Electrospun Bombyx mori gland silk

Solutions of Bombyx mori gland silk can be electrospun with the addition of some polyethylene oxide (PEO). Green fluorescent protein (GFP) can also be incorporated and electrospun without apparent phase separation from the silk. The dimensions of the fibers with and without the GFP are qualitatively similar. The results indicate the possibility of making fibers with uniform non-linear optical properties.     

The crystal modulus of silk (Bombyx mori)

It is shown that experimentally determined values of the crystal modulus of Bombyx mori silk agree reasonably well with the computationally determined values, if account is taken of the stress relaxation, which occurs during the experimental measurements. The experimental are 16-22 GPa depending on the sample and the computational are 13 or 16 GPa depending on the method of analysis.     

Electrospinning and rheology of regenerated Bombyx mori silk fibroin aqueous solutions: The effects of pH and concentration

In this study, we prepared regenerated silk fibroin (RSF) aqueous solution to approach the environmental condition in the gland of silkworm, Bombyx mori. Then electrospinning technique was used to prepare the silk fibers. The results showed that pH and concentration had a remarkable influence on the properties of RSF aqueous solutions. With the increase in concentration and the decrease in pH, the rheological behavior of RSF aqueous solutions exhibited a transition from Newtonion fluid to non-Newtonion fluid. At the same time, lowering the pH could induce gel formation and decrease the electrospinnable concentration of RSF aqueous solutions. With the decrease in pH and concentration, the morphology of the electrospun silk fibers changed from belt-like shape to uniform cylinder. The conformation of the electrospun silk fibers was characterized by RS, WAXD and DSC. It was found that electrospun fibers were predominantly random coil/silk I conformation.     

Post-spinning modification of electrospun nanofiber nanocomposite from Bombyx mori silk and carbon nanotubes

Electrospinning is an effective procedure for fabricating submicron to nanoscale fibers from synthetic polymer as well as natural proteins. We successfully electrospun regenerated silk protein from cocoons of Bombyx mori to produce random as well as aligned fibers with diameter less than 100 nm. The fibers were characterized using field emission environmental scanning electron microscope (ESEM), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy and wide angle X-ray diffraction (WAXD) studies. Post-spinning treatment with methanol and/or stretching and co-electrospinning with single walled carbon nanotubes (CNT) were carried out to alter the strength, toughness, crystallinity and conductivity of silk nanofibers. Addition of just 1% CNT along with post-spinning treatments resulted in 7-fold increase in the strength and 35-fold increase in the modulus of silk nanofibers. Raman spectroscopy confirmed that CNTs were incorporated in the silk fibers. FT-IR spectroscopy and WAXD studies proved that silk-CNT nanofibers had more crystallinity compared to silk nanofibers without CNT. Four-probe method demonstrated that silk-CNT nanofibers had 4 times higher electrical conductivity compared to silk nanofibers without CNT.     

Preparation of non-woven nanofibers of Bombyx mori silk, Samia cynthia ricini silk and recombinant hybrid silk with electrospinning method

Electrospinning is a good method to obtain nanoscale fibers from polymer solutions. In this paper, we successfully prepared non-woven nanofibers of Bombyx mori and Samia cynthia ricini silk fibroins, and of the recombinant hybrid fiber involving the crystalline domain of B. mori silk and non-crystalline domain of S. c. ricini silk from hexafluoroacetone (HFA) solution using electrospinning method. ¹³C cross polarization/magic angle spinning NMR spectroscopy was used to monitor the structural change of silk fibroins together with the detection of the residual HFA during the process of the fiber formation. Scanning electronic microscope was used to determine the diameters and their distributions of the fibers.     

