Edwin L. Aguirre
What material is tougher than steel or Kevlar but weighs much less and can be stretched up to three times its length without breaking?
It’s the silk spun by spiders. Spiders use this fine thread-like, protein-based fiber to weave webs for catching prey or as nests or cocoons for their offspring, as well as for several other purposes.
“Spider silk is important for many reasons,” says Biology Asst. Prof. Jessica Garb, who is studying the genetics behind spider silks and venoms
“First, scientists and engineers are interested in spider silk because of its superior mechanical properties — it can absorb much energy without breaking,” she says. “Second, there are many kinds of spider silks. For example, an orb-weaving spider makes seven different kinds of silk fibers, four of which are used to construct its orb web. These various silk types have distinctly different material properties — some spider silks have greater tensile strength, whereas others are more stretchy and some are primarily adhesive.”
A Versatile Biomaterial
Because spider silk has extreme toughness, high tensile strength and elasticity, is lightweight and biodegradable, scientists are interested in understanding its composition and production.
Spider silk can potentially be used in diverse applications requiring high-performance materials, including body armors, bandages, surgical sutures, artificial tendons or ligaments, ropes, fish nets, seat belts, airbags and parachutes.
“Spiders have evolved many specific uses of silk: different web types, adhesive silks, Velcro-like silks, silks just for egg cases, et cetera,” says Garb. “Also, spiders always rely on silk throughout their lives, and silk has played a key role in spider evolution.”
In contrast, insects such as silkworms — the larva or caterpillar stage of the domesticated silk moth — produce only one type of silk during a limited phase of their lifetime.
“The varied mechanical properties of different spider silk types stem in part from their constituent proteins,” she says. “My work on spider silks involves the characterization of these various silk proteins to understand the evolution of their diversity at the molecular level, and how this molecular variation is linked to differences in silk fiber mechanics and ecological function.”
Her findings were published in 2010 in the journal “BMC Evolutionary Biology,”
and she has previously reported on her work on spider silks in the publications“Science and PNAS, among others.
Making Spider Silk From Goat’s Milk, Silkworms or Plants
Spiders are highly territorial and cannibalistic so commercially farming them can be a challenge. Due to the difficulties of extracting and processing spider silk in substantial amounts, many scientists have used genetic engineering to clone spider silk genes and insert them into various organisms. For example, Randy Lewis, Ph.D., of Utah State University has put spider silk genes into domesticated goats. Milk produced by the goat’s mammary glands are then collected and purified to harvest spider silk proteins.
“More recently, other groups, including Dr. Lewis of Utah State and Dr. Malcolm Fraser of the University of Notre Dame, have had success in transforming silkworms with spider silk genes, which is very useful since domesticated silkworms are already able to produce silk in large quantities in farms,” says Garb.
Other researchers are trying to introduce silk genes into crop plants such as alfalfa, tobacco, potato and soy in the hope of harvesting even larger quantities of spider silk.
“The work I do in characterizing the different spider silk genes identifies the templates that can be used in such genetic engineering work,” says Garb.
She says more than 40,000 species of spiders have been discovered so far, and thousands more are yet to be discovered.
For more information, see Garb’s website