Abstract
To examine coefficients of friction (COFs) of articular cartilage, it is necessary to use cartilage as a friction partner. Irregularities of surfaces require special tribometers and calculation methods. The aim of this study was to establish a tribometer system for measuring a low COF of cartilage and to develop and validate an algorithm that takes the irregularities into consideration. We used a pin-on-plate tribometer that allows a vertical displacement of the pin to follow the surface of the plate and developed an algorithm that takes these irregularities into account. We were, thus, able to take into consideration a forward and backward movement, an upward and downward movement, and different force ratios. The algorithm was validated using a spherical POM (polyoxymethylene) pin against a stainless steel plate at slope angles up to 24°. First examinations with articular cartilage against articular cartilage samples of a stifle joint of a pig were then performed. The newly developed tribometer worked well when POM against a stainless steel hump was examined. The COF increased for slope angles steeper than ±15°. There was an interaction between the COF and the slope angle, but not for the range within ±15°. Cartilage examinations revealed COFs as published in the literature. The tribometer and the algorithm were suitable for the detection of low COF of irregular surfaces of the plate within a range of ±15°. The COF resulting from the forward and backward movements should be averaged.
Highlights
Low coefficients of friction (COFs) are well known to be a particular feature of articular cartilage (Caligaris and Ateshian, 2008; Katta et al, 2009; and Northwood et al, 2007)
We examined the COF of the femorotibial joint (FTJ) and of the patellofemoral joint (PFJ)
All data gained from the experiments were recorded; we were able to calculate the COF based on the measurements of force and position
Summary
Low coefficients of friction (COFs) are well known to be a particular feature of articular cartilage (Caligaris and Ateshian, 2008; Katta et al, 2009; and Northwood et al, 2007). The COF can increase in such experiments, while the COF stays low and unchanged when articular cartilage is moved against articular cartilage (Caligaris and Ateshian, 2008; Katta et al, 2009; and Northwood et al, 2007). In the literature, you can find only a few tribological experiments where the movement of articular cartilage against articular cartilage has been analyzed (Bonnevie et al, 2018; Caligaris and Ateshian, 2008; Caligaris et al, 2009; Mabuchi and Fujie, 1996; Northwood et al, 2007; and Warnecke et al, 2017).
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