Laser skin treatment using micro-lens arrays (MLA) and diffractive optical elements (DOE) have clinically been applied to treat pigmented lesions [1,2]. However, DOE hardly has a deep penetration depth and MLA shows a non-uniform distribution of lesions, making it difficult to target lesions deeply located in the dermis [2]. The purpose of this study is to investigate the feasibility of diffractive lens arrays (DLA, combination of MLA and DOE) to treat the pigmented skin via laser-induced thermal decomposition at various tissue depth. Porcine skin tissue and one farm pig were used to compare spatial distributions of the laser-induced damage after irradiation with DOE, MLA, and DLA. 1064 nm picosecond Nd:YAG laser light was irradiated on a target tissue at 3.0 ~ 6.0 J/cm2 under DOE, MLA, and DLA conditions. According to ex vivo tests, DOE generated laser-induced vacuoles near the basal membrane (208 ± 80 μm), and MLA distributed vacuoles more deeply located in dermis than DOE (382 ± 147 μm). On the other hand, DLA created laser-induced thermal decomposition deeply positioned in dermis (548 ± 137 μm). In vivo tests demonstrated that DOE generated the vacuolization in epidermis and dermis (235 ± 82 μm). On the other hand, DLA generated the deep laser-induced thermal decomposition in dermis (1057 ± 286 μm). The current study demonstrated that the picosecond laser irradiation with DLA could create the thermal decomposition in the deep dermis. Therefore, the DLA-assisted laser application may help to achieve selective skin treatment for deeply located pigments.
Melasma is caused by hyperpigmentation of the skin. The risk factors of melasma include ultra-violet light exposure, hormonal malfunction, and genetic predisposition. However, the precise risk factors of melasma is still unmapped. As melasma occurs regardless of regions and races, treatment planning should consider the optical characteristics of various skin colors to enhance clinical outcomes. The aim of the current study was to evaluate the laser-induced optical breakdown effects during picosecond laser irradiation with micro-lens arrays (MLA) and diffractive optical elements (DOE) on different colors of ex vivo porcine skin tissue. Two different radiant exposures (3.0 and 6.0 J/cm2 ) were irradiated 20 times with a 50-μm lateral movement on the black and white skin tissue that matched with photo skin type Ⅵ and Ⅰ. In the black skin tissue, MLA and DOE yielded laser-induced vacuoles in dermis (vacuole depth = 283 ± 114 μm for MLA vs. 140 ± 62 μm for DOE; vacuole size = 67 ± 34 μm for MLA vs. 40 ± 21 μm for DOE). However, the white skin tissue displayed the deeper and larger vacuoles in the dermis (depth = 368 ± 171 μm and size = 134 ± 100 μm for MLA), compared to the black skin tissue. However, DOE generated photo-disruption in the dermis with no laser-induced vacuolization in the white skin tissue. In conclusion, the white skin could lead to deeper laser-induced vacuoles at larger sizes, compared to the black skin after the picosecond laser treatment with MLA and DOE.
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