Interfacial polymerization of a thin film on contact lenses for improving lubricity

A large number of contact lens wearers drop out each year due to end of day discomfort, which could possibly be reduced by designing lenses with highly lubricious surfaces. We hypothesize that polymerizing a thin film of dimethyl acrylamide (DMA) on the surface of the lenses will improve lubricity.

The thin film is polymerized by loading a commercial contact lens (1-DAY ACUVUE® TruEye®) with N,N,N',N'-Tetramethylethane-1,2-diamine (TEMED) and soaking it in a solution of DMA and ammonium per sulfate (APS). The two components of the redox couple (APS and TEMED) mix near the surface of the lens due to diffusion and react rapidly to form free radicals. The free radicals lead the polymerization of the DMA monomer near the surface resulting in the formation of the thin hydrogel layer that is attached to the lens matrix through activation of unreacted vinyl groups or possibly through formation of entanglements with the lens polymer.

The thickness of the layer is controlled by the polymerization time which is limited to 30 s to create a layer of DMA only at the surface. The presence of the DMA layer is confirmed through measurements of Fourier-transform infrared spectroscopy (FTIR) spectra in total internal reflection mode. The layer is determined to be about 3-5 µm thick with a water content of about 285%. The presence of the layer significantly improves lubricity as is evident through the qualitative rubbing test and quantitative measurement of the friction coefficient. A preliminary one-week safety study in rabbits show that lens wear does not cause any toxicity.