Tribofilms on CoCrMo alloys: Understanding the role of the lubricant

Abstract

The tribological activation of a passive metal alloy in an aqueous biological environment have been highlighted by many researchers; better known as bio-tribocorrosion. Tribocorrosion processes, which can be found at a number of metal-based biomedical implant interfaces, can be affected by lubricant species such as proteins, amino acids and salts. To date, researchers have quantified how the presence of organic species and the environment affect the tribological and corrosion process. However, the nature of the bio-films is still broadly to be explored. This study aims to understand how the lubricant-surface interactions influence the evolving frictional, corrosion and material volume loss from CoCrMo alloys and how the formation of any tribo-film at the interface may influence the aforementioned processes. This current research uses reciprocating tribocorrosion tests of CoCrMo surfaces in saline, protein, and protein-free cell culture medium lubricants (0.9% NaCl, 25% Foetal Bovine Serum (FBS) diluted in Phosphate Buffered Saline (PBS), Dulbecco's Modified Eagle Medium (DMEM) and 25% FBS in DMEM solutions). Results show the addition of organic constituents give a better tribology and corrosion performances. XPS confirmed that chemical reactions happened on the tested surfaces. Calcium, phosphorus and sulphur are shown to be catalysed to react in tribology-induced processes and have important roles in tribocorrosion. These results contribute to the understanding of protein-metal interactions occurring in tribofilm formation on wearing surfaces.

The Effect of Protein Structure and Concentration on Tribocorrosion and Film Formation on CoCrMo Alloys

“…The presence of sulphur in the form of cobalt sulphide has been observed via XPS and SAED images within the tribofilm on the CoCrMo surface slid in bovine serum by Hesketh et al [41]. Furthermore, the authors have identified Mo-S speciation via XPS in a previous study [8]. The presence of sulphur on the surface and its tendency to reduce volume loss due to mechanical wear have been demonstrated in several studies [78,79].…”

“…A linear E-I response around zero net current was observed. The slope of measured current as a function of applied potential represents the R p which was calculated using the voltage window of ± 5 mV around zero net current as utilized in the previous studies [8,61]. The obtained R p was converted into a corrosion current density ʹ I corr ʹ (Ampere) using the Stern-Geary formula (Eq.…”

“…Atomic quantitative analysis was taken from two spots inside the wear scar in each sample (n = 3) by EDS. Previous studies [8,64] characterized that typical elements, e.g. carbon, nitrogen, sulfur, oxygen and metallic traces, were found on the retrieved implant surface.…”

“…However, the use of CoCrMo alloys is not without problems and issues associated with tribology, corrosion and implant-associated debris remain of interest to the community [4][5][6]. Tribocorrosion, the combined process of wear and corrosion, causes the simultaneous generation of metallic debris (mechanical wear) and ion release (electrochemical corrosion) [7,8]. The release of metal products has been seen to elicit adverse biological reactions requiring surgical intervention and the revision of an existing implant [9][10][11].…”

“…Fig.3Instrumented reciprocating tribometer scheme (this image is reproduced from the previous study[8])…”