Scientists Weave Stronger Spider Silk by Mixing In Metal
Monday, April 27, 2009
It's probably good that Charlotte isn't around to learn that her marvelous web has been improved upon -- and by people, no less.
Spider silk is one of nature's engineering triumphs, stronger on a per-weight basis than steel. Scientists reported last week that they had made it three to 10 times as strong (depending on how strength is measured) by infiltrating it with atoms of metals such as titanium, aluminum and zinc.
The process turns out to recapitulate something that locusts and marine worms -- animals not known for intelligence -- do. It is helping illuminate some fine points of protein chemistry. It might eventually lead to new types of strong and light material similar to carbon fiber.
The discovery, made by Seung-Mo Lee, a graduate student in engineering at the Max Planck Institute in Germany, occurred largely by chance.
"This is how it often is," said his supervisor, Mato Knez, a chemist at the research center. "You work toward some special goal that you hopefully can reach, but on the way you frequently find something different. That is often the most fascinating science."
Knez's research interest is nanotechnology -- creating infinitesimally tiny mechanical structures by manipulating small numbers of atoms. One of the techniques he uses is "atomic layer deposition" (ALD), in which substances are thinly coated with another material, often a metal.
When Lee, a native of Korea, came to Knez's laboratory, one of his projects was to investigate what ALD would do when applied to biological materials. Normally, it is used on hard, silica-based semiconducting materials, such as those in computer chips. But what would happen if the materials were soft and relatively fragile?
One way to get an answer would be to synthesize some sort of organic compound -- perhaps a long chain, called a polymer -- and subject it to ALD. But as a first pass at the question, Lee took an easier route. This was because he was pretty sure the process would destroy a soft material.
An Unexpected Discovery
The ALD machinery he used is housed in the basement of a building. The place is cluttered and, as it turns out, home to many spiders. So one day two years ago, Lee got the idea of testing spider silk as a model "soft biomaterial."
Lee found an Araneus arachnid with a dragline, the thread it generates from two glands on its abdomen. He reeled the thread in over a paper clip and put it in the ALD chamber.
When he took it out, it was almost a different material. He could hold the thread with a pair of tweezers -- dragline thread is somewhat less sticky than web thread -- and bounce the paper clip up and down without breaking the strand.
He showed this trick to Knez, who could hardly believe his eyes. Like Lee, he expected that ALD -- a process that involves heating something up to about 160 degrees Fahrenheit -- would destroy the biomaterial.