Effect of heat treatment on the structural and conformational changes of regenerated Antheraea pernyi silk fibroin films

Regenerated Antheraea pernyi silk fibroin films prepared from calcium nitrate solution were treated with heat for crystallization. The structural and conformational changes caused by heat treatment were investigated with X-ray diffraction, infrared spectroscopy, and differential scanning calorimetry. The temperature and treatment time of heat greatly influenced the conformation of the regenerated films. The conformational change was caused by heat treatment over 230°C, and the transition was enhanced by increasing time and temperature. The contents of α-helix, β-sheet, and random-coil conformations were calculated and examined to investigate the effect of heat treatment on the conformational changes. The β-sheet structure could be transformed from a random-coil conformation on heat treatment, whereas the content of α-helix structure was nearly unchanged, regardless of heat-treatment conditions. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2271–2276, 2001     

Preparation of regenerated Antheraea yamamai silk fibroin film and controlled‐molecular conformation changes by aqueous ethanol treatment

The methods of dissolving Antheraea yamamai (A. yamamai) silk fibroin fibers and preparing the regenerated silk fibroin were studied. The molecular conformations of A. yamamai silk fibroin film treated by different concentration ethanol solution were investigated by XRD, FTIR, and Raman spectra. The results indicated that A. yamamai silk fibroin fibers could be completely dissolved in dense lithium thiocyanate solution at about 35°C for 1 h. The initial regenerated film consisted of α‐helix and random coil components. The aqueous ethanol treatment of the film resulted in significant increase in β‐sheet component and improvement of water resistance of the film. This effect was strongly dependent on ethanol concentration, and 60–80% (w/w) ethanol was most effective. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Study on porous silk fibroin materials. I. Fine structure of freeze dried silk fibroin

Silk fibroin solution was prepared by dissolving the silk fibroin in triad solvent CaCl₂ · CH₃CH₂OH · H₂O. In this article we tested and analyzed the state of frozen silk fibroin solution and fine structure of freeze dried porous silk fibroin materials. The results indicated that the glass transition temperature of frozen silk fibroin solution ranges from −34 to −20°C, and the initial melting temperature of ice in frozen solution is about −8.5°C. When porous silk fibroin materials are prepared by means of freeze drying, if freezing temperature is below −20°C, the structure of silk fibroin is mainly amorphous with a little silk II crystal structure, and if freezing temperature is above −20°C, quite a lot of silk I crystal structure forms. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2185–2191, 2001     

Structural and conformational changes of regenerated Antheraea pernyi silk fibroin films treated with methanol solution

The regenerated Antheraea pernyi silk fibroin films were prepared from calcium nitrate solution and crystallized with aqueous methanol solution. The structural and conformational changes were investigated by the X-ray diffraction method and infrared spectroscopy upon methanol treatment. The concentration and treatment time of aqueous methanol solution have a great influence on the conformation of regenerated films. The conformational change from a random coil to β-sheet structure was occurred within 5 min by the treatment of 40–60% methanol solution. As the methanol concentration increases up to 100%, the transition time of conformational change is delayed, and the structural change is not occurred in the case of 100% methanol used. The content of a α-helix, β-sheet, and random coil conformation was calculated and examined to find out the effect of methanol treatment on the conformation changes. The β-sheet structure can be transformed from a random coil, while the content of α-helix structure is not changed, regardless of methanol treatment. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2887–2894, 1999     

Study on porous silk fibroin materials. II. Preparation and characteristics of spongy porous silk fibroin materials

Porous silk fibroin materials, with average pore size 10 ∼ 300 μm, pore density 1 ∼ 2000/mm², and porosity 35 ∼ 70%, were prepared by freeze drying aqueous solution of silk fibroin obtained by dissolving silk fibroin in ternary solvent CaCl₂ · CH₃CH₂OH · H₂O. Pore size distribution of such materials mostly accorded with logarithmic normal distribution. It is possible to control the aforementioned structural parameters and the physical properties of moisture permeability, compressibility, strength, elongation, etc., by adjusting freezing temperature and concentration of silk fibroin solution. Above glass transition zone (−34 ∼ −20°C) of silk fibroin, the freezing temperature has more significant effect on the structure and properties of porous silk fibroin materials. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2192–2199, 2001     

