Controlled release and targeting of drugs

Multilayers may also be used for their permeation properties. Accordingly, membranes covered by multilayers have been employed for gas permeability measurements and for pervaporation studies [88,181,185,333-335]. These measurements showed, for example, 02/H20,C02/02, or toluene/ heptane selectivity. The permeation properties of polyelectrolyte multilayers are also important when they are used for the encapsulation of enzymes [210] or living cells [336,337]. The deposition of polyelectrolyte multilayers or of hybrid polyelectrolyte/inorganic multilayers on latex particles, and the subsequent dissolution or calcination of the latex beads leads to the fabrication of hollow spheres [94-96,338-340]. Potential applications of such hollow spheres are numerous, for example, for the controlled release and targeting of drugs. 

To fabricate nano-engineered films on colloidal particles a layer-by-layer adsorption of oppositely charged macromolecules is used. Different templates can be coated with multilayer films and decomposed to form hollow capsules with defined size, shape and shell thickness. As example, polyelectrolyte capsules can be used as carrier for biological species, for a controlled release and targeting of drugs and as micro-containers to perform chemical reactions in restricted volumes. 

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