The paper aims to focus on the individual contribution of water to the lubrication regimes in articular joints because understanding of these regimes is crucial not only for the treatment of diseases like osteoarthritis but also for the development of new implants to have a longer service cycle.
Cartilage specimen and the synovial fluid were both isolated from bovine knee joints that are enclosed by a synovial membrane under sterile conditions of a biosafety Level 2 (BSL2) cabinet. Subchondral bone was removed from the cartilage because it not only creates a stable base to place the specimen on the holder, but it also acts as a primary shock absorber protecting the overlaying cartilage under high-impact loads. A specimen holder specially designed for tests and was attached to the linear oscillation (SRV) test machine. The SRV test machine provides a reciprocating sliding motion between the cartilage samples that are submerged into the selected biological media. The entire system can be mounted on the BSL2 cabinet, sealed with the convoluted gaiter and transported to the SRV machine with a specifically designed handle for the entire system. The process ensures sterile conditions for tests on biological samples that are highly sensitive to the environmental conditions.
A remarkably low coefficient of friction value for distilled water constitutes more evidence to support the assumption of the impact of water in the friction behaviour of the cartilage-against-cartilage contact. As the fluid in articular cartilage (AC) effectively serves as a synovial fluid reserve and 70-80 per cent of its composition is distilled water, it can be stated that the tribotest system mimics the natural working conditions of an actual knee joint adequately.
Time and limited availability of the animal-driven samples led to a focus on certain parameters mentioned in the approach. A planned scan of parameter matrix, such as variation of load and speed, would allow deeper knowledge on the lubrication regimes.
Study of relevant tribological contact in human joints might give ideas on new designs for artificial joints.
Understanding of lubrication regimes is crucial not only for the treatment of diseases like osteoarthritis but also for the development of new implants to adapt motion of related joint.
Exclusion of water and application as the primary lubricant in the test system brings a new perspective to joint lubrication.
This work was funded by the Austrian COMET Program (Project K2, XTribology, no. 824187/849109) and carried out at the “Excellence Centre of Tribology” (AC2T research GmbH).
Conflicts of interest: The authors declare no conflict of interest.
Göçerler, H., Pfeil, B., Franek, F., Bauer, C., Niculescu-Morzsa, E. and Nehrer, S. (2020), "The dominance of water on lubrication properties of articular joints", Industrial Lubrication and Tribology, Vol. 72 No. 1, pp. 31-37. https://doi.org/10.1108/ILT-02-2019-0064
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