Influence of iodine treatment on the carbonization behavior of Antheraea pernyi silk fibroin fiber

The effect of iodine treatment on the carbonization behavior of tussah silk fibroin (SF) fiber from a wild cocoon, Antheraea pernyi (A. pernyi), was investigated, and the carbon yield, fiber morphology, structural characteristics, and mechanical properties were evaluated. The SF fiber was treated with iodine vapor at 100°C for 12 h and was heated to 800°C under a multistep heating program as carbonization process, which corresponds to the constant thermal degradation rate of SF determined by dynamic thermogravimetric analysis (TGA). The carbon yield was ca. 39 wt %, which is much higher than those for untreated A. pernyi. Scanning electron microscopic (SEM) observation showed that obtained carbon fibers from iodinated SF were structurally intact, and the strength was higher than that from untreated SF. Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction, and Raman spectroscopy revealed that the structures of the carbon fibers obtained from both untreated and iodinated SF were almost the same and amorphous. At the early stage of carbonization of SF, amide bonding of SF molecules was begin to collapse at temperatures higher than 350°C and was completely dissociated by carbonization at 800°C. Dynamic viscoelastic measurements showed that with heating above 270°C the iodine component introduced intermolecular crosslinking of SF and the melt flow of the SF was inhibited, which enhances higher carbon yield and better performance of silk based carbon fiber. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Studies on some physical properties and structural characteristics of methyl methacrylate-grafted silk fiber

Structural characteristics and physical properties of methyl methacrylate-grafted silk fiber from Bombyx mori were studied by X-ray diffractometry, differential scanning calorimetry (DSC), thermogravimetry, and scanning electron microscopy. Methyl methacrylate (MMA)-grafted silk fiber with a grafting yield of more than 30% showed two endothermic peaks at 320°C and 390–410°C, which are attributed to the thermal decomposition of silk fibroin and MMA polymer filled in the fiber, respectively. These DSC results indicate that MMA-grafted silk fiber showed a poor compatibility in the relation between the silk fibroin molecules and MMA polymer. The weight of the MMA-grafted silk fiber decreased as observed at 160°C on the thermogravimetric thermograms due to the evaporation of water from the sample with increasing graft yield. The crystalline structure of MMA-grafted silk fiber remained unchanged regardless of MMA grafting. Taking into account the X-ray diffraction patterns and the increasing graft yield with reaction time, it is assumed that the graft chains of MMA polymer have penetrated into a weak aggregate region and not in the crystalline region of silk fibroin.     

Chemical composition and physical properties of Gonometa rufobrunnae silk

Chemical composition and physical properties of silk fibers from Gonometa rufobrunnae, a silkworm belonging to the family Lasiocampidae (order Lepidoptera, class Insecta) have been studied. G. rufobrunnae silk fibroin contains a large amount of glycine and alanine, as well as hydroxyl, acidic, and basic amino acids. The gly/ala ratio is 1.5, similar to that of Bombyx mori silk fibroin. The ratio between polar and nonpolar amino acids is higher than that of either domestic (family Bombycidae) or wild (family Saturniidae) silk fibroins. The sericin is characterized by a large amount of hydroxyl amino acids, mainly serine. The infrared spectrum of G. rufobrunnae silk fibroin showed characteristic absorptions at 1630, 1530, and 700 cm^?1 attributed to the β structure and at 1650 and 1540 cm^?1 due to the random-coil conformation. The birefringence and isotropic refractive index values were 0.027 and 1.559, respectively. The differential scanning calorimetry (DSC) curve showed two minor endothermic peaks at 222 and 288°C, together with a major endothermic peak at 344°C, attributed to the decomposition of the fibroin with β conformation. The fibers exhibited a maximum contraction peak (4.3%) at about 230°C. The dynamic storage modulus (E′) exhibited an abrupt drop at 190°C, while the loss modulus (E″) curve increased above 185°C with a sharp slope. The surface of degummed G. rufobrunnae silk fibers was very smooth. The shape of the cross section was triangular, round, or roundish shaped. Some fibers were very flat, showing a ribbonlike shape. © 1993 John Wiley & Sons, Inc.     

