Ex Vivo and In Vivo Histological Evaluation of a 3-μm Wavelength, 40-μm Spot Size Fractional Laser System for Dermatology.

[BACKGROUND AND OBJECTIVES] Ablative fractional lasers are widely used for skin renewal and rejuvenation. The typical diameter of beam incident on skin is in the range 100-500 μm, which has been shown to be safe and effective for skin treatment. This study presents the first in vivo analysis of a novel 3050/3200 nm Difference Frequency Generation laser, which has a beam diameter of 40 μm. The objective is to determine if treatment with such a small beam diameter-microfractional treatment-can induce skin renewal and improvement.

[MATERIAL AND METHODS] Experiments were performed with ex vivo mini-pig skin to determine the correlation between pulse energy and ablation depth. Laser treatment was then performed on in vivo human abdominal skin, which was planned for removal with abdominoplasty. Various pulse energies (range 3-29 mJ) and numbers of dots per cm² (range 2600-441 dost/cm) were applied at 3 months, 1.5 months, 7 days, and 48, 24, and 2 h before surgery. Excised skin samples were analyzed using hematoxylin and eosin staining to assess tissue morphology, immunochemistry to determine expression of transforming growth factor-β (TGF-β) and inflammatory markers, and enzyme-linked immunosorbent assay (ELISA) to quantify procollagen I synthesis.

[RESULTS] Pulse energy (range 2-40 mJ) can be chosen to obtain desired ablation depth (150-2000 μm)-this relationship was obtained. The microfractional skin ablation allows application of a high density, that is, number of dots per cm² with subsequent healing in a scar-free manner. The main steps of the regeneration processes induced by 3-μm laser are similar to those induced by other lasers. The treatment resulted in an increased number of fibroblasts (1.7-2.7 fold change), procollagen I synthesis (1.4-3.4 fold change), and neovascularization (1.9-2.7 fold change) 3 months after treatment. We also observed changes in the TGF-β isoforms, CD68, and neutrophil elastase, with timing of the changes showing slight dependance on treatment parameters. Finally, tissue response in terms of collagen synthesis and neovascularization is correlated with tissue ablation volume.

[CONCLUSION] The microfractional 3050/3200 nm laser treatment enables application of a high dot number/cm density, resulting in scar-free healing and tissue renewal and improvement. This makes it an efficient alternative to other fractional devices, offering advantages such as ease of use, and potentially reducing the number of treatment sessions required.