Kraig Biocraft had to alter the spider-silk proteins so that they would not just be made by the silkworms but also integrated into the structural matrix of the silk fibers. These proteins have chemical structures that fit together tightly to give silk fibers their integrity and strength. The company licensed Lewis’s gene sequences and modified them. Lewis says he’s verified that these spider proteins are chemically integrated into the core of the fiber.
The company’s system for making transgenic silkworms was developed by Malcolm Fraser, professor of biological sciences at the University of Notre Dame. Fraser’s methods for genetic engineering in insects and other animals were used to make the first artificial spider-protein-producing silkworms in the year 2000.
Kraig Biocraft has made 20 new varieties of transgenic silkworms by injecting silkworm embryos with Fraser’s DNA constructs incorporating the modified spider genes, then screening to find worms that have integrated the new genes into their genomes.
The company has not disclosed the results of mechanical tests performed on the fibers made by the engineered silkworms, nor has it released information about how much of the spider protein the animals make. But representatives claim that all of the animals make silks stronger and more flexible than natural silkworm silk and that one variety makes particularly strong fibers that the company has deemed “monster silk.”
“We don’t have much control over how much [spider] protein the transgenics express–some express a little, some a lot,” says Fraser. “We’re currently working on methods to ensure optimal transgenics.”
David Kaplan, chair of biomedical engineering at Tufts University, who has developed biomedical applications for silkworm silk, notes that Kraig Biocraft has not yet published its results in a scientific journal. Kaplan adds that a transgenic silkworm is a promising system for making spider fibers, but notes that over the long-term, large-scale industrial production may not be as viable as growing silk-producing bacteria in vats. The fiber-making process remains a challenge for approaches using bacteria, but researchers at the University of California, Berkeley, are working on microfluidics and other systems designed to mimic the silkworm’s fiber-spinning capabilities.
Kraig Biocraft’s Thompson says the company’s first product is likely to be based on the first versions of silk, which aren’t strong enough for specialized industrial applications. These products will target the $4-billion-a-year raw-silk market in 2011. The company will then pursue industrial applications using much stronger silk.