The packaged particles of magnetite also need a stealth layer so that the immune system guards do not fish the foreign particles out of the blood vessels on the way to their target cells. The cornucopia of polymers also provides the researchers with a suitable material: polyethylene glycol, PEG for short, which does not set alarm bells ringing in the immune defense system. The researchers then also stir constituents with PEG appendages into the magnetite packaging mix. The finished particles now not only carry hooks for the biochemical address labels, but also camouflaging PEG chains.
There is only one problem with the idea of ingenious multifunctional packaging for the magnetite particles: the particles initially oppose any type of polymeric capsules. If Anna Mus yanovych were to mix them with oil, water and the other constituents, they would then float only in the aqueous part and not in the oil droplets: magnetite clearly prefers to spend its time in water. “We must therefore hydrophobize the magnetite particles,” says Anna Musyanovych. The chemist reverses the preference for an aqueous environment into a preference for an oily environment by first surrounding the magnetite particles with a film of oleic acid before packing them into the multifunctional capsule.
If the nanoparticles allow themselves to be specifically sent to particular cells, it stands to reason that they could also be used as drug carriers. But active substances that are encapsulated in solid polymeric spheres are of no help here. They really need to arrive at the place they are to do their work in liquid form. And there is the additional point that some contrast agents for magnetic resonance imagers are available only in liquid form. “Our next thought was thus to encapsulate a liquid,” says Katharina Landfester. And an aqueous one, if possible, because the capsule contents with a dissolved active agent should ultimately mix with the aqueous medium of the cell interior.
At that time, the researchers already had a solution ready by which to create polymers in droplets of water: the inverse miniemulsion. It consists primarily of oil containing floating droplets of water. The starting materials of the polymer that form in the droplets must now dissolve in water instead of oil. And there are plenty of these substances around, as well.