Enhancing, Measuring Skin Penetration

Posted: March 27, 2007

Skin penetration is of great interest to personal care formulators for many reasons—from toxicology concerns to innovative delivery opportunities. With the introduction of nanotechnology to the industry, issues surrounding skin penetration have become more complex. The medical industry has spent much time focused on the mechanisms to increase and decrease skin penetration. Following are a few recent findings related to skin penetration, for your consideration.

According to a report on the University of Irvine, California, Undergraduate Research Opportunities Program Web site, the role of the skin is to provide a barrier to the external environment, which renders the absorption of therapeutic drugs problematic. Preliminary testing has shown that fatty acids such as linoleic acid incorporated into structurally configured polymers can act as penetration enhancers. This modification reportedly alters the barrier properties of the stratum corneum and the migration of topical drugs such as cortisol through human skin. Previous unpublished studies using an amine compound, polyoxyalkyleneamine D 400 (polyamine D 400), have suggested that topical corticosteroid solutions supplemented with novel polymers improve the penetration of therapeutic drugs.

Sets of unique polymers, synthesized at the university’s laboratory, were selected for initial assessment of penetration enhancement using the in vitro Franz diffusion model. The penetration and retention of cortisol into the skin layers were determined by measuring radiolabeled drug levels at the experimental endpoint by liquid scintillation counting. Linoleic acid and polyamine D 400 polymer achieved statistically higher cortisol penetration through the skin when compared to the commercial standard or the vehicle control. In the future, these unique polymers coulud be used as penetration enhancers to improve transdermal delivery of other topical drugs of therapeutic interest. View the complete study (PDF, < 1 MB).

Mid-infrared laser ablation of the stratum corneum is reported to enhance the in vitro percutaneous transport of drugs, according to the Oregon Medical Laser Center. The precise removal of stratum corneum from cadaveric swine skin by a mid-infrared erbium:yttrium scandium gallium garnet laser was assessed by electrical resistance measurements and documented by histology. The effects of stratum corneum removal by laser ablation and by adhesive tape-stripping on the in vitro penetration of 3H-hydrocortisone and 125I-gamma-interferon were determined.

Excised swine skin was irradiated with laser. For skin penetration studies, laser pulses were delivered to discrete 2-mm areas to ablate up to 12.6% of the total 3 cm² stratum corneum diffusional area. Franz in vitro skin penetration chambers were used to measure the cumulative 48 h penetration of 3H- hydrocortisone and 125I-gamma-interferon in laser-treated and tape-stripped skin. Electrical resistance measurements and histologic studies demonstrated that 10-14 laser pulses at the above energy density were required to abolish skin resistance and selectively ablate stratum corneum without damage to adjacent dermal structures.