Advanced Materials Research Vols. 175-176

Abstract: Silk fibroin (SF) and polyvinyl alcohol (PVA) solutions were prepared respectively by formic acid and deionized water as solvent, the solutions were then blended, and after that AgNO3 was added. The PVA/SF/AgNO3 solution was electrospun to form nanofibers. A number of particles were generated on the surface of nanofibers during electrospinning, which was confirmed by transmission electron microscopy (TEM). The diameter distribution of the nanofibers was narrow and the particles were nano-sized and well-dispersed. X-ray diffraction (XRD) patterns of the composite nanofibers indicated that the component of the nanoparticles was silver. By annealing the composite nanofibers at 155°C for 5 minutes, the silver nanoparticles possibly clustered into the larger size. The size of Ag nanoparticles was 2.25nm without post treatment, and this value increased to 3.76nm after the heat treatment. The antibacterial activity of the heat-treated PVA/SF composite nanofibers containing Ag nanoparticles was evaluated and the resultant nanofibers showed strong antimicrobial activity on Staphylococcus aureus and Escherichia coli. Moreover, the antibacterial PVA/SF composite nanofibers containing Ag nanoparticles have the possibility to be used in wound dressing due to the electrospun PVA nanofibers could preserve the web structure in water after the heat treatment.

Abstract: An improved method of water-in-oil-in-water (w1/o/w2) multi-emulsion was developed to prepare silk fibroin (SF) microspheres that had improved drug-loading amount and better drug-loading efficiency. SF and dexamethasone sodium phosphate (DSP) were used as one water phase(w1), liquid paraffin was used as oil phase and isopropanol was used as the other water phase(w2). In the preparation process, isopropanol was also used to induce the crystallization of SF. The SF microsphere was mainly composed of silk II proteins. The drug-loading amount of SF microsphere ranged from 28.45 µg/mg to 79.21 µg/mg, and the drug-loading efficiency varied from 30.80% to 87.16%. The spherical morphology of the microsphere was observed by SEM. The particle diameter was measured by the Laser particle sizer and their average sizes varied from 7.41 µm to 66.10 µm. The drug releasing profile of the microspheres was measured in vitro. The burst release was significant when isopropanol-to-SF ratio was lower than 3:1，although the drug-loading amount and the drug-loading efficiency was high; It showed a higher drug-loading amount and efficiency, as well as an obvious continuous release effect when the ratio was higher than 4:1; It also showed a certain continuous release effect when the ratio was 4:1.

Abstract: A transformation system was developed for stable germline transformation in the silkworm Bombyx mori L. using piggyBac, a transposon discovered in the lepidopteran Trichoplusia ni, and a helper plasmid. The transposon consists of the piggyBac inverted terminal repeats, the enhanced green fluorescent protein gene as the reporter gene and the spider dragline gene. A nonautonomous helper plasmid encodes the piggyBac transposase. The transformation system was cotransfected into BmN (Bombyx mori L. Nucleopolyhedrovirus) cells using lipofection. PCR amplification on cellular genomic DNA using specific primers showed that a fragment of reporter gene, the spider dragline derived gene and A3 promoter were successfully amplified respectively. Plasmids without being transpositioned were not assayed. Green fluorescence cells were observed at 48 hours after transfection and the fluorescence intensity increased at 72 hours after transfection.

Abstract: In this paper, the solvent mixing, polymer blending, multi-walled carbon nano-tubes(MWCNTs) reinforcing, steaming and heat treatments, and multi-layering with spunbond nonwoven were used to enhance the mechanical properties of the electrospun nonwovens of polystyrene(PS), polyvinyl chloride(PVC) and poly(phthalazinone ether sulfone ketone)(PPESK). The scanning electron microscopy, transmission electron microscopy and mechanical measurement were applied to characterize their microstructure and properties. The results showed that, the optimal mixture solvent can increase the tensile strength of PVC nonwovens by over 5 times; the polymer blending substantially improves the mechanical properties of PPESK nonwovens since the mechanical properties of virgin PPESK was so fragile that no data were obtained; the addition of MWCNTs to PS, PVC and PPESK improves their mechanical strength; the steaming and heating measures can be good viable route to lead to high strength for all of them; the multi-layering technique by using common spunbond nonwovens can be used to strengthen the nonwoven mats if the interfacial adhesion between the two mats can be solved well.

