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

Port-wine stains (PWS) are congenital vascular malformations typically treated using pulsed dye laser (PDL) therapy. This method exploits selective photothermolysis, wherein hemoglobin in red blood cells (RBCs) absorbs laser energy, inducing localized heat generation and subsequent endothelial damage. However, in microvessels, axial migration of RBCs results in a hemoglobin-depleted cell-free layer along the vessel walls, limiting laser efficacy. Hemoglobin vesicles (HbVs)—nano-sized artificial red blood cells—can distribute uniformly within these layers, potentially enhancing hemoglobin distribution and laser absorption. In this study, we constructed a three-dimensional numerical model of human skin tissue containing vascular networks to simulate the effects of HbV administration on PDL treatment outcomes. A Monte Carlo simulation was employed to evaluate light absorption, followed by a Thermal conduction analysis to compute temperature distributions and calculate thermal damage using the Arrhenius model. Simulations were performed for two conditions: Case 1 (without HbV administration) and Case 2 (with HbV administration). Results showed increased absorption in vessel walls and enhanced thermal damage in Case 2, particularly in subpapillary vessels. Importantly, the threshold energy fluence required for irreversible thermal damage decreased with HbV administration. Furthermore, HbV usage increased heat flux in upper vessel walls, aligning with previously reported thrombus formation patterns. These findings suggest that HbV administration improves the uniformity and efficacy of PDL-induced vascular damage, potentially enabling treatment at lower energy fluence and reducing off-target tissue injury. This study provides a foundation for optimizing PDL parameters in PWS treatment and highlights the potential for patient-specific protocols using artificial blood substitutes.