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a Reproduced from J. G. Pritchard, Poly(vinyl alcohol): Basic

Properties and Uses, Macdonald, London, 1970.

crosslinks are stable. This expansion on contact with water has been put to many uses, such as in the fabrication of expanding implants from crosslinked hydrophilic polymers which imbibe body fluids and swell to a predetermined volume. These materials, such as the poly(hydroxyethyl methacrylate)s (poly(HEMA)s), are insoluble and chemically stable because of their three-dimensional structure, (see I, II) and do not dissolve. Implanted in the dehydrated state, these polymers swell to fill a body cavity or to give form to surrounding tissues. The gels may be used as vehicles for antibiotics permitting protracted release of drug in the immediate environment of the implant. Antibiotic-loaded gels like this have been used in infections of the middle ear and other sites not readily reached by other methods of administration. Surgical suture material coated with antibiotic-containing hydrophilic gels acquires a chemotherapeutic role as the development of spread of infection along the suture fibre is prevented.

Hydrophilic contact lenses (such as Soflens) are made from crosslinked poly(2-hydrox-yethyl methacrylates). These have also been utilised as drug carriers. Conventional eye medication has been modified over the years through the addition to formulations of a variety of viscosity-enhancing agents, polymers such as hydroxypropylmethyl cellulose, poly(vinyl alcohol) and silicones. These all prolong contact of drug with the cornea by

CH3 CH3 CH3

CH3 CH3

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