Spiders are legendary as the materials-science experts of the animal kingdom: Individuals can produce as many as seven different kinds of silk. To begin a web, a spider anchors a strand of dragline silk—three times stronger than the Kevlar in bulletproof vests—and waits for a breeze to blow it to a second attachment point. The arachnid then completes the outer ring and spokes, and finally builds the spiral. The capture silk used in the web’s spiral is often coated with glue, and biologists at the University of Akron recently found that spiders that have been deprived of a meal splurge on a little extra glue to improve the odds of trapping prey. Scientists have long sought to mimic the chemical perfection of a spider’s web. At last they are making progress. Recent work characterizing the proteins responsible for the incredible strength and elasticity of spider silks could lead to durable and resilient new materials for artificial human tissues, surgical sutures, and ultrastrong armor.
STRONG START Molecular biologists at the University of Wyoming are planning to use the proteins from superstrong dragline silk to build artificial tendons and ligaments. The researchers needed more silk than they could harvest from spiders in captivity, so they genetically engineered goats to produce the proteins in their milk. After the silk proteins are extracted and purified, a machine spins them into the needed fibers.
SMOOTH OPERATOR Spiders store silk proteins as a fluid but then spin them almost instantly into a solid thread without creating clumps. In May chemists in Germany and Sweden reported how: Spiders precisely regulate their body chemistry where they store the proteins. High salt content and low acidity in the silk gland and spinning duct keep the proteins liquid, while reduced salt and increased acidity make the proteins link together rapidly during spinning.
WET AND WILD Despite a thickness of just a few microns, spider web threads can collect remarkable amounts of water—as any morning gardener can attest. Chemists in China have studied the structure of silk fibers and discovered that they channel water toward tiny knobs along the web’s strands that can hold large droplets. Artificial webs that follow a similar design might be able to collect drinking water from mist.
DEATH SPIRAL “Capture silk” in the web’s spiral is stretchy—as elastic as a rubber band—the better to hold on to entangled prey. But some parasites have evolved a way to use the spiders’ engineering for their own ends. This year, entomologist William Eberhard at the Smithsonian Tropical Research Institute found that parasitic wasp larvae release a chemical into infected spiders, causing them to weave a modified web that supports the wasp’s cocoon.