Chemical modification of Bombyx mori silk with calcium‐salt treatment and subsequent glycerin triglycidyl ether crosslinking

In this article, we propose a new modification method for obtaining porous silk fibers with excellent wet elastic resilience and flexibility. Bombyx mori silks were modified by calcium‐salt treatment and subsequent epoxy crosslinking with glycerin triglycidyl ether. The effects of temperature, time, and catalyst (sodium carbonate) on the crosslinking reaction of the silk fibers were investigated, and the best conditions of reaction were determined as a temperature of 120°C, a crosslinking agent concentration of 7%, and immersion for 1 h with 2% Na₂CO₃ solution before the crosslinking reaction. The change in the structure and the physical properties of the silk fibers after calcium‐salt treatment and epoxy crosslinking was studied. Separating behavior of the microfibers occurred on the surface of the silk fiber after calcium‐salt treatment, and a porous structure formed in the interior of the silk. This porous structure of the silk was enlarged by subsequent epoxy crosslinking, and accordingly, the moisture conduction of the silk fibers improved remarkably. The breaking strength, breaking elongation, and wet elastic resilience of the silk fibers increased evidently after modification, and the modified silks exhibited a better flexibility. The conformation of silk fibroin fibers changed from β sheet to random coil after calcium‐salt treatment, whereas the β‐sheet content in the silk fibers increased after subsequent epoxy crosslinking. The significant reductions in the crystallinity and crystalline sizes in the silk fibers after the crosslinking reaction indicated that the crosslinking reaction occurred within the crystalline region because the calcium‐salt treatment increased the reaction accessibility. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Grafting of methyl methacrylate onto silk fibers initiated by tri-n-butylborane

Structural characteristics of the methyl methacrylate (MMA)-grafted silk fibers using tri-n-butylborane as an initiator were analyzed by infrared spectroscopy and differential scanning calorimetry (DSC), and their refractive index and tensile properties were measured. Graft polymerization was promoted by FeCl₃ pretreatment of the silk. The graft yield reached a maximum by the immersion in 4% FeCl₃ solution for 1 min at 25°C. The infrared spectrum of poly(MMA)-grafted silk fibers showed overlapped absorption bands of silk fibroin with the β structure and of the grafted MMA polymer. A grafted silk fiber with graft yield of more than 140% exhibited two endothermic peaks at 321°C and 396°C on the DSC curve, attributed to the thermal decomposition of silk fibroin and grafted poly(MMA) chain, respectively. Refractive index measurements suggested that the molecular orientation and the crystallinity of the silk fiber decreased with increasing graft yield. Electron photomicrographs showed that silk was coated by grafted PMMA. The tensile strength of the grafted silk decreased rapidly by the grafting even at a lower level.     

Effects of superfine silk protein powders on mechanical properties of wet‐spun polyurethane fibers

Mechanical measurements were employed to investigate the effects of three types of superfine silk protein powder on tensile strength, elongation, and elasticity of wet‐spun Pellethane^® 2363‐80AE polyurethane (PU) fiber. These superfine silk protein powders included undegummed silk (with both native silk fibroin and sericin, water insoluble), native silk fibroin (with native silk fibroin only, water insoluble), and regenerated silk fibroin (with regenerated silk fibroin only, water soluble) in powder form. Experimental data derived from the mechanical measurements illustrated that the miscibility between the PU and regenerated silk fibroin were superior to that between PU and the other two silk proteins. This may be attributed to the similar chemical structure and microphase separation of PU and regenerated silk fibroin with lower molecular weight than native silk fibroin. This preliminary work may provide some information for biomimetic processing of silk‐inspired PU biofibers, which combine elasticity of synthetic PU with biofunction of natural silk fibroin for special biomedical applications. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

离子液体对丝素蛋白溶解性能的影响

合成了一系列碱性离子液体,其中离子液体1-丁基-3-甲基咪唑乙酸盐([Bmim]AC)对丝素蛋白具有良好的溶解性能。考察了丝素蛋白在该离子液体中的溶解特性及在离子液体中的溶解温度和溶解时间,结果表明,在75℃下,溶解840 min,该离子液体对丝素蛋白的溶解能力达到15%(质量分数)。XRD和FTIR分析表明,再生丝素蛋白的构象以α-螺旋为主,丝素蛋白在溶解过程中没有发生衍生化。因此,[Bmim]AC离子液体是丝素蛋白的优良溶剂。     

