Hydrophilic sponges based on 2-hydroxyethyl methacrylate: part VII: modulation of sponge characteristics by changes in reactivity and hydrophilicity of crosslinking agents.

Despite previous unsuccessful attempts to use hydrated poly(2-hydroxyethyl methacrylate) sponges as implantable biomaterials, recently these materials became important as peripheral components in an artificial cornea of the core-and-skirt design. The low mechanical strength of sponges prompted this study on possible improvement of tensile properties by the use of a variety of crosslinking agents. Three vinylic (dimethacrylates) and two allylic compounds were used at different concentrations (0.1 to 2% (mol)) as crosslinking agents in the production of sponges. Their influence on the mechanical properties, porous morphology and swelling behavior of resulting sponges was evaluated. The onset of phase separation during polymerization was also measured by visible spectrophotometry. The results suggested an inherent heterogeneity of sponges, i.e. pores of non-uniform size and structural inhomogeneities. While the effects of changes in the nature and concentration of crosslinking agents on the equilibrium water content of sponges were ambiguous, some of the mechanical properties, such as toughness and elasticity, were improved by crosslinking with allylic agents. Scanning electron microscopic examination suggested that the mechanical effect is related to the variation of size of the polymer particles constituting the sponge structure, which was proved to be dependent upon the onset of phase separation during polymerization. Copyright 2000 Kluwer Academic Publishers