Biological cells as templates for hollow microcapsules

Microcapsules in the micrometer size range with walls of nanometer thicknes s are of both scientific and technological interest, since they can be empl oyed as micro- and nano-containers. Liposomes represent one example, yet th eir general use is hampered due to limited stability and a low permeability for polar molecules. Microcapsules formed from polyelectrolytes offer some improvement, since they are permeable to small polar molecules and resista nt to chemical and physical influences. Both types of closed films are, how ever, limited by their spherical shape which precludes producing capsules w ith anisotropic properties. Biological cells possess a wide variety of shap es and sizes, and, thus, using them as templates would allow the production of capsules with a wide range of morphologies. In the present study, human red blood cells (RBC) as well as Escherichia coli bacteria were used; thes e cells were fixed by glutardialdehyde prior to layer-by-layer (LbL) adsorp tion of polyelectrolytes. The growth of the layers was verified by electrop horesis and flow cytometry, with morphology investigated by atomic force an d electron microscopy; the dissolution process of the biological template w as followed by confocal laser scanning microscopy. The resulting microcapsu les are exact copies of the biological template, exhibit elastic properties , and have permeabilities which can be controlled by experimental parameter s; this method for microcapsule fabrication, thus, offers an important new approach for this area of biotechnology.