Effect of synovial fluid, phosphate‐buffered saline solution, and water on the dissolution and corrosion properties of CoCrMo alloys as used in orthopedic implants

Abstract

The corrosion and dissolution of high- and low-carbon CoCrMo alloys, as used in orthopedic joint replacements, were studied by immersing samples in phosphate-buffered saline (PBS), water, and synovial fluid at 37 degrees C for up to 35 days. Bulk properties were analyzed with a fine ion beam microscope. Surface analyses by X-ray photoelectron spectroscopy and Auger electron spectroscopy showed surprisingly that synovial fluid produced a thin oxide/hydroxide layer. Release of ions into solution from the alloy also followed an unexpected pattern where synovial fluid, of all the samples, had the highest Cr concentration but the lowest Co concentration. The presence of carbide inclusions in the alloy did not affect the corrosion or the dissolution mechanisms, although the carbides were a significant feature on the metal surface. Only one mechanism was recognized as controlling the thickness of the oxide/hydroxide interface. The analysis of the dissolved metal showed two mechanisms at work: (1) a protein film caused ligand-induced dissolution, increasing the Cr concentration in synovial fluid, and was explained by the equilibrium constants; (2) corrosion at the interface increased the Co in PBS. The effect of prepassivating the samples (ASTM F-86-01) did not always have the desired effect of reducing dissolution. The release of Cr into PBS increased after prepassivation. The metal-synovial fluid interface did not contain calcium phosphate as a deposit, typically found where samples are exposed to calcium rich bodily fluids.

The entrapment of corrosion products from CoCr implant alloys in the deposits of calcium phosphate: A comparison of serum, synovial fluid, albumin, EDTA, and water

“…A hydrophobic adsorbed layer from synovial fluid reduces corrosion, and therefore reduces the oxide thickness that protects the bulk metal. A protective layer would explain the observation that synovial fluid produces a significantly thinner oxide layer than PBS after 35 days immersion of the ''as-received'' CoCr alloy, 30 identical to the samples used in the present work.…”

“…The ToF-SIMS depth profiles demonstrated that deposits of calcium phosphate on the sample surfaces immersed in serum contained Co and Cr ions, supporting the hypothesis that the deposits absorb and reduce the dissolved metals. An organic ligand is present in synovial fluid, which is highly reactive with Cr 3þ , 14,30 increasing the dissolution of Cr in relation to Co. This is reflected in the synovial fluid data in Figure 6 (dissolved Cr), contributing to the upper regression line, which includes EDTA and albumin in PBS and the elevated concentration of the synovial fluid points on Figure 8A.…”

“…14,30 As the synovial fluid and the albumin/PBS produced similar oxide thicknesses on the metal surface, and less than that of the water immersed sample, it would be easy to conclude that albumin is the organic compound acting as a barrier, but this is unlikely, as albumin is also present in the serum sample, where no barrier effect was observed. The observed oxide thicknesses were a result of independent processes or different organic barriers.…”

Tribocorrosion behavior and ions release of CoCrMo alloy coated with a TiAlVCN/CN multilayer in simulated body fluid plus bovine serum albumin

“…These facts could explain the low Co +2 ions release concentration detected in the 10 ml sample solution [52,53]. The media used in this experiment was similar to that used by Karimi [54].…”

Current in vivo wear of metal‐on‐metal bearings assessed by exercise‐related rise in plasma cobalt level

“…15 Moreover synovial fluid causes corrosion of the bearing surfaces that results in highest concentrations of chromium in the synovial fluid. 16 The natural variation in chromium levels due to exercise 17 and possibly the transient release from the synovial fluid makes this element less suitable to compare wear of bearing surfaces.…”