Not even the priciest threads can match the wonders of a simple spider web: Dragline silk is stronger than Kevlar and stretchier than nylon. For more than 100 years, that's had entrepreneurs and scientists scheming of ways to mass produce it. Now, a researchers have spliced dragline silk genes into mammalian cells and showed for the first time that harvested proteins can be spun into strong, lightweight fibers.
Researchers have struggled to splice spider silk genes into other organisms in hopes of recovering enough silk to produce bolts of high-strength material. And although they've inserted the genes into bacteria, yeast, and plants, the result has always been disappointing. Even when the proteins have been extracted and purified, they yield only worthless, brittle fibers.
A team led by researchers at Nexia Biotechnologies near Montreal, Canada, thought it might have more luck by transferring silk genes into certain mammalian cells that, like those in the spider, secrete silk-building proteins in a water-based solution. Led by molecular biologists Anthoula Lazaris and Costas Karatzas, the team spliced the silk genes into two different cell lines: bovine mammary cells, which excel at secreting proteins outside the cell; and hamster kidney cells, which produce large volumes of recombinant proteins. Both cell lines secreted soluble silk proteins outside the cells, where they could easily be collected.
Then came the big test: Could the proteins be spun into fibers? To find out, the Nexia researchers teamed up with fiber-spinning experts at the U.S. Army Soldier Biological Chemical Command in Natick, Massachusetts. When one of the proteins, dubbed MaSpI, was extracted from water and injected into a methanol solution, the proteins formed strong fibers, the group reports in the 18 January issue of Science (p. 472). Although this new fiber is less flexible than spider fibers, Karatzas thinks that may be because his team's fibers are made from only one of the two proteins spiders use to spin theirs.
The progress "is highly encouraging," says Randy Lewis, a molecular biologist and spider silk expert at the University of Wyoming in Laramie. Lewis says that if the process of harvesting silk from cell cultures is perfected, it will lead to ultrastrong, flexible fibers for everything from artificial tendons and ligaments to lightweight body armor and high-strength composites.