Media playback is unsupported on your device Media caption Darek learns to cycle again

A man who was paralysed from the chest down after a knife attack in 2010 can now ride an adapted tricycle.

In 2014, surgeons in Poland announced they had reversed Darek Fidyka's paralysis using cells taken from his nose to repair his spinal cord.

The former fireman says he has noticed a gradual return of feeling and muscle control below his injury.

The surgical team are now launching a search for two more paralysed patients who they will try to help walk again.

Mr Fidyka told me: "I can tell that sensation is coming back and I am getting stronger. A year ago I would not have been able to ride a tricycle. Now I can feel each muscle and each press of the foot on the pedals."

If we succeed we will have found a cure for paralysis Dr Pawel Tabakow, surgeon

The BBC's Panorama told the remarkable story of Darek Fidyka and the 40-year research programme involving scientists in Britain and Poland.

The medical team are now launching the worldwide search as they are looking for patients with an uncommon type of injury, where the spinal cord has been completely severed, which can happen after a knife injury.

The head of the project, surgeon Dr Pawel Tabakow said: "If we can bridge the gap between two spinal cord stumps then there will be no doubt that our technique works and this will be historic - if we succeed we will have found a cure for paralysis.

"Then we will be able to help other patients with the most common type of injury, caused by a crush or compression."

Image caption How Darek Fidyka's spinal injury was repaired

The Wroclaw Walk Again Project will be conducted in Poland, but patients anywhere in the world aged 16-65 will be able to apply via the team's website, which will be officially launched on 8th March in Wroclaw.

All the treatment will be free, but to be eligible patients must have no feeling or voluntary muscle function below the injury and they must be prepared to spend around three years in Poland.

They will undergo extensive physiotherapy before and especially after the transplant surgery.

The medical team are expecting to be inundated with applications in the months ahead.

They will make an initial shortlist based on patient scans and medical notes and then invite a few potential volunteers for assessment in Poland.

Those selected will undergo the same pioneering surgery that was performed on Darek Fidyka which was published in Cell Transplantation.

Analysis

Scientists have spent decades searching for a means of enabling the paralysed to walk again. Motorised exoskeletons, which are strapped on the body, bypassing the injury, are now available commercially.

Electrical stimulation techniques use implants to enable patients to flex their lower limbs. But neither method involves repairing the damaged spinal cord.

The approach in Poland aims to reconnect the brain with the lower limbs along the neural superhighway that is the spinal cord, enabling both motor control commands to travel down the body and sensation to travel up.

Darek Fidyka's spinal cord had been almost completely severed as a result of a knife attack, apart from a thin thread of external connective tissue and prior to the transplant, he had no feeling or control below his injury.

Now he has had to re-learn how to control his muscles and interpret sensations. He said: "I realise how important the brain is while cycling, and that thinking is more tiring than the exercise itself."

But the results from one patient, however impressive, would never be sufficient evidence on which to base a new approach to spinal cord injury.

The forthcoming trial in Poland will be crucial if the wider scientific community is to be convinced that a patient's own cells can be used to regenerate their spinal cord.

It is also worth stressing that the patients selected will have to show enormous determination if they are to see the full benefits of the treatment.

In the first of two operations, surgeons will remove one of the patient's olfactory bulbs, which sit above the nasal cavity at the base of the brain, and process the sense of smell.

The bulb contains specialist cells known as olfactory ensheathing cells (OECs) which act as a pathway that enables nerve fibres in the olfactory system to continually renew.

In a second operation the patient's OECs will be injected above and below the injury and strips of tissue laid across the gap in the cord.

The team believe the OECs will enable nerve fibres to regenerate across the cord and so repair the damage.

An independent team of assessors led by neurophysiologists from Imperial College London will also be closely involved in monitoring the research.

Peter Ellaway, emeritus professor of physiology, at Imperial said: "I'm excited because this is a novel treatment with a lot of promise."

But he cautioned that even if it works it would take some years to refine and so would not be immediately available for patients.

The treatment in Poland will cost £250,000 per patient and is being funded by a small British charity, the Nicholls Spinal Injury Foundation (NSIF).

It was founded by chef David Nicholls after his 18-year-old son Daniel was paralysed from the neck down in a swimming accident.

Mr Nicholls said: "I know how important progress is to people living with spinal cord injury and am optimistic that success with the next two patients will result in an announcement that paralysis is curable."

Image caption Darek Fidyka still undergoes five hours of physiotherapy a day

NSIF and the UK Stem Cell Foundation both support the research of Prof Geoff Raisman, chair of neural regeneration at University College London (UCL), who has pioneered the use of OECs to repair the damaged spinal cord and leads the British side of the Walk Again project.

Prof Raisman said: "Darek's latest progress demonstrates the extraordinary power of (neuro) plasticity. But it depends on the patient's own efforts. It is like a baby learning to walk. We cannot teach it how. The progress comes from inside."

Darek underwent his transplant in April 2012, and he still spends five hours a day undergoing physiotherapy.

He can now walk slowly using crutches or a small walking frame, but usually relies on a wheelchair as it is simply quicker and less tiring.

The return of sensation below his injury has brought other benefits like bladder control and the return of sexual function.

Darek was happy to discuss sex and explained that the reawakening of the erogenous zones was a crucial part of his recovery.

He said: "The return of sexual satisfaction - which travels along the spinal cord to the brain - is very important psychologically and is another part of my growing sense of independence."