Methods of generating highly-crystalline recombinant spider silk protein fibers
Provided herein are scalable methods of processing wet-spun fiber comprising recombinant spider silk polypeptides to generate a three-dimensional crystalline lattice of beta-sheet structures in the fiber.
1. A drawn fiber comprising a recombinant silk polypeptide comprising SEQ ID NO: 1, wherein the fiber is generated by:
dissolving a powder comprising the recombinant silk polypeptide into a solvent to generate a spin dope, wherein the recombinant silk polypeptide is non-naturally occurring;
extruding the spin dope into a coagulation bath to form a precursor fiber;
collecting the precursor fiber without drawing the precursor fiber; and
drawing the precursor fiber over a hot surface to generate a drawn fiber,
wherein the drawn fiber has a crystallinity index of at least 6% as measured using X-ray diffraction.
2. The drawn fiber of claim 1 , wherein the powder comprising the silk polypeptide is comprised of at least 60% silk polypeptide by weight, at least 70% silk polypeptide by weight, or at least 80% silk polypeptide by weight.
3. The drawn fiber of claim 1 , wherein the drawn fiber is drawn over the hot surface at a draw ratio of at least 2×, at least 3×, at least 4×, or at least 6×.
4. The drawn fiber of claim 3 , wherein the draw ratio is computed by determining the draw ratio at failure.
5. The drawn fiber of claim 4 , wherein determining the draw ratio at failure comprises determining the distribution of maximum elongation at break of one or more precursor fibers using an apparatus designed to draw the fiber over a hot surface while increasing the draw ratio.
6. The drawn fiber of claim 1 , wherein the generation of the fiber further comprises drawing the drawn fiber over a hot surface one or more times.
7. The drawn fiber of claim 6 , wherein the sum of the draw ratios at each drawing step is approximately equal to or less than the draw ratio at failure of the precursor fiber.
8. The drawn fiber of claim 6 , wherein the generation of the fiber comprises:
determining a draw ratio at failure of the precursor fiber; and
distributing the draw ratio at failure of the precursor fiber over each of said drawing steps.
9. The drawn fiber of claim 1 , wherein generating the fiber further comprises annealing the precursor fiber prior to drawing the fiber.
10. The drawn fiber of claim 9 , wherein annealing the precursor fiber comprises annealing the precursor fiber with alcohol vapor.
11. The drawn fiber of claim 1 , wherein the solvent comprises formic acid or N-methyl morpholine N-oxide (NMMO).
12. The drawn fiber of claim 11 , wherein the solvent comprises 20% to 60% by weight NMMO.
13. The drawn fiber of claim 11 , wherein generating said fiber comprises heating said spin dope before said step of extruding the spin dope into said coagulation bath.
14. The drawn fiber of claim 11 , wherein extruding the spin dope into said coagulation bath comprises extruding the spin dope through an air in the range of 2 to 20 cm.
15. The drawn fiber claim 1 , wherein the drawn fiber has increased beta-sheet formation relative to the precursor fiber.
16. The drawn fiber of claim 15 , wherein the drawn fiber has increased beta-sheet formation relative to the precursor fiber proportional to the draw ratio used to draw the fiber over the hot surface.
17. The drawn fiber of claim 1 , wherein the hot surface is at least 190 degrees Celsius or at least 200 degrees Celsius.
18. The drawn fiber of claim 1 , wherein the hot surface is at least 20 degrees Celsius greater than the glass transition temperature of the precursor fiber.
19. The drawn fiber of claim 1 , wherein the tenacity of the drawn fiber is greater than 20 cN/tex, greater than 25 cN/tex or greater than 26 cN/tex.
20. The drawn fiber of claim 1 , wherein the Herman orientation factor of the drawn fiber is approximately the same as native silk fiber.
21. The drawn fiber of claim 1 , wherein the drawn fiber has a crystallinity index of at least 7% as measured using X-ray diffraction.
22. The drawn fiber of claim 1 , wherein the drawn fiber has more than 1.5 times, more than 2 times, or more than 2.5 times increased beta-sheet content as compared to air drawn fibers subject to identical drawing conditions except not drawn over a hot surface.
23. The drawn fiber of claim 1 , wherein the drawn fiber has an increased 3D β-sheet content as compared to air drawn fibers subject to identical drawing conditions except not drawn over a hot surface.