Optical implants, hydrogels

Hydrogels were first developed as contact lenses or optical implants, and are usually composed of glycol methacrylates. Gels consist of insoluble polymers with aqueous, interactive, hydrophilic sites. The two basic types are (1) a flexible sheet, comprised of a 3-dimensional macro structure, that does not change physical form as fluid is absorbed but swells until equilibrium is reached, and (2) a non-fixed amorphous gel whose viscosity decreases as fluid is absorbed until the gel assumes the shape of the wound. In the latter case, the fluid continues to be absorbed until all cohesive properties are lost and the gel becomes a dispersion of the polymer in water (19). Several types of gels are available on the market but the properties are similar whether the product is in the form of a sheet or a gel. Hydrogels could be excellent... 

Tokuda T, Takahashi M, Uejima K, Masuda K, Kawamura T, Ohta Y, et al. CMOS image sensor-based implantable glucose sensor using glucose-responsive fluorescent hydrogel. Biomedical Optics Express 2014 5(ll) 3859-70. 

We had occasion to extend the concept to the development of materials for potential use in intraocular lenses [45]. Appropriately shaped dry resin lenses were to be surgically implanted. Upon exposure to the fluids in the eye, the polymer was to swell and assume the correct optical shape for proper vision. This concept required that the polymer should take up at least 409/o of its weight as water to produce a swollen polymer that had a refractive index of no less that 1,40 to permit the proper optical corrections to be applied to the lens. Assuming that refractive indices of mixtures or solutions are additive, this requires a polymer with a refractive index about 1.5 so that 40 70 of water with nn 1.33 will result in a hydrogel in the desired... 

Visual inspection of the dextran hydrogel implants between days 3 to 30 at approximately weekly intervals showed that they remained optically clear without discoloration and no apparent change in size or integrity due to biodegradation or body movements of the test animal. There were no signs of encapsulation of the implant, fluid accumulation, abscess, hemorrhage or adhesion due to cellular or fibrous tissue ingrowth. 

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