Advanced Materials Research Vols. 175-176

Abstract: The sericin coated around silk fibroin fiber is a natural protein-based polymer and presents a layered structure. According to the solubility in water under different temperatures and pressures, the sericin is divided into three parts of outer, middle and inner sericin layers accounting for 15%, 10.5% and 4.5% to the total silk protein (included sericin layers and fibroin fiber) in terms of the mass respectively. The partition within the sericin layer presents the relative proportions of 50%, 35% and 15% from the outer to inner layer. Furthermore, the differences of three layers in the amino acid composition are very significant. The non-polar amino acids in the outer, middle and inner sericins are gradually increased, in particular for alanine, which are accounted for 5.20, 6.13 and 11.58 mol% respectively; while its content jumps to 33.38 mol% in the silk fibroin fiber. Nevertheless, the polar amino acids, especially the neutral ones, are gradually decreased accounting for 39.34, 38.62 and 23.82 mol% respectively. Concentration of Serine drops most prominently, i.e. 28.00, 25.57 and 13.32 mol% respectively; while its content goes to 7.65 mol% in the silk fibroin fiber. On the other hand, the hydrophobic amino acids gradually increase and the hydrophilic amino acids go to oppsite way. These results indicate that the amino acid compositions of the outer and middle sericins are similar to each other, but those of the inner sericin are different from the others. The closer the sericin layer is to the silk fibroin fiber, the closer its amino acid composition is to that of the fibroin fiber. These obtained results are of important reference value for processing of silk sericin peptides and their applications in cosmetics, cell culture, healthy food and other areas.

Abstract: Solvent-water suspension free-radical polymerization method was used to synthesize acrylonitrile(AN)-acrylamide(AM) copolymers in this paper. The copolymerization was carried out with azobisisobutyronitrile (AIBN) as an initiator and dimethysulfoxide (DMSO)/ water solution as solvents at a constant monomer ratio (AN:AM(wt)=85:15). The ratio(wt) AN:AM=100:0 was also be used for a comparison. The structure and properties of the copolymers was studied by fourier transform infrared (FT-IR), X-ray diffraction (XRD) and thermogravimetry(TG). The nanofibers were obtained by electrospinning AN-AM copolymer solution with N,N-Dimethyl acetamide(DMAc) as a solvent. Then, the fibers were pre-oxidized in relaxation state and in air by using an oven. The structure of pre-oxidized nanofibers was investigated by scanning electron microscopy (SEM) and FT-IR. The results showed that the ratio of dimethysulfoxide (DMSO)/water 50/50(v) was optimum for the copolymer properties and nanofiber spinnability as a carbon nanofiber precursor. The copolymer fibers only needed lower preoxidation temperature and shorter preoxidation time to reach the same degree of cyclization due to the introduction of AM.

Abstract: Electrospun Silk-Fibroin (SF) mats were fabricated by electrospinning with regenerated Bombyx mori silk-fibroin/formic acid solutions. After spinning, the water soluble and mechanical properties of pure fibroin nanofibers were poor. So electrospun SF mats were crosslinked with N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC), a low cell cytotoxicity crosslinking agent, and N-hydroxysuccinimide (NHS), which can increase the reaction rate. The scanning electron microscope images indicated that the diameter of fibers increased with crosslinking reaction. When EDC/NHS reached to 7.5wt.%, the diameter of fibers achieved the maximum. The mechanical test showed that tensile strength enhanced after crosslinking with EDC/ NHS. While EDC/NHS reached to 7.5wt %, the rupture strength reached to (38.31±5.30) Mpa, and the breaking elongation ratio reached to (182.00±31.27) %. FTIR results showed the the proportion of β-sheet increased while random coil and α-helix decreased after treatment.

Abstract: Silk fibroin modified viscose fiber (SFVF) was a new fiber with silken handling and luster, which was produced via adding silk fibroin (SF) during the viscose process. In this paper, a series of testing had been done to study the structure and properties of SFVF. The amino acid content of SFVF was measured by HITACHI-835-50 amino acid tester. The morphology, structure, thermal and mechanical property of SFVF were characterized by SEM, FTIR, DSC and electronic strength tester. The results indicated that SFVF consisted of many kinds of amino acids compared with pure viscose fiber (VF) yarn. The results of SEM showed more continuous multi fine slots existed in the longitudinal section of SFVF than in that of VF, demonstrating that wet permeability and vapor transmission could be enhanced for the SFVF to certain extent. Results from FTIR indicated that the secondary structure of SFVF was mainly β-sheet and random coil, and its absorption peaks were 1616cm-1 and 1644 cm-1 respectively. The DSC curve shown the thermal decomposition temperature of SFVF was about 328.39°C, which was close to that of VF. It suggested that the SF modification had no obvious influence on thermal stability of VF. At last, the dry-strength and wet-strength of SFVF was close to that of VF. Therefore, the application of VF would be expanded with the SF modification.

Abstract: Based on our experimental data of neovascularization of porous silk fibroin films (PSFF)，in this study we characterized the formation of new blood vessel system at different periods. Firstly, we regarded a wound as two sections, namely, an interface layer and a material layer. Angiogenesis of the interface layer underwent three periods that were rehabilitation period of primary vascular plexus (postoperative 1st day-3rd day), rapid growth period (postoperative 3rd day - 7th day) and remodeling period (after the 7th day). In addition, angiogenesis of the material layer underwent initiation period (postoperative 5th day - 7th day), rapid growth period (postoperative 7th day - 13th day) and remodeling period (after the 13th day). According to the analysis results for angiogenesis, we realized that the efficacy of PSFF on repairing wound was reflected in coordination between infiltration of cells in the pores and angiogenesis, and in timeliness of the newly formed blood vessels’ extention from the interface layer to the material layer.

