Soft contact lens poly

The Effect of Monomer Purity on Protein Adsorption onto Poly-(HEMA). The importance of relatively minor contamination of the monomers used in formulating hydrogels to be used in biomedical applications has not been recognized widely as yet, although Bruck has referred to this problem in connection with the soft contact lens (26). Protein adsorption studies performed with hydrogels made with monomers of typical commercial quality illustrate this potential problem. 

YNTHETIC HYDROGEL POLYMERS, first introduced in the early 1960s, made a major impact, initially in the soft contact lens field, and more recently in other biomedical or specialty applications. The first synthetic poly(2-hy-droxyethyl methacrylate) [poly(HEMA)] hydrogel developed by Wichterle (i) remains very important, as do its copolymers with monomers such as N-vinyl-2-pyrrolidinone, acrylic and methacrylic acids, glycerol methacrylate, various acrylamides, and alkoxyalkyl methacrylates. 

A hydrophilic polymer (especially the aoss-linked form) may transition from hard and rigid to soft and elastic when immersed in aqueous media. A good example of this is cross-linked poly(2-hydroxyethyl methacrylate) (pHEMA), the original soft contact lens polymer. When dehydrated, pHEMA is a hard, hrittle polymer. When hydrated, it is a soft elastomer. The hydrated (swollen) form of cross-linked pHEMA contains about 40% by weight of water. Polymers that swell to an equiUhrium level in aqueous solutions are referred to as hydrogels. 

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... 

The most famous gel is the soft contact lens developed in Czechoslovakia in 1960 using poly(hydroxyethyl methacrylate). In the late 1970s, superabsorbent polymers were developed in the United States and their use in feminine products was worldwide. In 1980, Professor Toyoichi Tanaka discovered phase transition in gels. Today many researchers study those transitions from the basics to applications. Gel applications or functional uses due to phase transitions are found in the chapters that follow and will not be discussed here. 

In this work we present a theoretical discussion regarding this interaction parameter for 10 polymer-polymer-solvent systems, 4 copolymer-solvent systems along with their corresponding polymer pairs. Our polymer blends are real mixtures of 5 homopolymers consist of poly(N,N-dimethyl methacrylamide) (PDMAA), poly(2-dimethyl aminoethyl methacrylate) (PDMAEMA), poly(acrylic acid) (PAA), a typical membrane of commercial soft-contact lens i.e. poly(2-hydroxyethyl methacrylate) (PHEMA), and poly(N-vinyl-2-pyrrolidone) (PVP) all with water solvent. Copolymers studied are poly(acrylonitrile-co-butadiene) in acetonitrile, poly(styrene co acrylonitrile) in 1,2 dichloroethane, poly (acrylonitrile-co butadiene) in hexane and poly (acrylonitrile-co butadiene) in pentane. 

Lens hazing and protein deposition are common problems for wearers of soft contact lenses. Previous experiments with hydrophobic-hydrophilic copolymers exposed to plasma showed protein adsorption to be minimal at intermediate copolymer compositions. Adsorption of proteins from artificial tear solutions to a series of polymers and copolymers ranging in composition from 100% poly (methyl methacrylate) (PMMA) to 100% poly(2-hydroxyethyl methacrylate) (PH EM A) was measured. The total protein adsorption due to the three major proteins in tear fluid (lysozyme, albumin, and immunoglobulins) was at a minimum value at copolymer compositions containing 50% or less PH EM A. The elution of the adsorbed proteins from these polymers and copolymers with various solutions also was investigated to assess the binding mechanism. 

Soft contact lenses (SCLs) are one of the major products constructed from poly(HEMA) hydrogels. Since their introduction, a variety of such poly-(HEMA)-based hydrogels have been developed to improve lens properties. Both excellent protein adsorption resistance and wettability are required for SCLs, making MFC a good candidate as a suitable monomer. Biocompatible Co. has produced MFC polymer-based SCLs that contain 20% MFC, 80% HEMA, and a small amount of crosslinker (Froclear , omafilcon A), with such lenses now commercially available from CooperVision Co. The Froclear is the only contact lens for reduction of dry-eye syndrome that has been approved by the FDA in the USA. 

Polymeric soft contact lenses came into existence in the 1950s (12]. Otto Wich-terle discovered the hydrogel poly(hydroxyethyl methacrylate) (HEMA), a transparent, soft, hydrophilic material that could be used to prepare contact lenses, Wichterle utilized a free radical polymerization of the HEMA monomer (including cross-linker, solvent, initiator, and stabilizer) with either thermal or ultraviolet initiation of the reaction. Initially, the len.ses were produced via spin casting, which involved the use of a concave mold that is spun at a particular rate. The rate of the mold spin determines the resultant lens power (13). After production of the lens in the mold, the lens would be hydrated from the mold in a warm water solution. Once hydrated, the lens would float free from the mold. Each lens is inspected for rips, tears, and clarity. Finally, the lens is packaged, sterilized, and boxed for shipping. The surface quality of the mold determines the surface chemistry and morphology on the anterior surface of the lens produced. 

The first plastic ( hard ) comeal contact lens was developed in 1936, fabricated from poly(methyl methacrylate), PMMA (VI).However, these lenses were not commercially available until the mid 1960s. In comparison, soft contact lenses were first comprised of poly (hydroxy ethyl methacrylate), PHEMA (VII), and became commercially available shortly thereafter. Both types of lenses are comprised of a 3-D amorphous network of cross-linked polymer chains. However, the soft hard character of a lens material is directly related to the ambient operating temperature relative to its glass-transition temperature (Tg). Whereas PMMA has a Tg of 100-120°C, the Tg of PHEMA ca. 10-15°C) lies below room temperature. ... 

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