Development of silk-like materials based on Bombyx mori and Nephila clavipes dragline silk fibroins

In order to develop new silk-like materials in the form of fiber and non-woven nano-fiber, this study synthesized a new silk-like protein by selecting the sequence from the crystalline region of Bombyx mori silk fibroin, (GAGSGA)₆, to imitate the processing condition of the silk fibroin with the combination of the sequence YGGLGSQGAGRG, the hydrophilic motif of spider dragline silk which was considered as the origin of supercontraction of spider dragline silk (Yang Z, et al. J Am Chem Soc 2000;122: 9019-25). The CD pattern of the silk-like protein in hexafluoroacetone (HFA) indicates that it takes helical structure. The solid-state structures of the silk-like protein before and after methanol treatment were determined to be random coil and Silk II structure (mainly β-sheet structure), respectively, using ¹³C CP/MAS NMR. The ¹³C CP/MAS NMR spectra of the protein after methanol treatment in hydrated state showed that the random coil peaks from Ala Cβ and Ser Cβ carbons become sharper compared with the corresponding peaks in the dry state. The 2D-WISE spectra in the hydrated state also showed increase of the narrow components for these carbons. Thus, water molecules are relatively easy to access at the random coil regions of the protein. The fiber formation of the silk-like protein was possible with wet-spinning or electrospinning methods using HFA as dope solvent and methanol as coagulation solvent.     

X-ray diffraction and computational studies of the modulus of silk (Bombyx mori)

X-ray diffraction with the assumption of uniform stress has been used for determining the crystal modulus of polymers. Values of the modulus of silk obtained previously using such an approach were found to be an order of magnitude lower than, those obtained by computational modeling. The differences are outside the limits of experimental and computational errors. This study re-examined the values in an improved manner. For the X-ray technique, moduli of different samples along the length of cocoon fibers were measured. The values obtained are 20-28 GPa depending on the crystallinity index and degree of orientation of the samples. For the computational calculation, the longitudinal acoustic mode (LAM) frequency of silk systems having three different c-axis dimensions were calculated. An acoustic dispersion curve was generated from the frequency values. The slope of the curve at the origin gave a crystal modulus of 13 GPa. A 3D-fluctuation analysis yielded an average modulus of approximately 16 GPa. These low values result from the out-of-plane torsioning of molecules in the β-pleated structure of the silk crystals. The experimental and computational results are in reasonable agreement with one another as well as with data reported in the literature for other pleated molecules.     

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     

Regeneration of Bombyx mori silk by electrospinning—part 1: processing parameters and geometric properties

We studied the effect of electrospinning parameters on the morphology and fiber diameter of regenerated silk from Bombyx mori. Effects of electric field and tip-to-collection plate distances of various silk concentrations in formic acid on fiber uniformity, morphology and diameter were measured. Statistical analysis showed that the silk concentration was the most important parameter in producing uniform cylindrical fibers less than 100 nm in diameter.     

Regeneration of Bombyx mori silk by electrospinning. Part 3: characterization of electrospun nonwoven mat

Regenerated Bombyx mori silk fibroin in formic acid was electrospun and the morphological, chemical and mechanical properties of these nanofibers were examined by field emission environmental scanning electron microscopy (FESEM), Raman spectroscopy (RS), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and tensile testing. FESEM indicated that the average fiber diameter was less than 100 nm and circular in cross section. This paper maps the silk fibroin molecular conformations of each step of the sample preparation and the electrospinning process. The secondary structural compositions (random and β-sheet) of the fibroin were determined by FTIR and RS. The crystallinity index of the electrospun fiber, calculated as the intensity ratio of 1624 (β-sheet) and 1663 (random) cm⁻¹ FTIR bands was higher than that of the pristine fiber. Raman spectra of the amide I (1665 cm⁻¹, random) to amide III (1228 cm⁻¹, β-sheet) ratio of the electrospun fiber was less than that of the pristine fiber indicative of higher β-sheet content. The fiber crystallinity, determined by XRD, showed a lower value for the electrospun fiber. The electrospun fiber shows small but significant increases in the β-sheet content in comparison with the pristine fiber. Dissolution of fibroin in formic acid enhances β-sheet crystallization and may facilitate β-sheet formation in electrospun fiber. The electrospun random silk mat had a Young's modulus, ultimate tensile strength and strain of 515 MPa, 7.25 MPa and 3.2%, respectively.     

