Influence of Solution pH on Drug Release from Ionic Hydrogel Lens

Hydrogel contact lenses have shown the possibility for uses in ophthalmological treatment for the last decades. Moreover, structural changes responsive to solution pH have given further applications toward more complicated drug delivery for physiological and pathological states of a wearer. However, unpredicted variables, swelling degree, and polymer degeneration, have been hurdles for the evaluation and quantification of a designed pharmaceutic system. Many scientists believe understanding empirical/semi-empirical mechanisms behind the drug release can offer simple solutions to quantify and furthermore control the drug release. In this study, we developed silicon-copolymerized hydrogel contact lenses with various functional monomers for delivery of hydroxypropyl methylcellulose, one of the commonly used dry eye drugs. Under the physiological pH, the prepared hydrogels showed different swelling reactions in response to ionic interaction. In addition, analysis of the pH sensitivity and maximum release amounts against the artificial tear pH suggested possible molecular changes in the functional groups and swelling behaviors. Accordingly, the mathematical parameters were calculated to better understand the drug release mechanism from hydrogels. By evaluating these parameters, the primary rate-limiting factors of the silicone hydrogel contact lenses were determined at the investigated pH. These results, with the simple mechanistic study, imply the potentials of silicone hydrogel contact lens in controlled drug delivery under the physiological conditions. [Figure not available: see fulltext.].