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

Abstract

The isolation of metal wear particles from hip simulator lubricants is important for understanding wear mechanisms and the tissue response to particulate material. Part I of this study demonstrated that isolation protocols involving digestion reagents can chemically attack metal-metal wear particles, reducing their size and changing their shape. In part II of this study, Co and Cr ion concentrations in solution after each digestion protocol were measured by flame atomic absorption spectrometry, and wear particle composition was determined by X-ray analysis spectra. The exposure of wear particles in water to alkaline solutions caused an increasing release of Cr ions in solution with alkaline concentration and time, and a corresponding decrease in particle Cr peak intensity on X-ray spectra. As a result, particles exposed to 12N KOH for 48 h displayed Co peaks and no Cr. In contrast, enzymatic protocols caused a release of Co ions in solution and a corresponding decrease in particle Co peak intensity on X-ray spectra, especially with sodium phosphate as a buffer. However, when isolating particles from 95% serum, there was an initial protective effect of serum proteins, presumably because of their binding to Co and Cr. As a result, the extent of Cr ion release from metal wear particles in 95% serum after alkaline treatments was diminished, although still present, whereas both enzymatic protocols resulted in a negligible release of Co and Cr ions into solution. Particle composition analysis after enzymatic treatments revealed the presence of chromium oxide particles and CoCrMo particles with variable Co/Cr ratios. After alkaline treatments, the chromium oxide particles increasingly disappeared with time and alkaline concentration, demonstrating a change in particle composition after these treatments. This study demonstrated that digestion reagents can induce chemical changes that affect particle composition. Of all the protocols tested, the enzymatic protocols were the least damaging to the particles and appeared to be the best compromise for isolation and characterization of metal particles, especially in 95% serum. Special care on the choice of buffers should be taken when isolating particles from a lower concentration of serum.

The John Charnley Award: An Accurate and Extremely Sensitive Method to Separate, Display, and Characterize Wear Debris Part 2: Metal and Ceramic Particles

“…Each sample was then treated according to an optimized proteolytic digestion protocol (Fig. 2) to avoid particle degradation caused by more aggressive digestion protocols, such as bases and acids [10,11]. The protocol is reported in detail in Appendix 1 (supplemental materials are available with the online version of CORR).…”

Characterization of wear particles generated from CoCrMo alloy under sliding wear conditions

“…Compared to polyethylene particles, the isolation of metallic wear particles requires a more sophisticated protocol using enzymatic digestion to remove organic components, especially proteins, without damaging the particles. Particles in the present study were isolated following the protocol developed by Catelas et al [18, 19, 24], as briefly described below, with minor changes. This protocol was shown to minimize particle damage [18, 24].…”

New Insights into Wear and Biological Effects of Metal-on-Metal Bearings

“…Wear Particle Characteristics M ultiple studies have described metal-on-metal particle characteristics, but they remain difficult to compare because of differences in the metallurgy of the prosthetic component alloys and differences in the isolation and characterization protocols that can affect the particles as demonstrated by Catelas et al 36,37 . Despite that, there is now a general consensus that the average particle size ranges from about 30 to 100 nm [4][5][6] .…”