On the Growth Rate of Tribomaterial in Bovine Serum Lubricated Sliding Contacts

Alfons Fischer,Daniel Stickel,Christian Schoss,Rob Bosman,Markus Wimmer

doi:10.3390/lubricants4020021

Abstract

Considering total hip arthroplasty, so-called tribolayers (aka tribomaterial), consist of carbonaceous material from the periprosthetic joint fluid or bovine serum mixed with nanometer size metal and oxide wear particles. Currently, its growth sequence and rate are unknown. Thus, smooth surfaces of low-Carbon (LC-) vs. high-Carbon (HC-)CoCrMo (Cobalt-Chromium-Molybdenum) alloys have been worn in a conforming contact under bovine serum lubrication by means of a pin-on-ball wear tester. These tests were interrupted at certain numbers of cycles in order to weigh the specimens, characterize the topography, and investigate the wear appearances. In addition, after cleaning in ethanol and anionic detergent, before-and-after comparison rendered the weight of the tribomaterial. This revealed that, during run-in, the specimens gained weight by generating tribomaterial. Afterwards the loss of material surpassed the generation of new tribomaterial and a steady weight-loss was measured. Topography measurements were used as input data for contact mechanics calculations. Apparently the incipient, locally high contact stresses accelerated tribochemical reactions. After run-in, the contact situation changes and leads to a much smaller generation rate. This paper provides information about the growth sequence and rate of such tribomaterial formation. It further highlights the significance of highly localized contact stress as an important factor for tribomaterial generation.

Highlights

Until about three years ago, approximately one third of the more than 300,000 annually performed hip arthroplasties in the United States were made of self-mating cobalt-chromium (CoCr) alloy bearing surfaces [1]
This paper aims to elucidate growth rigs running under mild-sliding wear generate wear rates in the range of μm/h
The total material loss of pins and heads gained from weight loss measurements are comparatively shown in Figure 3 for both cleaning procedures

Summary

Introduction

Until about three years ago, approximately one third of the more than 300,000 annually performed hip arthroplasties in the United States were made of self-mating cobalt-chromium (CoCr) alloy bearing surfaces [1] Some of these metal-on-metal (MoM) devices failed at a high rate [2]. Many papers of protein lubricated metal-on-metal sliding contacts in vivo and in vitro report on tribochemically generated layers [9,10,11,12] These socalled tribofilms, aka tribomaterial, consist of carbonaceous material from the periprosthetic joint fluid mixed with nanometer size metal and oxide wear particles, while other constituents are still under investigation [13,14,15]. According to the basics of the 3rd-body-model of [16] in combination with [17,18]

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