Enhancing Topical Delivery of Hydrophobic Drugs: A Study on Elongated Silica Microparticles and Tailorable Nanoemulsions

This study is the first of its kind to test the use of elongated silica microparticles (EMP) and tailorable nanoemulsions (TNE) to improve the topical delivery of hydrophobic drug surrogates.

The EMPs penetrate through the skin's outer layer and stop at the dermal-epidermal junction (DEJ), while the TNEs, which are highly stable, allow for high drug loading levels due to their oil core.

The researchers used a fluorescent lipophilic dye, DiI, as a hydrophobic drug surrogate and tested four different coating approaches to combine EMP and TNE in human skin. They also used 6-carboxyfluorescein, a model molecule for topically delivered hydrophobic drugs, in volunteers for the first time. 

Industry application

This research is relevant to the pharmaceutical and healthcare industries, particularly those involved in the development and application of topical drug delivery systems. 

The study found that EMPs can penetrate to the DEJ and then release the TNEs in a controlled manner. The freeze-dried formulations with crosslinking resulted in a sustained release profile, while those without crosslinking showed an immediate burst-type release profile.

The imaging data from volunteers showed a 6-carboxyfluorescein signal deep in the skin, supporting the hypothesis that EMP can enhance the delivery of TNE in human skin.

No adverse events were recorded, suggesting that 6-carboxyfluorescein is a safe and detectable drug surrogate for topical drug research.

The study concluded that dry formulations with controllable release profiles can be obtained with TNE coated EMP, effectively enhancing the delivery of hydrophobic payloads deep into the human epidermis.

Yamada M, Tayeb H, Wang H, Dang N, Mohammed YH, Osseiran S, Belt PJ, Roberts MS, Evans CL, Sainsbury F, Prow TW. Using elongated microparticles to enhance tailorable nanoemulsion delivery in excised human skin and volunteers. J Control Release. 2018 Oct 28;288:264-276. doi: 10.1016/j.jconrel.2018.09.012. Epub 2018 Sep 15. PMID: 30227159; PMCID: PMC7050638.