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Hydrogels that contain phosphate groups in side chains were studied for their usefulness in drug-delivery soft contact lenses (SCLs). Naphazoline, a model drug having a cationic group, was incorporated into an SCL because of its phosphate groups and was released over a period of about 14 h. For the SCL, the naphazoline content was equivalent to the phosphate group content. It is suggested that drug-delivery SCLs can be designed to contain the needed amount of a drug through the choice of the ionic group for the ligand. Furthermore, the SCL having amide groups and phosphate groups had high transparency and an unchanged shape. It is suggested that amide groups and phosphate groups must be introduced into the polymer in equimolar amounts to give the necessary polymer-drug interaction. Therefore, hydrogels having a drug-delivery system were synthesized by the inclusion of a phosphate group and an amide group. These hydrogels are also applicable to SCL materials.

These results indicated the possibility for the zwitter ionic SCL as a lens to be worn concomitantly with ophthalmic drug instillation.

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