This study systematically investigates the oxygen and carbon dioxide permeability of dry gases and those dissolved in water through hydrophobic high free-volume silicon- or fluorine-containing nonporous glassy polymers including poly(trimethylsilylmethylmethacrylate) (PTMSMMA), poly(1-trimethylsilyl-1-propyne), 4,4′-(hexafluoroisopropylidene) diphthalic anhydride-4,4′-(9-fluorenylidene) dianiline, and 4,4′-(hexafluoroisopropylidene) diphthalic anhydride-2,3,5,6-tetramethyl-1,4-phenylene-diamine. The dry state gas permeability coefficient was almost higher than that of the wet state because the effect of the boundary layer, which is the water resistant layer, on the membrane surface depends on the gas permeability in the wet state. In addition, the gas permeability difference between the dry and wet states depends on the combination of competitive sorption between water and gas species and plasticization by water. Carbon dioxide/oxygen permselectivity increased with the decrease in gas permeability, except for PTMSMMA. The gas permeability in the wet state of PTMSMMA with low glass transition temperature was approximately equal to that in the dry state because plasticization by water increased in the wet state. Therefore, the mobility of the polymer segment depends on the plasticization by water.

-PURPOSE: Enhance skin penetration of hydrophilic and lipophilic compounds using liposomes that are responsible to the pH of the skin surface. METHODS: pH-sensitive liposomes were prepared by a thin layer and freeze-thaw method with dioleoyl phosphatidyl ethanolamine and cholesteryl hemisuccinate. Liposomal fusion with stratum corneum lipid liposomes was measured using fluorescence resonance energy transfer. Particle diameter and zeta potential of the liposomes after fusion were measured by dynamic light scattering and electrophoresis. RESULTS: Under neutral pH conditions, the diameter of the pH-sensitive liposomes was 130 nm and their zeta potential was -70 mV. In weakly acidic conditions, the diameter was larger than 3,000 nm and the zeta potential was -50 mV. In contrast, the particle diameter and the zeta potential of the non-pH-sensitive liposomes remained constant under various pH conditions. A skin penetration study was performed on hairless mice skin using vertical diffusion cells, showing that the fusion ability of pHsensitive liposomes was higher than that of non-pH-sensitive liposomes. In the skin penetration study was carried out using hydrophilic (calcein) and lipophilic (N-(7-nitrobenz-2-oxa-1,3-diazol-4yl)-PE) (NBD-PE) model compounds which were applied to the skin with pH-sensitive liposomes as carrier. The fluorescent compounds contained within the pH-sensitive liposomes permeated the skin more effectively than those within non-pH-sensitive liposomes, and this ability was further enhanced with the lipophilic compound. CONCLUSION: These studies suggest that pH-sensitive liposomes have potential as an important tool for delivery of compounds into the skin.

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