title: Electron paramagnetic resonance analyses of surface radical chemistries of gamma-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.
authors.affiliation: Department of Chemistry, College of Science and Technology, Temple University, Beury Hall, Philadelphia, PA 19122, USA. mikedicicco2001@yahoo.com
authors.forename: Michael
authors.initials: M
authors.lastname: DiCicco
authors.forename: Ryan
authors.initials: R
authors.lastname: Compton
authors.forename: Thanh
authors.initials: T
authors.lastname: Duong
authors.forename: Susan A
authors.initials: SA
authors.lastname: Jansen-Varnum
mesh_terms: D001672:Biocompatible Materials / Q000032:analysis / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D005720:Gamma Rays; D007249:Inflammation / Q000139:chemically induced / Q000209:etiology*; D008422:Materials Testing; D015394:Molecular Structure; D009983:Orthopedic Equipment / Q000009:adverse effects*; D011095:Polyethylenes / Q000737:chemistry* / Q000528:radiation effects / Q000633:toxicity*; D013242:Sterilization; D013499:Surface Properties / Q000528:radiation effects
chemical_list: D001672:Biocompatible Materials; D011095:Polyethylenes; C111601:ultra-high molecular weight polyethylene