Flow analysis of aqueous solution of silk fibroin in the spinneret of Bombyx mori silkworm by combination of viscosity measurement and finite element method calculation

Bombyx mori silk fibers possess outstanding mechanical properties in spite of being spun at room temperature and from the aqueous solution. Therefore, the mechanism of the structural transition has been studied with great attention, but still not be well understood. In this study the flow simulation of the silk fibroin aqueous solution using finite element method was performed on the basis of both the relationship between the viscosity and shear rate of the silk fibroin solution prepared from the silk gland, and the detailed structure of the spinneret including silk press part of the silkworm obtained from the optical micrographs. The viscosity of the silk fibroin solution decreased with power-law till the shear rate, about 1.5 s⁻¹ with increasing shear rate. Then the viscosity increased reversely which is speculated due to the fiber formation as a result of aggregation of the molecules. In the flow simulation analysis, the initiation site of the fiber formation was calculated by regulating the extrusion pressure. The fiber formation occurs in 550 μm from the spigot at 1 MPa and in 600 μm from the spigot at 50 MPa. The extrusion pressure in the range from 1 MPa to 50 MPa induces the fiber formation in the stiff plates (550-600 μm from the spigot), that is, the silk press part in the spinneret.     

微流控纺丝制备丝素纳米带增强再生丝素蛋白纤维

为获得力学性能优异的再生丝素蛋白(RSF)纤维,采用单通道微流控湿法纺丝,将RSF溶液与丝素纳米带(SNR)以1 000∶0、1 000∶1、500∶1、300∶1的质量比混合成质量分数33％的纺丝液,制备RSF基复合纤维.采用傅里叶红外光谱仪(FTIR)、扫描电子显微镜(SEM)、材料试验机等对所得纤维的结构和性能进...     

Regeneration of Bombyx mori silk by electrospinning. Part 2. Process optimization and empirical modeling using response surface methodology

The response surface methodology was used to model and optimize the electrospinning parameters for the spinning of regenerated nanoscale silk fibers from domestic silkworm, Bombyx mori. Electric field and silk concentrations were chosen as variables to control fiber diameter at different spinning distances. Fiber diameter was correlated to these variables by using a second order polynomial function. The predicted fiber diameters were in agreement with the experimental results. Response surfaces were constructed to identify the processing window suitable for producing nanoscale fibers.     

Micro-computerized tomographic observation of the spinning apparatus in Bombyx mori silkworms

Silkworms and spiders have evolved complex spinning apparatus thought to use highly controlled conditions to optimize protein folding and crystallization to provide a tough fiber. Accordingly, the structure and function of the natural spinning apparatus has been studied with great attention as an interesting piece of biological engineering with potential for mimicry in an industrial process. However it is still not well understood. Here we used Micro-Computerized Tomographic equipment (mCT) to visualize the three-dimensional structure of the spinning apparatus in Bombyx mori silkworms. Multidirectional tomograms obtained by X-ray radioscopy provided valuable information on the detailed arrangement of each muscle of the silk press. It is suggested that the duct in the silk press part plays a part as an extrusion die whose cross-sectional area can be controlled by muscles to optimize applied stresses in the partially gelled silk within its lumen.     

The preparation of high performance silk fiber/fibroin composite

An all-silk composite, in which uniaxially-aligned and continuous-typed Bombyx mori silk fibers were embedded in a matrix of silk protein (fibroin), was successfully prepared via a solution casting process. The structure, morphology, mechanical and thermal properties of such silk fiber/fibroin composites were investigated with X-ray diffraction, scanning electron microscopy, tensile and compression tests, dynamic mechanical analysis and thermogravimetric analysis. The results demonstrated that the interface adhesion between silk fiber and the fibroin matrix was enhanced by controlling the fiber dissolution through 6 mol L⁻¹ LiBr aqueous solution. Compare to those of the pure fibroin counterparts, the overall mechanical properties as well as the thermal stability of such silk fiber/fibroin composites were significantly improved. For example, the composite with 25 wt% fibers showed a breaking stress of 151 MPa and a breaking elongation of 27.1% in the direction parallel to the fiber array, and a compression modulus of 1.1 GPa in the perpendicular direction. The pure fibroin matrix (film), on the other hand, typically had a breaking stress of 60 MPa, a breaking elongation of 2.1% and a compression modulus of 0.5 GPa, respectively. This work suggests that such a controllable technique may help in the preparation of animal silk based materials with promising properties for various applications.     

