Water dispersible siloxane nanogels: a novel technique to control surface characteristics and drug release kinetics

Amphiphilic, water-dispersible, crosslinked siloxane nanogels were synthesized via a free radical solution polymerization and then applied as optically clear, functional coatings on the surface of lens substrates to demonstrate the feasibility of siloxane-nanogels to generate covalently tethered surfaces on intraocular lens substrates. Siloxane nanogels were synthesized from 3-(trimethoxysilyl)propyl methacrylate and polyethylene glycol diacrylate and subsequently chain-end functionalized with mercaptosuccinic acid to yield a clear, water-dispersible nanogel. The nanogels were then spin-coated onto lens substrates as a coating and covalently tethered via a two-part interfacial redox polymerization using N'N'-tetramethylethylenediamine and ammonium persulfate. Covalently crosslinked, stable nanogel coatings on the lens substrate were shown to increase the hydrophilicity of the material surfaces while maintaining optical clarity, with >85% of white light transmittance. No significant changes were observed in the cytocompatibility, refractive index and mechanical properties of the substrate before and after the coatings were generated. The coatings were also modified to facilitate the sustained release of an anti-inflammatory drug dexamethasone in which >90% of the incorporated drug within the nanogel was released within 5 days, thereby demonstrating the feasibility of this approach to also enable the multi-day sustained delivery of an active pharmaceutical agent (API) at therapeutically relevant doses.