Biomimetic spinning of artificial spider silk. a) Highly concentrated spider silk protein solution in a syringe is pumped through a pulled glass capillary with a tip size of 10-30 mm, with the tip submerged into a low pH aqueous collection bath. Fibers can be taken up from the collection bath (arrow) and rolled up onto frames. b) Photo of a fiber as it is spun in the low pH aqueous collection bath. c) Wet fiber nest in low pH buffer. d) As-spun fibers on a frame. Fiber diameter in (b-c) is approximately 40 micrometre and in (d) 15 micrometre. Scale bar in (a) 3cm, (b) 3 mm, and (c-d) 5 mm.

A team of researchers from the Swedish University of Agricultural Sciences and Karolinska Institutet has, step by step, developed a method to synthesize kilometer long threads that for the first time resemble real spider silk. The results were published on Jan. 9th in the journal Nature Chemical Biology.

Spider silk is made of proteins that are stored as an aqueous solution in the silk glands, before being spun into a fiber. Spider silk is well tolerated when implanted in tissues as it is lightweight, yet stronger than steel, and most importantly biodegradable. However, spider silk is difficult to acquire naturally and any large scale production would rely on the use of artificial silk proteins and mostly like a biomimetic spinning processes (that mimics nature). Nevertheless, water soluble spider silk proteins have yet to be obtained from bacteria or other production systems and thus strong solvents has to be introduced in the aforementioned spinning processes.

Dr. Anna Rising and her colleagues Jan Johansson and Marlene Andersson at the Swedish University of Agricultural Sciences and at Karolinska Institutet have previously shown that the well-regulated pH gradient in the spider silk gland affects specific parts of the spider silk proteins and ensures that the fiber forms rapidly in a defined place of the silk production apparatus. They applied the knowledge to design a chimeric recombinant spider silk protein (spidroin) whose aqueous solubility equals that of native spider silk dope and a spinning device that is based solely on aqueous buffers, shear forces and lowered pH. The process recapitulates the complex molecular mechanisms that dictate native spider silk spinning and is highly efficient and that can be produced in large quantities in bacteria. The production is scalable and potentially applicable to industrial manufacture. Spidroin from one liter of bacterial shake-flask culture is enough to spin a kilometer of the hitherto toughest as-spun artificial spider silk fiber.

To mimic the spider silk gland, the research team constructed a simple but very efficient and biomimetic spinning apparatus in which they can spin kilometer-long fibers only by lowering the pH (Figure above)

"This is the first successful example of biomimetic spider silk spinning. We have designed a process that recapitulates many of the complex molecular mechanisms of native silk spinning. In the future this may allow industrial production of artificial spider silk for biomaterial applications or for the manufacture of advanced textiles," says Anna Rising.

Two videos can be found on the university's website: http://www.slu.se/en/ew-news/2017/1/spinning-spider-silk-is-now-possible/