Scientists believe a novel way of stretching nerve cells might eventually provide a way of repairing damaged spinal cords.

While the technique is still in its infancy, the team, from the University of Pennsylvania in Philadelphia, claim that fibres made using it could bridge gaps between damaged nerves.

Trials have begun to see if the process works in laboratory animals.

However, other researchers in the field say that nerve cells grown in such circumstances would be little or no use in the treatment of spinal injury.

Hundreds of people each year in the UK are left paralysed to some degree after suffering spinal cord damage in an accident.

No regrowth

Nerve cells do not regrow on their own, restricting the possibilities for any sort of recovery.

The Philadelphia team took bunches of human nerve cells grown in the laboratory, then gently stretched out the central linking fibre, the axon, over a long period of time.

Each axon is only a micron wide - a thousandth of a millimetre.

However, over 10 days, the gradual application of tension "persuaded" it to grow by as much as a centimetre.

The end result was groups of tens of thousands of axons - each one a centimetre longer than before.

However, even if the animal trials prove successful, implanting and linking up the cells to a damaged human spinal cord is a massive obstacle.

When transplanted, adult neurons do not normally survive in their new environment, although the team is using a cell-line of neurons that did manage to live on in stroke patients.

Other techniques proposed by scientists studying spinal repair involve trying to encourage the patient's existing neurons to start regrowing.

This could be done by implanting a microscopic "scaffold" coated with chemicals which promote growth.

However, Dr Geoffrey Raisman, from the National Institute for Medical Research in London, said that while it might be possible to extend the length of axons in a tissue culture in a laboratory, this was of no practical benefit in spinal injuries.

He said: "The problem in spinal cord injuries is that once they are cut, they do not grow back - this is not a practical approach."

The research was reported in New Scientist magazine and the journal Tissue Engineering.