Abstract
An artificial spinning system using regenerated silk fibroin solutions is adopted to produce high-performance silk fibers. In previous studies, alcohol-based agents, such as methanol or ethanol, were used to coagulate silk dope solutions, producing silk fiber with poor mechanical properties compared with those of native silk fibers. The alcohol-based coagulation agents induce rapid β-sheet crystallization of the silk molecules, which inhibits subsequent alignment of the β-sheet crystals. Here, we induce gradual β-sheet formation to afford adequate β-sheet alignment similar to that of native silk fiber. To this aim, we developed an amorphous silk fiber spinning process that prevents fast β-sheet formation in silk molecules by using tetrahydrofuran (THF) as a coagulation solvent. In addition, we apply postdrawing to the predominantly amorphous silk fibers to induce β-sheet formation and orientation. The resultant silk fibers showed a 2.5-fold higher extensibility, resulting in 1.5-fold tougher silk fibers compared with native Bombyx mori silk fiber. The amorphous silk fiber spinning process developed here will pave the way to the production of silk fibers with desired mechanical properties.
Highlights
Silk is a lightweight and tough structural material with excellent strength and ductility, which plays a structural role in silkworm cocoons and spider dragline and web.[1,2] In addition, silk is naturally derived, biocompatible with low cytotoxicity, and biodegradable,[3,4] suggesting that silk has the potential to substitute petroleum-based polymeric materials.[5]
Silk is difficult to dissolve in commonly used organic solvents due to the high density of hydrogen bonds, silk is soluble in concentrated chaotropic agents, such as lithium bromide or lithium thiocyanate, hexafluoroisopropanol, and CaCl2-formic acid mixed solvent, which results in regenerated silk fibroin solutions.[6,7]
We found that tetrahydrofuran (THF), which is a heterocyclic ether, can solidify the regenerated silk fibroin solution and effectively prevent crystallization of the silk molecules
Summary
Silk is a lightweight and tough structural material with excellent strength and ductility, which plays a structural role in silkworm cocoons and spider dragline and web.[1,2] In addition, silk is naturally derived, biocompatible with low cytotoxicity, and biodegradable,[3,4] suggesting that silk has the potential to substitute petroleum-based polymeric materials.[5]. We used THF instead of water as the second coagulation bath to induce further solidification of silk molecules to enhance the tensile strength of the silk fibers to a comparable level to that of native silk fiber.
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