Insight into the Structure of Single Antheraea pernyi Silkworm Fibers Using Synchrotron FTIR Microspectroscopy

Abstract

Synchrotron FTIR (S-FTIR) microspectroscopy was used to monitor both protein secondary structures (conformations) and their orientations in single cocoon silk fibers of the Chinese Tussah silk moth ( Antheraea pernyi ). In addition, to understand further the relationship between structure and properties of single silk fibers, we studied the changes of orientation and content of different secondary structures in single A. pernyi silk fibers when subjected to different strains. The results showed that the content and orientation of β-sheet was almost unchanged for strains from 0 to 0.3. However, the orientation of α-helix and random coil improved progressively with increasing strain, with a parallel decrease in α-helix content and an increase in random coil. This clearly indicates that most of the deformation upon stretching of the single fiber is due to the change of orientation in the amorphous regions coupled with a conversion of some of the α-helix to random coil. These observations provide an explanation for the supercontraction behavior of certain animal silks and are likely to facilitate understanding and optimization of postdrawing used in the conjunction with the wet-spinning of silk fibers from regenerated silk solutions. Thus, our work demonstrates the power of S-FTIR microspectroscopy for studying biopolymers.

Silk: Optical Properties over 12.6 Octaves THz-IR-Visible-UV Range

“…Furthermore, A. pernyi survives at the lowest temperatures among all silk moths. Raw cocoons were degummed three times using 0.5% Na${}_2$CO${}_3$ solution at 98 ${}^{\circ }$C for 1 h for A. pernyi cocoon, but 30 min for B. mori cocoon [30,31]. Finally, the degummed silk fibers were thoroughly rinsed with warm deionised water (60 ${}^{\circ }$C) prior to being dried in air.…”

Intrinsic tensile properties of cocoon silk fibres can be estimated by removing flaws through repeated tensile tests

“…There are differences of opinion about the changes in microstructure of silk fibres on application of load. Some studied showed no changes in crystallinity and orientation while others suggested a decrease in crystallinity [30][31][32][33]. There is also no consensus on the change in amorphous domains during straining [21].…”

Silk patterns made by direct femtosecond laser writing

“…15 Crystallinity and b-sheet content in A. pernyi fibroin are lower as compared to B. mori. 16 This makes the mechanical strength of A. pernyi fiber lower than B. mori fibers, however, has superior elasticity and toughness. 17,18 Laser writing was carried out using k ¼ 1030 nm wavelength, t p ¼ 230 fs duration pulses (Pharos, Light Conversion) operating at a frequency of 100 kHz.…”