Carbon-centered radicals in γ-irradiated bone substituting biomaterials based on hydroxyapatite.

Gamma irradiated synthetic hydroxyapatite, bone substituting materials NanoBone® and HA Biocer were examined using EPR spectroscopy and compared with powdered human compact bone. In every case, radiation-induced carbon centered radicals were recorded, but their molecular structures and concentrations differed. In compact bone and synthetic hydroxyapatite the main signal assigned to the CO2 − anion radical was stable, whereas the signal due to the CO3 3− radical dominated in NanoBone® and HA Biocer just after irradiation. However, after a few days of storage of these samples, also a CO2 − signal was recorded. The EPR study of irradiated compact bone and the synthetic graft materials suggest that their microscopic structures are different. In FT-IR spectra of NanoBone®, HA Biocer and synthetic hydroxyapatite the HPO4 2− and CO3 2− in B-site groups are detected, whereas in compact bone signals due to collagen dominate.