Molecular insights into the effects of laser-induced optical breakdown (LIOB) after 1064 nm picosecond laser irradiation using a novel melanocyte-containing 3D skin model

Abstract Picosecond lasers use a mechanism known as laser-induced optical breakdown (LIOB). However, the underlying molecular mechanisms are not yet fully understood. The aim of this study was to gain insights into the molecular effects of LIOB using novel melanocyte-containing 3D skin models. Since the threshold of LIOB depends on the melanin content of the skin, we established a new human 3D skin model comprising melanocytes. Irradiation was done with a diffractive optical elements (DOE-) assisted fractional 1064 nm Nd: YAG picosecond laser utilizing the energy setting of 0.2 J/cm 2 , with a spot size of 7 × 7 mm and one pulse per area. In a further approach, we post-treated the models topically with a dexpanthenol-containing ointment. Examination was done histologically and using next-generation sequencing. The histological analysis revealed intra-epidermal vacuoles with an intact environment immediately after irradiation of the models and even after 24 h. Post-treatment with the dexpanthenol-containing ointment accelerated the repair processes in the models, with vacuoles no longer visible after 24 h. We found an upregulation of matrix metalloproteinases, collagens, heat shock proteins, cytokines and chemokines, reflecting repair mechanisms and tissue remodeling after picosecond laser irradiation. Initial stimulation effects of laser therapy were maintained even after topical dexpanthenol post-treatment. We present the first in vitro study investigating the effects of LIOB after 1064 nm picosecond laser irradiation using a novel standardized melanocyte-containing 3D skin model. LIOB-induced intraepidermal vacuoles promoted skin regeneration processes, which could be supported and accelerated by post-treatment with a dexpanthenol-containing ointment.