Preparation of insoluble fibroin films without methanol treatment

Insoluble fibroin films were prepared without methanol treatment. A 15 wt % fibroin solution was obtained through concentration, and then, the insoluble film was achieved by the adjustment of the drying temperature and rate. These films were examined through Fourier transform infrared–attenuated total reflection, X‐ray diffraction, and scanning electron microscopy to determine the structure of the silk fibroin. The physical and mechanical properties were investigated to discover the feasibility of using these films as biomedical materials. When fibroin films were dried above 60°C, abundant β‐sheet crystals existed in the fibroin films, and many globule‐containing micelles aggregated and interacted with each other, which resulted in excellent mechanical properties of the regenerated fibroin films in the wet state. Interestingly, the amide III band of the random coil structure in the fibroin films dried at 70 and 80°C was shifted to a lower frequency, 1228 cm^?1, which meant that a partly orientated structure formed. This may have also affected the mechanical properties of the fibroin films. The tensile strength and breaking elongation of the films dried at 70°C were 29.8 MPa and 59.6%, which is distinctly superior to fibroin films treated with methanol. If the drying temperature was raised to 60°C, the stability of the films in water was also excellent. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2168–2173, 2005     

Production of antimicrobially active silk proteins by use of metal‐containing dyestuffs

The work presented here discusses a new technique for preparing silk fibers and films with persistent antimicrobial activity through use of metallic dyestuffs during the fiber dyeing process. The length of the silk fibers investigated contracted when the fibers were immersed in concentrated neutral salt solutions, such as calcium or potassium nitrate, at elevated temperature levels. The birefringence and molecular orientation of the silk fibroin molecules became less ordered by the action of the neutral salt solutions, resulting in increased dyestuff absorption. Subsequently, contracted silk fibers were dyed with metallic dyestuffs containing Cr or Cu for the purpose of obtaining silk fibers with antimicrobial activity. Silk fibers dyed with metallic dyestuffs showed significant antimicrobial activity against the plant pathogen Cornebacterium and the human pathogen Coli bacillus. Tensile strength of the silk fibers after the salt shrinking and dyeing processes did not show a significant change, whereas the elongation at break was increased slightly. The techniques described here for preparing significantly active antimicrobial silk fibers are effective and economic ways of providing new materials for industrial and biomedical applications. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1181–1188, 2002     

Structural changes and dyeability of silk fibroin fiber following shrinkage in neutral salt solution

The fine structural changes of Bombyx mori silk fibroin fibers, induced by shrinking with concentrated calcium chloride aqueous solution at elevated temperature were investigated as a function of shrinking rate. Tensile strength decreased and elongation at break increased in the shrinkage range 13–67%, the shape of the stress–strain curve changing from rubberlike to brittle at high shrinkage values (70–90%). The birefringence gradually decreased over the entire shrinking range examined, the curve becoming steep as the shrinkage exceeded about 67%. The behavior of isotropic refractive index (n_iso) closely resembled that of birefringence (Δn) in the shrinking range 13–67%. Beyond shrinkage of 67%, the n_iso showed a tendency to increase, especially for the sample with 80% shrinkage. Dichroism measurements showed that the molecular orientation within the amorphous regions decreased sharply at the beginning of the shrinking treatment, within the range 0–13%, then attained a saturation at about 55%. The position and intensity of the major X-ray diffraction peak at 20.5° remained essentially unchanged regardless of the shrinking treatment. The results of dyeing behavior showed that the saturation value attained by shrunk silk fibers was significantly larger than that of the untreated control sample. Both standard affinity and the heat of dyeing increased slightly for the shrunk silk fibroin fiber, suggesting that a larger number of reactive sites became available for the interaction between dye molecules and fibroin chains. A schematic model is proposed for explaining the relation between structural changes and enhanced dyeability of the silk fibers following shrinkage in neutral salt solution. © 1994 John Wiley & Sons, Inc.     

