Dominant Role of Molybdenum in the Electrochemical Deposition of Biological Macromolecules on Metallic Surfaces

Abstract

The corrosion of CoCrMo, an alloy frequently used in orthopedic implants, was studied with an electrochemical quartz crystal microbalance (QCM) in three physiologically relevant solutions. Mass changes were measured during potentiodynamic tests, showing material deposition in protein solutions at potential levels that caused mass loss when the proteins were not present. X-ray photoelectron spectroscopy (XPS) data indicated that the deposited material was primarily organic and therefore was most likely derived from proteins in the electrolyte. Material deposition consistently occurred at a critical potential and was not dependent on the current density or total charge released into solution. Corrosion studies on pure Co, Cr, and Mo in protein solutions found material deposition only on Mo. We hypothesize that organic deposition results from the interaction of Mo(VI) with proteins in the surrounding solution. The organic layer is reminiscent of tribochemical reaction layers that form on the surface of CoCrMo hip bearings, suggesting that these types of layers can be formed by purely electrochemical means.

In-situ generated tribomaterial in metal/metal contacts: Current understanding and future implications for implants

“…In the transpassive potential, protein adsorption on an oxide film was also observed [79]. At this transpassive potential, the dissolution of Mo(VI) ions may additionally promote protein deposition [81]. Although the bilayer tribofilm is compatible with both a passive and transpassive state of the alloy, transpassive potentials require the presence of strong oxidising agents.…”

“…Those oxidising agents can be present in the synovial fluid due to inflammatory cell processes in the surrounding tissues [101] or can be in principle be generated locally at contact spots undergoing high temperatures. In the former case, based on mechanisms proposed by Martin et al [81], one would expect a reaction film that covers the whole surface, while in the latter case, the tribofilm would form in the localized contact zone only.…”

“…Albumin adsorbed on CoCrMo alloys inhibits oxygen reduction [78] while at the same time increases passive film dissolution [79]. Protein surface interactions with Molybdenum ions have been reported as crucial factors affecting the transpassive behaviour of CoCrMo alloys [80, 81]. Protein adsorption is a complex process in which the prevailing electrochemical conditions, the structure of proteins, the ionic strength and the pH of the solution, and metal surface properties influence the affinity of the protein for a given interface [82].…”

The effect of contact load on CoCrMo wear and the formation and retention of tribofilms

“…One of our own studies concluded that the occurrence of proteins directly affects the synergism of wear and corrosion in the tribocontact [32]. The release of molybdenum(VI)-ions during tribocorrosion might be responsible for the formation of a proteinaceous layer on the surface [33], which then undergoes mechanical mixing under the applied tribological stresses to form a tribofilm [34,35]. The results of this study suggest that the presence of a tribofilm diminishes the load sensitivity of wear and leads to a constant rate of material loss over a substantial range of applied contact stress.…”

Electrochemical Quartz Crystal Microbalance and X-Ray Photoelectron Spectroscopy study of cathodic reactions in Bovine Serum Albumin containing solutions on a Physical Vapour Deposition-CoCrMo biomedical alloy

“…Albumin influences the corrosion process of CoCrMo by enhancing passive [4,5] and transpassive dissolution [6] as well as modifying surface chemistry [5,7]. Wear of these alloys is also highly dependent on the presence of Albumin [8] in the electrolyte, which can affect the corrosion response to friction as well as the mechanical mechanisms leading to wear.…”