Not being able to create the supporting vascular system - the branching network of blood vessels which supply nutrients and oxygen to tissues - has proved a major stumbling block preventing scientists from creating large functioning organs such as liver or kidneys.

Now, according to a report in New Scientist, researchers from MIT and Harvard have used computers to design branching networks of venous and arterial capillaries just 10 microns in diameter.

The networks were etched onto tiny silicon wafers and the paths were then used as a mold to set a layer of biodegradable polymer. Two of these were then sealed together with a microporous membrane sandwiched between them, producing a mini artificial vascular system.

Blood vessel cells were injected into the network on one side of the membrane and either liver or kidney cells were injected on the other side. The blood vessel cells coated the inside of the polymer nanotubes. These nanotubes biodegraded to leave a living shell of vessels similar to a natural vascular network.

The one-layer systems of kidney and liver cells were successfully implanted into rats for two weeks - 95 per cent of the cells survived. "So in the next 10-15 years, we will hopefully have reached a point where we can do this procedure clinically in human patients," said lead researcher Mohammad Kaazempur-Mofrad of MIT.