Sustained release properties of polyelectrolyte multilayer capsules

Layer-by-layer (LbL) assembly of oppositely charged polyelectrolytes was used to coat fluorescein particles. These particles, with a size of 4-9 mum, were prepared by precipitation of fluorescein at pH 2. Polystyrensulfonate (PSS) and polyallylamine (PAH) were used to form a polyelectrolyte shell on the fluorescein core. The permeation of fluorescein molecules through the polyelectrolyte shell during core dissolution was monitored at pH 8 by the increasing fluorescence intensity as a result of dequenching. The number of polyelectrolyte layers sufficient to sustain fluorescein release was found to be 8-10. Increasing the number of layers prolonged the core dissolution time for minutes. The permeability of polyelectrolyte multilayers of the thickness of 20 nm for fluorescein is about 10(-9) m/s. The features of the release profile and possible applications of the LbL method for shell formation in order to control release properties for entrapped materials are outlined.