PHEMA

pHEMA, or poly(2-hydroxyethyl methacrylate), is a hydrophilic polymer produced by polymerizing the monomer 2-hydroxyethyl methacrylate. In the absence of crosslinking, polymerized pHEMA forms a soluble polymer; when crosslinked it yields hydrogels capable of absorbing water up to several times their dry weight, while remaining insoluble. Dry pHEMA has a glass transition temperature around 105–125 C, and hydration markedly reduces stiffness, enabling flexible, water-rich networks.

Synthesis and properties are dominated by free-radical polymerization, often with a difunctional crosslinker such as ethylene glycol dimethacrylate to create a three-dimensional network. The pendant hydroxyl groups promote water uptake and biocompatibility, but residual monomer must be removed to minimize cytotoxicity. pHEMA hydrogels are typically transparent, biocompatible, and their mechanical and swelling properties can be tuned by adjusting crosslink density and formulation.

Applications center on its role as a hydrogel material. The most well-known use is soft contact lenses, where high water content and optical clarity are essential. pHEMA hydrogels are also used in ocular inserts, wound dressings, tissue engineering scaffolds, and drug delivery systems. Crosslinked pHEMA systems serve as matrices for controlled release of therapeutics and as biocompatible components in various medical devices.

History: pHEMA was developed in the 1960s by Otto Wichterle and Drahoslav Lim in Czechoslovakia, leading to the first soft contact lenses. Since then, pHEMA-based hydrogels have become foundational in ophthalmic materials and biomedical applications, prized for their tunable hydration, transparency, and biocompatibility.