Effect of Mechanical Deformation on the Structure of Regenerated Bombyx mori Silk Fibroin Films as Revealed Using Raman and Infrared Spectroscopy

Abstract

To better understand the effect of mechanical stress during the spinning of silk, the protein orientation and conformation of Bombyx mori regenerated silk fibroin (RSF) films have been studied as a function of deformation in a static mode or in real time by tensile-Raman experiments and polarization modulation infrared linear dichroism (PM-IRLD), respectively. The data show that either for step-by-step or continuous stretching, elongation induces the progressive formation of β-sheets that align along the drawing axis, in particular above a draw ratio of ~2. The formation of β-sheets begins before their alignment during a continuous drawing. Unordered chains were, however, never found to be oriented, which explains the very low level of orientation of the amorphous phase of the natural fiber. Stress-perturbed unordered chains readily convert into β-sheets, the strain-induced transformation following a two-state process. The final level of orientation and β-sheet content are lower than those found in the native fiber, indicating that various parameters have to be optimized in order to implement a spinning process as efficient as the natural one. Finally, during the stress relaxation period in a step-by-step drawing, there is essentially no change of the content and orientation of the β-sheets, suggesting that only unordered structures tend to reorganize.

Dual-Crystallizable Silk Fibroin/Poly(L-lactic Acid) Biocomposite Films: Effect of Polymer Phases on Protein Structures in Protein-Polymer Blends

“…In the case of SF/PLLA films, hydrogen bonding forms between C=O on the PLLA molecular chains and N-H on the SF chains. Earlier studies have shown how this causes the charge from the C=O double bond to delocalize to other atoms, reducing the double polarity and their absorption frequency [26][27][28][29], effectively shifting the characteristic peak of C=O to a lower wave direction [17,22,[30][31][32]. The FTIR results in this study reflect this phenomenon.…”

“…In addition, the S-orbital of the electron acceptor and the P-orbital of the electron donor can effectively overlap through intermolecular actions between the two compo-nents. This causes a change in the original force constant of the chemical bonds and causes the position of the spectrum absorption peak to move [25][26][27][28][29]. In the case of SF/PLLA films, hydrogen bonding forms between C=O on the PLLA molecular chains and N-H on the SF chains.…”

Experimental Methods for Characterizing the Secondary Structure and Thermal Properties of Silk Proteins

“…[37] In another instance, a device that applies strain to silk fibroin films was coupled with Raman to study the effect of mechanical deformation on the structure and orientation of silks (Figure 7). [93] In another case, the ratio of the intensities of the double at 850 and 830 cm −1 (I 850 /I 830 ), which has been shown to be sensitive to the hydrogen bonding environment of tyrosine groups, [94] was used to study the role of structural water in silk gels. [95] …”

“…It is also amenable to experimental modifications, such as controlling relative humidity or adding devices to strain the sample. [93] However, Raman scattering is a relatively low probability event, and therefore low signal intensity can be problematic. Additionally, background fluorescence can be quite strong and interfere with the already low Raman signals.…”

Multi-wavelength coherent random laser in bio-microfibers

“…SF was obtained from Bombyx mori silks using a previous method [33,34]. First, the sericin and impurities on the surface of the silks were removed for their low crystallinity.…”