Abstract: Due to the exceptional biocompatibility of spider silk and poly-L-lactic acid (PLLA), electrospun PLLA or spidroin fiber mat is one of the best biomaterials. The diameter of electropun PLLA fiber decreased and mechanical property of such fiber mats was improved once some spidroin was added into PLLA/Hexaflorisopropanol (HFIP) solution. The influence of electrospinning voltage and distance on the shape and mechanical properties of spidroin/PLLA composite fibers was investigated as well as the molecular conformation and crystalline structure of the electrospun fibers. The results revealed that the diameter of spidroin/PLLA fiber was non-uniform, which varied from 300nm to 1000nm. The content of random coil or α-helix structure was about 45%, and spidroin presented a crystal structure separated with PLLA in their composite fibers. With the raise of voltage, the proportion of nano-sized fibers in an electrospun spidroin/PLLA fiber mat increased and tended to be unchanged. The breaking strength of the mat was improved following the increase of voltage. Meanwhile, the ratio of nano-sized fibers and initial modulus of the spidroin/PLLA fiber mat underwent the convex change against the electrospinning distance between the needle and collector.

Abstract: The method of extracting protein from wool was studied for the purpose of reusing the waste wool. The aqueous solution of wool keratin was prepared with Sodium Shlfide as reductive agent. In this paper, PVA was used to mix with keratin in different proportions. Both solutions were cast to obtain blended films. Scanning electron microscopy investigation showed that the surface of blended films was rough and uneven and the surface of the pure keratin film had small peridiole. FTIR analysis indicated that the secondary structure of the keratin was influenced by the blending ratios. Compared with wool fiber, the keratin film cast from aqueous solution showed a decrease in the amount of α-helix structure, while β-sheet and random coil conformations increased. When the keratin solution and PVA solution were blended in the ratios of 40:60, the film was flexible and rigid, and had good mechanical properties. This study encourages the further investigation of the applications of wool keratin films in the biomedical field, which could provide a new way to reuse various waste feathers.

Abstract: The Bombyx mori silk fibroin gel with three dimensional structures is an important form to be developed for tissue engineering materials. In this paper, silk fibroin gels were prepared with adding polyalcohol into silk fibroin solution. The gel structure was analyzed by X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy. The results demonstrated that when adding more than 100% of polyalcohol, both of glycerol and polyethylene glycol 400 (PEG400) can accelerate the gelation process markedly. With the increase of the percentage of PEG400 and glycerol, it promoted silk fibroin molecules to cluster rapidly and inhibit silk fibroin molecules transforming from the random coil or α-helix to β-sheet in a ratio of 900% especially. Silk fibroin gels containing 100% of polyalcohol had more uniform morphology and the pores distributed uniformly.

Abstract: Silk fibroin hydrogels is an important morphous of biomaterial. As a natural protein collosol, purified native silk fibroin solution can be gelatinized under certain conditions. The main mechanism of the gelation is that the fibroin molecules turn into the β-sheet conformation from the random coils. This transformation of silk fibroin molecules would be influenced by various parameters such as the temperature, pH value, ion concentration and so on. In this paper, the effect of ultrasonication on the gelation velocity and structure of silk fibroin were discussed. It is believed that the cavitations caused by sonication could accelerate the process of gelation of silk fibroin. Our experiments demonstrated that the ultrasonic treatment could greatly reduce the silk fibroin gelation time, especially at a high sonication power exceeding 400W. The results of XRD, FTIR, and Raman spectra indicated that the ultrasonication had no significant effect on the final structure and composition of the silk fibroin gels except the acceleration for the molecular transition from random coil and α-structure to β-sheet conformation of silk fibroin. The SEM images showed freeze-dried fibroin gels close to the ultrasonication source had compact structure, while the structure was more loosening far away to the source.

Abstract: Habotai silk was hydrolysis-aged by HCl and NaOH to study the change of its crystallinity, orientation, tensile mechanical properties, weight loss rate etc. The results show that the hydrolysis-aging degree of silk by HCl was slight, but that by NaOH was significant. Both the crystallinity and orientation were reduced significantly by NaOH but slightly by HCl. The weight loss rate of silk samples rose like the parabola with the increase of alkali concentration, and it rose linearly against time. The breaking strength of silk fibers was affected significantly by the alkali hydrolysis aging, particularly in the initial stage and its weight loss rose linearly with the increase of alkali concentration. The PH values of the hydrolysis solution both by HCl and NaOH were close to neutral.

Abstract: Silk hydrogels have mechanical properties and structural features that are similar to load-bearing soft tissues, and can be implanted for tissue restoration. In the present study, we investigate silk fibroin sol-gel transition processes in detail. The effect of different surfactants and high temperature pretreatment were studied detailedly. Based on the study, a mechanism was summarized. The result showed that the surfactant accelerated sol-gel transitions while heat pretreatment decelerated sol-gel transitions. Gelation time was decreased to several hours when added surfactant with negative charge. On the contrary, gelation time was increased to dozens of days when extended the time of high-temperature processing. Upon gelation, a random coil structure of the silk fibroin was transformed into a β-sheet structure.