From the issue dated September 25, 1991
Researchers Study Silk-Producing Ability of Spiders to Mimic Process, Produce New Synthetic Materials
Potential uses range from flexible bullet-proof vests to artificial tendons and stronger bridge cables
By Peter Monaghan
Seattle, Washington -- If a web of spider silk can catch a fly, could a large bundle of artificial silk fibers be made to stop an airplane landing on an aircraft carrier? Or could the silk cocoon that surrounds spider eggs be cloned and spun into resilient, flexible fibers for clothing?
Some scientists think the answer to both questions is Yes. They believe that by fully understanding how spiders make silk, they can replicate the process, perhaps come up with even more versatile fibers, and produce an array of revolutionary materials for military, medical, engineering, and textile applications.
Getting there is proving to be no small task. The scientists admit they are not likely to match overnight the fibers that spiders have had an estimated 380 million years to perfect.
However, researchers at the Universities of Washington, Wyoming, and British Columbia are figuring out what spider silk consists of, structurally and genetically, and how it gets its extraordinary physical properties -- a rare combination of strength, stiffness, and toughness.
Strength, to materials scientists, refers to a material's resistance to breaking; stiffness, the inverse of elasticity, refers to resistance to lengthening under weight; and toughness refers to the ability to absorb impacts.
Scientists say spider silk is almost as stiff and strong as the best synthetic fibers, including Kevlar, a material used to make bullet-proof vests.
Natural spider silk is also 10 times as tough as any man-made fiber, including steel wire.
"You have a material which has some very impressive mechanical properties," says Christopher Viney, assistant professor of bioengineering at the University of Washington here.
Mr. Viney and other researchers hope to pioneer the manufacture of a revolutionary synthetic silk that could be put to such uses as making flexible bullet-proof vests and a protective coating for military vehicles, artificial tendons, and stronger cables for suspension bridges.
At the very least, they believe, it could supersede existing polymers like Kevlar as a reinforcing fiber in composite materials that are kept at temperatures typically found on the earth. At significantly higher temperatures, spider silk disintegrates.
"What is exciting about the material," says Mr. Viney, "is that the raw material isn't petroleum. Processing apparently, at least in nature, is done at room temperature, which is more or less unheard of. And it's done from a very convenient and environmentally sensible solvent, called water." As an added bonus, he says, spider silk ends up waterproof.
He, like other researchers, believes artificial silk can be made at room temperature: "If nature can do it, then why can't I?" he asks.
All types of spiders make silks, which are spun fibers of protein secreted from silk glands and "spinnerets" in the spiders' abdomens. There the silk is produced and stored in soluble form until it moves down a narrow duct, becoming insoluble as it goes.
Most of the work being done by various American and Canadian teams studying spider silk involves "dragline" or frame silk, from which spiders make the radial supporting strands of their webs.
Randolph V. Lewis, professor of molecular biology at the University of Wyoming, is trying to find what proteins are in the silk, how they are organized, and how that organization gives silk its mechanical properties.
He has applied for patents on two proteins he has discovered in the spider silk that he says will be the basis for development of a synthetic spider silk. With knowledge about the ratios of the two proteins in different types of silk, he hopes eventually to be able to decipher the genetic instructions that guide the production of the proteins to make spider silk artificially.
Mr. Viney, at the University of Washington, is trying to determine what molecular changes occur as spider silk is being formed. He and a graduate student there, Keven Kerkam, recently published their finding that while silk is being spun, it becomes a liquid crystal. (Liquid crystals are substances that exhibit the properties of liquids and crystals. They are commonly used in digital watches.)
The two scientists, like most of the other researchers, are concentrating on the Golden Orb Weaver spider from Florida, chosen because it is large (about four inches in diameter) and produces large quantities of silk. They have designed a rig that allows them to trap the spiders gently and draw threads of silk from them for study.
Mr. Viney had suspected a liquid-crystalline phase was involved because that would provide the highly aligned molecules needed to get the silk's strength and stiffness. "Spiders don't do that by way of spinning and then stretching," he says.
Still to be worked out, he says, are the concentrations of proteins necessary, and the details of the molecular-level changes that provide the silk with its special properties.
A third research team, based at the U.S. Army Research, Development, and Engineering Center in Natick, Mass., is examining how the properties of silk are dictated at the genetic level. Like Mr. Lewis in Wyoming, the Army researchers are trying to understand the genetic make-up of silk. They say that by inserting the proper genetic instructions in bacteria, they can make silk synthetically on a large scale.
Stephen J. Lombardi, a research molecular biologist at the Army lab, says that by about 1995, he and his colleagues hope to make a synthetic form of the silk based on sequences they find in the spider silk, and that eventually should lead to the creation of synthetic fibers and even films with similar properties.
"We don't say we're going to produce vats of the material," he says, "but we feel that within the next few years we can come up with enough material that we can start working with it."
The Army lab also has applied for patents on methods scientists there have developed to clone silk genes. Researchers there have published general descriptions of that work and plan to publish additional details about the gene sequences involved. To date only Mr. Lewis in Wyoming has publicly released details about the gene sequences.
At the University of British Columbia, John M. Gosline, professor of zoology, is trying to build models of the mechanics and structure of spider silk. He and his colleagues want to decipher and model the ways in which genetic sequences are processed into silk fibers, and to arrive at a basic understanding of the production of silks. Then, Mr. Gosline says, researchers will be able to ask: "Are there any tricks spiders use in processing fibers that are useful to direct spinning techniques" that could help the development of synthetic silks?
All the researchers say they are a long way from being able to produce affordable synthetic silk that would not require procedures using corrosive solvents, such as are used in making Kevlar. Mr. Lewis says new complexities accompany each discovery. "Technically, spider silk is so different from anything anyone has cloned or expressed before," he says.
Researchers also point out that it is stronger and more resilient than the silk from silkworms.
They say that once they understand the processes they are currently studying, they will have to compare them with those involved in the methods spiders use to make other kinds of silk. To this end, Mr. Lewis is also trying to clone spider cocoon silk and a variety of silk that reinforces the draglines that spiders use to lower themselves.
Other silks yet to be closely studied include the wrapping silk in which spiders enclose their captured prey and the sticky pads that anchor the web's frame silk to a wall or tree.
Once a broader understanding of silks is reached, says Mr. Viney, "then I might be able to say: `We need solutions pulled at this rate from this concentration.' Temperature doesn't seem to matter. Then it would be up to the chemical engineers to scale up the process." That stage, he believes, would present industrial engineers, chemical engineers, or polymer technologists with relatively few problems. It may even be possible, he says, to use the same machines now used to make rayon.
Researchers agree that exploring the nature of spider silk could lead to new processing approaches in industry, by providing a way to make durable, high-performance mechanical materials from water solutions at room temperature. The research, Mr. Lewis says, is certain to offer new insights into elastic proteins, because the elastic protein of spider silk differs greatly from, say, elastin, which is found in ligaments.
Adds Mr. Viney: "Making interesting things out of proteins is a big and largely unexplored field."
The U.S. Army has to date been the best source of financial support for the research, which is interdisciplinary and hence a hard sell, researchers say. The problem, says Mr. Viney, is that "I can think of all sorts of products and I know we'll get there, but I can't produce a product by tomorrow."
Private companies may be working on similar projects, but they are not financing university research, and are considered unlikely to get involved until they can buy rights to manufacture synthetic spider silk.
Mr. Viney says such companies know that in the process of developing a synthetic spider silk, university researchers may come up with completely unforeseen materials. "Perhaps the processing route to get there may be adapted to producing material we haven't even thought of yet," he says.
Copyright © 1991 by The Chronicle of Higher Education
