Silicon hydrogel lenses

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... 

TABLE 6 Effect of SAM on Clinical Performance of Silicone Hydrogel Lenses... 

Various fluoroalkyl SAM molecules were incorporated in silicone hydrogel contact lens formulations to evaluate their effect on silicone hydrogel lens surface compatibility with tear fluid [47-49). The clinical measures of compatibility were wettability and deposition as described in the experimental section. Typical clinical results in Table 6 showed that the presence of SAMs at the lens surface had a positive effect on lens performance. Both the wettability by tear fluid and deposition from tear fluid were improved by the presence of the SAMs in the hydrogel lenses. However, the desired performance levels of 3.9 wettability and <0.1 deposition were not achieved. 

Medina et al. (1) photodimerized maleimide derivatives, (I), as a method for preparing semitelechelic silicone hydrogel polymers useful as for lens coatings as illustrated in Eq. (1). 

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... 

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. 

N. Efron, and P.B. Morgan, Trends in use of silicone hydrogel contact lenses for daily wear. Contact Lens Anterior Eye, 31, 242-243,2008. 

So-called soft contact lenses are actually made from a polymer hydrogel with a composition of up to about 50% water (the older hard lenses were a solid piece of plastic). If you are a contact lens wearer, you will know what happens when you leave a soft lens to dry out it shrinks and becomes hard like plastic. Dried up lenses will regain their former shape if soaked in water as the polymer network swells and refills with water. Some of the most current contact lens technologies, such as overnight or continuous wear lenses, are based on silicone hydrogels (polymers with a silicon backbone). 

Silicone Hydrogels Materials for Contact Lens Applications... 

Keywords Biocompatibility, contact lens, silicone hydrogel, hydrophilic polymers... 

Previous in vitro studies have confirmed the cdfin-ity of certain deposits for certcun materials [102, 103]. Furthermore, ui in vivo study hcis shown that despite significant interaction between lens matericd cuid Ccffe system, the main contributor to the amount of cholesterol and lysozyme deposited on silicone hydrogel materials is lens material [112]. This effect was particularly remarkable for lotrafilcon B that deposited between 0.1 to 0.5 mg of cholesterol irrespective of the care system used. Polar and non-polar lipids show differences in their pattern of adhesion to different Si-Hy CL materials [103,113]. 

Kiinzler, J. Ozark, R. Low Modulus Fluorosiloxane-Based Hydrogels for Contact Lens Application. In Silicones and Silicone-Modified Materials Glarson, S. J., Fitzgerald, J. J., Owen, M. J., Smith, S. D., Eds. AGS Symposium Series 729 American Chemical Society Washington, DC, 2000 pp 296-307. 

Ophthalmologic Intraocular lens Contact lens Corneal bandage Poly(methyl methacrylate) Silicone-acrylate, hydrogel Collagen, hydrogel... 

Dracopoulos, A. In vitro assessment of medical device toxicity Interactions of benzalkonium chloride with silicone-containing and p-HEMAcontaining hydrogel contact lens materials. Eye Contact Lens... 

The optimal polymer material for use in ultrasound medical devices would have an impedance matching that of human tissue, 1.5 MRayls, and minimal attenuation at the frequencies of interest, which are typical between 5 and 10 MHz. Use of a material with a large impedance mismatch against tissue results in reflection of energy at the tissue/transducer interface, or more likely, the interface between the coupling gel, which is often silicone or a hydrogel, and the device lens. A polymer with an impedance mismatch and low attenuation can result in multiple... 

Hydrogel Surfaces through In Situ Polymerization Techniques. Several research groups have reported on efforts to design wettahle silicone-hased materials through in situ polymerization techniques. These are attempts to design wettahle, hiocompatihle surfaces without the need for surface treatment. The primary driver for this research is cost. Without the need for a secondary surface treatment, a large reduction in lens cost would he achieved. 

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