Nanoemulsions Enhance in vitro Transpapillary Diffusion of Model Fluorescent Dye Nile Red

While the feasibility of transpapillary drug delivery has previously been established, localized transport via the mammary ducts may be improved with tailored drug delivery formulations. The objective of this study was to investigate the impact of nanoemulsion encapsulation on transpapillary delivery in vitro. Nanoemulsion formulations composed of isopropyl myristate and Tween 80 encapsulating a fluorescent dye were applied topically on porcine nipples using a Franz diffusion cell. A combination of dye extraction and fluorescence image analysis was used to quantify the total amount of dye retained within the nipple and to characterize the penetration routes. After diffusion for 6 hours, the amount of dye deposited in the nipple was proportional to the formulation’s water concentration. The 90% water formulation deposited significantly more dye via both the stratum corneum and mammary ducts, while the 80% and 70% water formulations moderately increased ductal penetration, but minimally altered stratum corneum penetration as compared to the control solution. Similar trends were found after diffusion for 48 hours; however, the overall impact was diminished, likely due to the nanoemulsion’s topical instability. This study indicates that drug delivery vehicles, nanoemulsions specifically, enhance delivery of encapsulated molecules via the stratum corneum and mammary ducts in a formulation-dependent basis.