Polymers of 1-vinyl-2-pyrrolidinone as potential vitreous substitutes: physical selection.

More than 300 polymers of 1-vinyl-2-pyrrolidinone (VP) were synthesized, subjected to hydration, and characterized with the aim to select the most suitable materials as potential artificial substitutes for the vitreous body of the eye. The materials include cross-linked homopolymers, uncross-linked copolymers of VP with 2-hydroxyethyl methacrylate (HEMA), and cross-linked copolymers VP/HEMA. Five different cross-linking agents, both hydrophobic and hydrophilic, were used in this study. The resulting hydrogels, with equilibrium water contents ranging between 66.5 and 99.1%, were first subjected to a selection based on their physical behavior during manipulation, after which only the transparent, viscoelastic gels were further considered. Subsequent injectability and visual acuity tests, as well as the evaluation of light transmission characteristics, reduced further the number of potential candidates for vitreous substitution to only thirteen hydrogels. An eliminatory strategy based on physical properties of the potential vitreous substitutes is essential in order to avoid unnecessary sacrifice of experimental animals for in vivo assessment.