A study of the effect of X-ray irradiation on the structure of Narafilcon A biopolymer soft contact lenses

The effects of external factors such as X-ray irradiation on the structure and physical properties of contact lenses are very important for both the patients using contact lenses and medical personnel. The aim of the study was to investigate the effect of X-rays on the structure of Narafilcon A silicone-hydrogel contact lenses. In order to study the structural changes caused by X-rays in Narafilcon A polymer contact lenses, the following spectroscopy methods were used: positron annihilation lifetime spectroscopy (PALS), Fourier transform middle infrared spectroscopy (FTIR) and Raman spectroscopy (RS). Irradiation of the investigated sample was carried out using an Elekta Synergy accelerator. The contact lenses were irradiated with the following total doses of X-rays: 0.05 Gy, 0.5 Gy, 0.8 Gy, and 1.0 Gy. The PALS measurements showed that X-ray irradiation caused slight changes in the size of the free volume and the fractional free volume in the structure of the polymer contact lenses examined. However, the FTIR and RS measurements showed that X-rays did not break the monomer bonds in the polymeric structure of the sample. The changes revealed by the PALS method may be related to possible displacement of monomer chains, resulting in changes in the dimensions and numbers of free volumes. The finding that X-ray radiation does not affect or damage polymer bonds can in the future contribute to the use of X-ray and gamma radiation to sterilize contact lenses.