Electron paramagnetic resonance analyses of surface radical chemistries of γ-sterilized orthopedic materials: Implications pointing to cytotoxicity via wear debris-induced inflammation

• Published in: Journal of biomedical materials research. Part B, Applied biomaterials Applied biomaterials, 2005-10, Vol.75B (1), p.6-17
• Main Authors: DiCicco, Michael, Compton, Ryan, Duong, Thanh, Jansen-Varnum, Susan A.
• Format: Article
• Language: English
• Subjects: Biocompatible Materials - analysis; Biocompatible Materials - chemistry; cytotoxicity; DUDMA; Electron Spin Resonance Spectroscopy; EPR; Gamma Rays; hydroxyl radical; Inflammation - chemically induced; Inflammation - etiology; Materials Testing; Molecular Structure; Orthopedic Equipment - adverse effects; orthopedic materials; Polyethylenes - chemistry; Polyethylenes - radiation effects; Polyethylenes - toxicity; Sterilization; Surface Properties - radiation effects; UHMWPE
• ISSN: 1552-4973; 1552-4981
• DOI: 10.1002/jbm.b.30164

In this research, electron paramagnetic resonance (EPR) spin‐trapping was utilized to determine if surface radical chemistries occur for gamma (γ)‐sterilized orthopedic materials—ultra‐high molecular weight polyethylene (UHMWPE) and the novel, hybrid, diurethane dimethacrylate (DUDMA)‐based RHAKOSS™. The materials' ability to competitively chelate catalytic ferrous ions (Fe2+) or readily reduce ferric ions (Fe3+), and hydrogen peroxide (H2O2) directly, in facilitating the Fenton reaction (FR), is indicative of cytotoxicity. Validations with a radical scavenger aids to confirm a radical mechanism. In conjunction, materials were thermally annealed and characterized by attenuated total reflectance–Fourier‐transform infrared (ATR‐FTIR) spectroscopy in order to explore accelerated oxidative degradation induced by residual radicals evolving from γ‐sterilization. Particularly, there was a significant decrease in spin‐adduct peak areas obtained from the reduction of H2O2 in the presence of RHAKOSS or UHMWPE, evaluated against their respective controls. Additionally, chelated Fe2+ accelerated the rate of FR. This phenomenon suggests that the materials are not better chelators than the Fe‐activating chelator, edta. Neither material had the propensity to readily reduce Fe3+ to the relevant Fe2+, as certified by a nonradical mechanism. Alternatively, the false spin‐adduct signal acquired when chelated Fe3+ is employed arises via the nucleophilic addition of water onto the DMPO spin trap. Residual radicals in UHMWPE did not recombine/terminate following thermal annealing in an inert atmosphere. The radicals in RHAKOSS, however, did recombine under mild heating in an oxidizing or inert atmosphere. Both materials displayed quenching of ˙OH; however, for UHMWPE, this mechanism was jointly accountable for its accelerated degradation, evidenced by ATR‐FTIR. Quenching of ˙OH by the silica found in RHAKOSS manifested in a competing effect that counterbalanced the observed FR. Implanted RHAKOSS is not likely to promote cytotoxicity and should not degrade, but the damaging effect of γ sterilization on UHMWPE is a serious dilemma confronting its long‐term durability and biocompatibility. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2005