The orb-weaving spider produces one of the world's toughest fibers.
Using recombinant DNA technology, DuPont scientists have created
spider silk as a model for a new generation of materials.
Imagine a silk-like material so strong it could stop a 747 in flight, and yet also so light and stretchable it could be used to clothe a ballerina.
DuPont scientists have long admired the ability of spiders to create material with characteristics similar to two of DuPont's most famous products--DuPont Kevlar® aramid fiber and DuPont Lycra® brand spandex--with such apparent ease. A research effort led by John O'Brien at the company's renowned Experimental Station just outside Wilmington, Delaware, has been studying the properties of spider silk in an attempt to improve on existing DuPont product, or even discover entirely new materials.
"It is the combination of strength and stretch that makes the energy-to-break of a spider silk so high," O'Brien notes. "We felt that if we could duplicate that combination of great strength and stretch, and do it economically, this could be the beginning of a new materials revolution."
Spider silk is among the toughest materials known, but it is not entirely unique. "It is merely one of the most dramatic examples of a sizable family of biopolymers that can teach us much about how to improve upon man-made products," O'Brien says. "In many cases the biopolymers posses a combination of properties that synthetic materials cannot yet approach."
Terry Fadem, business director of corporate new business development, adds: "At DuPont, our researchers are looking to these natural materials as a framework for the design and synthesis of a new generation of structural materials. Basically, the idea is to copy, to the extent possible, the way that nature manufactures products. It's called biosynthesis."
Fundamental to achieving these new structural materials is the ability to control all aspects of the material architecture, beginning at the molecular level. "Recombinant DNA technology provides a practical route to harnessing the power of the biosynthetic process to control polymer sequence and chain length to a degree that is otherwise impossible," says O'Brien. "A broad range of mechanical properties is accessible by careful selection of the appropriate building blocks, as are more sophisticated properties that are common among proteins."
In the case of spider silk, all the data gathered by O'Brien and his team, including the latest sequence information from university laboratories, have been modeled by computer. Advanced simulation techniques were used to design a molecular model that integrates all the information available to date about the structure of this amazingly strong and elastic fiber. Synthetic genes were designed to encode replicas of the silk proteins. These genes were inserted into yeast and bacteria and the protein replicas were produced. Then the biosilk was dissolved in a solvent and the protein was spun into fibers using spinning techniques similar to those of the spider. "Basically," says Fadem, 'our people figured out what the spider does, how it does it, and then did pretty much the same thing--but in a computer and in test tubes."
Robert Dorsch, director of biotechnology development, notes that although the DuPont researchers used both yeast and bacteria to prepare the material, the result is a protein similar to that produced by the spider. "We break open the bacteria, separate out the globules of protein and use them as the starting material," he says. "But in the yeast process, the gene system can be designed so that the yeast secretes the protein outside the yeast for better access.
"Either way, the bacteria and yeast are producing similar proteins, structurally equivalent to one the spider uses in the drag lines of the web. The spider dissolves the protein into a water-based solution and then spins into a solid fiber in one go."
Dorsch adds: "While we are not as clever as the spider and are not using organisms nearly as sophisticated, we have substituted man-made approaches and dissolved the protein in chemical solvents. The resulting solution is then spun by extruding the material through small holes to form the solid fiber."
Will synthetic spider silk change the world? "Whether it takes off commercially or not is one of the great unknowns," says Fadem. "But the potential is there. We can imagine many possible uses for biosilk--including textile applications as a very obvious example. It is lightweight, tough and elastic, and may also have applications in satellites and aircraft."
"More importantly, the new generation of advanced materials that spider silk research represents has the potential to transform our lives in ways we can scarcely imagine," Fadem adds, noting that it has been over 50 years since the discoveries of DuPont scientist Wallace Carothers and his team gave the world nylon and ushered in the age of polymers.
"Based on the success of our initial demonstrations, we believe that harnessing the power of nature's biosynthesis will play a major role in the new materials revolution," he says.
Joe Miller, DuPont's chief technology officer and senior vice president of research and development, notes that DuPont is pursuing several leads in biotechnology. "We are particularly interested in developing new materials from renewable resources, such as corn and sugar beet, and in processes that reduce humanity's environmental impact," he says. "This research and development work will result in important new products that will help drive the company's and our customers' success far into the future."
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