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Abstract
In the present study, the influence of vesicle size on the penetration of two fluorescently
labeled substances into the human skin was investigated. For the measurements either
a hydrophilic fluorescent compound [carboxyfluorescein (CF)] or a lipophilic one [1,1'-dioctadecyl-3,3,3',3'-tertramethylindocarbo-cyanine
perchlorate (DiI)] were encapsulated into vesicles. Liposomal formulations were prepared
by extruding the vesicles through polycarbonate membrane filters with pores of different
sizes. In vitro penetration studies into human abdominal skin were performed by using
the Franz diffusion cell and a standardized skin stripping technique in attempt to
find an optimum size for topical drug delivery by liposomes. Confocal laser scanning
microscopy (CLSM) was used to visualize the effect of penetration ability of liposomal
DiI. The maximum DiI fluorescence in the skin was observed with smaller liposomes
of 71 nm diameter. The liposomes with a size of 120 nm diameter showed statistically
enhanced penetration of CF into the skin as compared to larger ones. The results indicated
that the CF penetration was inversely related to the size of the liposomes, which
was confirmed by the data of the confocal laser scanning microscopy studies.