Polyhydroxyethylmethacrylate

Poly(2-hydroxyethyl methacrylate) (pHEMA) is a polymer that forms a hydrogel in water. It was invented by Drahoslav Lim for use in soft contact lenses. Copolymers of pHEMA are still widely used today.

pHEMA functions as a hydrogel by rotating around its central carbon. In air, the non-polar methyl side turns outward, making the material brittle and easy to grind into the correct lens shape. In water, the polar hydroxyethyl side turns outward and the material becomes flexible. Pure pHEMA yields lenses that are too thick for sufficient oxygen to diffuse through, so all contact lenses that are pHEMA based are manufactured with copolymers that make the gel thinner and increase its water of hydration. These copolymer hydrogel lenses are often suffixed "-filcon", such as Methafilcon, which is a copolymer of hydroxyethyl methacrylate and methyl methacrylate.