Microencapsulation of uncharged low molecular weight organic materials by polyelectrolyte multilayer self-assembly

Two uncharged microcrystalline substances, pyrene (PYR) and fluorescein dia cetate (FDA), were rendered water dispersible by treatment with various amp hiphilic substances and subsequently encapsulated by exposure to an alterna ting sequence of cationic and anionic polyelectrolytes. The amphiphilic com pounds employed to charge the microcrystals were ionic surfactants, phospho lipids, and polyelectrolytes with an amphiphilic nature. Polyelectrolyte la yers were self-assembled onto the pre-charged microcrystalline templates by means of electrostatic layer-by-layer deposition, thus forming a multilaye red polymeric shell around the crystalline cores. The semipermeable nature of the polymer multilayer shell was thereafter exploited to remove the temp lated core by exposure to a mild organic solvent. The release behavior of s olubilized PYR and FDA from the crystalline core was examined by monitoring their fluorescence after dissolution with ethanol. Complete removal of the core yielded hollow polymer capsules of micrometer dimensions. The capsule porosity was found to be influenced by the amphiphile used to pre-charge t he microcrystal surface. The strategy presented is expected to be a general approach for the encapsulation of hydrophobic, low molecular weight compou nds such as drugs, as well as providing a novel and facile pathway to the f abrication of polymer multilayered microcapsules with controlled release pr operties for drug delivery.