of the samples confirmed the formation of AgNPs by showing surface plasmon resonance (SPR) band in the range of (= 428–435?nm. The XRD study revealed metal silver with the face-centered cubic (FCC) crystal structure. DLS measurements showed the dose-dependent average size of the AgNPs. TEM images showed formed AgNPs are nearly spherical in shape with smooth edges. From this study, it was found that the increasing radiation dose increases the rate of reduction and decreases the particle size. The size of the AgNPs can be tuned by controlling the radiation dose.     

低温诱导桑蚕体内腺体相行为的高分辨13C固体核磁共振研究

为什么蚕在常温常压水溶液条件下即能纺出力学性能优异的蚕丝纤维,一直是科学家们感兴趣的问题. 在过去的几十年,人们曾用多种表征手段,如双折射、扫描电镜、原子力显微镜和电子散射等,在界观尺度下对蚕在吐丝过程中腺体的相行为进行研究. 发现腺体在靠近吐丝口时呈液晶态,并认为这是导致蚕丝力学性能的重要因素. 本文则在分子水平尺度下利用核磁共振方法, 对五龄蚕活体在常温和6 ℃下存储数天后解剖的腺体进行研究. 经对化学位移及其线型的各向异性分析发现,当将体内腺体沿吐丝方向分为3部,即后部、中部及靠近吐丝口的前部时,常温下,腺体后部和中后部分子呈无规线团,而腺体中中部、中前部和前部分子呈液晶态. 6 ℃时, 中后部分子亦呈液晶态,前部分子排列则各向异性更大,说明更为有序. 这种液晶态呈分形结构,在小于纳米尺度下为无规线团,大于纳米尺度呈有序排列. 这表明,降温过程可使呈无规线团的丝素蛋白分子转变为液晶态,其效果如同蚕在吐丝过程中对其腺体施加的剪切应力. 该结果对于人们探索人工合成高性能类丝素纤维的纺丝工艺和条件将有启发和指导作用.      

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.     

Surface modification and properties of Bombyx mori silk fibroin films by antimicrobial peptide

The Bombyx mori silk fibroin films (SFFs) were modified by a Cecropin B (CB) antimicrobial peptide, (NH₂)-NGIVKAGPAIAVLGEAAL-CONH₂, using the carbodiimide chemistry method. In order to avoid the dissolution of films during the modification procedure, the SFFs were first treated with 60% (v/v) ethanol aqueous solution, resulting a structural transition from unstable silk I to silk II. The investigation of modification conditions showed that the surface-modified SFFs had the satisfied antimicrobial activity and durability when they were activated by EDC·HCl/NHS solution followed by a treatment in CB peptide/PBS buffer (pH 6.5 or 8) solution at ambient temperature for 2 h. Moreover, the surface-modified SFFs showed the smaller contact angle due to the hydrophilic antimicrobial peptides coupled on the film surface, which is essential for the cell adhesion and proliferation. AFM results indicated that the surface roughness of SFFs was considerably increased after the modification by the peptides. The elemental composition analysis results also suggested that the peptides were tightly coupled to the surface of SFFs. This approach may provide a new option to engineer the surface-modified implanted materials preventing the biomaterial-centered infection (BCI).     

Microarray-based gene expression profiles of silkworm brains

Background  

Molecular genetic studies of Bombyx mori have led to profound advances in our understanding of the regulation of development. Bombyx mori brain, as a main endocrine organ, plays important regulatory roles in various biological processes. Microarray technology will allow the genome-wide analysis of gene expression patterns in silkworm brains.     

