You want strong - we've got strong!
Visitors to Cornell University's "spider lab" in Ithaca, N.Y., aren't likely to forget what they see. There, with tweezers in hand, students lean over a table of palm-size female spiders lying on their backs with legs taped securely in place, and carefully pull silk from their abdomens.
After 40 minutes of "silking," the students collect a spool with about one milligram of silk from each of the lab's 30 nephila clavipes, or golden orb weaver spiders. That's anywhere from 100 feet to 100 yards of dragline, the strongest of the seven different silks the spider makes. Dragline holds the spider as she swoops down to catch prey, and it forms the elastic spokes around which she builds her three-to-six-foot web.
What makes the painstaking process even more memorable is realizing that the silk, which is 30 times thinner than a human hair, rivals the strength of Kevlar, but is far more elastic and lightweight. A dragline half the diameter of a human hair can hold two medium-size people, according to some estimates. DuPont researchers say that bundled into a cord as thick as a pencil, dragline spider silk can stop a jet in flight on an aircraft carrier. The arresting wires that do the job today are made of wound steel cables four times as thick. By analyzing the properties of spider silk and the process by which spiders make it, scientists at university and industry labs are working to devise ways to make synthetic spider silk in large amounts for commercial purposes. The synthetic silk could be used for surgical sutures, suspension bridge cables, and endurance fabrics for athletes and the military.
Spiders are among the myriad of animals and plants being researched for potential new materials, a field known as biomimicry. Other hard substances under study are reindeer antlers, sea urchin spines, porcupine quills, and abalone.
Scientists at Sandia National Laboratories in Albuquerque, N.M., for example, have created tough structures based on how an abalone makes its shell. They say the structures could be used to make scratch-proof lenses or almost unbreakable windshields. "Biologically inspired materials could revolutionize materials science," says Janine Benyus, author of the book "Biomimicry: Innovation Inspired by Nature," (William Morrow). "People looking at spider silk and abalone shells are looking for new ways to make materials better, cheaper, and with less toxic byproducts."
A larger toxic cleanup effort
The move to imitate nature is part of a larger effort to clean up industrial processes. For example, Nexia Biotechnologies, a Montreal company that is breeding goats with a spider gene to make artificial spider silk, says its processes will be much cleaner than those needed to make Kevlar and other strong petroleum-based materials at high temperature and pressure in a sulfuric acid bath.
"We feed our production system - goats - oats, hay, corn, and water. And our silk-spinning process needs only water and normal temperature and pressure," says Jeffrey Turner, president of Nexia.
Nexia's first transgenic goats - those specially bred to contain a spider silk-making gene - will be born this fall. Each goat will be able to produce about 1,000 times as much dragline silk in its milk per day as one spider, Mr. Turner says. Of course, the goat milk must first be purified and then spun. The company still is working on the process. And until the goats are born and artificial spider silk is spun, it remains to be seen how strong the goat-made spider silk will be.
The spider's web, Turner aptly explains, is a miracle of nature. Strong and resilient, it absorbs energy when prey fly into it, stretches with the wind, and then retracts into place again at night when the evening dew shrinks the dragline.
"We're after this same strength, fineness, lightness, and flexibility," he says.
Cornell University is using nuclear magnetic resonance imaging technology to look at the smallest details of the composition of spider silk. "We are looking at what is going on at a molecular level that causes the fibers to be so strong. It most likely is a genetic reason," says Oskar Liivak, a graduate student in physics in Cornell's spider lab.
Spider dragline silk is a protein made of a series of amino acids arranged in a specific order. The silk stays in the major ampullate gland until the spider anchors it onto a branch or other object and pulls it out. Scientists believe that as the liquid is pulled out of a long tube called a spinneret at the end of the gland, it is stretched, wrung out, and dehydrated into a solid. In the process, it gains its properties of elasticity and strength.
As the silk is pulled from the spider, it folds every once in a while into protein sheets called "beta sheets." These sheets are believed to make the dragline silk strong, and the silk in between them makes it flexible. As it pulls out the silk, the spider can apply the appropriate tension to get the proper elasticity in the silk.
"Nature has gotten it right," says Lynn Jelinski, who founded the Cornell spider lab and is now dean of the graduate school of Louisiana State University in Baton Rouge. "It's our challenge as scientists to find out what nature did." DuPont's central R&D lab in Wilmington, Del., the inventors of Lycra and Kevlar, are focusing on replicating the properties of silk. Using computer simulations, the company designed synthetic silk genes that could encode analogs of silk proteins, that is, proteins with the same function as silk proteins. It inserted those genes into yeast and bacteria to produce the protein analogs. The proteins were then extracted and spun into fibers using spinning techniques similar to those of a spider.
Stockings that never run
"There is a potential to have very strong materials from synthetic silk analogs," says John O'Brien, a research fellow in the DuPont lab. "It could be used to make anything from sports clothes to high-performance industrial fibers for body armor, conveyor belts, or seat belts."
So far, DuPont has made small samples of a prototype fabric for a stretchable ladies' hose that feels like silk but does not bag, sag, or run.
"The silk fibers we've made in the lab aren't as strong as the strongest spider silks, but they are usable in apparel and textile applications," says O'Brien, adding that the first product is about five years away. "Our primary emphasis is to develop a scale-up process to make these materials in large volumes with reasonable economics."
DuPont is not alone in trying to mimic nature's processes. The Department of Energy's Sandia National Laboratories is copying the way abalone builds its shell to produce materials that might some day be used to make body armor, super tough windshield coatings, and ultrasensitive chemical detectors.
The secret of why the abalone shell is strong, hard, and tough lies in its structure. Layers of hard calcium carbonate (essentially chalk) alternate with layers of flexible, cushioning biopolymers.
An abalone shell made of 1 percent of the cushioning biopolymer and 99 percent calcium carbonate is twice as hard and 1,000 times as strong as either of those constituent materials alone, according to Sandia.
Using a similar process, Sandia researchers have created structures known as nanospheres, made much like Russian dolls that fit inside each other, alternating hard silica (sand) and soft cushioning polymers.
The submicroscopic nanospheres also are very porous. The researchers created films that might be used to coat windshields or glasses. They also made a spray version of the nanospheres that can carry medicines or industrial particles.
By adding magnetic particles to the aerosol nanospheres, for example, the scientists are creating ultrasensitive devices to detect minute levels of dangerous gases dispersed by terrorists.
Sandia currently is testing the magnetic aerosols using honey bees to detect land mines, says Yungfeng Lu, a post-doctoral researcher and materials scientist at Sandia. Land mines are made mostly of TNT, and they give off TNT residue in fields or water.
The aerosols are sprayed onto the bees, which are sent into fields. They attract particles of dust, soil and pollen to their fuzzy bodies and the magnetic nanospheres as they look for nectar and pollen. They then fly back to their hive, where they are examined for any chemicals they might have brought back from the fields.
"With the spray on them, they can absorb more than 1,000 times the TNT that they would if they weren't sprayed," Dr. Lu says. Because the spray is so porous, it dramatically increases the surface area of the bees. Lu adds that sheet and aerosol versions of the nanospheres can be applied to future high-performance, contaminant-detection systems.
All this came from unlocking how an abalone builds its shell.
(c) Copyright 1999. The Christian Science Publishing Society
