Preparation and characterization of electrospun silk fibroin/sericin blend fibers
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s work, the silk fibroin/sericin (SF/SS) blend aqueous solutions with different SF/SS mass ratios (100/0, 90/10, 85/15, 75/25, and 65/35) were prepared and electrospun to get regenerated fibers. It was found that the addition of SS in the SF solution could increase the apparent viscosity of the solution and improve its electrospinnability so that the fine uniform electrospun SF/SS fibers could be obtained. The quantitative analysis result of Raman spectroscopy showed that the presence of SS facilitated the conformational transition of SF from random coil/a-helix structure to b-sheet structure. Combined with the differential scanning calorimetry result, it was further hypothesized that SS could affect the structural change of SF by dehydrating SF and inducing the formation of hydrogen bonds between SF molecules. Consequently, SS also played an important and positive role in the thermal and mechanical properties of the resultant SF/SS fibers.
I. INTRODUCTION
During the past few decades, silk fiber, which is mainly composed of two protein components—silk fibroin (SF) and silk sericin (SS)—has attracted considerable attentions due to its outstanding mechanical properties.1–4 Many attempts to produce regenerated SF fibers have focused on reconstructing its crystalline structure and ultimately enhancing the mechanical properties5–7 using various methods such as wet spinning,8–11 electrospinning,12–15 and microfluidics.16 But the roles of SS in the spinning process of silkworm and the conformational transition of SF were not well investigated in earlier researches although SS has a content of about 25 wt% in natural silk fiber. Recently, it was reported that the crystallization and structure of regenerated silk could be affected by SS. Lee proposed the existence of hydrogen bonds between SF and SS molecules and supposed that SS might retard the crystallization of SF during methanol treatment for the casted regenerated SF/SS blend film.17 Ki et al. prepared SF/SS blend dope for wet-spinning process using 98% formic acid as solvent and found that SS improved the structure and mechanical property of the regenerated silk by affecting the conformational transition of SF molecules.18 However, few researches have been reported investigating the role of SS in the spinning and formation process of regenerated SF aqueous solution similar to the natural dope in the gland of silkworm. Recently, regenerated silk fibers were prepared from SF solutions by electrospinning process, which offers a practical approach to produce very fine fibers.19–21 The a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.356
II. EXPERIMENTAL METHODS A. Preparation of regenerated silk fibroin aqueous solutions
A regenerated SF solution was prepared according to the method reported previously.26 Bombyx mori cocoons were degummed twice in boiling Na2CO3 (0.5 wt%) aqueous solution for 30 min each at a bath ratio of 1:50 (w/v), then thoroughly rinsed to extract sericin, and dried at room temperature to get degummed natural silk. T
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