A number of synthetic and natural materials have been tried in cell culture and tissue engineering applications in recent years. Now Jeffrey Perkel takes a look at one new culture component that might surprise you—spider silk.
At the north end of the Utah State University (USU) campus in Logan, Utah, Randy Lewis’ lab in the new USTAR Bioinnovations Center is on the cusp of a materials science gold rush.
Lewis’ gold isn't hidden deep in the snow-capped peaks just beyond his corner office though; it's buried in the bacteria, silkworms, genetically modified alfalfa sprouts, and even goat's milk found in his lab. These are the recombinant biofactories that Lewis and his colleagues have harnessed to generate what many hope will be a new bioengineering treasure: spider silk.
Stronger than steel, yet springy like a green tree branch, biocompatible, biodegradable, and relatively non-immunogenic, the potential applications of spider silk span a wide range of industries. “We're working with people on everything from medical products to sporting goods to tires to almost everything in between,” Lewis says.
But first researchers must actually obtain useful quantities of spider silk for testing and product development—and that has not been easy.A Tangled Web
Unlike silkworms, spiders cannot be domesticated. They are territorial, and they are cannibals. Collecting spun webs, says Lewis, the USTAR Professor of Biology at USU, “is kind of a defeatist proposition,” because different silks have different properties, and mixing them together dilutes the batch. The only way to acquire significant amounts of pure native spider silk is to collect wild spiders and then pull the silk from their bodies, like dental floss.
Many researchers, including Lewis, instead express spider silk proteins in transgenic organisms, a strategy that offers significant advantages for both scaling and arachnophobes. But to generate those silks, spiders produce multiple silk proteins, each with distinct properties. According to the World Spider Catalog at the American Museum of Natural History , there are 44,540 known spider species. Some, like the widely studied Nephila clavipes, produce massive webs comprising at least five distinct silks—some stronger, some weaker, some elastic, some less so; two additional silks are used to protect N. clavipes offspring. Tarantulas spin no webs at all, instead putting out feeler lines to detect approaching prey. A recent genome sequencing analysis—referred to by the author as “silkomics”—identified 19 candidate silk genes in the African social velvet spider, Stegodyphus mimosarum, and 7 in the Brazilian white-knee tarantula, Acanthoscurria geniculata. [1,]
“Spider silk proteins are actually a class of materials,” says Thomas Scheibel, Chair of Biomaterials at the University of Bayreuth, Germany.
And many in the biomedical community see great promise in them.A Day at the Museum
In 2009, the American Museum of Natural History in New York played host to an extraordinary 11-foot by 4-foot textile made of N. clavipes spider dragline silk—a magnificent fabric whose natural shimmering golden color reflects the spider's common name: the Golden Orb weaver.
That textile was the labor of four years and dozens of people—not to mention over one million wild spiders silked by hand in Madagascar. That's obviously wholly impractical for production work in the lab (or the textile industry). But that doesn’t mean researchers can't use native spider silk on a smaller scale.
That textile was the labor of four years and dozens of people—not to mention over one million wild spiders silked by hand in Madagascar. That's obviously wholly impractical for production work in the lab (or the textile industry). But that doesn’t me an researchers can't use native spider silk on a smaller scale.
Jörn Kuhbier, a plastic surgeon and medical researcher in the Department of Plastic, Hand and Reconstructive Surgery at the Hannover Medical School in Germany, was a doctoral student in 2006 when he joined a lab that was exploring the biomedical application of spider silk. At the time, he wasn't exactly president of his local spider-appreciation club: “I did not like the idea of being in a room together with a spider,” he says. Nevertheless, he was tasked with developing methods to grow cells on spider silk fibers, a first step towards using the material for tissue engineering.
The team's collection of N. clavipes spiders was housed in unused offices, where they were allowed to roam free and spin webs. Kuhbier and his colleagues created a map of each spider's approximate location in the office. The spiders were each named, and pins bearing a spider's name were affixed to the map to track which spiders were used and when, “to be sure that, for example, when Rosy was harvested on Wednesday, that she does not get harvested on Thursday as well.”