BIODEGRADATION IN-VITRO AND RETENTION IN THE RABBIT CROSS-LINKED POLY(1-VINYL-2-PYRROLIDINONE) HYDROGEL AS A VITREOUS SUBSTITUTE

To elucidate the relatively short retention of crosslinked poly(1-viny l-2-pyrrolidinone) hydrogels in the eye when used as potential vitreou s substitutes, a C-14-labeled hydrogel was produced and subjected to b oth in vitro biodegradation assays and in vivo experiments. The polyme r was synthesized by the free-radical copolymerization of 99% 1-vinyl- 2-pyrrolidinone with 1% C-14-methyl methacrylate in the presence of et hylene glycol dimethacrylate (0.1%) as crosslinking agent. The in vitr o protocol for assessing the biodegradation include the incubation of hydrogel with hydrolases (trypsin or collagenase), followed by examina tion of changes in its physical characteristics and by monitoring its residual radioactivity, as well as by detection of possible degradatio n products. Within the maximum duration of experiments (4 weeks), none of the procedures indicated biodegradation of polymer. The hydrogel w as also injected into the vitreous humor of rabbits and followed up to 4 weeks. Residual radioactivity measurements of the vitreous contents indicated that 50% of the polymer was removed by the end of the perio d. Histopathologic examination revealed cell infiltrates of the mononu clear phagocyte system in both vitreous and retinal tissue. A possible phagocyte-mediated mechanism of the dissipation of hydrogel is discus sed. (C) 1998 John Wiley & Sons, Inc.