Polyhydroxyethylmethacrylate

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Poly(2-hydroxyethyl methacrylate) (pHEMA) is a plastic commonly used to make contact lenses. The invention of this polymer stands out as a milestone in material science as the first time a polymer was designed to have specific properties before it was synthesized. The inventor, Drahoslav Lim, designed it for use in soft contact lenses where it is still widely used today.

pHEMA functions as a hydrogel by rotating around its central carbon atom. 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 hydrated and 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 the amount of water it will absorb[1]. These copolymer hydrogel lenses are often suffixed "-filcon", such as methafilcon, which is a random copolymer of hydroxyethyl methacrylate and methyl methacrylate and ocufilcon B is a copolymer with methacrylic acid.

References

  1. Ratner, Buddy D. "Biomaterials Science, An Introduction to Materials in Medicine" Elsevier Academic Press 2004
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