Non-ablative fractional laser: Dr. Woan-Ruoh Lee et al. used non-ablative fractional 1,550 nm Er-glass laser (Dinona, Sellas evo®, Daejeon, Korea) as an enhancement approach to promote drug permeation. The spot size of MTZ at the target was 100 μm. The spot densities used in this study were 256 and 529 spots/cm2. The pulse time was <1 ms with one pulse on the skin phase. The laser fluence of 30 mJ was generated on the pigs and nude mice skin with air cooling. The fractional laser selectively created an array of photothermal dots deep into the dermis with the preservation of the stratum corneum and epidermis.
The barrier function of the skin could be recovered 8–60 h post-irradiation depending on the laser spot densities. Quantum dots with a diameter of 20 nm penetrated into the skin with the assistance of the non-ablative laser. Skin delivery of dextrans with a molecular weight of at least 40 kDa could be achieved with the Er-glass laser, too. The penetration enhancement level by the laser was decreased following the increase of permeant lipophilicity (for example, 2 folds for tretinoin v.s. 1200 folds for 5-aminolevulinic acid).
Hair regeneration
Non-ablative fractional laser: Recently, non-ablative laser has been proposed as a potential treatment for alopecia. Yueh-Feng Wu et al. irradiated mice skin with a 1,550-nm fractional Er-glass laser (Fraxel RE: STORE SR 1,500 Laser System, Solta Medical, U.S.A.) with varied beam energies (5–35 mJ) and beam densities (500–3,500 MTZ/cm2). Anagen induction in the irradiated skin showed an all-or-none change. As beam energy increased from 10 mJ to 35 mJ, they found a decreasing trend of beam density (25 mJ with 500 MTZ, 15 mJ with 1000 MTZ, or 10-12 mJ with 1500 MTZ) that could induce anagen entry within 7–9 days with activation of hair follicle stem cells. A threshold change within the irradiated skin should be induced by laser before hair can regenerate.
Above this threshold, all the hair follicles within irradiate skin enter anagen. Appropriate laser irradiation here may induce inflammation comparable to skin adjacent to an open wound and this inflammation may directly or indirectly induce anagen entry. Anagen induction and ulcer formation were affected by the combination of beam energy and density. Intense and persistent inflammation leads to ulcer formation, followed by scarring. By choosing an appropriate therapeutic window of energy and density, physicians can create anagen induction without ulcer formation.
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Cosmetic tattoo removal
Ablative fractional laser: Since the introduction of fractional laser to Taiwan, its most application is for depressed acne scar. Because it is very difficult to remove cosmetic non-black colored tattoos, Dr. Chia-Chen Wang et al. studied CO2 ablative fractional resurfacing (120 μm spot size, 17.5 mJ, 10% density) to treat white and flesh-colored cosmetic tattoos on rats for five sessions at 1-month intervals. As we mentioned before, they found immediate ablation of tattoo pigments in the MTZ. Tattoo pigments in the MTZ migrated to the epidermis and became part of the microscopic exudative necrotic debris appearing on day 2 that was exfoliated after 5 days.
-To be continued
