A numerical study on the effect of laser therapy against port-wine stain by administering artificial red blood cells.

Port-wine stain (PWS) is a congenital vascular malformation commonly treated with pulsed dye laser (PDL) therapy. PDL exploits selective photothermolysis, in which hemoglobin in red blood cells (RBCs) absorbs laser energy, generating localized heat that induces endothelial damage. However, in microvessels, axial RBC migration creates a hemoglobin-depleted cell-free layer along the vessel walls, reducing laser efficacy. Hemoglobin vesicles (HbVs)—nano-sized artificial RBCs—distribute uniformly within these layers, offering the potential to enhance hemoglobin distribution and laser absorption. To investigate the impact of HbV administration on PDL therapy, a three-dimensional numerical model of human skin tissue containing vascular networks was developed. Monte Carlo simulations were used to evaluate laser absorption, and thermal conduction analysis was performed to compute temperature distributions and estimate thermal damage via the Arrhenius model. Two conditions were considered: Case 1 (without HbV administration) and Case 2 (with HbV administration). In Case 2, HbV administration increased optical absorption in vessel walls and enhanced thermal damage, particularly in subpapillary vessels. The threshold energy fluence required to induce irreversible thermal damage was reduced, and heat flux at the upper vessel walls was elevated. These findings indicate that HbV administration enhances the homogeneity and efficacy of PDL-induced vascular damage, potentially allowing effective treatment at lower energy fluences while minimizing off-target tissue injury. The study provides a theoretical basis for optimizing PDL parameters in PWS therapy and underscores the potential of patient-specific treatment protocols using artificial blood substitutes.