The fabrication of functional hybrid materials composed of nanoscale building blocks represents one way in which nanotechnology can contribute to biology and medicine. For example, the synthesis of three-dimensional hollow sphere structures has attracted enormous interest in recent years for a variety of different applications, ranging from drug delivery systems and targeted gene therapy to biosensor devices.

Hereby, the fundamental challenge is to fabricate biocompatible multifunctional vehicles whose properties can be tuned at the nanoscale. In this context several systems have been suggested and also demonstrated, such as liposomes, block copolymers, and dendrimer polymers. Polyelectrolyte multilayer capsules, e.g. polymer walls around cavities, have also been used in such systems for several reasons. Firstly, they can be synthesized under mild conditions by using numerous different materials. Secondly, their functional properties can be well-defined by embedding different nanoscale building blocks (as colloidal inorganic nanoparticles or biomolecules) within and on top of their wall. Thirdly, they can efficiently host (biological) macromolecules within their cavity for numerous biomedical applications. Finally, they can be composed of biocompatible materials for the delivery of encapsulated materials into cells.