Sturdier gossamer threads: introducing metal into spider silk

Spider silk is one of natures engineering triumphs,stronger on a per-weight basis than steel.

Spider silk is one of natures 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 by infiltrating it with atoms of metals such as titanium,aluminum and zinc. The discovery,made by Seung-Mo Lee,a graduate student in engineering at the Max Planck Institute in Germany,occurred largely by chance.

When Lee,a native of Korea,came to work with Mato Knez,a chemist at the research centre,one of his projects was to study the nanotechnology technique of atomic layer deposition (ALD)in which substances are thinly coated with another material,often a metaland investigate what ALD would do when applied to biological materials. Normally,it is used on hard,silica-based semiconducting materials. But what would happen if the materials were soft and relatively fragile?
One way to get an answer would be to synthesise an organic compoundperhaps a long chain,called a polymerand subject it to ALD. But Lee took an easier route. This was because he was pretty sure the process would destroy a soft material.

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 and bounce the paper clip up and down without breaking the strand. Knez could hardly believe his eyes. He expected that ALDwhich involves heating something up to about 160 degrees Fahrenheitwould destroy the biomaterial.

Knez initially thought the process had coated the spider silk like a ceramic sheath. But Lee,the engineer,knew the thread would not remain springy and easily bendable if that were the case. He found that,unlike with hard materials,ALD infiltrated soft materials with metal atoms in addition to depositing atoms in a thin surface film.
The result,Lee believes,was a strand that is a bit more amorphous overall than native spider silk but whose various regions are more tightly locked together. The thread is denser and stronger. If we can transfer the process,there are a huge amount of potential applications,things like artificial bones and artificial skin, Knex said. The Max Planck Institute is looking into patenting the process.
_David Brown,LATWP