Control of size and permeability of nanocomposite microspheres

This work reports on progress in controlling the size and porosity of spontaneously assembled composite polyelectrolyte microspheres for their potential use in targeted drug delivery applications. In this study, the composite polyelectrolyte microsphere is exemplified by PLK/TSC containing magnetic nanoparticles. The stability of these microspheres against environmental alterations such as pH, ionic strength, and dilution is a critical issue for practical considerations. The effects of ionic strength and dilution on the size of these hybrid spheres were investigated by the addition of salts with different cationic charges and deionized water. Increasing both ionic strength and dilution caused a decrease in the average size of microspheres from similar to 700 to similar to 200 nm. Ions of +2 charge were observed to screen interactions between the assembling components via a substitution effect. The composite polyelectrolyte microspheres could be mechanically stabilized by cross-linking with glutaraldehyde (GA). The microsphere permeabilities were analyzed using fluorescein-tagged dextran molecules of different MW with confocal laser scanning microscopy and fluorescence recovery after photobleaching. Microsphere permeabilities and critical pore sizes could be controllably decreased by altering the extent of cross-linking, which was monitored by UV-vis spectroscopy. Quantitative analysis revealed that cross-linking can be used to control the diffusion coefficient of dextran and can reduce it by 4 orders of magnitude.