Improving wettability and lubricity of commercial contact lenses by polymerizing a thin film of dimethylacryamide

Dryness and discomfort are considered to be the biggest causes of dropouts in contact lens wearers. We propose a new method to improve lubricity by polymerizing a thin film of a hydrophilic polymer poly-dimethylacrylamide (DMA) on the contact lens. The proposed approach involving soaking the lens in a solution of azobisisobutyronitrile (AIBN) in methanol to load the hydrophobic thermal initiator into the lens. The AIBN-loaded lens is then placed in an N, N-dimethylacrylamide (DMA) solution at elevated temperature to initiate the thermal polymerization of the monomer to polymerize a film on the surface of the lens. Though AIBN is hydrophobic, it is released into the solution at high temperatures due to the high solubility of the free radicals generated by decomposition of the initiator, which results in polymerization of the bulk solution as well. The processing parameters must be optimized to achieve a surface DMA film of desired thickness without causing the bulk solution to gel and without significant changes to the lens shape. ACUVUE (R) ADVANCE (R) lenses were successfully modified using 3.4% AIBN solution to load the initiator and then placing that in a 4% DMA solution at 70 degrees C for 12 h. The FTIR spectra confirm a surface DMA film and the results are further substantiated by measuring the weight of the surface-film as well as wettability (contact angle) and lubricity (coefficient of friction). The optimized poly-DMA film has a hydrated weight of about 10 mg with a water content of about 400%. The film reduces contact angle from 105.9 +/- 0.1 degrees to 45.3 +/- 0.12 degrees for ACUVUE (R) ADVANCE (R) lens, and reduces the coefficient of friction in contact with excised cornea significantly from 0.0385 +/- 0.010 to 0.0063 +/- 0.0017. This method is effective only in lenses in which the release duration of the AIBN is sufficiently long to initiate the DMA film within the release duration. The release duration is about 30 min in ACUVUE (R) ADVANCE (R) and AIR OPTIX (R) contact lenses. For other lens types, a modified approach can be developed by first loading vitamin E, which is an effective diffusion barrier into the lens to slow the AIBN release from the lens. This method can be successfully used with other lenses, such as ACUVUE (R) OASYS (R).