Subconjunctival biocompatibility of a viscous bioerodable poly(ortho ester)

The biocompatibility of a viscous poly(ortho ester) (POE) intended for prolonged intraocular drug delivery was studied. This hydrophobic and bioerodable carrier was subconjunctivally injected in rabbits and evaluated both clinically and histologically. To assess the cause of the triggered transient acute inflammatory reaction, the two monomers, the intermediate and final degradation products, and the local toxicity of different solvents used during the polymer preparation were tested. Since the two initial monomers and the intermediate degradation products induced only moderate inflammation, the main acute inflammatory reaction is attributed to the formation of an acidic by-product which has been monitored in vitro by measuring the progressive decrease of the environmental pH. The influence of the sterilization procedure on tissue biocompatibility was established by comparing two polymers of similar molecular weight: one after gamma-sterilization, and an aseptically synthesized one. The biocompatibility was significantly improved by avoiding irradiation of the polymer.