The main point of this work is that we have processed the nanotubes into a form that is of practical use

Dr Philippe Poulin

But the tubes are difficult to produce in bulk and order in a way that would allow researchers to tap their undoubted potential.

Now, scientists from the Paul Pascal Research Centre at the University of Bordeaux, and colleagues, have devised a method to fabricate "indefinitely long" ribbons and fibres from literally trillions of individual nanotubes. These ribbons and fibres will bend without breaking and can even be tied into knots.

The work brings the industrial production of materials based on carbon nanotubes one step nearer.

Flowing stream

Carbon nanotubes are essentially sheets of graphite, a single atom deep, that have been folded back on themselves.

The fibres demonstrate their flexibility by knotting without breaking

Their discovery in 1991 followed quickly that of buckminsterfullerene, the spherical cage of carbon atoms that looks like a soccer ball.

The tubes can be single-walled, or multi-walled with one "skin" of atoms siting neatly inside another. To make buckyballs and tubes, scientists vaporise carbon in the presence of a catalyst.

But, not only is it an expensive process, the individual molecules are difficult to organise.

The French work tackled the ordering problem. The team dispersed a raw nanotube soot into a surfactant, or detergent, solution, which was then injected into a flowing stream of a polymer solution.

This caused the nanotubes to recondense into a mesh, and the flow aligned the mesh into ribbons. When dried, the ribbons collapsed into narrower fibres.

Fibres could eventually make super-strong textiles
(Scale bar: 1mm)

The fibres made by the French team were between 10 and 100 millionths of a metre in diameter.

"The main point of this work is that we have processed the nanotubes into a form that is of practical use," co-researcher Dr Philippe Poulin told BBC News Online. "And we are very pleased because we think the method is simple enough to be scalable to an industrial level."

Dr Ray Baughman, a material scientist with Honeywell International, said long and ultra-strong nanotube fibres could be used in a variety of future applications, from artificial muscles to hydrogen storage.

Commenting on the French study, he said: "By building on their discoveries, it will be possible to devise an economically viable process for spinning strong nanotube fibres.

"However, at the current price of purified single-walled nanotubes (about $1,000 per gram), single-walled carbon nanotube fibres are only attractive for devices requiring little material.

But, if this price fell, as expected, large-scale, commercially viable applications would also be possible, he said.

The French research is published in the journal Science.