Permeability of Ibuprofen in Various Polyelectrolyte Multilayers

Ibuprofen microcrystals sized between 25–45 μm have been encapsulated with various types of polyelectrolyte multilayers (PEMs) constructed with polyallylamine (PAH), polyethylenimine (PEI) or poly(4-vinylpyridine) (P4VP) as polycations and polystyrenesulfonate (PSS), polyanetholesulfonate (PAS) and dextran sulfate (DEXS) as polyanions. The release of ibuprofen from the microcapsules was monitored in situ by UV-vis spectroscopy for the quantitative characterization of PEM permeability. Our results revealed that PEMs formed by PAH/DEXS, PEI/PSS, P4VP/PSS and P4VP/PAS are highly permeable to ibuprofen because their film cavities are much larger than the size of ibuprofen molecules. The PEMs formed by PAH/PSS and PAH/PAS are less permeable to ibuprofen due to their smaller film cavities. It is believed that the high charge density and well-matched charge interactions between the coupling polyions in PAH/PSS and PAH/PAS multilayers allow the films to form small cavities. In addition, it was found that the permeability coefficient of PEMs decreases with increasing multilayer thickness before the film reaches a certain number and achieves structural homogeneity. Above that, the permeability coefficient remains constant with further increase of film thickness.