Effect of Polymer-stabilized Liquid-liquid Phase Separation on the Permeability Across the Corneal Barrier.

Liquid-liquid phase separation (LLPS) is a metastable state in which a highly supersaturated solution phase separates into a drug-rich nanoaggregate phase dispersed in a drug-lean phase. LLPS-driven formation of drug-rich nanoaggregates has emerged as a key determinant of oral drug absorption. Despite this growing recognition, the influence of LLPS on ocular delivery remains unexplored. In this study, we investigated whether the nanoaggregate phase generated by LLPS modulates transcorneal permeation and compared the resulting drug flux with that of a dialysis membrane. Ketoconazole (KTZ) undergoes LLPS by gradual addition of a DMSO solution in simulated tear fluid (STF), pH 7.4, in the presence and absence of a polymer (HPMC-E15). The LLPS onset concentration and its stability were characterized by turbidity at 500 nm and count rate (kcps) using dynamic light scattering (DLS). Permeability studies were conducted using a diffusion experiment, and fluorescence microscopy was performed to investigate the uptake of a lipophilic dye Nile Red in the corneal membrane. Our findings demonstrate that polymer-stabilized nanoaggregates formed via LLPS significantly enhance flux across porcine cornea (p < 0.05). Diffusion assays combined with fluorescence microscopy suggest that this enhancement could be due to direct uptake of nanoaggregate phase or rapid partitioning of free drug into the corneal epithelium, facilitating transcorneal permeation. Strikingly, this effect was absent in the dialysis membrane, underscoring the role of biological tissue architecture in governing drug diffusion. The corneal permeation assay is not only a biorelevant model but also a discriminatory platform for evaluating LLPS-derived nanoaggregates.