The Effects of Gamma Irradiation on Medical Grade Poly(Methyl Methacrylate)
Within developing countries the most cost-effective polymer used in the fabrication of rigid intraocular lenses (IOLs) is poly(methyl methacrylate) (PMMA), for which gamma irradiation is increasingly being used as the preferred method of sterilisation. Medical grade PMMA samples sterilised using a dose of 29kGy of gamma irradiation, were immersed in a simulated aqueous humour solution (SAHS) (pH 7.4, 35 °C), and periodically removed to assess changes in their thermal and structural properties with respect to control samples. Triple-detection gel permeation chromatography indicated that substantial chain scission had occurred during gamma irradiation, an adverse effect that also resulted in a small increase in the rate of diffusion of the SAHS into the PMMA. The diffusion coefficient of SAHS into the gamma-sterilised PMMA was 2.7 ± 0.6 × 10−12 m2s−1, and that for the control samples was 2.0 ± 0.5 × 10−12 m2 s−1. Thermomechanical analysis revealed a decreasing Tg with time for samples incubated in SAHS, showing that the solution caused plasticisation irrespective of irradiation; however, the γ-sterilised PMMA had a Tg 7 °C lower than the control PMMA, which indicates the effect of the γ-irradiation on the rigidity of the polymer.