Effects of digestion protocols on the isolation and characterization of metal-metal wear particles. I. Analysis of particle size and shape

Isolation of metal wear particles from hip simulator lubricants or tissues surrounding implants is a challenging problem because of small particle siz e, their tendency to agglomerate, and their potential for chemical degradat ion by digestion reagents. To provide realistic measurements of size, shape , and composition of metal wear particles, it is important to optimize part icle isolation and minimize particle changes due to the effects of the reag ents. In this study (Part I of II), transmission electron microscopy (TEM) was used to examine and compare the effects of different isolation protocol s, using enzymes or alkaline solutions, on the size and share of three diff erent types of cobalt-based alloy particles produced from metal-metal beari ngs. The effect on particle composition was examined in a subsequent study (Part II). Large particles (<1200 nm) were generated by dry abrasion of CoC rMo alloy against itself and small particles (<300 nm) were generated by hi p simulator testing of a metal-metal implant pair in the presence of either distilled-deionized water or a 95% bovine serum solution. The reagents cha nged particle size and to a lesser extent particle shape. For both large pa rticles and small particles generated in water, the changes in size were mo re extensive after alkaline than after enzymatic protocols and increased wi th alkaline concentration and time in solution, up to two-fold at 2 h and t hreefold at 48 h. However, when isolating particles from 95% serum, an init ial protective effect of serum proteins and/or lipids was observed. Because of this protective effect, there was no significant difference in particle size and shape for both oval and needle-shaped particles after 2 h in 2N K OH and after enzymatic treatments. However, round particles were significan tly smaller after 2 h in 2N KOH than after enzymatic treatments. Particle c omposition may also have been affected by the 2N KOH treatment, as suggeste d by a difference in particle contrast under TEM, an issue examined in deta il in Part II. (C) 2001 John Wiley & Sons, Inc.