As the particles contain iron oxide, they group together when they are magnetized by an external magnetic field. The scientists construct the magnetic field with four coils so that the microparticles are literally remote controlled and form diamond shapes or cog wheels. "The shape they assemble into depends crucially on the geometry of the channels," explains Tobias Sawetzki, who a doctoral student is working on the project. The microparticles then remain in this shape as long as the magnetic field is switched on.
The geometry also determines the function of the aggregates. By tipping backwards and forwards, a rhombus creates openings and acts like a valve. On the other hand, if it rotates in a chamber with two inflows, it mixes the incoming liquids. The micro stirrer is also driven by a magnetic field that rotates clockwise or anticlockwise parallel to the chip. In the same way, the researchers in Stuttgart roll a cog wheel through a channel with a serrated wall. The cog wheel, which completely shuts the channel off, agitates liquid back and forth and only in combination with two valves, acts like a pump.
"Compared to other approaches to equipping microlaboratories with moving parts, our ship-in-a-bottle technique has several advantages," says David Marr. Some scientists use pneumatic systems to pump liquids through microchannels, for example. However, this requires each component to be connected with a separate hose to the outside so that it can be supplied with compressed air. This is very complex and limits the integration density on microfluidic devices considerably, i.e. the total number o
|Contact: Clemens Bechinger|