静电纺丝PLA/丝素复合纤维膜的结构和性能

以氯仿、丙酮为混合溶剂,制得质量分数为5%的聚乳酸(PLA)纺丝液,经静电纺丝制备PLA纤维膜;以98%的甲酸为溶剂,制得丝素纺丝液,在PLA纤维膜上喷射丝素纺丝液制成PLA/丝素复合纤维膜.采用扫描电镜观察其形貌结构,并测定其微细结构、力学性能、溶失率及生物性能.结果表明:PLA/丝素复合纤维膜呈规整排列的多孔网状结构.与丝素膜相比,PLA/丝素复合纤维膜的丝素蛋白转向β折叠结构,断裂比功提高18倍,水中溶失率降低3倍,更有利于人脐静脉内皮细胞在纤维膜上的生长.     

Effect of plasma treatment of silk fibroin powder on the properties of silk fibroin powder/polyurethane blend film

In this study, silk fibroin powder was treated by dielectric barrier discharge (DBD) plasma. The objective is to improve the performance of the silk fibroin powder/polyurethane (PU) blend film used in biomechanical field. The scanning electron microscope (SEM) showed that the plasma‐treated powder was broken into small particles and the film from the treated powder became homogeneous and dense. Fourier transform infrared spectroscopy (FTIR) revealed that the hydrophobic groups in silk fibroin powder were oxidized during plasma treatment. Little change in chemical composition was found on the surface of the blend film from plasma‐treated powder. The fracture strain of the blend film from plasma‐treated powder was remarkably raised, whereas its tensile strength was influenced significantly by the plasma treatment conditions. The wet‐out time of the plasma‐treated powder/PU film was shortened considerably. This indicates the improved hydrophilicity of the blend film. In addition, the decreased values of water vapor permeability suggested that the structure of the blend film became dense. This might result from the strong interfacial adhesion between plasma‐treated powder and PU. POLYM. ENG. SCI., 50:1705–1712, 2010. © 2010 Society of Plastics Engineers     

Water-annealing treatment for edible silk fibroin coatings from fibrous waste

Silk fibroin (SF) is an engineered biopolymer with properties that are desirable for the development of food preservation materials, such as edible coatings or packaging. In this study, SF from fibrous waste was assessed for the first time as an edible coating for strawberries. Relationships were established between the structural properties of SF thin films obtained from silk waste, both untreated (SFW) and water annealed (WA-SFW) and their morphology and performance as edible strawberry coatings. According to the results obtained, the water-annealing treatment led to a structural modification in SF films. The strawberries coated with WA-SFW exhibited better performance during storage by reducing weight loss and preserving its visual appearance. The analysis of metal contaminants showed that SFs obtained from fibrous waste are relatively nontoxic. Therefore, using this raw material for the development of edible coatings in perishable fruits is considered promising. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48505.     

Preparation of non-woven mats from all-aqueous silk fibroin solution with electrospinning method

In the present study, we successfully prepared non-woven mats from stable regenerated silk fibroin aqueous solution at high concentration. Scanning electronic microscope (SEM) was used to observe the morphology of the fibers. The structure of the fibers was characterized using Fourier transform infrared (FTIR), wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC). The mechanical tests were also performed. In the as-spun fibers, silk fibroin was present in a random coil conformation, the stress and strain at break were 0.82 MPa and 0.76%, respectively, while after methanol treatment, the silk fibroin was transformed into a β-sheet-containing structure, the stress and strain at break increased to 1.49 MPa and 1.63%, respectively. This study provided an option for the electrospinning of silk fibroin without using organic solvent or blending with any other polymers, which may be important in tissue engineering scaffold preparation.     

Photoluminescent and tough hydrogels from silk fibroin and polyacrylic acid complexed with europium

Biocompatible, tough, and photoluminescent hydrogels are highly desirable for biomedical applications in vivo. Herein, hybrid hydrogels prepared from silk fibroin (SF) and polyacrylic acid (PAA) and complexed with europium, named as SF-PAA-Eu³⁺ hydrogels, exhibit good comprehensive properties. Owing to the intensive molecular interactions among SF, PAA, and Eu³⁺, SF-PAA-Eu³⁺ hydrogels show a greatest tensile strength of 0.58 MPa, elongation of 443%, and work of fracture of 1.65 MJ/m. In vivo imaging experiment in a mouse subcutaneous implantation model revealed excellent and sustained photoluminescence of the SF-PAA-Eu³⁺ hydrogels for 24 h. The work provides a strategy for designing functional SF-based hydrogels for imaging applications in vivo.