These materials have been attracting much attention in medical and mechanical engineering fields. Also, hydrogels have been used in the medical device industry as contact lenses, artificial corneas, dressings as coatings for sutures, catheters and electrode sensors. Such a wide range of uses requires easy manipulation of physical properties—attainable by changing monomers and/or polymerization conditions. Since biocompatibility apparently depends on water content, characterization of the amount of imbibed water in the swollen gel is essential.