Background

Penetration of nanoparticles through the skin, and specifically via hair follicles, have emerged as a potential delivery route for drugs. Nanoparticles can serve as carriers for drugs for topical treatments and systemic delivery, directed to the blood vessels at the hair bulb. Various types of nanoparticles were studied for follicular drug delivery, differing from each other by composing materials, size, and shapes (Costa et al., 2021; Patzelt and Lademann, 2013). While our method was developed with gold nanoparticles, this can be relevant for particles made of different materials, such as polystyrene, lipids, etc., and varied fluorescent labeling.

One of the most significant characterizations for follicular nanocarriers is the particles' penetration depth. Determination of penetration depth can be performed using several methods, for instance histology followed by confocal microscopy and tape striping (Escobar-Chávez et al., 2008; Lohan et al., 2017). In our manuscript (Friedman et al., 2021), we have studied the follicular penetration of fluorescently labeled gold nanoparticles, and the impact of particle shape on penetration depth. To assess the depth of penetration into human skin, we have developed a method for the incubation of skin samples with nanoparticles, and the sectioning of samples horizontally and vertically for further confocal microscopy analysis.

In the method detailed here, we are using human skin samples and polymeric nanoparticles with fluorescent labeling. Serial horizontal sectioning of the samples is performed for the evaluation and quantification of the particles in each section using confocal microscopy imaging.