Oxygen permeability coefficients of polymers for hard and soft contact lens applications

The oxygen permeability of several polymeric materials used for hard and soft contact lens applications was determined using a gas-to-water oxygen permeation technique. The technique measures oxygen permeation through polymeric films kept between a gaseous and an aqueous phase at 34°C, where the oxygen is dissolved and measured with an oxygen analyzer. Oxygen permeabilities were measured for poly(methyl methacrylate), cellulose acetate butyrate, a blend of PMMA and CAB with silicone networks, poly (hydroxyethyl methacrylate) hydrogels, and a series of amorphous and semicrystalline poly (vinyl alcohol) hydrogels. Dissolved oxygen permeabilities ranging from 0.155 x 10−10 cm3(STP)·cm/sec·cm2·cmHg for PMMA to 78.95 x 10−10 cm3(STP)·cm/sec·cm2·cmHg for an amorphous PVA membrane with degree of hydration of H = 0.866 were observed. For amorphous hydrogels, the oxygen permeability is a function of thickness and degree of hydration. Boundary layer effects and the effect of structural characteristics of the polymer on the permeability coefficients are discussed.