By Jonathan Fildes
Science and technology reporter, BBC News
Spider silk is strong, elastic and biodegradable
A device that partially mimics the process by which spiders produce fine, yet super-strong, silks has been built.
It could help produce a new generation of tough, lightweight materials for use in medical equipment, for example.
A simple method for manufacturing strands of artificial gossamer has long been coveted as - weight for weight - it is five times stronger than steel.
Writing in the journal PNAS, the German team says their work sheds light on how spiders produce their unique materials.
"We can observe the initial steps of fibre formation, which was not possible before," explained Sebastian Rammensee of the Technical University of Munich and one of the authors of the Proceedings of the National Academy of Science's paper.
"Now we can better understand how the processing conditions affect the quality of the silk."
Despite years of research, scientists have been unable to produce useful quantities of artificial spider silk.
Spiders make their silk naturally as water-soluble proteins which are secreted from cells. These solutions are forced through tiny holes in their body - known as a spinneret - which extrude the thread.
The device allows precise control of the levels of proteins and salts
To mimic this process, the team manufactured two genetically-engineered spider silk proteins using bacteria. These were fed into a device that consists of three channels etched into glass.
"The protein is introduced from one channel and from the two other channels salt solutions are introduced," explained Mr Rammensee.
The salt causes the proteins to clump together, which are then forced down a narrow channel that extrudes the mixture as a fibre.
The team extruded different grades of fibre using different combinations of proteins and salts.
However, according to Professor Fritz Vollrath of the University of Oxford, none were of a particularly high quality.
It's another important small step towards making the material," he said. "It adds a piece to the puzzle but it's a very big puzzle and there are many pieces missing."
Professor Vollrath holds a US patent, filed in 2002, for a device similar to the one outlined by the team.
The new research is the latest in a long line of attempts to crack the secret of spider silk.
In 2002, a Canadian company called Nexia demonstrated a method to cultivate the necessary proteins using transgenic goats.
A micrograph shows the artificial silk in more detail
The process involved implanting a single gene from a golden orb-weaving spider into a goat egg to produce animals that would secrete spider silk into its milk.
The technique was successful but the company later abandoned the research.
The company also had difficulty producing high quality fibres, according to Professor Vollrath.
As a result, others are turning to other sources of natural silks to build the kinds of applications envisaged for fibres.
"We are finding certain wild silks which are stronger when you unravel them than natural spider silks," said Dr David Knight, a colleague of Professor Vollrath and chief scientific officer at Oxford Biomaterials.
The firm exploits silks for medical applications such as sheaths to help nerve regrowth.
Dr Knight could not say which species produced the silks, for business reasons, but said they were available in "potentially commercial" quantities.
Harvesting silks had significant advantages over the techniques outlined in the latest research, he said.
"Genetic engineering is completely out for producing high-strength polymers - it's just much too expensive," he told BBC News.
"You have to have very precise environmental controls, you have to have very pure chemicals, you have to have a single strain genetically engineered bug - all that is just a recipe for capital and energy intensivity."