Abstract
Hydroxyl radical (·OH)‐induced inflammation is a primary mode for in vivo cytotoxicity. A legitimate concern is whether particulate wear debris from orthopedic composites can stimulate inflammation via ferrous ion (Fe^2+^)‐mediated production of ·OH. The purpose of this research was to utilize electron paramagnetic resonance (EPR) spin trapping in investigating and comparing the potential for postsurgical cytotoxicity induced specifically by ·OH in the presence of two composites: Simplex P® and the novel, hybrid, CORTOSS™. Cytotoxicity is evaluated based on the composites competitively chelating catalytic Fe^2+^ or readily reducing ferric ions (Fe^3+^), in facilitating the Fenton reaction (FR). ·OH that are produced were then validated by a radical scavenger to confirm a genuine radical signal and mechanism. Spin adduct peak areas decreased in the presence of CORTOSS as opposed to increasing in the presence of Simplex P, evaluated against their respective controls. A plausible theory elucidating this finding is that CORTOSS may sequester the Fe form, by virtue of its monomers. Principally, direct comparison of composites indicated that Simplex P had greater tendency to produce ·OH, yielding 25.6 and 48.7% greater spin adduct peak areas when chelated and non‐chelated Fe^2+^ are used, respectively. Moreover, the rate of FR accelerated when chelated Fe^2+^ was used, leading to the formation of a ternary complex with the composites. This was more prominent in Simplex P, as coordination of chelated Fe^2+^ occurs on its surface via an electrostatic attraction to allow a seventh coordination site for ligand exchange in the ternary complex, stabilized by Ba^2+^. Conversely, the silica found in CORTOSS possesses radical quenching abilities that deactivate generated ·OH in impeding the efficiency of FR. Neither composite demonstrated a capacity to readily reduce Fe^3+^ to the relevant Fe^2+^, as validated by a non‐radical pathway. Instead, the artificial spin adduct signal attained when employing chelated Fe^3+^ was due to the nucleophilic addition of water onto DMPO. Simplex P may also serve as a template for surface catalysis of the nucleophilic addition of water onto DMPO involving chelated Fe^3+^. CORTOSS is thought not to induce cytotoxicity, whereas the propensity of Simplex P in promoting Fenton chemistry is a serious issue that must be addressed. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 72B: 146–155, 2005