Controlled and sustained release properties of polyelectrolyte multilayer capsules

Method of layer-by-layer (LbL) assembly of oppositely charged polyelectrolytes was applied to coat fluorescein particles. These particles with a size of 4-9 m were prepared by precipitation of fluorescein at pH 2. Polysterensulfonate (PSS) and polyallylamine (PAH) were used to compose the polyelectrolyte shell on the fluorescein core. The release of fluorescein molecules through the polyelectrolyte shell core dissolution was monitored at pH 8 by increasing fluorescence intensity. The number of polyelectrolyte layers sufficient to sustain fluorescence release was found to be 8-10. Sequentially adsorbed layers prolong core dissolution time for minutes. The permeability of polyelectrolyte multilayers of the thickness of 20 nm is about 10 −8 m/s. Mechanism of fluorescence diffusion and osmotically supported release is under discussion. The features of release profile and possible applications or LbL method for shell formation in order to control release properties for entrapped materials are outlined. Also ambient conditions of pH, temperature and salt concentration were changed to control the permeability of polyelectrolyte multilayer capsules.