Comparative stability of intraocular lenses during 2-20 years of artificial aging, potential effects in terms of biocompatibility

Intraocular lenses (IOLs) are worldwide used for cataract surgery. Mostly made of acrylate polymers, they can lead to an unexpected biocompatibility reaction such as posterior capsular opacification (PCO). Acrylate polymers suffer from both oxidative and heat/thermal aging that affect their properties. We examined the stability of four currently available acrylic IOLs, three hydrophobic and one amphiphilic, under artificial aging that simulate intraocular conditions from 2 to 20 years. Released degradation products were detected by reversed-phase high performance liquid chromatography. Thermal properties were investigated using thermogravimetric analysis, and differential scanning calorimetry measurements. Surface topography was analyzed by atomic force microscopy. The effect on biocompatibility was estimated with protein sorption of the aged lenses. Both surface and thermal properties changed under aging. Surface roughness of implants increased under aging in a kinetic in two steps. The aging also changed the polymer structure. These changes lead to a variable release of degradation products according to the chemical design of the copolymer. Glass temperature transition (T-g) and thermal degradation stability also suffered from aging. The aging has led to significant changes in protein sorption affinity to IOL surfaces. For pure hydrophobic acrylic copolymer, stability was higher for copolymers containing at least one fluoro methacrylate. The amphiphilic polymer appeared to have a time-dependent aging that can affect the implant flexibility and could impact late biocompatibility reaction and tolerance.