2-Hydroxyethyl methacrylate hydrogel preparation

Liu, Q., Hedberg, E. L., Liu, Z. W. et al. 2000. Preparation of macroporous poly(2-hydroxyethyl methacrylate) hydrogels by enhanced phase separation. Biomaterials 21 2163-9. 

Medicine. The polymethacrylates have been used for many years in the manufacture of dentures, teeth, denture bases, and filling materials (116,117) (see Dental materials). In the orthodontics market, methacrylates have found acceptance as sealants, or pit and fissure resin sealants which are painted over teeth and act as a barrier to tooth decay. The dimensional behavior of curing bone-cement masses has been reported (118), as has the characterization of the microstmcture of a cold-cured acryUc resin (119). Polymethacrylates are used to prepare both soft and hard contact lenses (120,121). Hydrogels based on 2-hydroxyethyl methacrylate are used in soft contact lenses and other biomedical appHcations (122,123) (see Contactlenses). 

Polyurethane hydrogels derived from UV curable urethane prepolymer and hydrophilic monomers were prepared and their properties were evaluated. The urethane prepolymer used in this study contained well-defined hard segments centered with a polyether-based soft segment and end-capped with methacrylate groups. The hydrophilic monomers studied were 2-hydroxyethyl methacrylate (HEMA), N-vinyl pyrrolidone, and glycerol methacrylate. Methacryloxypropyl tris(trimethysiloxy) silane (TRIS) was also used in some cases to modify properties. All compositions were UV... 

Polyesters synthesized from terephthaloyl chloride and isohexides were prepared, and characterized by differential scanning calorimetry, n.m.r. spectroscopy, and viscosity measurement.25,128 Another polyester, prepared by copolymerization of (2-hydroxyethyl)methacrylate with isoman-nide dimethacrylate (172), forms a hydrogel when allowed to swell in isotonic sodium chloride solution. This gel has useful properties for manufacturing contact-lens material.265... 

Regarding the initiation process of polymerization, it can be started by y-radiation. It is a method that has been used for the synthesis of hydrogels of PEO as well as hydrogels based on vinyl monomers " in this latter case, azo-compounds such as 2,2-azo-isobutyroni-trile (AIBN)f or 2,2 -azobis (2-amidine-propane) dihydrochloride or V-SO, and aqueous salt solutions such as aqueous ammonium peroxodisulfate are also used. Among the monomers most used in the preparation of hydrogels through free-radical polymerization are 2-hydroxyethyl methacrylate (HEMA) and A-vinyl-2-pyrrolidone (VP). ... 

Reagents. Hydroxyethyl methacrylate (HEMA) was extracted with hexane to remove bis-esters and distilled in vacuo, b.p. 69 / 0.1 mm Hg. p-Mltrobenzenesulfonyl isocyanate (b.p. 160 /A mm Hg) was synthesized in 63% yield by phosgenatlon of p-nltrobenzene-sulfonamlde in the presence of butyl isocyanate (9 ). Homo- and copolymers of HEMA were prepared by solution polymerization in DMF in the presence of benzoyl peroxide and the results are summarized in Table I. The hydrolytic stability of the hydrogels was estimated by slurrying 0.5-1.0 g of polymer in 5.0 mL 0.35 KOH in 10 mL culture tubes equipped with teflon lined screw caps. The samples were heated at 100 for up to 24 hr in an aluminum constant temperature block. Immediately upon removal from the heating block, the samples were cooled and acidified with 6N HCl. The precipitated gel was washed and soaked in distilled water for 30 min before the carboxylic acid content was estimated by titration with standard NaOH. 

Polyt2-hydroxyethyl methacrylate) Cp-HEMA) is a hydrophilic methacrylate polymer which was first prepared by Wichterle and Lim (.1). This polymer, and many other synthetic hydrogels, has been extensively examined for potential biomedical applications (2 ). Although many studies have focused on the physicochemical nature of these hydrogels, many questions remain unanswered. 

More recently, iodonium salts have been widely used as photoinitiators in the polymerization studies of various monomeric precursors, such as copolymerization of butyl vinyl ether and methyl methacrylate by combination of radical and radical promoted cationic mechanisms [22], thermal and photopolymerization of divinyl ethers [23], photopolymerization of vinyl ether networks using an iodonium initiator [24,25], dual photo- and thermally-initiated cationic polymerization of epoxy monomers [26], preparation and properties of elastomers based on a cycloaliphatic diepoxide and poly(tetrahydrofuran) [27], photoinduced crosslinking of divinyl ethers [28], cationic photopolymerization of l,2-epoxy-6-(9-carbazolyl)-4-oxahexane [29], preparation of interpenetrating polymer network hydrogels based on 2-hydroxyethyl methacrylate and N-vinyl-2-pyrrolidone [30], photopolymerization of unsaturated cyclic ethers [31] and many other works. 

Copolymers of 2-hydroxyethyl methacrylate (HEMA) and l-vinyl-2-pyr-rolidone (VP) in the form of cylindrical hydrogels (8 mm x 20 mm) have been prepared radiochemically and the sorption of water into these cylinders has been studied by the mass-uptake methods and by magnetic-resonance imaging at 310 K. The equilibrium water contents for the cylinders were found to vary systematically with the copolymer composition. NMR-imaging studies showed that, while the profiles of the water diffusion fronts for cylinders with high HEMA contents were Fickian, those for the 1 1 copolymer was not and indicated that the mechanism was Case III. The polymers which were rich in VP were characterized by a water-sorption process which follows Case-III behavior. 

Poly(vinyl alcohol) (PVA) is one of the hydrogels most often used in biomaterial applications. Because of the presence of excessive hydroxyl groups, PVA contained a significant amount of water. PVA was also claimed to have good mechanical strength. Another hydrogel, poly(2-hydroxyethyl methacrylate) (poly-HEMA), is well known for its excellent biocompatibility. xhe versatile biomedical applications of poly-HEMA are demonstrated by its uses in contact lenses, vitreous humor replacements and suture materials. To explore a new formulation and other usages of these two pol ers, we have copolymerized HEMA with PVA-MA (PVA esterified with maleic anhydride), the preparation and properties of this copolymer are discussed in this article. 

Details are given of the preparation of pH sensitive hydroxyethyl methacrylate-dimethylaminoethyl methacrylate copolymer hydrogels initiated by potassium persulphate in an aqueous medium. Data are given for morphology and swelling in water. 22 refs. 

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. 

Two approaches are discussed for the preparation of enzymatically controlled drug delivery systems a calcium-responsive biodegradable drug delivery system based on a mixture of starch with HPMC (hydroxypropyl methyl cellulose ether) (biodegradable) and the starch hydrolytic enzyme, alpha-amylase, in its non-active form and a glucose responsive insulin delivery system based on the hydrogel poly(2-hydroxyethyl methacrylate-co-N,N-dimethylaminoethyl methacrylate), with entrapped glucose oxidase, catalase and insulin. In both systems, the sensitivity... 

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