The Development of Silicone Hydrogels

THE STRUCTURE OF hydrogel materials can be described as ‘washingline’ polymers. In this analogy the hydrogels are composed of a long backbone (ie the ‘washing line’) from which a variety of chemical groups may be suspended (the ‘washing’). The function of these chemical groups, or monomers, is to attract and bind water. In conventional hydrogel materials, frequently used monomers include Nvinyl pyrrolidone (NVP), methacrylic acid, and HEMA. The washing lines may be fastened together at intervals by the use of cross-links to give greater physical stability. The same ‘washing line’ principle can also be applied to the silicone hydrogels but groups containing silicon-oxygen bonds (silicones) are attached to increase oxygen permeability.