PH sensitive soft contact lens for selective drug-delivery

In this study, we evaluated contact lenses as drug delivery media and the effect of tear physiological pH on drug release behavior. Anionic or cationic hydroxyethyl methacrylate (HEMA) lenses were polymerized with either vinylpyrrolidone (VP) or N-isopropylacrylamide (NIPAAm). The pH of artificial tears was prepared as between 5.8 and 8.35. One of common treatments, hydroxypropyl methylcellulose (HPMC), to dry eye disease was used as a test drug. As a result, drug releases from anionic 100% p-HEMA and p-HEMA-VP lens were both increased with increasing tear pH. However, released drug amounts from cationic the p-HEMA-NIPAAm lens were decreased with increasing pH. In weak basicity (pH 8.03), the p-HEMA-VP (20 wt%) lens swelled resulting releasing drugs 3.5 times more compared to in weak acidity (pH 5.80). On the other hand, the p-HEMA-NIPAAm (20 wt%) lens de-swelled in basic solution resulting decreased drug release compared to in acidic solution. The hydrogel contact lenses showed various physical properties and drug releasing properties including diffusion coefficients in response to ionization reactions between ionic groups in the lens and pH of solution. It suggests that hydrogel contact lens has potential as selective drug delivery media.