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Silk sericin (SS) can be obtained as a byproduct during the silk fiber process, but its application has been limited due to the brittleness of the SS film. To enhance the flexibility of the SS film, glycerol (Glc) has been added as a plasticizer. The addition of Glc enhanced the elongation property of the SS film when the Glc content was 50-70 wt% of SS. Glc also induced the structural transition of SS from a random coil structure to a β-sheet structure. The inconsistent increase of elongation and β-sheet structure of the SS/Glc film were explained by the content of moisture in the SS/Glc film. The moisture content of the SS/Glc film increased proportionally when the Glc content was higher than 50 wt% of SS, which was the same Glc content range that exhibited the plasticizing effect. Therefore, the plasticizing effect on the SS film may occur not only because of Glc but also because of water. Furthermore, water also contributed to the increase in the β-sheet structure development. Our results suggest that the moisture content in the plasticized protein film may play an important role when the plasticizer has hygroscopic properties., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Silk has attracted the attention of biomedical researchers because of its good biocompatibility. Although various characteristics of silk are needed for its successful application in biomedical fields, the performance of silk material is limited. Although there are many varieties of Bombyx mori silkworm, the effect of different silkworm varieties on regenerated silk has not been considered in detail. That is, the use of a diverse variety of silkworms has not been considered in non-textile applications resulting in limited performance of silk materials. In this study, the effects of different silkworm varieties on the structural characteristics and properties of silk cocoon and regenerated silk fibroin (SF) were examined. Structural characteristics of silk cocoon including color, fiber diameter, and porosity, differed depending on the silkworm variety. Furthermore, molecular weight, solution viscosity, and mechanical properties of regenerated SF were influenced by the variety of silkworm, while the amino acid composition, β-sheet crystallization by formic acid, and cyto-compatibility of regenerated SF did not differ between the samples from different varieties of silkworm. These results imply that diverse performance of silk can be obtained by controlling the silkworm variety, and that the use of different varieties of silkworm might be a good way to strengthen the performance of silk in biomedical fields., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Silk fibroin (SF) is known to be a biocompatible material, and different forms of SF are used for various applications. However, the application of SF in particle form is rarely reported, compared to other forms. In this study, SF microparticles with a diameter of approximately 250 μm were prepared by the electrospray method, using 1 M LiCl/DMSO as a solvent. The dissolution time of SF in the CaCl2/CH3CH2OH/H2O solution and the concentration of the SF dope solution affected the final morphology of the microparticles. A long dissolution time and a low SF concentration led to the formation of irregular microparticles, but a short dissolution time and a high concentration produced sphere-like microparticles. The shear viscosity of the SF dope solution was the main parameter that affected the morphology of the SF microparticles. Regardless of the dissolution time in the CaCl2/CH3CH2OH/H2O solution and the concentration of the SF dope solution, the shear viscosity of the dope solution must be higher than 0.33 Pa s to produce sphere-like microparticles. Finally, cell adhesion experiments demonstrated that these SF microparticles show potential for use as cell carriers., (Copyright © 2015 Elsevier B.V. All rights reserved.)

The application of silk on tissue engineering scaffolds has been studied intensively because silk has an electrospinning technique using a good blood compatibility, excellent cytocompatibility and biodegradability. Silk consists of two polymers, fibroin and sericin. In spite of importance of sericin, most studies were focused on the fibroin only and the effect of residual sericin on the electrospinning performance of silk has not been considered. In this study, regenerated silk with different residual sericin contents was prepared by controlling the degumming conditions. The effects of the degumming conditions on the solution properties and electrospinning performance of silk were examined. The fast protein liquid chromatography (FPLC) measurements confirmed that the molecular weight of the regenerated silk decreased slightly with increasing residual sericin content. More molecular aggregation of silk occurred with increasing sericin content, resulting in an increase in the solution turbidity of formic acid. All silk formic acid solutions exhibited almost Newtonian fluid behavior and the viscosity increased with increasing sericin content. Interestingly, the dope solution viscosity of silk increased remarkably at sericin contents <1% (or degumming ratio >25%) leading to significant improvements in electrospinnability and an increase in the fiber diameter of the silk web., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Four regenerated silk fibroin (SF) samples were prepared under different dissolution conditions and their molecular weight (MW) distributions and solution properties in water and formic acid were examined. SFL, produced by dissolving in LiBr aqueous solution for 6h, showed the highest MW level. In the three SFC samples, produced by dissolving SF in CaCl(2)/H(2)O/EtOH solution for dissolution times ranging from 3 to 180 min, the MW of the SFs decreased with increasing dissolution time and a new band appeared at low MW. Interestingly, SFL presented as a relatively transparent aqueous solution with 10-30 nm particle size, whereas the three SFC samples exhibited a turbid solution with 100-300 nm particle size. SF formic acid solutions showed a higher viscosity than SF aqueous solutions and exhibited almost Newtonian fluid behavior, whereas SF aqueous solutions displayed abrupt shear thinning in the low shear rate region (0.1-3 s(-1))., (Copyright © 2012 Elsevier B.V. All rights reserved.)

