Magnetic Tweezers Used to Manufacture Microfluidic Devices

A collaboration of German and American scientists has created a novel technique that can be used to assemble miniature lab-on-a-chip devices. Using a magnetic field like a pair of tweezers to assemble the components inside the chip, the investigators hope their technology one day will be used to commercially manufacture diagnostic microchips or implantable therapeutic gadgets.
From the Max Planck Society:

Researchers working with Clemens Bechinger who is a Professor at the University of Stuttgart and a Fellow at the Max Planck Institute for Metals Research, and David Marr, a professor at the Colorado School of Mines, have now found a new way to equip these miniaturized laboratories with moving parts and how to drive the tiny machines. They introduce colloidal particles, tiny plastic spheres with a diameter of just about five micrometers, into the channels and cavities on the chip.
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 of components on the chip.
With the new method, it is possible to accommodate up to 5,000 pumps on one square centimetre. Moreover, the new approach does not rely on elastic materials as are required for pneumatic pumps. “It is much easier to produce suitable chips for applications if they only consist of a single material, silicon, if at all possible,” says Clemens Bechinger. As the electrical control components like the mini-coils can be fabricated based on silicon, it would be ideal to make the microchannels from the same material. This would allow for integration of all the components on one chip, as in microelectronics,” says Bechinger.

Image: In a magnetic field the microspheres (orange) form diamond shaped valves and a cog wheel. With skilful manipulation of a magnetic field, the wheel rolls through the cavity, and together with the valves pumps a fluid with colloid particles (blue) through the system.
Press release: Ship in a bottle kit on a microchip …