Dr Pascal Dohmen, head of tissue engineering research at Charite Hospital in Berlin said the new type of valves would eliminate the risks usually associated with mechanical, pig and cattle valves or those taken from human cadavers.

Diseased heart valves operate improperly and can damage the heart. If drug treatment does not work, surgeons replace them with one of the aforementioned valves.

Mechanical, pig and cattle valves work well for patients older than 60, but may not be appropriate for younger patients since they wear out too soon, said Dr Dohmen.

Valves taken from human cadavers can involve other health hazards through an immune reaction to another person's tissue.

To eliminate that risk, Dohmen and colleagues made valves using a patient's own cells.

The scientists started with valves from human cadavers and pigs, and then removed the living cells until only a scaffold of collagen and elastin remained. The scaffold retained the valve's original shape.

They then took endothelial cells, the cells that make up the lining of blood vessels, from a patient's vein in a leg or forearm and grew them on the scaffolding in the laboratory.

The valves have been implanted in 23 patients with an average age of 44, according to data presented at an annual meeting of the American Heart Association.

Dohmen said the patient's own cells form a completely new scaffold after about a year.

His patients have been studied for up to three years since receiving the tissue-engineered valves. "The patients are in very good shape," he said.

Imaging tests of the patients' hearts showed the valves were functioning normally and showed no signs of the calcium build-up that can destroy other types of valves, he said.

Patients also had a shorter recovery than usual for valve-replacement surgery, and had no post-operative fever, a common phenomenon with other valves, Dohmen said.