Biosynthesis of insulin-silk fibroin nanoparticles conjugates and in vitro evaluation of a drug delivery system

Silk fibroin derived from Bombyx mori is a biomacromolecular protein with outstanding biocompatibility. When it was dissolved in highly concentrated CaCl₂ solution and then the mixture of the protein and salt was subjected to desalting treatments for long time in flowing water, the resulting liquid silk was water-soluble polypeptides with different molecular masses, ranging from 8 to 70 kDa. When the liquid silk was introduced rapidly into acetone, silk protein nanoparticles with a range of 40–120 nm in diameter could be obtained. The crystalline silk nanoparticles could be conjugated covalently with insulin alone with cross-linking reagent glutaraldehyde. In vitro properties of the insulin-silk fibroin nanoparticles (Ins-SFN) bioconjugates were determined by Enzyme-Linked Immunosorbent Assay (ELISA). The optimal conditions for the biosynthesis of Ins-SFN bioconjugates were investigated. The Ins-SFN constructs obtained by 8 h of covalent cross-linking with 0.7% cross-linking reagent and the proportion of insulin and SFN being 30 IU: 15 mg showed much higher recoveries (90–115%). When insulin was coupled covalently with silk nanoparticles, the resistance of the modified insulin to trypsin digestion and in vitro stability in human serum were greatly enhanced as compared with insulin alone. The results in human serum indicated that the half-life in vitro of the biosynthesized Ins-SFN derivatives was about 2.5 times more than that of native insulin. Therefore, the silk protein nanoparticles have the potential values for being studied and developed as a new bioconjugate for enzyme/polypeptide drug delivery system.     

Influence of dietary fibre on gluten proteins structure – a study on model flour with application of FT‐Raman spectroscopy

Dietary fibres are regarded as the source of polysaccharides and antioxidants such as polyphenols. However, addition of dietary fibre to bread causes significant reduction in its quality. The bread quality is connected with the structure of gluten proteins. For this reason, Fourier transform Raman spectroscopy was applied to determine changes in structure of gluten proteins modified by seven dietary fibres. The fibres were added to model flour reconstituted with wheat gluten and wheat starch. The model flour was used to provide gluten proteins of definite structure. The obtained results showed that six out of seven fibres caused similar changes in β‐turn structures. The appearance of the band at 1642 cm⁻¹ and the shift toward lower wavenumbers of the band at 1670 cm⁻¹ in the difference spectra indicated hydrogen bonding of carbonyl groups in β‐turns leading to protein folding/aggregation. Addition of fibre preparations caused also changes in conformation of disulfide bridges (S–S), corresponding to transformation to trans‐gauche‐gauche and trans‐gauche‐trans conformations at the expense of the stable gauche‐gauche‐gauche conformation. The S–S bonds in less stable conformations were formed inside the protein complex as well as between protein complexes in the form of β‐structures. Generally, the observed changes in gluten proteins after addition of dietary fibres were results of interactions between fibre polysaccharides and gluten proteins rather than between polyphenols and gluten proteins. Copyright © 2015 John Wiley & Sons, Ltd.     

低温诱导桑蚕体内腺体相行为的高分辨^13C固体核磁共振研究

为什么蚕在常温常压水溶液条件下即能纺出力学性能优异的蚕丝纤维, 一直是科学家们感兴趣的问题. 在过去的几十年, 人们曾用多种表征手段, 如双折射、扫描电镜、原子力显微镜和电子散射等, 在界观尺度下对蚕在吐丝过程中腺体的相行为进行研究. 发现腺体在靠近吐丝口时呈液晶态, 并认为这是导致蚕丝力学性能的重要因素. 本文则在分子水平尺度下利用核磁共振方法, 对五龄蚕活体在常温和6 ℃下存储数天后解剖的腺体进行研究. 经对化学位移及其线型的各向异性分析发现, 当将体内腺体沿吐丝方向分为3部, 即后部、中部及靠近吐丝口的前部时, 常温下, 腺体后部和中后部分子呈无规线团, 而腺体中中部、中前部和前部分子呈液晶态. 6 ℃时, 中后部分子亦呈液晶态, 前部分子排列则各向异性更大, 说明更为有序. 这种液晶态呈分形结构, 在小于纳米尺度下为无规线团, 大于纳米尺度呈有序排列. 这表明, 降温过程可使呈无规线团的丝素蛋白分子转变为液晶态, 其效果如同蚕在吐丝过程中对其腺体施加的剪切应力. 该结果对于人们探索人工合成高性能类丝素纤维的纺丝工艺和条件将有启发和指导作用.