In the miniemulsions mixed by Mohammed El-Aasser’s group, however, the droplet-shaped nanoreactors stayed tightly sealed. Katharina Landfester thus sensed quite early on that it also had to be possible for them to create more complex chemical constructions. But she never dreamed back then that they would be able to make many of nano technology’s promises a reality. That is exactly what is happening today.
The particles that Katharina Landfester and her fellow scientists build come quite close to a vision that, in the 1990s, was associated with the world of tiny things. At that time, many researchers redesignated their experiments on the nanoscale to an independent research field they called nanotechnology. This quickly created the idea that, in the not-too-distant future, robots smaller than a thousandth of a millimeter could carry out precision medical work within our body: delivering medicines, cleaning blood vessels, destroying proliferating tissue.
This idea will probably remain a vision, because nanorobots for these tasks will not be available for a long time yet. Still, Katharina Landfester and her team teach their nanoparticles to do some of these jobs one step at a time – even if they are less spectacular in appearance than nano-science fiction envisaged for the tiny machines.
The researchers headed by Katharina Landfester equip the particles with an opening mechanism, provide them with an anchor for certain cells, or a stealth layer, so that the particles can move though the body unhindered. The particles owe these special accessories to a variety of chemical tricks that the polymer researchers use. But this was made possible only by the fundamental insights Katharina Landfester gained as head of a research group on miniemulsions under Markus Antonietti, Director at the Max Planck Institute of Colloids and Interfaces.
The miniemulsions of the first generation were not suitable for producing a large number of different polymer particles. When the chemists changed their composition, the oil droplets on the water merged to form a layer of oil before the polymer had formed. And when they did stay stable, this was just a matter of chance. At least that is how it appeared. “This made it clear that we had to take a close look at the physical- chemical processes in the miniemulsions,” says Landfester. If these were understood, she thought, it might be possible to specifically select the composition of the miniemulsions so that multifunctional nanoparticles could be produced.
When she explains these connections today, she starts with the factors that keep milk homogeneous: it begins with the proteins that enclose the fat droplets. They act as a surfactant, just like a detergent, which prevents the droplets from merging. Nevertheless, the cream quickly separates out in milk that comes fresh from the cow. Some of its fat droplets are large, and due to their low density, they rise and form a layer of cream. The milk is therefore homogenized: it is sprayed onto a metal plate so that the fat droplets split to form smaller spheres. These are so small that their buoyancy is no longer sufficient to move them to the surface.
The chemists from Mainz homogenize their miniemulsions with an ultrasonication tip. This is routine work for Anna Musyanovych. She heads the group working on chemistry in miniemulsions. The lab specifically equipped for this purpose houses several metal cabinets, each one about the size of a wall cupboard in a kitchen. Anna Musyanovych fixes little glass vessels containing a mixture of oil, water and a surfactant under the ultrasonication tip in such a way that it hangs just above the bottom of the vessels. With a hissing sound and vibrations that are not very strong but very fast, the ultrasonication tip breaks up the oil droplets into nanodroplets.