Scientists have built a minute, functioning vascular system — the branching network of blood vessels which supply nutrients and oxygen to tissues — in a significant step towards building whole organs.

Using living vessels as a guide to model factors such as the angle and size ratio between branching vessels, the networks were etched on to 15 centimetre-wide silicon wafers and the paths were then used as a mould 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.