Skin penetration and distribution of polymeric nanoparticles.

Encapsulation using nanoparticulate systems is an increasingly implemented strategy in drug targeting and delivery. Such systems have also been proposed for topical administration to enhance percutaneous transport into and across the skin barrier. However, the mechanism by which such particulate formulations facilitate skin transport remains ambiguous. In this study, confocal laser scanning microscopy (CLSM) was used to visualize the distribution of non-biodegradable, fluorescent, polystyrene nanoparticles (diameters 20 and 200 nm) across porcine skin. The surface images revealed that (i) polystyrene nanoparticles accumulated preferentially in the follicular openings, (ii) this distribution increased in a time-dependent manner, and (iii) the follicular localization was favoured by the smaller particle size. Apart from follicular uptake, localization of nanoparticles in skin "furrows" was apparent from the surface images. However, cross-sectional images revealed that these non-follicular structures did not offer an alternative penetration pathway for the polymer vectors, whose transport was clearly impeded by the stratum corneum.