Although it examined an uncommon nanomaterial (fluorescent food dye) of a size that is not truly nanoscale (320 nm), a recent paper looked into the ability of nanoparticles to penetrate into hair follicles for potential drug delivery purposes.
The paper used in vitro porcine skin testing to compare the penetration abilities of nano food dye against the same substance in non-nano form. The scientists found the nano food dye penetrated much deeper into hair follicles than its counterpart when a mechanical massage was applied to the porcine skin. Penetration results without massage were essentially the same for the two materials. The study concluded “movement of hairs may act as a pumping mechanism pushing the nanoparticles deep into the hair follicles.”
The scientists also conducted a second experiment — in vivo human skin — to determine how long the nano food dye was retained in hair follicles compared to its non-nano counterpart. The scientists found the nano food dye was stored in hair follicles for 10 days, while its counterpart was stored for only 4 days. As a result, the paper concludes “hair follicles represent an efficient reservoir for topically applied substances,” and noted this "reservoir" extends up to 200 nm into the underlying tissue. The scientists also explained the follicle "release" mechanism was natural sebum production.
Combining both tests, the scientists believe hair follicles may be used as a successful reservoir for possible use in nanoscale dermal drug delivery applications. The paper concludes particle size “plays an important role in follicular penetration," and “[p]enetration into the hair follicles is a fast process in comparison to the release of the nanoparticles our of the follicles, which continues for some days.”
J. Loderman, et al., “Nanoparticles — An efficient carrier for drug delivery into the hair follicles,” European Journal of Pharmaceuticals and Bio pharmaceutics,” Vol. 66, Issue 2, p. 159-164 (May 2007).