Structure and properties of regenerated Antheraea pernyi silk fibroin filaments

Degummed Antheraea pernyi silk fibroin (APSF) fibers were dissolved in a lithium thiocyanate solution that was dialyzed against distilled water for 3 days. Solution‐cast APSF films were dissolved in hexafluoroisopropanol to prepare a spinning solution. Wet spinning was employed to prepare APSF filaments. Scanning electron microscopy, X‐ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, solid‐state ¹³C cross‐polarization/magic angle spinning nuclear magnetic resonance, and differential scanning calorimetry were employed to study the regenerated APSF filaments. The results showed a uniform distribution of molecular weights, and the largest one may have been greater than 200 kDa. The regenerated filaments contained β‐sheet, α‐helix, and random‐coil conformations, and their breaking strength was 52.20% of the breaking strength of the native fibers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Surface modification of textile material through deposition of regenerated silk fibroin

Regeneration of silk fibroin from calcium chloride/ethanol/water solution is of high interest to shape biomaterial based products for medical and technical application. In this study a continuous process for surface modification of cellulose or polyamide fibers by regenerated fibroin deposits has been investigated. The decomposition of the fibroin‐calcium complex was initiated by addition of K₂CO₃ followed by a methanol rinse. Reactive Blue 19 labeled fibroin was used to monitor the deposition of fibroin on the substrates by colour measurement. The fibroin deposits on the fabric were characterized by microscopy, N‐content, calcium, and protein content. Stiffness and surface resistivity of modified fabrics were determined as representative physical parameters. The reduced mobility of fibers increased fabric stiffness. Surface resistivity of treated samples was reduced by a factor of 10 to 100, which gives an example for the potential of the technique as coating for man‐made fiber textiles. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45098.     

再生蚕丝蛋白纤维的染色性能研究

主要研究染料种类、染料质量分数、氯化钠质量浓度、染色时间、染色温度等5个因素对再生蚕丝蛋白纤维上染率的影响,分析了再生蚕丝蛋白纤维的染色性能.结果表明:对纤维素纤维染色性能较好的染料对再生蚕丝蛋白纤维也有很好的染色性能.运用直接染料对再生蚕丝蛋白纤维进行染色,得到的最佳工艺为:染料质量分数1％ (omf)、氯化钠质量浓度12 g/L、染色温度85℃、染色时间50 min.     

Curcumin loaded electrospun Bombyx mori silk nanofibers for drug delivery

Silk fibroin from Bombyx mori silk cocoons was electrospun into silk nanofibers (SNFs). SEM images show that 9% w/v of SNFs was smooth and beadless having an average diameter in the range 30–150 nm. Curcumin (0.5–1.5 wt%) was incorporated into the silk fibroin solution and electrospun to obtain curcumin incorporated silk nanofibers (CSNFs) with diameters between 50 and 200 nm. The dispersion of curcumin in the SNFs was confirmed by TEM. The amorphous nature of curcumin upon incorporation into SNFs was confirmed by XRD. The functional groups of SNF and CSNF were confirmed by Fourier transform infrared spectroscopy. The SNFs and CSNFs were thermally stable up to ca 350 °C as evidenced by TGA. The glass transition temperature (T_g) of SNFs (168 °C) increased to 184 °C in the case of CSNFs as confirmed by DSC. The storage modulus, loss modulus and tan δ were determined by dynamic mechanical analysis. The percentages of porosity and water uptake of SNFs were 85% and 150%, respectively. The percentage in vitro cumulative release of curcumin at the end of the tenth day for 0.5, 1 and 1.5 wt% formulations was 82%, 84% and 80%, respectively. © 2013 Society of Chemical Industry     

Molecular weight and secondary structure change in eri silk during alkali degumming and powdering

Changes in molecular weight and secondary structure of eri silk during alkali degumming and silk powdering were studied. An increase in silk degumming intensity, through increased alkali concentration, treatment temperature, and time, reduced the fibroin molecular weight and, therefore, the fiber tenacity, but at the same time, increased the β‐sheet fraction. These changes reduced the time required to mill the degummed silk fibers into fine powders. Mechanical forces used in wet attritor and air jet milling disturbed intermolecular packing along the direction of side chains, but the conformation remained essentially β‐sheet even in the sub‐micron silk particles. Dry milling drastically reduced molecular weight and changed the conformation of the fibroin chains. The rate of the spontaneous conformation transition in regenerated fibroin solution prepared from fibers and powders increased with a decrease in fibroin molecular weight, affecting the time fibroin solutions could be stored before gelling. Overall, the study showed that molecular weight and secondary structure of silk powders could be manipulated by suitably changing the degumming and milling conditions. It also suggests that wet media milling and air jet milling are better than dry media milling to prepare less degraded and more crystalline ultrafine silk particles. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011