An innovative micro-pump makes it possible for tiny quantities of liquid - such as medicines - to be dosed accurately and flexibly.

Active composites and an electronic control mechanism ensure that the low-maintenance pump works accurately in both directions.

Medicines sometimes have to be administered in extremely small quantities; just a few tenths of a millilitre may be sufficient to give the patient the optimum treatment. Micro-pumps greatly facilitate the dosage of minute quantities. Pumps like these have been developed for over 25 years. They find application in numerous areas - from medical engineering to microproduction technology - wherever tiny volumes have to be variably dosed with extreme accuracy.

However, these micro-pump systems are usually not as versatile as desired: they often work in only one direction; bubbles in the liquid impair their operation; they do not tolerate particles; they have a fixed pump output; and they contain expendable parts such as valves or gearwheels. Together with partners from research institutes and industry, researchers at the Fraunhofer Institute for Mechanics of Materials (IWM) in Freiburg, Germany, have developed an innovative pump system that solves all these problems: a controllable peristaltic micro-pump. I

WM project manager Dr Bärbel Thielicke explains: “The peristaltic pump is a highly complex system. It contracts in waves in a similar way to the human oesophagus, and thus propels the liquid along - it changes shape of its own accord. To achieve this, we had to use a whole range of different materials and special material composites.” The researchers use lead-zirconate-titanate (PZT) films that are joined in a suitable way with bending elements made of carbon-fibre-reinforced plastic and a flexible tube.

Thielicke says: “PZT materials change their shape as soon as you apply an electric field to them. This makes it possible to control the pump system electronically.” In addition, special adhesives hold the various pump components together. Thanks to the special control electronics, tiny quantities can be pumped accurately.

The peristaltic pump system has already passed its first functional tests. Now the researchers are working to adapt the peristaltic micro-pump to the various different applications. Thielicke says: “We work with special simulation models to do this. We calculate in advance how the structure of the pump needs to be modified in order to administer other dosages or other liquids. This helps us save time and money during the development phase.”

Fraunhofer Institute