Moving research

Researchers at the University Hospital in Zurich have already succeeded in cultivating the heart valve of a sheep using the creature's cells.

Heart surgeon Simon Hoerstrop hopes to eventually be able to implant in human patients functioning valves grown out of their own stem cells.

This means that many heart patients, particularly young people, may one day not have to undergo rounds of painful transplant surgery to replace artificial valves that they have outgrown.

Research to help children

To date, surgeons have used artificial valves made out of synthetic materials or dead animal tissues in order to avoid any chance of the body rejecting the replacement part.

One big problem however, particularly in the case of children, is that these substitute valves do not grow within the body. This means young patients must endure new transplant surgery every few years.

Some children require as many as five of these operations before they reach adulthood.

Sheep are ideal guinea pigs

Simon Hoerstrop would like to change this. Sheep are particularly well suited to test the procedure, according to Hoerstrup. "It is an ideal model because its anatomy is very similar to that of a human," he said.

In addition, sheep organs quickly calcify if they are not working properly, he added. This means that scientists can spot much more quickly if something is going wrong than they could in human patients.

To create a heart valve, Hoerstrup extracts cells from an artery in the sheep's neck. The cells are then propagated in the laboratory and are deposited on a scaffold. This template corresponds almost exactly to the shape of a heart valve.

This is then put in a bioreactor where the cells continue to grow and attach themselves to the scaffold, which graduallly dissolves.

Meanwhile, the nutrient solution is kept constantly in movement while the valve is growing. It simulates the motion of the heart and is intended to train the new component for its future duty in the body. The whole process takes a mere eight weeks.

The valve is then transplanted back into the sheep, whose stem cells were used to grow the bodily component. This process allows researchers to avoid any chance of rejection.

Valve replacement in humans foreseeable

In the laboratories of the University Hospital of Zurich about one hundred human valves are already being successfully grown.

Although heart surgeon Simon Hoerstrup and his team are already looking forward to the day when they will be able to transplant a living heart valve into a human patient, he cautions that it is still likely to be a few years from now.

Author: Basil Honegger/Maria Lesser (gmb)

Editor: Julie Gregson