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

Abstract

In this research, electron paramagnetic resonance (EPR) spin-trapping was utilized to determine if surface radical chemistries occur for gamma (gamma)-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 (Fe(2+)) or readily reduce ferric ions (Fe(3+)), and hydrogen peroxide (H(2)O(2)) 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 gamma-sterilization. Particularly, there was a significant decrease in spin-adduct peak areas obtained from the reduction of H(2)O(2) in the presence of RHAKOSS or UHMWPE, evaluated against their respective controls. Additionally, chelated Fe(2+) 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 Fe(3+) to the relevant Fe(2+), as certified by a nonradical mechanism. Alternatively, the false spin-adduct signal acquired when chelated Fe(3+) 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 gamma sterilization on UHMWPE is a serious dilemma confronting its long-term durability and biocompatibility.

Probing Liquid/Solid Interfaces at the Molecular Level

“…Hydroxyl and carboxylate radicals have been used to model by ESR the potential for hydrogen abstraction in biological compartments and for the formation of hydrogen peroxide in the phagosome during phagocytosis as well. In a materials science project connected with biological applications, ESR was utilized to evaluate the feasibility of surface radical chemistry in γ-sterilized orthopedic materials, including ultrahigh molecular weight polyethylene and the hybrid diurethane dimethacrylate-based RHAKOSS . The failure of those materials to competitively chelate catalytic ferrous ions or readily reduce ferric ions directly was used as an indication of lack of cytotoxicity.…”