Vacanti caused a sensation with his ear mouse

Details of his method were announced at a meeting of the UK Tissue and Cell Engineering Society at the Hammersmith Hospital, London. Lord Winston, a pioneer of In Vitro Fertilisation, described the results as "truly astounding".

But the work has not yet been fully reviewed by independent scientists and some at the meeting were said to have expressed scepticism.

Professor Vacanti's team, which works at the University of Massachusetts Medical Center, began their experiments by removing 2.5 centimetres (one inch) of spinal cord from eight mice. This left their limbs paralysed.

Artificial cords

The missing spinal cord was then replaced with a polymer mixture implanted with immature nerve cells from healthy mice.

The nerve cells had been multiplied in the laboratory before implantation to create "neurospheres". These are clumps of nerve cells that seem to be able to communicate with each other.

After a few weeks, the connections from the brain and across the artificial spinal cord had been re-established allowing seven of the eight to recover limb movement.

The scientist found that encouraging the treated mice to exercise made for a faster and fuller recovery. They did this by placing the mice in a bucket of water, forcing them to swim or drown.

Tissue engineering is believed to be one of the most promising areas of medical research, with the promise to deliver radical new treatments. Last year, Professor Vacanti hit the headlines by regrowing the tissue of a man's thumb after it had been sliced off by a machine.