Extending extended-wear contacts.

New polymer blends may lead to care-free contact lenses that wearers can leave in for weeks at a time. By mixing and matching three polymer building blocks, chemists have developed a lens material that lets oxygen pass through 25 times better than current soft lenses, says Jay Kunzler of Bausch and Lomb, Inc., in Rochester, N.Y. A lack of adequate oxygen can irritate the eye tissue underneath, he adds.

Several research groups seek to make new lenses based on a type of siloxane, a silicon-oxygen compound that produces strong, flexible films. But by themselves, siloxanes do not wet very easily, so they are uncomfortable. They also tend to become distorted or cloud up because they attract lipids to their surfaces, Kunzler says.

To overcome these shortcomings, he and his colleagues start with siloxane building blocks that contain fluorine atoms. They then cap chains of these building blocks with another fluorinated compound. The fluorine atoms make the final film much less likely to attract lipid-based molecules, says Kunzler.

In addition, the researchers chemically attach a wetting agent that changes its molecular shape when boiled in salt solutions: It opens up a ring of atoms, exposing its water-loving parts so that tears easily wet the final film, Kunzler explains.

"Our hope is that this would be the ultimate extended-wear lens," he says. "The eye doesn't even know it has a lens on." But the material still needs improvement, he adds. He is working on modifying the polymer so that the new lens no longer tends to stick too tightly to the eye.