Size-dependent penetration of nanoemulsions into epidermis and hair follicles: implications for transdermal delivery and immunization

Abstract

Nanoemulsions have been widely applied to dermal and transdermal drug delivery. However, whether and to what depth the integral nanoemulsions can permeate into the skin is not fully understood. In this study, an environment-responsive dye, P4, was loaded into nanoemulsions to track the transdermal translocation of the nanocarriers, while coumarin-6 was embedded to represent the cargoes. Particle size has great effects on the transdermal transportation of nanoemulsions. Integral nanoemulsions with particle size of 80 nm can diffuse into but not penetrate the viable epidermis. Instead, these nanoemulsions can efficiently fill the whole hair follicle canals and reach as deep as 588 μm underneath the dermal surfaces. The cargos are released from the nanoemulsions and diffuse into the surrounding dermal tissues. On the contrary, big nanoemulsions, with mean particle size of 500 nm, cannot penetrate the stratum corneum and can only migrate along the hair follicle canals. Nanoemulsions with median size, e.g. 200 nm, show moderate transdermal permeation effects among the three-size nanoemulsions. In addition, colocalization between nanoemulsions and immunofluorescence labeled antigen-presenting cells was observed in the epidermis and the hair follicles, implying possible capture of nanoemulsions by these cells. In conclusion, nanoemulsions are advantageous for transdermal delivery and potential in transcutaneous immunization.

Two optical coherence tomography systems detect topical gold nanoshells in hair follicles, sweat ducts and measure epidermis

“…The adnexal structures of skin consist of hairs, hair follicles, sebaceous glands, eccrine glands and sweat ducts delivering the sweat to the skin surface. The hair follicles are pathways from the upper skin layers to lower skin layers and therefore contrast agents can be delivered through the pilous route.…”

Optimized skin optical clearing for optical coherence tomography monitoring of encapsulated drug delivery through the hair follicles

“… In another work, nano‐emulsions with various particle sizes, that include a dye P4 and coumarin 6 as a cargo, have been investigated. The 80‐nm emulsions have penetrated inside the skin along the hair follicle to a depth of 588 μm, and 500‐nm emulsions have been found deposited in the root of the hair follicle after 48 hours of nano‐emulsion application.…”

Bio-Based Nanoemulsion Formulations Applicable in Agriculture, Medicine, and Food Industry

“…On the other hand, NEs with mean particle size of 500 nm, cannot penetrate the stratum corneum and can only migrate along the hair follicle canals, while NEs with median size, e.g. 200 nm show moderate transdermal permeation effect (Su et al 2017). Capsaicin O/W NEs with droplet sizes 20−62 nm were reported to permeate all skin layers from the stratum corneum to the dermis (Kim et al 2014a).…”