Hydrogel materials

Because of the many choices of hydrophilic monomers, cross-linkers, and hydrophobic monomers, a large number of formulations have been developed and manufactured into hydrogel lenses. The water content of these hydrogel lenses ranges from about 38%, for HEMA-based lenses, to 80%, for poly(vinyl alcohol) and partially hydrolysed acrylonitrile lenses. Table 2 gives a representative Hst of FDA approved hydrogel materials available to the consumer in the early 1990s. 

Rajagopal K, Lamm MS, Haines-Butterick LA et al (2009) Tuning the ph responsiveness of beta-hairpin peptide folding, self-assembly, and hydrogel material formation. Biomacromolecules 10 2619-2625... 

Applied to wounds, bums or surgical incisions, hydrogel materials cover the injured parts of skin (wounds) and promote healing and skin growth. 

The sealing of corneal perforations using whole enucleated bovine eyes required the same attention to tissue preparation. The epithelial layer in the bond area was removed. After the puncture of the cornea, the stroma was rinsed and blotted to remove potentially interfering aqueous humor components. The Hy-pan hydrogel material, which is 80-90% water, was routinely presoaked in PBS. Maximum bond strengths using 53 /ig of MAP per cm2 patch were obtained in 10 min after application. 

Porm-fit intracanalicular long-term Hydrogel material... 

Other materials are also available for patients deemed suitable for more permanent occlusion. Form Fit intracanalicular plugs (OASIS) are made of hydrogel material that once inserted into the vertical canaliculus and exposed to tears expands to form a gelatinous plug. The SmartPLUG (Medennium) also expands into a gelatinous plug after insertion into the canaliculus. Instead of hydration, body temperature conforms the thermodynamic acrylic polymer to the puncta. 

The structures of a number of synthetic hydrophilic polymers as a representative range of those commonly used are shown in Fig. 1. Many common hydrophilic polymers are based on methacrylate or acrylate backbones. One of the most common is polyacrylic acid, which forms the basis of many hydrogel materials (Fig. lA). Although simple polyacrylic acid is water soluble, it can be easily cross-linked to form an insoluble network polymer that still, however, retains high affinity for water and is capable of adsorbing large amounts of water to form hydrogels these are discussed later. Polymethacrylic acid-based polymers are similar in nature (Fig. IB). One of the most commonly used polymers for contact lenses, polyhydroxyethyl methacrylate, is based on a similar backbone (Fig. 1C). 

Fig. 5 Characterisation of different hydrogel materials (type A, B, C). (a) star-PEG and heparin content of the swollen gels (b) cross-linking degree counted for the heparin carboxylic acid groups. Data are presented as mean root mean square deviation from n = 4...

West, J.L. and J.A. Hubbell, Photopolymerized hydrogel materials for drug delivery applications. Reactive Polymers, 1995, 25, 139-147. 

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