Abstract: 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 10 to 200 kDa. When the liquid silk were introduced rapidly into acetone, silk protein nanoparticles (SFNs) with a range of 40~120 nm in diameter could be obtained. The crystalline silk nanoparticles could be conjugated with β-glucosidase with cross-linking of reagent glutaraldehyde. In this work, the activity of β-glucosidase-silk fibroin nanoparticles (βG-SFNs) bioconjugates was determined by p-nitrophenyl-β-D-glucoside (p-NPG) as a substrate and the optimal conditions for the biosynthesis of βG-SFNs bioconjugates were investigated. βG-SFN constructs obtained by 5h of covalent cross-linking time at the experimental conditions of 0.25% cross-linking reagent, 37 °C and the proportion of β-glucosidase and SFNs (75 : 100, U/mg) showed 46% of recoveries. Results showed that kinetic parameters of βG-SFNs were the same as for the free β-glucosidase. The optimal pH was 5.0 and the optimal temperature was 60°C. When β-glucosidase was coupled covalently with silk nanoparticles, the thermal stability of βG-SFNs was slightly enhanced as compared with free β-glucosidase. The apparent Km of βG-SFNs (1.41×10-3 mol•L-1) was near five-fold less than that of the free enzyme (7.26×10−3 mol•L-1), this fully shows that after the free enzyme conjugated with silk fibroin nanoparticles, the enzyme affinity with substrate increased. These results fully demonstrated the silk protein nanoparticles were good carriers as bioconjugation or modification of enzymes. Moreover, they had potential values for research and development in food processing and flavor processing agents.

Abstract: The paper concentrated on the optimization of the recombinant strain BL21 (DE3)-PE7-Nit. The component of culture medium and the culture conditions were optimized. The optimized medium was: yeast extract 10 g/l, L-glutamate sodium 8 g/l, MgSO4.7H2O 0.7 g/l, Isopropyl-β-D-thiogalactopyranoside 0.3 mmol/L, potassium hydrogen phosphate 0.5 g / L, phosphate Potassium 0.5 g / L and the culture condition was: initial pH 7.0, inoculum 2%. The result showed that the activity of nitrilase prepared with these conditions increased by 130.37 % through optimization.

Abstract: Artificial nerve conduits (NC) can be used as an alternative to autologous nerve grafts to enhance the repair of small nerve gaps. Many natural and synthetic biomaterials have been processed to be tubular scaffolds. However, current NC lack adequate molecular and structural functionalities. Thus, we prepared silk fibroin (SF)-based nanofibrous tubular scaffolds (inner diameter=1.5 mm) for nerve repair. The Bombyx mori silk fibroin was firstly dissolved in hexafluoroisopropanol (HFIP), and then was electrospun to be nanofibrous silk fibroin tube which topographically functionalized with aligned and non-aligned SF nanofibers. Effects of electrospinning parameters (including collection distance, rotational speed and translational speed) on the micro-morphology of SF tube were investigated. The nanofibers orientation in SF tube affects the mechanical property of SF tube. The results suggest that this tubular scaffold shows promising application in nerve tissue engineering.

Abstract: The cactus is a kind of abundant foliage used for the Chinese medicine, which has special physical-chemistry properties and physiological function. It has been utilized for various fields. The B. mori silk fiber was slightly dissolved with CaCl2-EtOH-H2O solution and subsequently treated with the cactus extracts solution in aqueous acetic acid. The weight gain of the slightly dissolved B. mori silk fiber after cactus extracts modification was much higher than that of original silk fiber, and it increased remarkably with the CaCl2-EtOH-H2O dissolution time and cactus extracts concentration increasing. Scanning electron microscopic photographs showed that the microvoids appeared inside the slightly dissolved silk fiber and the fiber surface was changed after the series reaction with cactus extracts. Infrared spectra of the modified silk fiber suggested that the conformation of fibroin molecules had a trend to β sheets. The crystallinity of the modified silk fiber did not change remarkably by the X-ray diffraction analysis. Furthermore, with the cactus extracts treatment, the mechanical strength and elongation of silk fiber decreased slightly, whereas the initial modulus and elastic deformation of the silk fiber enhanced. Meanwhile, the cactus extracts modified B. mori silk fiber possessed a good antibacterial property.

Abstract: It was studied that metal ions affected light-degradation of silk fabric in this paper. The contrast of the weight and the tensile properties of silk fabric treated without or with different concentrations of metal ions (copper sulfate solution and chromium sulfate solution) by different time of light conditions were carried out. The results showed that after the treatment of silk with metal ions solution, the weight gain of the silk fabric increased with increasing the concentration of metal ions solution. There were different changes in the breaking strength of silk fabric treated with different metal ions when subjected to light exposure. In the same light conditions, comparing with the fabric without treatment, the breaking strength of the fabric with copper (ii) ions treatment increased while the breaking strength of the fabric with chromium (iii) ions treatment obviously decreased. Besides, fabric samples with copper ions treatment slowed down the decreasing rate of the breaking strength and fabric samples with chromium ions treatment accelerated the decreasing rate with increasing light exposure time. The results indicated copper (ii) ions had an inhibitory effect on light-degradation of silk fabric, and chromium (iii) ions enhanced light-degradation of silk fabric. Meanwhile, their respective function for fabric increased along with the increment of adsorption values of metal ions on silk fabrics. When being treated with the same concentration of metal ion solution, weight loss of the silk fabric improved and the breaking strength of the fabric decreased with increasing light exposure time, and the two had linear relationship.