Insights into Silk Formation Process: Correlation of Mechanical Properties and Structural Evolution during Artificial Spinning of Silk Fibers

Abstract

The extraordinary comprehensive mechanical properties of animal silk (especially spider and silkworm silk) have led to extensive research on the underlying mechanisms involved. Herein, we selected various regenerated silk fibroin (RSF) fibers by choosing different postdraw conditions in a wet-spinning process developed in this laboratory to study their structure−property relationship. We use synchrotron radiation infrared and X-ray diffraction techniques to monitor the structural differences in these RSF fibers and correlate them with their mechanical properties. The results show that with the increase of post draw-down ratio, the β-sheet content, crystallinity, and molecular orientation in these RSF fibers increase while the crystalline size decreases. The relationship between structural changes and the draw-down ratio reflects the corresponding variation in mechanical properties, namely, an increase in breaking stress with a decline in breaking strain in relation to increases in draw-down ratio. Therefore, these results provide solid and direct evidence on the evolution of structure during the artificial spinning process and on how structure determines the final mechanical performance of silk fibers. We believe this study provides a good background on the relationship between microscopic structure and macroscopic properties in polymer science and may prove useful in the production of high performance materials, not only for silk fibers but also for other natural and synthetic polymeric materials.

Polymorphic regenerated silk fibers assembled through bioinspired spinning

“…1c–e ) is to prefabricate a spinning dope with suitable rheological properties, which has high viscosity along with stability 29 . Previous attempts focused on increasing the concentration of silk in solution, with different single-solvent, binary-solvent systems, such as HFIP 30 , 31 , HFA 32 , 33 , NMMO/H 2 O 34 – 38 , LiBr/H 2 O 39 – 42 , and CaCl 2 /formic acid 15 assessed (details can be found Supplementary Table 1 ). However, the structural hierarchy of natural silks, an important element in determining bulk material properties 22 – 27 , is destroyed during these dissolution processes 43 .…”

Bioinspired Fabrication of Polyurethane/Regenerated Silk Fibroin Composite Fibres with Tubuliform Silk-Like Flat Stress–Strain Behaviour

“…However, surprisingly when RSF concentration is greater than 25% a slight increase in tensile strength was observed in RSF dominated fibre. Perhaps, this is due to comparatively better orientation of crystalline hard segments at higher concentrations of RSF component [ 43 ]. Similarly, strain at breaking of 100% PU was found to be 752% ± 15.7%, in contrast PU/RSF 10/90 produced only 10%.…”

The silk of gorse spider mite Tetranychus lintearius represents a novel natural source of nanoparticles and biomaterials

“…Mechanical properties of silk fibres are therefore determined by the proportion of the semi-amorphous matrix, commonly in random coil conformation, and β-sheet crystallites. It is well known that the β-sheet nanocrystals serve as molecular cross-links that provide silk fibres with their great stiffness, while the amorphous regions play the opposite role and are responsible for their superb elasticity 51 , 52 . So far, there has been no reported experimental research to correlate the size of β-sheet crystallites to the mechanical properties of silkworm silk fibroin fibres.…”