In Vitro Characterization of Insulin-Loaded Soft Contact Lenses and Their Effect on Corneal Epithelial Cell Viability and Permeability

Background/Objectives: Corneal epithelial defects and ulcers remain a significant clinical challenge, often leading to vision impairment and requiring prolonged treatment. In this context, topical insulin has recently gained attention in ophthalmic research. However, conventional eye drops suffer from short residence time and poor bioavailability. To overcome these limitations, the present study evaluates, for the first time in vitro, multiple commercially available soft contact lenses as sustained insulin delivery platforms, analyzing how protein loading influences the essential physicochemical and optical properties of these materials. Methods: The physicochemical properties of eight different commercially available soft contact lens materials, including light transmittance, wettability, and central thickness, were examined before and after insulin loading via a soaking method. Loading efficiency and in vitro release profiles were assessed over time. Corneal cytotoxicity and permeability were evaluated using a human epithelial cell-based model (HCE-2). Results: Among the eight commercial materials screened, Nesofilcon A, Stenfilcon A, and Delefilcon A were selected due to their superior physicochemical performance after insulin loading. At initial concentrations of 1750 and 875 μg/mL, drug loading efficiency reached maximum values of up to 69.3% and 63.1%, with cumulative release values reaching up to 32.4% and 55.1% after 24 h, respectively. Permeability studies confirmed effective insulin diffusion across the HCE-2 cell layer, while cell viability assays indicated no significant cytotoxicity at the lower loading concentration. Conclusions: Insulin-loaded commercial soft contact lenses represent a promising drug–device combination product for the management of persistent epithelial defects and refractory corneal ulcers. These in vitro findings suggest that this approach may enhance drug performance by prolonging residence time and improving corneal bioavailability, while maintaining essential lens properties. However, further in vivo and clinical studies are required to confirm these potential benefits and establish therapeutic efficacy for the management of persistent epithelial defects.