Synthesis

Today, I focused on the physical process of silk synthesis in a laboratory.

The process used in SLU's biomimetic spinning process is as follows:

"Highly concentrated NT2RepCT spinning dope in a syringe is pumped through a pulled-glass capillary with a tip size of 10-30 μm, with the tip submerged into a low-pH aqueous collection bath. Fibers can be taken up from the collection bath and rolled up onto frames."

This method yields fibers 40 μm in diameter (wet; 30 μm capillary). SLU has reported that it has been able to produce strands up to a km in length.

The dope used by SLU (NT2RepCT) is of course a chemical I won't be able to replicate- it is a chimeric protein created by genetically modifying e coli bacteria. However, like in real spiders, they used the dope in a highly concentrated solution, with the concentration interval being 100-500 mg/ml. The low-pH solution that the dope is pumped into should have a pH from 5.5 to 3. That interval supposedly produced the strongest, continuous fibers. pH's lower than 2.5 yielded no fibers, and any pH higher than 6 yielded discontinuous fibers. SLU also varied the diameter of their syringe (which was a custom, pulled-glass capillary), from 10 μm in diameter to 30 μm.

The silk fibers produced in this process are extraordinary, but still not as impressive as nature. "The mechanical characteristics of the fibers were highly reproducible, although the toughness and ultimate tensile strength were lower than native silk. One possible way to increase the toughness could be to spin NT2RepCT fibers with diameters closer to that of native dragline silk, as this apparently has an impact on the mechanical properties of silk fibers."

The SLU report also encouraged that their method can be further developed. It said some examples could be a pH gradient, and an ion composition gradient. This would make their current set-up more like an actual spider, and may result in stronger fibers. I aim to implement such developments in a biomimetic spinning device, along with other things that I may encounter in the future.

The ultimate goal of refining this method is to make artificial spider silk fibers that perform at or above the level of natural spider silk in terms of mechanical properties. And with that, have the process be economically feasible enough that it can be used in an industrial level for mass production of synthetic silk to be used in whatever product/industry necessary.

- Noah