Assessment of γ-sterilization and/or cross linking effects on orthopedic biomaterial using optical diffuse reflectance spectroscopy

The effects of gamma sterilization and/or cross linking on the band gap properties of ultra-high molecular weight polyethylene (UHMWPE) were studied with diffuse reflectance spectroscopy (DRS). Sheets of UHMWPE were prepared and irradiated for total dose values of 25 kGy, 50 kGy, 100 kGy, and 150 kGy, respectively. After irradiation, samples were tested for reflectance measurements over the wavelength range of 200 nm to 1200 nm. Kubleka-Munk function obtained from each measurement was then used to extract the band gap properties of each sample. The properties included were: Urbach energy (Eu), direct and indirect energy band gaps and number of atoms in CC unsaturation and/or conjugation. The results revealed that Urbach energy (Eu) had linear correlation with absorbed dose having goodness of fit, slope, and intercept values of 94%, 0.70, and 156 meV, respectively. In addition to this, linear decrease and dependence of CC unsaturation and/or conjugation on direct energy band gaps and absorbed dose were also evident. This behavior was attributed to radiation induced structural damage and alterations which included both chemical and physical alterations.