Dithiol-PEG-PDLLA micelles: preparation and evaluation as potential topical ocular delivery vehicle.

Thiol-modified nanoparticles have potential applications in mucoadhesive drug delivery and have been examined in this regard for topical ocular delivery. In this paper we provide a simple method for the synthesis of a dithiol terminated amphiphilic diblock copolymer. Bidentate dithiol-poly(ethylene glycol)-poly(d,l-lactide) (SH2-PEG-PDLLA) was synthesized and micelles with dithiol-containing coronas were prepared from this block copolymer via the emulsion method. In vitro release studies indicated that the presence of the thiol groups at the surface did not affect the rate of release of dexamethasone, used as a representative ocular drug. The micelles also showed low cytotoxicity to human corneal epithelial cells (HCEC) and murine fibroblast cells (3T3 cells). A hydrophobic red fluorophore, Nile red, was loaded into the core of micelles and confocal microscopy was used to study HCEC uptake and retention of the micelles. The micelles were rapidly endocytosed by the HCEC, with intracellular micelle levels remaining unchanged with incubation times from 5 to 120 min. Interestingly, Nile red was eliminated significantly more slowly from HCECs treated with the thiolated micelles. These results suggest that these dithiolated micelles may be effective for topical ocular drug delivery.