Structural stability of biofilms produced from silkworm cocoon fibers

Abstract

Biofilms were obtained from cocoons of the silkworm, Bombyx mori, involving the removal of sericin, extraction and solubilization of fibroin fibers, dialysis of fibroin dispersions and preparation of biofilms by the casting process. Biofilm transparency was verified by UV–Vis spectroscopy and thermal stability by thermogravimetric/differential scanning calorimetry (TG/DSC). Soon after preparation, the solidification of the fibroin solution prepared from the cocoons and extracted by the Ajisawa method was monitored until the biofilm stabilized, using attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) as a function of time. The results showed that there was a change in the conformation from the silk I structure (α-helix) to silk II (β-sheet). In order to improve the characterization of the biofilms obtained by the Ajisawa method and LiBr solubilization of fibroin fibers, Raman spectroscopy was used to verify the stabilization of the different possible molecular conformations for the fibers in these materials, by comparison with the cocoon spectra and those of the solid (freeze-dried precipitated by dialysis for 72 h. By comparing the Raman spectra of the biofilms in terms of the intensities of the broadened band characteristic of amide I, it was possible to assess the conformational changes in both materials based on the possible transitions between β-sheet conformations and flexible α-helix and β-turn structures. The results showed a dispersion of these conformations in the biofilms generated and in the solid freeze-dried hydrogel spectrum, and the β-sheet conformation was found to be predominant. The TG and DSC curves showed that the materials with higher β-sheet content exhibited higher thermal stability. Thus, the data obtained further elucidated the properties of these materials that are widely used in various processes.

Keywords

• silk fibroin
• raman spectroscopy
• bombyx mori
• molecular conformation