Abstract
The formation of tribochemical reaction layers, better known as tribofilms, on cobalt-chromium-molybdenum (CoCrMo) alloys commonly used in orthopaedic applications has been hypothesized to reduce degradation owing to wear and corrosion. However, the mechanisms and pathways influencing tribofilm formation remain largely unknown. This study aims to develop a clearer understanding of the role of protein structures and its concentration on tribocorrosion and surface tribofilms formed on CoCrMo alloys during boundary regime sliding. A reciprocating tribometer with a three-electrode electrochemical cell was employed to simulate and monitor the tribocorrosion of CoCrMo in situ. As-received Foetal Bovine Serum (as-FBS) and pre-heated FBS at 70 °C for 1 h (de-FBS) were diluted with saline (0.9% NaCl) at different concentrations (25% and 75% v/v) and utilized as electrolytes during the tribocorrosion tests. The result shows that the denatured protein structure in electrolyte tends to reduce the volume losses due to wear and corrosion on the CoCrMo samples with an appreciation of the protein tribofilms. On the other hand, an increased protein concentration increased the total volume loss due to corrosive processes. A novel finding revealed in this study is that the tribocorrosion mechanism of the CoCrMo surface is dependent on the protein structure, concentration and sliding duration due to the change in surface condition.
Highlights
CoCrMo is one of the most widely used bearing materials in Total Hip Replacements (THRs) owing to its excellent mechanical properties, self-mating performance and perceived biocompatibility [1,2,3]
That study showed that range of the critical temperature for protein denaturing was within 50–60 °C
Protein structure in de-Foetal Bovine Serum (FBS) electrolyte used in this study was suggested to be fully denatured since the preheating treatment has passed the unfolding critical temperature
Summary
CoCrMo is one of the most widely used bearing materials in Total Hip Replacements (THRs) owing to its excellent mechanical properties, self-mating performance and perceived biocompatibility [1,2,3]. Tribocorrosion, the combined process of wear and corrosion, causes the simultaneous generation of metallic debris (mechanical wear) and ion release (electrochemical corrosion) [7, 8]. Examples of tribocorrosion within orthopaedic applications include metal-on-metal (MoM) THR, MoM hip resurfacing and three-body abrasion within metal-on-polymer bearings [12,13,14]. Whilst the second generation metal-on-metal hip replacements have largely been withdrawn from the market due to their higher than acceptable revision rates, MoM hip resurfacing is still being implanted and presents satisfactory results among certain patient demographics [15]. Questions around the long-term risk associated with the implant derived debris, safety and longevity performance of metal-based implants remain [16,17,18]
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