To a certain breed of materials scientist, there is nothing quite so tantalizing as silk. Spider silk, pound for pound, is stonger than steel. Its production comes at a far less severe environmental cost than extracting and forging metal.
The problem with spiders, though, is that the arachnids do not produce silk in copious amounts. Nor are these animals always content to live in harmonious groups. That has not stopped researchers from trying to wring forth spider silk in creative ways. A company called Nexia Biotechnologies genetically engineered goats to produce spider silk in their milk, which it called BioSteel. No one could figure out how to cheaply separate the strands from the goat milk, though, and Nexia went bankrupt in 2009.
Enter silkworms, the larvae of the moth Bombyx mori. Unlike spiders, these insects have been coaxed into spurting out the stuff in profitable amounts thanks to thousands of years of human influence. Given plenty of mulberry leaves on which to munch, they are only too happy to spin their cocoons by the basketful. Silkworm silk can be spun into luxurious clothing, but it lacks the bullet-absorbing potential of the stronger spider kind.
Researchers are now creatively approaching silk from the Bombyx mori angle. In a new study in the journal Nano Letters, a team of chemists from Tsinghua University, in Beijing, found that by feeding silkworms a diet enhanced with carbon nanomaterials, the animals produced silk as much as 50 percent stronger. After it was heated, too, the altered silk was able to conduct electricity. (Conductive fabrics enable computers to be woven into smart clothes, a goal of programs like Google’s Project Jacquard.)
The scientists, led by nanotube expert Yingying Zhang, sprayed mulberry leaves with single-walled carbon nanotubes, or graphene, a honeycomb-like sheet of carbon molecules. After the worms digested the treated leaves, the nanomaterials were either “incorporated into the as-spun silk fibers,” the scientists wrote, or simply excreted.
Scientists do not yet know how the nanomaterials end up as part of the silk, or even if it is healthy for the animals to consume. But the idea holds promise for industrial production, at least according to some chemists in the field. Donghua University’s Yaopeng Zhang, who performed similar experiments feeding titanium pigments to silkworms, recently told Chemical & Engineering News that the technique is an “easy way to produce high-strength silk fibers on a large scale.”