Transdermal Delivery of Gold Nanoparticles by a Soybean Oil-Based Oleogel under Iontophoresis

Developing a facile mechanism for transporting nanoparticles across the whole skin by overcoming the stratum corneum is a challenging task. Herein, a stimuli-responsive and noninvasive transport of gold nanoparticles (AuNPs) has been reported through the fabrication of AuNP-incorporated soybean oil-based oleogels (AuG) using stearic acid as a gelator. A series of AuG was formulated by incorporating different proportions of AuNPs and a fixed amount of ciprofloxacin hydrochloride (drug) to establish that the composition with the highest concentration of AuNP (d-AuG4) was associated with the best iontophoretic response, validated via the corresponding in vitro drug release under AC field-induced iontophoresis. The sample d-AuG4 exhibited both drug and AuNP permeation across the whole pig ear skin thickness within as early as 1 h under the iontophoresis condition. With relevant control experiments, it was shown that the transport of AuNPs through the stratum corneum tissue and across the whole skin was possible upon the simultaneous fulfillment of two conditions: the presence of a skin permeation enhancer (stearic acid) within the oleogel and iontophoresis. While the literature reported that the permeation time for any free inorganic nanoparticle through the full-skin thickness varied within a few days, the permeation enhancement technique developed here reduced the corresponding delivery time for the AuNPs to a few hours. The extent of AuNP permeation that occurred in the microgram (per cm^-2) scale was found to be affected by the duration of iontophoresis, suggesting that AuNPs' rapid transdermal entry can be simultaneously triggered and modulated by iontophoretic conditions.