Using transgenic silkworms with their natural spinning apparatus has proven to be a promising way to spin spider silk-like fibers. The challenges are incorporating nativesize spider silk proteins and achieving an inheritable transgenic silkworm strain. In this study, a CRISPR/Cas9 initiated fixed-point strategy was used to successfully incorporate spider silk protein genes into the Bombyx mori genome. Native-size spider silk genes (up to 10 kb) were inserted into an intron of the fibroin heavy or light chain (FibH or FibL) ensuring that any sequence changes induced by the CRISPR/Cas9 would not impact protein production. The resulting fibers are as strong as native spider silks (1.2 GPa tensile strength). The transgenic silkworms have been tracked for several generations with normal inheritance of the transgenes. This strategy demonstrates the feasibility of using silkworms as a natural spider silk spinner for industrial production of high-performance fibers.

Silkworm silk has become increasingly relevant for material applications. However, the industry as a whole is retracting because of problems with mass production. One of the key problems is the inconsistent properties of the silk. A means by which to improve the silk material properties is through enhanced sericulture techniques. One possible technique is altering the feed of the silkworms to include single-wall carbon nanotubes (SWNTs) or graphene (GR). Recently published results have demonstrated substantial improvement in fiber mechanical properties. However, the effect of the surfactant used to incorporate those materials into the feed on the fiber mechanical properties in comparison to normal silkworm silk has not been studied or reported. Thus, the total effect of feeding the SWNT and GR in the presence of surfactants on silkworms is not understood. Our study focuses on the surfactant [calcium lignosulfonate (LGS)] and demonstrates that it alone results in appreciable improvement of mechanical properties in comparison to nontreated silkworm silk. Furthermore, our study demonstrates that mixing the LGS, SWNT, and GR directly into the artificial diet of silkworms yields improved mechanical properties without decline below the control silk at high doses of SWNT or GR. Combined, we present evidence that mixing surfactants, in this case LGS, directly with the diet of silkworms creates a high-quality fiber product that can exceed 1 GPa in tensile strength. With the addition of nanocarbons, either SWNT or GR, the improvement is even greater and consistently surpasses control fibers. However, feeding LGS alone is a more economical and practical choice to consistently improve the mechanical properties of silkworm fiber.

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