Oh, What a Newfangled Web We Weave
Genetic engineering coaxes silk from mammal cells
THURSDAY, Jan. 17, 2002 (HealthDayNews) -- It really is possible to spin a silk purse from a sow's ear. At least, in theory.
Commercial and government scientists say they've used genetic engineering to convert mammalian cells into silk factories that churn out ultra-tough fibers similar to those spiders employ. Since silk is many times stronger than steel, the feat could one day lead to important new materials for everything from surgical sutures to bulletproof vests. A report on the effort appears in tomorrow' s issue of Science.
A ready supply of spider silk would be a boon to all manner of industries. However, scientists have been frustrated in their quest to husband arachnids because they are highly territorial creatures and make poor stock.
Researchers have already tried to turn genetic engineering to the problem of silk farming, with generally disappointing results. So the latest attempt marks the best effort yet, says Steven Arcidiacono, study co-author and a microbiologist at the U. S. Army Soldier Biological Chemical Command in Massachusetts.
"This is a big breakthrough," says Arcidiacono, who helped test the physical properties of the genetically engineered silk.
Researchers from the Army and Nexia Biotechnologies in Canada inserted two sets of silk-producing genes, culled from two species of orb-web spider, into kidney cells taken from baby hamsters and mammary cells taken from cows.
Thanks to the added genes, the tweaked cells began producing fibrous, silky proteins. The researchers were then able to create strands of the material by spinning it carefully out of a water solution.
The threads proved to be almost as tough but roughly half as strong as the "dragline" strands spiders knit into webs as safety lines. For materials scientists, toughness is a measure of how much energy a compound can absorb before breaking, while strength refers to how much force it can withstand before deforming catastrophically.
For example, glass is a relatively strong material that's not so tough. Rubber, on the other hand, is the quintessential tough material, capable of absorbing tremendous amounts of energy, but it's not especially strong.
Arcidiacono says the engineered silk as it's currently being produced is too stretchy to be useful for the Army's purposes: making lightweight bulletproof vests and helmets and better surgical supplies such as stitches and bandages.
"What we would like to do is to reduce the amount of stretching it does," he says. "The fiber is similar to silk, but it is not a duplicate. The spider is not really giving up its secrets very easily."
"We still have some humility," says Brad Cilley, Nexia's vice president for business development. "The spider's been spinning dragline silk for 400 million years. We are still optimizing our spinning process, and we believe the strength will be improved."
On the plus side, the engineered silk holds up well in water, an important quality for nearly every conceivable use. The researchers say the fibers are biodegradable, and neither they nor the production process pose a threat to the environment.
Nexia owns the commercial rights to develop the mammalian silk, which it is calling BioSteel. A major challenge, Arcidiacono says, will be to make enough of it to matter. Right now, the company has managed to generate its silk in gram quantities, but for the military, or any other customer, to be interested they'll need access to pounds or even tons of the fibers.
Bring on the goats. To mass produce its silk, Nexia has bred a herd of genetically engineered goats who will pump out the protein in their milk. The company hopes to distill the milk, and collect the fibers. Although the animals aren't yet mature enough to lactate, Cilley says they are expressing the transferred protein.
Cilley adds the company hopes to market its first product in late 2003 or early 2004.
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