In silico Evaluation of Near-Infrared Laser Irradiation for Safe and Effective Laser Adjuvants in Human Skin

Purpose This study was performed to explore the potential of a novel vaccine adjuvant using near-infrared light (1064 nm and 1270 nm) by investigating effective irradiation conditions in human skin through ray-tracing and heat-transfer simulations. Results Ray-tracing and heat-transfer simulations in mouse skin validated the model. Under irradiation conditions comparable to those used in mice, neither wavelength (1064 nm nor 1270 nm) delivered sufficient light to the connective tissue in human skin, and the potential for thermal skin damage was observed. The simulations demonstrated that appropriate adjustment of irradiance enables effective and safe irradiation conditions to be achieved. Discussion Pulsed irradiation at 1064 nm with an irradiance of 100 W/cm ² , a 60 s irradiation time, a 2.5 Hz frequency, and a 0.01 s pulse width, as well as 1270 nm with an irradiance of 60 W/cm ² , a 60 s irradiation time, a 2.5 Hz frequency, and a 0.01 s pulse width, efficiently promoted light penetration into the deeper connective tissue while suppressing the increase in skin surface temperature compared with continuous irradiation. Conclusion The simulations strongly support the potential effectiveness of laser adjuvants for human applications. Future work should focus on optimizing experimental and clinical use based on the numerical analysis results, thereby enhancing the generalizability and clinical relevance of the model developed in this study.