By lacing goat's milk with synthesised spider proteins, researchers in Quebec plan to make an incredibly light fabric that is both biodegradable and strong enough to stop bullets. Called biosteel, it could become a green alternative to the high- strength plastics used to package shampoos or make commercial fishing nets.
Jeff Turner, president of Nexia Biotechnologies, says the biodegradable fabric would need to be sealed from the environment if used in critical applications such as body armour or spacecraft. This is because bacteria could get in and digest it.
Turner's team has already taken the first step towards creating biosteel by transferring the spider gene for the protein into goat mammary cells and collecting soluble protein from the milk. And they expect genetically engineered goats to start producing the protein in the next few months.
While nobody has yet made a fabric from biosteel, Turner is convinced the protein can be turned into a supermaterial because of its natural role in the silk of a spider's web. "When you think of what a web has to do, its extreme strength makes perfect sense," he says. The silken threads of the web must be nearly invisible to prey and yet be able to bring a fly to a screeching halt.
Evolution came up with a two-pronged answer to this problem. First came a rock-solid protein, capable of making many bonds with its neighbours. Then, the spider developed a unique way of spinning the protein into a whisper-thin thread. As the spider secretes the protein solution, the silk dries and pulls taut, transforming the proteins into a nearly crystalline and completely insoluble cable. This explains why webs don't dissolve in the rain. Tests on natural silk show that it can be stronger and more elastic than high- tensile steel or the Kevlar found in body armour.
But the very properties that make silk proteins strong also make them difficult to produce. When bacteria are engineered to produce large quantities of the protein, for example, it links up in chains into a disordered, insoluble mess. Its ability to bond with its neighbours can happen in a very ordered or a disordered fashion-depending upon how the proteins fold as they form. Which is why Turner and his colleagues decided to mimic the spider's own method of production by using goat mammary cells. It turns out that the way mammals produce milk proteins and spiders make silk proteins are broadly similar. Both are produced in skin-like epithelial cells, then held in a space, or lumen, where shear stresses on the protein are minimised.
So far so good. But Turner cautions that the work is still in its early stages. It will take about a year before the herd of biosteel goats is large enough for Nexia's scientists to collect the protein they need to start making fabric. Then they will face the next great hurdle: how to match the spider's spinning skill. "Nature probably took a long time to get this process right," he says. "I suspect the same will be true for us."
Author: Phil Cohen, San Francisco
New Scientist issue dated 10 October 1998, page 11
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