Angewandte Chemie International Edition
© WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
For full article and contact information, see Angew. Chem. Int. Ed. 1998, 37 (16), 2201 - 2203
Drugs in Satchels
Berlin Researchers develop a microscopically small
packaging system for transport of medication
We are all familiar with the idea of using plastic carrier bags to take our shopping home. Molecules can be packed up in a similar way - for example in the microscopically small plastic hollow spheres made in the laboratory by Edwin Donath, Gleb B. Sukhorukov, Frank Caruso, and Sean A. Davis in the Helmuth Möhwald Department at the Max-Planck Institute for Colloid- and Surface-Boundary Research in Berlin. These containers are simpler to handle and produce than previously known systems such as microcapsules and lipid vesicles; one possible application for them is in the transport of medication inside the human body.
Donath and his co-workers have prepared the "microsatchels" using a technique reminiscent of the way children make paper lanterns at kindergarten out of a balloon, transparent paper, and paste. Firstly, following a known process, they make tiny spheres out of a solid, electrically charged material with the crucial property that it dissolves in hydrochloric acid. Then they deposit a layer of material with the opposite charge on the surface of these spheres. On top of this layer follows another charged layer, but again with a charge of opposite sign to the preceding one - and so on, until an onion-like structure with between four and nine layers and a hard nucleus is formed from the original sphere. Because the layers of opposing charge attract each other, the thin shells are held very firmly together. The inner material is then removed with hydrochloric acid, leaving the empty shells behind; they survive the acid just like the hardened shell of a paper lantern when the balloon inside is popped. What is more they can be folded and crumpled without being destroyed.
The "mini plastic bags" are only a fraction of a thousandth of a millimetre in size; under even very powerful microscopes they show a relatively smooth surface; nevertheless they possess tiny pores through which small molecules can pass effortlessly. This is obviously important because otherwise they could not be used to transport anything, and is an advantage over previously known lipid vesicles - relatively loose hollow balls made from fat molecules - which do not allow many types of pharmaceutical molecule through their layers.
Meanwhile the Max-Planck researchers find it a waste to restrict the use of the microspheres to just the transport of chemicals. In particular they aim to use the mini-vessels as miniaturized test tubes for chemical reactions: they have already been able to grow tiny crystals inside the spheres.