Hydrophilic polymers having suitable properties for soft contact lenses have been produced in the past by crosslinking major amounts of a single hydroxyethyl methacrylate with a diester crosslinking agent. Those polymers typically exhibit water contents of 50 to 80% by weight when fully hydrated.
It is preferred that hydrophilic contact lens materials have as high a water content as possible so that tear exchange is not limited and corneal respiration is maintained as close to uninterrupted as possible. At the same time, the lens material must have sufficient strength to resist tearing during manufacture and insertion as well as not dissolving under use.
Since oxygen permeability is dependent on the water content of the lens, a greater water content results in increased permeability and, thereby, greater respiration. However, increasing water content requires that the porosity and water holding quality of the hydrophilic polymer be increased which normally results in a decrease in the physical strength of the polymer.
The present invention has determined that a macroporous hyperhydroxy polymer exhibiting a significantly increased water holding capability can be produced from a monomer mixture comprising substantially similar fractions of functional acrylic monomers with a minimum amount of a polymerization initiator. The resulting polymer has a crosslinked skeleton with a pore size of at least 90 .ANG. and a high ratio of free water to solid when hydrated. Water contents of 95% to 99.75% are possible while maintaining sufficient integrity of structure to permit practical use as a material for contact lenses and other uses.
USPTO Backgrounds
USPTO Backgrounds