Photothermal transport for guiding nanoparticles through the vitreous humor

Visual impairments affect over 2.2 billion people worldwide, yet delivering drugs to the eyes posterior segment, including the retina, remains a major challenge. Intravitreal injection, the standard administration route to the posterior segment of the eye, often results in suboptimal drug diffusion through the vitreous, preventing drugs from reaching the retina. While various strategies have been explored to enhance the mobility of drug molecules and nanomedicines (drugs encapsulated in nanoparticles) in the vitreous, no method has demonstrated guided transport of drugs and particles through the vitreous. In this study, we explore photothermal transport of nanoparticles in the vitreous using a pulsed-laser and indocyanine green added to the vitreous, both being clinically approved modalities. We found that photothermal transport allows to guide nanoparticles from one place in the vitreous towards the laser illuminated area in the vitreous, at a distance of the injection spot of the nanoparticles. Using multiple-particle tracking and numerical simulations, we found that both thermal convection and thermophoresis contribute to photothermal transport of nanoparticles in the vitreous. We identified parameters for optimizing this effect, including dye concentration, particle size, distance from the laser focus, and laser fluence. Our findings establish a novel and clinically relevant paradigm for light-guided drug delivery in the eye. This study represents, to our knowledge, the first demonstration of guided light-controlled particle transport in the vitreous using ocular dyes and pulsed-lasers which are routinely used in ophthalmology.