A new technique that promises to make the mass production of complex plastic microstructures a routine, one-step process has been developed by John Fourkas, professor of chemistry at the University of Maryland (www.umd.edu) in the United States.

To solve the problem of mass-producing plastic parts smaller than the diameter of a human hair, Fourkas´s team modified a technique known as microtransfer moulding, reports "Proceedings of the National Academy of Sciences". In that process, a mould is made by curing polydimethylsiloxane (PDMS) over an original object attached to a surface. The hardened mould is then removed and used to create copies.

"Moulds for producing large objects are usually composed of two or more pieces that fit together," says Fourkas. This makes it possible to create components with extremely complicated shapes that include features such as holes – the dust guard on a computer keyboard, for example. But when the same procedure is used to create microscopic objects, a number of problems, such as aligning the different parts of the moulds arise.

The difficulty with microtransfer moulding is when the original object contains so-called closed loops. Up to now, this has been addressed by moulding in layers. However, the layer-by-layer technique can be used only to mould a limited range of structures, and it requires precise alignment of each mould, says Fourkas. "We realised that we could take advantage of a property of PDMS that is usually viewed as a problem, which is that it likes to stick to itself."