Soft contact lenses materials

Observations Soft contact lens materials represent a balance between hydrophilic... 

ATR spectroscopy in the infrared has been used extensively in protein adsorption studies. Transmission IR spectra of a protein contain a wealth of conformational information. ATR-IR spectroscopy has been used to study protein adsorption from whole, flowing blood ex vivo 164). Fourier transform (FT) infrared spectra (ATR-FTIR) can be collected each 5-10 seconds165), thus making kinetic study of protein adsorption by IR possible 166). Interaction of protein with soft contact lens materials has been studied by ATR-FTIR 167). The ATR-IR method suffers from problems similar to TIRF there is no direct quantitation of the amount of protein adsorbed, although a scheme similar to the one used for intrinsic TIRF has been proposed 168) the depth of penetration is usually much larger than in any other evanescent method, i.e. up to 1000 nm water absorbs strongly in the infrared and can overwhelm the protein signal, even with spectral subtraction applied. 

Table 2 Selected soft contact lens materials...

Hyon S-H, Cha W-I, Ikada Y, Kita M, Ogura Y, Honda Y (1994) Poly(vinyl alcohol) hydrogels as soft contact lens material. J Biomater Sci Polym Ed 5 397... 

PERFORMANCE SILICONE SOFT CONTACT LENS MATERIALS... 

PVA is attractive as matrix because it is water soluble, has excellent chemical resistance, and is biocompatible and biodegradable. PVA has been studied in terms of its biomedical applications, like tissue reconstruction and replacement, cell entrapment and drug delivery, soft contact lens materials, and wound covering bandages for bum victims (Siro and Plackett 2010). 

Tranoudis, I. and Efron, N. (2004) Tensile properties of soft contact lens materials. Contact Lens Anterior Eye, 11, 177-91. 

Robinson, J.R. and Eriksen, S.P., 1978. Drug delivery from soft contact lens materials. In "Soft Contact Lenses Clinical Applied Technology." M. Ruben,ed. London Balliere-Tindall. pp. 265-280. 

Because fluorescein sodium can penetrate into many hydrogel contact lenses, the lenses become discolored, which raises bacterial growth issues and renders the lenses cosmetically objectionable. In addition, the boimd-ary between lens and tears becomes obscured, which precludes the use of fluorescein in soft contact lens fitting. Fluorexon, a molecule similar in fluorescent characteristics to that of fluorescein, is less readily absorbed by the soft lens material, which renders it useful in fitting and evaluating soft and hybrid design lenses. 

MAJOR APPLICATIONS Biomaterial applications such as dermal implant, carrier of drugs, cell culture matrix, wound dressing, material for hybrid organ, drug delivery system, soft contact lens, tissue implants, cardiovascular graft, artificial heart, etc. Synthetic sausage casings in food industry. ... 

This chapter will examine the production of one particular biomedical device soft contact lenses. The surface properties of soft contact lenses influence the biocompatibility of the lens, or the ability of the material to perform with the appropriate host response in a specific application [1]. Three case studies will be u.sed to exemplify how surface science is utilized in the soft contact lens market. The case studies will examine methods of producing surfaces for biocompatible high-performance soft contact lenses as well as alterations in surface chemistry and morphology caused by manufacturing methods used to produce the lens. However, first it would be appropriate to provide some history, design goals, and background on soft contact lenses. 

Many materials are employed in the production of soft contact lenses. The material with the widest application in the industry is HEM A [13]. HEM A became a popular soft contact lens because of its clarity, comfort, good vision, and excellent wetting characteristics. HEMA is a hydrogel, and hydrogels are cross-linked polymer networks that are swollen in water. Hydrogels are typically classified by whether they are neutral or ionic. Anyone who has had a piece of dirt in the eye understands the need for good wettability when it comes to a contact lens. The wettability of a soft contact lens in the ocular environment is a function of the surface chemistry while it is hydrated, which determines the biocompatibility of the lens [6]. A lens surface that does not wet will cau.se discomfort and potentially increased deposits. These deposits can affect vision and the physical properties of the lens [3,4]. The major drawback of HEMA is the permeability of the material to oxygen [12]. Extended wear can result in increased vascularization of the cornea... 

FIGURE 7.1. The dewetting process has been studied in three different geometries (a) supported films resting on a solid substrate. The process controls the spontaneous drying out of liquid films without the intervention of heat, as well as the stability of liquid films (b) inserted films, sandwiched between a rubber-like material and a solid, with applications to the process of adhesion onto a wetted solid surface and to the stability of the lachrymal film between a soft contact lens and the cornea (c) suspended viscous films (in air or in a liquid with low viscosity) this configuration controls the stability of polymer and glass foams as well as that of emulsions. 

At present, soft contact lens are very popular. High ophtalmic compatibility is demanded fro the contact lens materials. According to Nicolson and Vogt (2001), the lens... 

Hydroxyethyl methyl Methacrylate n A monomer that polymerizes to a hydrophilic polymer that is rigid when dry but when saturated with water becomes a soft, clear material (Hydron ). Applications include masonry coatings, soft contact lens, and other biomedical devices. 

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