In this study, we elucidated the effect of residual silk sericin (SS) on structure and mechanical properties of regenerated silk filament as well as on fiber formation. The dope viscosity markedly increased with increasing residual SS content in dope solution which was prepared by dissolving the silk protein in formic acid. As a result of FTIR, (13)C NMR, and XRD, a small amount of SS (9.6%) contained in the filament showed highest content of beta-sheet conformation and maximum crystallinity. It seems that the SS affects the structural change of SF up to a certain level by inducing the beta-transition easily. The tenacity of the filaments, containing 9.6-18.9% SS, was in the range of 2.1-2.4 gf/d, which was about 50% higher than the filament without SS (pure SF). Consequently, with the enhancement of spinnability in wet spinning process, the SS can play an important role for developing the crystalline structure of SF as well as for improving mechanical properties of the regenerated silk fiber.

Many studies on flexible strain and pressure sensors have been reported due to growing interest in wearable devices for healthcare purposes. Here, we present flexible pressure and strain (motion) sensors prepared with only graphene oxide (GO) and commercial silk fabrics and yarns. The pressure sensors were fabricated by simply dipping the silk fabric into GO solution followed by applying a thermal treatment at 400 °C to obtain reduced GO (rGO). The pressure sensors were made from rGO-coated fabrics, which were stacked in three, five, and seven layers. A super-sensitivity of 2.58 × 103 kPa−1 at low pressure was observed in the seven-layer pressure sensor. The strain sensors were obtained from rGO-coated twisted silk yarns whose gauge factor was 0.307. Although this value is small or comparable to the values for other sensors, it is appropriate for motion sensing. The results of this study show a cost-effective and simple method for the fabrication of pressure and motion sensors with commercial silk and GO. [ABSTRACT FROM AUTHOR]

The article discusses a study which investigated electrospun three-dimensional silk fibroin nanofibrous scaffold by developing new fabrication process with silk fibroin (SF) by electrospinning. The authors also evaluated the features of the SF nanofiber scaffold (SFNS) through the morphological and cell-culture analyses. It was observed that Foam type of the SFNS exhibited high porosity as well as large pores.

Abstract: Silk fibroin (SF)/poly(vinyl alcohol) (PVA) blend filaments were prepared by a wet spinning process. Regenerated SF and PVA were dissolved in formic acid and the dope solution exhibited good fiber formation in a methanol coagulation bath. Due to the miscibility of SF/PVA in formic acid, the filament had a smooth surface and dense structure with a circular cross-section. The crystalline structure and thermal properties were varied with different SF/PVA ratios. The mechanical properties of the filament were also controlled by blending PVA with SF. Especially, the knot strength of the SF filament, which is a very important suture property, could be significantly improved by blending with PVA. [Copyright &y& Elsevier]

