Effects of digestion protocols on the isolation and characterization of metal-metal wear particles. II. Analysis of ion release and particle composition

The isolation of metal wear particles from hip simulator lubricants is impo rtant for understanding wear mechanisms and the tissue response to particul ate material. Part I of this study demonstrated that isolation protocols in volving digestion reagents can chemically attack metal-metal wear particles , reducing their size and changing their shape. In part II of this study, C o and Cr ion concentrations in solution after each digestion protocol were measured by flame atomic absorption spectrometry, and wear particle composi tion was determined by X-ray analysis spectra. The exposure of wear particl es in water to alkaline solutions caused an increasing release of Cr ions i n solution with alkaline concentration and time, and a corresponding decrea se in particle Cr peak intensity on X-ray spectra. As a result, particles e xposed to 12N KOH for 48 h displayed Co peaks and no Cr. In contrast, enzym atic protocols caused a release of Co ions in solution and a corresponding decrease in particle Co peak intensity on X-ray spectra, especially with so dium phosphate as a buffer. However, when isolating particles from 95% seru m, there was an initial protective effect of serum proteins, presumably bec ause of their binding to Co and Cr. As a result, the extent of Cr ion relea se from metal wear particles in 95% serum after alkaline treatments was dim inished, although still present, whereas both enzymatic protocols resulted in a negligible release of Co and Cr ions into solution, Particle compositi on analysis after enzymatic treatments revealed the presence of chromium ox ide particles and CoCrMo particles with variable Co/Cr ratios. After alkali ne treatments, the chromium oxide particles increasingly disappeared with t ime and alkaline concentration, demonstrating a change in particle composit ion after these treatments. This study demonstrated that digestion reagents can induce chemical changes that affect particle composition. Of all the p rotocols tested, the enzymatic protocols were the least damaging to the par ticles and appeared to be the best compromise for isolation and characteriz ation of metal particles, especially in 95% serum. Special care on the choi ce of buffers should be taken when isolating particles from a lower concent ration of serum. (C) 2001 John Wiley & Sons, Inc.