The Effect of Freezing on the Elution of PVA from Contact Lenses

Abstract

Contact lenses are widely used, with over 140 million wearers globally. Wearing contact lenses can cause symptoms of discomfort and dryness, which affect nearly half of all wearers. To address this concern, this thesis explores the release of polyvinyl alcohol (PVA) from contact lenses, aiming to improve comfort through controlled elution. PVA forms a protective film when placed on the ocular surface and serves to reduce ocular discomfort. This research specifically studies the impact of freezing on PVA interaction with various contact lens materials and its subsequent release kinetics. This thesis hypothesizes that freezing enhances the hydrogen bonding of PVA to lens materials, enabling the formation of a surface layer on contact lenses and increasing PVA elution. To investigate this hypothesis, commercial lenses (Acuvue® Oasys – senofilcon A, DAILIES® AquaComfort PLUS® - nelfilcon A, 1-Day Acuvue® Moist® - etafilcon A) were soaked in 2.5% w/v high molecular weight PVA solutions at 37°C for 48 hours, followed by 1 hour at either room temperature or freezing at -80°C. The results demonstrate a significant (p<0.05) increase in the cumulative PVA release from nelfilcon A lenses after 24 hours following freezing at -80°C for one hour, with 55.07 ± 2.46 μg of high molecular weight PVA released in comparison to lenses kept at room temperature which showed 46.16 ± 6.94 μg of PVA release. In contrast to nelfilcon A, etafilcon A and senofilcon A did not show a significant (p>0.05) change in the amount of PVA released after freezing. Etafilcon A lenses released 17.03 ± 3.03 μg and 20.21 ± 2.51 μg (p>0.05), and senofilcon A showed 20.33 ± 6.60 μg and 24.14 ± 2.58 μg (p>0.05) at room temperature and after freezing at -80°C for one hour, respectively, suggesting that freezing enhances these iv effects only for nelfilcon A lenses. To further explore the impact of PVA with lenses, experiments with synthesized lenses (pHEMA and PVA loaded pHEMA) were performed, which demonstrated that the presence of PVA inside the lens significantly (p<0.05) impacts subsequent PVA loading and release and the freezing effect. The cumulative release of PVA over 24 hours from pHEMA lenses were 32.64 ± 5.48 μg and 36.25 ± 6.11 μg (p>0.05), at room temperature and after freezing at -80°C for one hour, respectively. PVA loaded pHEMA lenses, in contrast, showed a significant (p<0.05) increase in the cumulative PVA release over 24 hours after freezing, rising from 42.88 ± 4.96 μg to 47.39 ± 6.26 μg after one hour at -80°C. The study emphasizes the importance of PVA incorporation within contact lenses to observe a substantial impact on release after soaking or freezing. The findings suggest that the freezing technique has potential applications in enhancing the release of comfort agents such as PVA from contact lenses, especially those containing PVA internally. In conclusion, this research provides insights into optimizing contact lens design for improved comfort by utilizing PVA release. The demonstrated impact of freezing on nelfilcon A lenses indicates a promising avenue for enhancing the release of comfort agents.