In the present study, the effects of different degumming methods on the structural characteristics and properties of regenerated silk fibroin (SF) were examined. The crystallinity index of the degummed silk increased with the degumming ratio. The crystallinity index at any given degumming ratio differed depending on the degumming method. The soda method and the soap/soda method using sodium carbonate resulted in a higher crystallinity index than the other methods The degumming method strongly affects the molecular weight (MW) and solution viscosity of the regenerated SF. The MW and viscosity of the regenerated SF, according to the degumming method, was in the order of urea method > HTHP method ≈ acid method > soap/soda method ≈ soda method. The turbidity of a silk formic acid solution decreased as a result of increasing the degumming ratio and was a minimum at a degumming ratio of around 26%. However, it was not affected by the degumming method. The mechanical properties of a regenerated SF film were strongly affected by the degumming method and the trend in the strength and elongation with the various degumming methods was the same as that of the MW and viscosity of the regenerated SF. [ABSTRACT FROM AUTHOR]

Abstract: Although the technique for extracting the Bombyx mori sericin has been extensively known, the extraction of sericin from wild-silkworm cocoons is not yet standardized. The aim of this study was to find the optimal conditions for the extraction of sericin from Antheraea mylitta cocoons, with high yields and minimum degradation. We attempted to apply various protocols for the extraction of the A. mylitta sericin (AmS). Among these, we found that the extraction of AmS with a sodium carbonate solution exhibited the highest yield except the conventional soap-alkali extraction. To find the optimal conditions for the AmS extraction with the sodium carbonate, we changed the concentration of sodium carbonate and the treatment time. With an increase in the sodium carbonate concentration and the extraction time, the yield of AmS increased, but the molecular weight (MW) of AmS decreased. Considering the yield, molecular weight distribution (MWD) and amino acid composition of AmS, we suggest that the optimal conditions for the AmS extraction require treatment with 0.02M sodium carbonate and boiling for 60min. [Copyright &y& Elsevier]

Abstract: In order to improve some inherent disadvantages in the mechanical properties of silk sericin (SS), we prepared ethanol-precipitated sericin (EpSS) by adding ethanol into hot-water extracted sericin (HS) solution. EpSS had higher viscosity compared to HS and it was due to the differences in their molecular weight distribution (MWD). The different MWD of EpSS was due to the different solubility of sericin molecules at various concentrations of ethanol, and the amino acid composition of EpSS showed that the more hydrophobic sericin is precipitated more readily in the presence of ethanol. The secondary structure of sericin is also changed from a random coil to β-sheet structure when the amount of ethanol added is high enough. The DSC analysis also revealed that EpSSs has a more compact structure. Finally, when beads were prepared from EpSS, they had enhanced compressive strength compared to those from HS. [Copyright &y& Elsevier]

[Display omitted] • Green synthesis Gold nanoparticles (AuNPs) using hydrophilic silk sericin. • Sericin acted as a reducing agent and capping agent in the formation of AuNPs. • The hydroxyl and carboxyl groups of sericin mainly participated in AuNPs synthesis. Various natural materials were used recently for the synthesis of gold nanoparticles (AuNPs). These natural materials are attracting attention because they are more environmentally friendly than conventional chemicals used for AuNP synthesis. Silk sericin (SS) is a protein that is removed during the silk degumming process, and it has been studied for the synthesis of several inorganic materials, such as hydroxyapatite and silica. The present study synthesized AuNPs using SS. To optimize the conditions for the synthesis of AuNPs, the effects of reaction pH, SS concentration, reaction time and temperature during the formation of AuNPs were monitored using visual observation, a UV–Vis spectrophotometer, and energy-filtered transmission electron microscopy (EF-TEM) analysis. When the concentration of HAuCl 4 was 1 mM, the optimal conditions for synthesizing AuNPs were an SS concentration of 1 mg/ml, a reaction pH of 7, a reaction temperature of 70 °C and a reaction time of 12 h. The AuNPs prepared under the optimal conditions had a size of approximately 17 nm, and the particles were well dispersed. When ethanol was added, the secondary structure of SS transitioned to β-sheets, the size of the gold nanoparticles increased to approximately 20 nm, and the amount of AuNPs increased. Amino acids bearing a hydroxyl group or negative charge were effective in the synthesis of AuNPs, and SS has a high content of these amino acids. Therefore, SS reduced gold ions and induced the synthesis of AuNPs. High-resolution TEM (HR-TEM), energy-dispersive X-ray spectroscopy (EDS), and thermogravimetric analysis (TGA) revealed that SS remained in a form that capped the synthesized AuNPs. [ABSTRACT FROM AUTHOR]