Hydrogels Oxygen permeable

Cross-linked versions of water-soluble polymers swollen in aqueous media are broadly referred to as hydrogels (52) and have a growing commercial utility in such apphcations as oxygen-permeable soft contact lenses (qv) (53) (Table 4) and controUed-release pharmaceutical dmg deflvery devices (54). Cross-linked PVP and selected copolymers fit this definition and are of interest because of the following stmcture/performance characteristics ... 

The number of contact lens wearers has grown to an estimated 24 million in the United States and 50 million worldwide. Concurrendy, there has been a proliferation of contact lens manufacturers and products. The 1980s saw the widespread introduction of lens products made of more oxygen-permeable materials, ie, rigid gas-permeable (RGP) materials that made PMMA lenses virtually obsolete and high water content hydrogels that competed with HEMA-based lenses. 

Examples of silicones in ophthalmic application have been described.5 1 However, some problems have been reported with the use of silicones in retinal tamponade.542 Silicones are widely used in contact lenses because of their unusually good oxygen permeability and bioinertness, but the need for novel materials continues. Low-modulus fluorosiloxane-based hydrogel lenses with a wide range of water content and high-oxygen permeability have been described in a number of papers.543-... 

Kunzler et al. (5) prepared silicone hydrogels containing vinyl carbonate end-capped with fluorinated polysiloxanes that had an oxygen permeability of at least about 120 Barters, a water content of at least about 20wt%, and high modulus. 

Cross-linked versions of water-soluble polymers swollen in aqueous media are broadly referred to as hydrogels and have a growing commercial utility in such applications as oxygen-permeable soft contact lenses and... 

Fumarate- and fumaramide-containing hydrogels have been prepared with silicone as a co-component that are highly oxygen permeable. These agents are biocompatible and useful as biomedical devices, particularly as contact lenses. 

While the silicone polymer phase provides a high enough oxygen permeability, it also dominates the surface characteristics, i.e., the surface of silicone hydrogel is too hydrophobic to be used as a contact lens. The silicone phase also readily absorbs... 

In addition to these materials, several others, such as polyurethanes, polysulfones, polyvinyl alcohol, and various copolymers, have been tried or are under development. Recently, silicon hydrogel lenses with high oxygen permeability were marketed. The future... 

The more recently developed silicone hydrogels have the potential to solve this problem because although they have relatively low water contents (about 30%). in comparison to the conventionally used hydrogels, their oxygen permeability is far higher. This characteristic, combined with their good biocompatibility, has allowed them to be manufactured into lenses that can be worn continuously for up to a month. 

V. Compan, A. Andrio, A. Lopez-Alemany, E. Riande, M. Refojo, Oxygen permeability of hydrogel contact lenses with organosilicon moieties. Biomaterials 23 (2002) 2767—2772. 

Fig. 4. (Photo)-Rigid oxygen permeable contact lenses and a new generation extended wear hydrogel lens incorporate a variety of organosilicon substituted monomers (courtesy L. Seidner, Permeable Technologies).

Wang, J. Li, X., Preparation and Characterization of Interpenetrating Polymer Network Silicone Hydrogels with High Oxygen Permeability. J. Appl. Polym. Sci. 2010,116, 2749-2757. 

Silicone Hydrogels. A new class of hydrogels based on silicone has been developed (14). These materials were developed in an attempt to combine the high oxygen permeability of polydimethylsiloxane and the excellent water absorption characteristics of conventional non-silicone hydrogels. This new class of hydrogels was developed primarily for contact lens application. These silicone hydrogels are also prepared by free-radical poljnnerization techniques. 

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