Nondegradable intraocular sustained-release drug delivery devices
Nondegradable sustained-release devices can be either matrix or reservoir systems. In matrix systems, the drug is homogeneously dispersed inside the matrix material, and slow diffusion of the drug through the polymatrix material provides sustained release of the drug (Fig. 1A). Reservoir systems consist of a central core of drug surrounded by a layer of permeable or semipermeable nondegradable material and the majority of ocular nondegradable devices used clinically to date have been reservoir designs (Fig. 1B). Ocular nondegradable devices with a reservoir design typically consist of a layer of permeable nondegradable material, such as polyvinyl alcohol (PVA) typically surrounding the central drug core (1,2). The impermeable layer surrounding the drug core is usually made of ethylene vinyl acetate polymer or silicones which are used in conjunction with PVA to alter the surface area available for release (Fig. 2) (1,2).
