Ex vivo and computational investigation of corneal iontophoresis to enhance penetration of high-molecular-weight compounds: a study using albumin as a model molecule

Efficient ocular drug delivery remains a major challenge due to the strong barrier properties of the corneal epithelium and the rapid clearance of topically applied formulations. This limitation is particularly critical for hydrophilic and high-molecular-weight (HMW) therapeutics such as proteins and biologics. In this study, we investigated transcorneal iontophoresis as a strategy to enhance the delivery of HMW compounds using albumin (66 kDa) as a model macromolecule. Ex vivo rabbit corneas were exposed to iontophoretic currents ranging from 0.5 to 7 mA for clinically relevant conditions, while an extreme non-clinical current (500 mA) was included as a destructive positive control to model irreversible tissue disruption. Albumin permeation was quantified by intrinsic fluorescence spectroscopy, and corneal structural responses were assessed using Fourier-transform infrared (FTIR) spectroscopy. In parallel, computational thermal modeling based on the Pennes bioheat equation was employed to evaluate current-dependent Joule heating and thermal safety margins. Results demonstrated that iontophoresis significantly enhanced albumin transport compared with passive diffusion, with increased permeation at higher currents, particularly at 6-7 mA. Thermal simulations indicated that currents ≤ 2 mA maintained corneal surface temperature within the normal physiological range (32-36 °C), while currents ≥ 3 mA progressively increased corneal temperature, approaching established thermal stress thresholds depending on exposure time. FTIR analysis revealed current-dependent spectral alterations consistent with changes in hydration dynamics, protein conformational environment, and lipid organization, suggesting reversible molecular adaptation at low-to-moderate currents and pronounced disruption at extreme electrical exposure. Collectively, this study identifies a practical current-time operational window for transcorneal iontophoresis that enhances macromolecular transport while maintaining corneal thermal and molecular integrity, supporting its potential for non-invasive ocular delivery of biologic therapeutics.