Polarographic method for measuring oxygen diffusivity and solubility in water-saturated polymer films: Application to hypertransmissible soft contact lenses

An electrochemical-polarographic method is described for measuring the diffusivity, D, and solubility, k, of oxygen in aqueous-saturated polymer films. While the apparatus and procedure are general for such films, it is here applied to determine D and k for oxygen in hypertransmissible soft contact lenses. Usually, only oxygen permeability, P, the product of D and k, is measured because P gauges the steady flux of oxygen through hydrogel membranes. However, we utilize the polarographic technique in the unsteady state and, hence, obtain D and k separately. Determination of each of these properties is critical for designing better lens materials that ensure sufficient oxygen supply to the cornea. We have measured oxygen diffusivities and solubilities for nine commercial soft contact lenses. Our data indicate that oxygen diffusivity is primarily responsible for the range of oxygen permeability observed for hypertransmissible soft contact lenses. For 2-hydroxyethyl methacrylate (HEMA)-based lenses, measured solubilities suggest that over 90% of the dissolved oxygen partitions to the polymer phase.