Skin is a multilayered organ which covers and protects the surface of human body by providing a barrier function against exogenous agents. Meanwhile, the efficacy of several topically applicated drugs is directly related to their penetration through the skin barrier. Several techniques are commonly used to evaluate the rate, the speed and the depth of penetration of these drugs, but few of them can provide real-time results. Therefore, the use of nondestructive and structurally informative techniques permits a real breakthrough in the investigations on skin penetration at a microscopic scale. Confocal Raman microspectroscopy is a nondestructive and rapid technique which allows information to be obtained from deep layers under the skin surface, giving the possibility of a real-time tracking of the drug in the skin layers. The specific Raman signature of the drug enables its identification in the skin. In this study, we try to follow the penetration of Metronidazole, a drug produced by Galderma as a therapeutic agent for Rosacea treatment, through the skin. The first step was the spectral characterization of Metronidazole in the skin. Then micro-axial profiles were conducted to follow the penetration of the drug in the superficial layers, on excised human skin specimens. For more accurate information, transverse sections were cut from the skin and spectral images were conducted, giving information down to several millimeters deep. Moreover, the collected spectra permit us to follow the structural modifications, induced by the Metronidazole on the skin, by studying the changes in the spectral signature of the skin constituents.

Human skin is directly exposed to different exogenous agents. Many research works have studied the diffusion, interactions, absorption mechanisms, and/or toxicity of these agents toward different cutaneous structures. With the use of living animals for such tests being more and more rejected; and the number of human volunteers being limited; different types of skin models are used. In the last few years, reconstructed epidermis from cell cultures has been frequently employed, and recent changes in the European chemical policy have approved and encouraged the use of these reconstructed models for skin‐related research works and assessments. Among the techniques used actually to study the skin, Raman microspectroscopy is a rising and powerful nondestructive technique that detects characteristic molecular vibrations. In this study, we created a spectral database to index the vibration peaks and bands of a well‐known reconstructed epidermis model, the Episkin®. The comparison with a native epidermis signal enabled us to put in evidence several spectral differences associated with molecular and structural differences between the skin and the reconstructed model, both maintained in living conditions. In addition to that, we have showed the feasibility of tracking the penetration of a pharmaceutical molecule through the Episkin model. © 2007 Wiley Periodicals, Inc. Biopolymers 87: 261–274, 2007.This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com

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Background and Objectives: Although laser skin resurfacing performed with CO 2 or Er:YAG lasers is efficient, side effects such as prolonged postoperative erythema, delayed healing, scarring, and pigmentation, have been reported. These side effects are due to skin characteristics but also to variations of the thermal effects associated with laser skin resurfacing. The study aimed to evaluate a new laser resurfacing method based on a previous topical application of an exogenous chromophore in order to have reproducible thermal effects. Materials and Methods: Exogenous chromophore consisted in carbon dispersed and mixed with film-forming polymers and water. The resultant solution was applied to the skin surface using an airbrush. Experimental evaluation was performed in vivo on hairless rat skin using the following parameters (532 nm, 2.7 W, 1 mm, 50-200 ms, 17.2-68.8 J/cm 2 , single pass). Skin biopsies were taken to evaluate histological changes and to quantify epidermis ablation and dermal coagulation depth. Wound healing was followed up during 10 days. Results: Total epidermis ablation was achieved with all pulse durations used. Dermal coagulation depth increased as a function of exposure time. Scar formation was correlated with dermal coagulation depth. Conclusion: The concept of applying a carbon-based solution onto skin in order to obtain laser light conversion into heat followed by heat transfer to the tissue is valid for laser skin resurfacing. By selecting exposure time, the thermal effects are predictable and dermal coagulation depth can be either that observed with a Er:YAG laser or that obtained with a CO 2 laser. Moreover, frequency doubled Nd:YAG laser, already used in dermatology for angiodysplasias treatment, could be easily used for resurfacing of periorbital or perioral zones. Lasers Surg. Med. 25:43-50, 1999.

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