Silk: It’s not just for breakfast anymore
In reading the most recent issue of Science News (gated), I’m reminded of how I always giggle when someone describes silk as delicate or fragile. Did you know silks have six times the tensile strength of steel? Or that a silk cable, one inch in diameter, could pull a 747 from the sky? Regardless of how delicate designers think silk is, scientists have been long interested in its unique properties in part owing to its strength. Likewise, many insects other than silkworms make silk such as spiders, bees and ants.
As with anything, the issue is quality not quantity, and diversity. A single cocoon of the silkworms we’re most familiar with, can produce a single strand of silk 600 to 900 meters in length but spiders, only produce about 130 meters. Perhaps you’d think homogeneity would make for better research -silkworm silk is homogeneous- but the genetic diversity of spider silk is more complex and interesting. Spiders make five kinds of silk, most notably silk to wrap their egg cases, silk to wrap prey and web silk. Even the stage of insect development brings differences. For example, Weaver ants, another silk making insect, use silk produced by their larvae placing it here and there as needed (only baby weaver ants make silk, bringing new meaning to child labor).
Of greatest interest to researchers is the golden silk spider (Nephila clavipes), a type of golden orb spider. They’re also prolific producers, with webs spanning a meter across. These are sometimes known as writing spiders due to the zig zag patterns in the center of their webs but these shouldn’t be confused with their cousin Argiope Aurantia most commonly described as the writing spider (although the one I photographed before could have been better described as illiterate or as someone said, had writer’s block or was writing x’s using cuneiform or another alphabet).
Spider silk has a great deal of potential from an environmental and safety standpoint. Among imagined applications are bulletproof vests (spider silk is stronger than Kevlar), scaffolding and linkages for use in surgery to grow cartilage and nerves.
The biggest problem with spider silk production is the nature of spiders. Unlike the placid silkworm suited to a mass production environment, spiders are antisocial predators who tend to eat each other if raised together. In this scenario, males always lose being very tiny in comparison to females. And with no males, there’s no baby spiders either.
Previously I’d mentioned that researchers were producing spider silk in goats milk. Science News says:
Lewis has collaborated with scientists at the Canadian firm Nexia Biotechnologies, part of the team that spliced spider silk genes into bovine cells in 2002 and later into goats. Today, transgenic goats roam at the University of Wyoming. While present in every goat cell, the spider silk genes are turned on only in the mammary glands, yielding goat milk laced with silk proteins. While promising, the yield is still low, Lewis says. A gallon of milk may have only 60 grams of silk, which means it would take about 600 gallons of milk to make one bulletproof vest. And there are still problems with purifying the proteins. After a few grams of silk have built up, the milk starts coagulating, perhaps because the silk proteins are binding to proteins in the milk, Lewis says.
Which circuitously, makes me grin when Mr. Fashion-Incubator pours Silk® over his breakfast cereal.