A multidisciplinary experimental framework addressing the relationship between the mechanical behaviour and the structure of the knee articular cartilage

Articular cartilage is an extremely specialized connective tissue composing the synovial joints. The response of articular cartilage – along with the damping system provided by the other tissues composing the fundamental unit of synovial joints, i.e., the osteochondral unit – is essential in deploying multiaxial forces generated during locomotion. The dynamic interaction between homeostasis and remodelling of the osteochondral tissues is essential in maintaining joints functional capabilities. Several traumatic and degenerative pathologies may deregulate the dynamic remodelling of the osteochondral tissues, especially considering highly-stressed articulation as the knee joint. The knowledge on osteochondral tissues is essential in understanding the onset and progression of several pathologies affecting synovial joints, moreover, allowing to elucidate the main aspects on which relative treatments should focus on. In this perspective, the approaches investigating the peculiarities – i.e., mechanical response, structure, and composition – of such a unit are away far from providing reliable and complete information, particularly concerning articular cartilage. Ex-vivo studies focusing on the knee articular cartilage mostly evaluate such a tissue through single-layer tests, yielding insights through multidisciplinary approaches only occasionally.
Within this thesis, a multidisciplinary experimental framework was developed to explore the relationship between functionality and structure of one of the three tissues composing the knee osteochondral unit, the articular cartilage, with a particular focus on tissue biomechanics. Although the approaches here proposed were tailored to articular cartilage, the peculiarities at the base of these techniques are defined aiming to extend their application to study the features of the osteochondral unit in a comprehensive way. First, an indentation protocol was optimized to investigate the articular cartilage viscoelastic response; the implementation of a reliable mechanical testing protocol is crucial to achieve reliable insight on the mechanical response of articular cartilage. Second, the relationship between articular cartilage functionality – i.e., mechanical response – and structure/composition has been investigated, evaluating articular cartilage through the previously optimized indentation protocol and, moreover, an experimental, spectroscopic-based approach. Third, considering the previously mentioned purpose and, further, moving towards a comprehensive evaluation of the osteochondral unit, the use of a specific contrast-agent X-ray imaging was explored to investigate the articular cartilage composition. Fourth, we assessed also the suitability of a full-field, X-ray-based approach in studying the comprehensive functional behaviour of the osteochondral unit.
The implemented multidisciplinary framework represents a key step forward investigating the main features of the knee articular cartilage, providing the potential of assessing properly the efficacy of clinical and tissue-engineering treatments addressing the pathologies of the knee.