Poly(1-vinyl-2-pyrrolidinone) hydrogels as vitreous substitutes: a rheological study

In order to develop an artificial vitreous, a large series of hydrogels have been previously produced by polymerization of 1-vinyl-2-pyrrolidinone, with or without crosslinking. Based on the assumption that a functional vitreous substitute should possess viscoelastic properties after its delivery, a number of selected gels were characterized rheologically by both oscillatory shear stress analysis and shear creep analysis, using a controlled stress rheometer in the cone/plate configuration. The experiments demonstrated a dramatic effect of injecting the gels through small-gauge needles, as many lost their viscoelasticity to become free-flowing fluids, probably because of the cleavage of chains and crosslinks. It was also found that the increase of comonomer content (2-hydroxyethyl methacrylate) and of crosslinking level generally had a strengthening effect. However, the effects of hydrophilic crosslinking agents (diallyl ether and divinyl glycol) were irregular. Eventually, only four hydrogels in this series showed viscoelastic characteristics after injection through a 30-gauge (0·13mm diameter) needle, maintaining behaviour typical of crosslinked networks and warranting further assessment as potential vitreous substitutes.