Effect of gamma-radiation on a polyanhydride implant containing gentamicin sulfate

Septacin, a polyanhydride implant containing gentamicin sulfate, was sterilized by gamma-radiation. Its copolymer molecular weight (M(w) by GPC) was increased after this radiation. No cross-linking was shown in the radiated samples as no gel content was found by the filtration method. The chemical structure as detected by 1H NMR for non-radiated and radiated samples was comparable. For samples radiated at higher dose levels (70-100 kGy), the IR spectra showed that the intensity of absorbance attributable to the C-H stretching vibration (at 2852 and 2927 cm(-1)) was attenuated, indicating free-radical formation or loss of hydrogen atoms from C-H bonds. However, the mass spectra for the gamma-radiated and the non-radiated controls after they were completely depolymerized in methylene chloride were virtually identical. Therefore, it could be concluded that the increase in copolymer molecular weight for radiated Septacin was a result of chain extension in the copolymer backbone during radiation. In addition, wide-angle X-ray diffraction and polarizing light microscopy (PLM) revealed a change in the physical structure of the radiated copolymer. There was an increase in crystallinity of the copolymer with increasing radiation doses; the greatest increase in crystallinity occurred at the dose range of 70-80 kGy, which was also shown to result in the greatest molecular-weight increase. The crystalline morphology of the samples as detected by PLM was not altered by gamma-radiation, regardless of the dose levels.