Contact lens Swelling equilibrium

Knowledge of the swelling characteristics of a polymer is of utmost importance in biomedical and pharmaceutical applications since the equilibrium degree of swelling influences the solute diffusion coefficient through these hydrogels [1], the surface properties and surface mobility [1,2,8], the optical properties, especially in relation to contact lens applications, and the mechanical properties. 

The successful development of eye contact lenses led in turn to a demand for soft contact lenses. Such a demand was eventually met by the preparation of copolymers using a combination of an acrylic ester monomer such as methyl methacrylate, a cross-linkable monomer such as a dimethacrylate, and a monomer whose homopolymer is soluble or highly swollen in water such as N-vinyl pyrrolidone. Such copolymers swell in water (hence the term hydrophilic), the degree of swelling being controlled by the specific type and amount of the monomers used. In use the lens is swollen to equilibrium in water, a typical soft lens having a water content of about 75%. 

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