The precise removal of stratum corneum from cadaveric swine skin by a mid-infrared erbium:yttrium scandium gallium garnet laser ( \lambda = 2.79 µ m; 250 µ s pulse width) 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 (1 J/cm 2 ; 31 mJ/pulse; 1 Hz; 2 mm spot diameter). For skin penetration studies, laser pulses were delivered to discrete 2 mm areas to ablate up to 12.6% of the total 3 cm 2 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. Laser ablation of 12.6% of the surface area of stratum corneum produced a 2.8 and 2.1-times increase in permeability constant (kp) for 3H-hydrocortisone and 125I-gamma- interferon, respectively. These studies demonstrate that a pulsed mid-infrared laser can reliably and precisely remove the stratum corneum, facilitating penetration of large molecules such as 125I-gamma-interferon that cannot penetrate intact skin. This new technique may be useful for basic and clinical investigation of skin barrier properties.
J. S. Nelson, J. L. McCullough, T. C. Glenn, W. H. Wright, L. H. Liaw, S. L. Jacques, "Mid-infrared laser ablation of stratum corneum enhances in vitro percutaneous transport of drugs," Journal of Investigative Dermatology,97, 874- 9 (1991).