Quantification of cartilage wear morphologies in unidirectional sliding experiments: Influence of different macromolecular lubricants

Quantifying surface damage on articular cartilage after exposure of the tissue to extreme or prolonged mechanical stress is not only relevant for evaluating clinically relevant alterations, e.g. when the physiological lubrication mechanisms fail, but also useful for assessing the suitability of artificial cartilage replacement materials, implants or synovia-mimetic lubricants. Here, we establish a systematic quantification method for cartilage wear formation which is based on optical profilometry - a variant of confocal microscopy. With this approach, we compare three different macromolecular lubricants, i.e. solutions containing either hyaluronic acid, lubricin or porcine gastric mucin. Depending on the counter material used for tribological testing and the macromolecule used for lubrication, we detect different types of tissue damage which we quantify with suitable topographical parameters. In our setup, mucin solutions outperform the other two lubricants: when using mucin solutions for lubrication, we do not find any signs of topographical alterations on the cartilage surface. Our results underscore the supreme protective abilities of mucin solutions - even on biological surfaces where they do not occur physiologically.