Fig. 6

Comparison of classic and biomimetic fiber spinning methods. A Classic spinning methods include dry spinning, electrospinning, and wet spinning of silk proteins from a concentrated solution to form randomly aligned fibers. Often, organic and highly volatile solvents are used. B Bioinspired spinning methods require aqueous solvents and recapitulate the natural spinning mechanism by utilizing changes in pH and ion concentration to induce LLPS. Biomimetic spinning (left) induces LLPS prior to the spinning process via the dialysis of a spidroin solution against a phosphate-containing buffer, resulting in a low-concentration and a high-concentration micellar phase. Bioinspired microfluidic spinning (right) utilizes a microfluidic system. Citrate-phosphate buffer (CPB) and negative pressure induce LLPS and fiber formation under continuous flow spinning conditions, mimicking the native spider silk formation process (adapted from [42]). Furthermore, both methods can be combined by using a preassembled micellar spidroin phase for microfluidic spinning (middle). C Stress‒strain curves of microfluidically spun recombinant spider silk fibers from classic (CSD, colored dashed lines) and biomimetic (BSD, colored solid lines) spinning dopes in comparison to those of natural spider silk fibers (solid black line). The C- and N-terminal NR domains (CTD and NTD) attached to eADF3 and eADF4 are vital for fiber assembly. Pink lines depict the results for fibers spun from eADF3/eADF4 homo- and heterodimer dopes derived in vivo in E. coli. The green lines indicate the results from the spinning of in vitro-produced mixed dopes. The orange and blue lines show the stress‒strain curves of eADF4 and eADF3 homomeric dopes. The mechanical properties of the BSD fibers clearly exceeded those of the CSD fibers. Microfluidic spinning of a BSD consisting of an eADF3/eADF4 homo- and dimeric mixture prepared in vivo (solid pink line) resulted in mechanical properties comparable to those of natural spider silk fibers. Adapted from [43]; parts of the figure were prepared in BioRender