Tiny machines will be able to build themselves

How do you build a micro-machine whose components are thousands of times smaller than a pinhead? The answer, according to American scientists, is that you don't - you let them build themselves.

Sometime in the new millennium, such machines could be injected into people to clean up their blood.

Now, using techniques borrowed from biology, a team at Harvard University in Massachusetts has taken the first step towards such self-assembling machines, by mixing together different parts with the required shape, adding some photosensitive glue, and mixing them until the shape they wanted appeared. A beam of ultraviolet light then set the glue.

With a market value estimated at pounds 40bn in the next 10 years, "nanotechnology" is attracting huge investment. But teams trying to make such systems - such as gears the size of pollen grains and electric motors smaller than a pinhead - have previously faced the same problem: it is very difficult to put the pieces together without dropping them. "In most fabrication, you do things by fixing them in place - welding or screwing them to something. They're systems which are metastable," said George Whitesides of Harvard's chemistry department.

His team tried using the assembly techniques of the human cell - certain shapes fit together, even at the molecular level, and that liquids and bubbles can bring surfaces into contact. Early experiments in a six-month project, reported today in the science journal Nature, produced millimetre- sized plastic components. The team aims to make machines which could be used to manufacture microelectronic and mechanical systems, Mr Whitesides said. That, though, could take 10 years.