Magnetic Micromachines

Chinese researchers have used lasers to made tiny springs and turbines out of a polymerized ferrofluid, which could be used in micro- or nanomachines.

Nano- or micromachines may sound like science-fiction, but they are fast becoming a reality. Such machines have many uses already in sensors and in-the-body treatments. Until now, micromachines have mainly been made from inorganic components, although recently scientists have been turning to polymers as these should give better control over the resolution and size. However, it has never been easy to drive these tiny machine components, and for many applications remote control (i.e., no touching) is required which makes driving them even more tricky.

Professor Hong-Bo Sun and his team from Jilin University, China, think they have solved the problem of how to drive the machines by creating components that respond to an external magnetic force by stretching, swaying, or turning. The team created a homogenous dispersion of magnetic nanoparticles in a carrier fluid, known as a ferrofluid, and then polymerized the whole system using a technique called two-photon photopolymerization (TPP). Because TPP is carried out with a laser, they were able to precisely shape the resulting polymer into springs or turbines by controlling the laser as the polymerization occurred.

Springs made in this way respond to a magnet by elongating but then return to their original shape and position when the magnet is switched off. They can also be made to sway if the magnet is applied sideways on. A tiny turbine that the scientists made in the same way can be made to turn at up to six revolutions per second when the magnet is switched on.

Professor David Gracias, an expert in micro- and nanotechnology from Johns Hopkins University, Baltimore, USA, called the methodology “innovative”. In particular he noted that the method was elegant because of the use of a cross-linker group which could be used with a range of different nanoparticles. He said that “Our ability to build in 3D and to build structures with moving parts on this scale is still lacking. Any demonstration of these is exciting”.

The researchers describe their work as a breakthrough in nanotechnology and hope that their miniature components will enable others to produce real-life micromachines for a multitude of purposes.

H. Xia et al., Adv. Mater., DOI: 10.1002/adma.201000542

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