Medical devices such as ophthalmic lenses made from silicone materials have been investigated for a number of years. Such materials can generally be sub-divided into two major classes, namely hydrogels and non-hydrogels. Non-hydrogels do not absorb appreciable amounts of water, whereas hydrogels can absorb and retain water in an equilibrium state. Hydrogels generally have water content between about 15 to about 80 weight percent. Regardless of their water content, both non-hydrogel and hydrogel silicone medical devices tend to have relatively hydrophobic, non-wettable surfaces that have a high affinity for lipids. This problem is of particular concern with contact lenses.
Polyfumarate prepolymers and compositions comprising the prepolymers have been developed to make highly oxygen permeable hydrogels which may be used to make biomedical devices including contact lenses. Examples of these fumarate and fumaramide prepolymers and compositions containing the prepolymers can be found in U.S. Pat. Nos. 5,374,662 and 5,496,871, the contents of each being incorporated by reference herein. Because of the polar character of amide functionality, this class of monomer shows good compatibility with both hydrophobic monomers such as tris(trimethylsiloxy)silane (TRIS) and hydrophilic monomers such as N,N-dimethylacrylamide (DMA). These prior art prepolymers provide silicone hydrogels with excellent oxygen permeability and mechanical properties. However, like other silicone hydrogels, they are not wettable enough to be useful as continuous wear lenses unless the surface is treated. Therefore there is a need for new prepolymers that do not have the limitations of prior art prepolymers