October 10, 2016

Eating graphene turns a silkworm into Spiderman, study finds

Silk is one of the strongest naturally-made materials, but now it appears researchers may have improved in that strength by feeding silkworms carbon nanotubes and graphene.

According to a report published in the journal Nano Letters, researchers provided silkworms with mulberry leaves covered in aqueous solutions containing 0.2 percent of either carbon nanotubes or graphene. The study team then gathered the silk after the worms spun their cocoons.

In the month or so before a silkworm begins its metamorphosis into a moth, it is constantly eating mulberry leaves. Silk is generated by pairs of salivary glands and is comprised of two distinct constituents: fibroin and sericin. Fibroin is the solid, resilient part of silk. It's released as liquid through two holes in the silkworm's face where it hardens into two filaments once it hits the air. At the same time, the worm is secreting sericin, which behaves as a bonding agent, gluing the filaments with each other.

Increasing Durability

In comparison to conventional silk, the carbon-enhanced silks are twice as tough and can stand up to a minimum of 50 percent greater stress before splitting. The team warmed the silk fibers at 1,050 degrees C to carbonize the silk protein and then analyzed their conductivity and structure. The altered silks were found to conduct electrical current, unlike regular silk.

"This natural feeding strategy could be easily scaled up, paving a new path for the production of supertough silk fibers at a large scale," the study said.

Spectroscopy and electron microscopy imaging revealed the carbon-enhanced silk fibers had a more structured composition as a result of incorporated nanomaterials. The carbon materials could not be seen in cross-sections of the silk threads, perhaps due to low nanoparticle content.

"It is worth noting that there are still several interesting and important questions that cannot be answered by our current work, such as what is the safety limit of nanocarbons in the diets for the silkworms, how much of the nanocarbons taken by the silkworms are incorporated into the silk, and what is the detailed biological process,” the study team noted in their report.


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