(580e) Interfacial Polymerization of a Thin Lubricious Film for Improving Wettability and Lubricity

Authors: 
Yu, Y., University of Florida
Chauhan, A., Colorado School of Mines
Title: Interfacial polymerization of a thin lubricious film for improving wettability and lubricity

Purpose: High rates of dropouts in contact lens wearers can be attributed to several factors, but the most commonly cited reasons in many studies are dryness and discomfort. Effectively reducing these symptoms may result in better patient outcomes. Wearer comfort has been shown to have a direct correlation to friction experienced by the user. It is believed that improving the lubricity of contact lenses, or minimizing the friction coefficient between the lens and the ocular surface, can significantly relieve dryness and discomfort. Here, we used different approaches to fabricate innovative ultra-lubricious contact lenses.

Methods: We have developed two simple scalable approaches for incorporating highly lubricious layers on the surface of contact lenses. The basis of the first approach is polymerizing a thin film of N, N-dimethylacrylamide (DMA) on the surface of lenses. The thin film is created by loading DMA monomer in an aqueous solution along with one of the components of a redox pair (APS) for initiation of polymerization. The other component of the redox pair (TEMED) is loaded in the lens by soaking. After the lens loaded with N, N, N′, N′-Tetramethylethane-1, 2-diamine (TEMED) is brought in contact with DMA, DMA and ammonium persulfate (APS) begin diffusing into the lens while TEMED simultaneously diffuses out. Contact between TEMED and APS leads to rapid generation of free radicals that cause polymerization of DMA. We speculate that the poly-DMA that forms is covalently attached to the lens polymer through activation of unreacted vinyl groups or possibly through formation of loops with the lens polymer. The thickness of the layer is governed by the polymerization time which is kept to within 30 seconds to create a layer of DMA only at the surface. In the second approach, we loaded the lens with a hydrophobic thermal initiator, Azobisisobutyronitrile (AIBN), by soaking the lens in a solution of AIBN in methanol. The lens was then placed in saline for a short time (15 seconds) to extract all excess methanol, and then soaked in N, N-dimethylacrylamide (DMA) solution at high temperatures to polymerize the surface film. Because the initiator is restricted to the lens, DMA was polymerized only near the surface and inside the lens, which led to a lubricious surface.

Results: Fourier-transform infrared spectroscopy confirms that DMA was polymerized into poly-DMA on the lens, creating a lubricious layer. The optimized process results in the polymerization of 2.1±1.4 µm thick layer on each surface, which represents about 4% of the total lens thickness. The water content of the surface layer is ~285% and water contact angle of the modified lenses has been decreased from 93.7° into 20°. These modified lens’ characteristics imply a tremendous improvement for wettability of the contact lenses. Additionally, the lubricity of the modified lens is increased by the factor of 9.

Conclusions: The modified lenses made by both methods exhibit reduced contact angle and lower friction coefficient which suggests improved wettability and lubricity. Many selected brands of commercial lenses were modified successfully. Since the manufacturing process is very easy to control, it can be commercialized at a very low cost. The improved wettability and lubricity of the modified contact lenses may be beneficial to the lens wear comfort, which may lead to a reduction of contact lens wearer dropouts. These upgraded features and ease of production may usher in a new generation of contact lenses.