Articular cartilage is fluid-swollen tissue at the ends of synovial joints, which functions by providing a lubricated surface for articulation and facilitates efficient transmission of loads. Cartilage biomechanical function is highly dependent on the integrity of its matrix, consisting of water, collagen and proteoglycans (PG), and the interaction between these components. Consequently, alteration of articular cartilage matrix components, either by injury or degenerative conditions such as osteoarthritis (OA), results in compromised functional behaviour. This makes the assessment of this tissue essential early in the degenerative process to prevent or reduce further joint damage, often characterised by pain and immobility, with associated socio-economic impact.

Mechanical compression and indentation techniques have long been used to assess the biomechanical and functional integrity of articular cartilage in vitro. Although they have led to a general understanding of the bulk properties of the tissue and its subsequent changes due to osteoarthritis, there are limitations to these studies. This thesis aims to develop a new mechanical indentation framework to address the limitations of the conventional indentation techniques.

In this research, two new mechanical indentation frameworks were established where the two different indenters (cylindrical and ring-shaped flat-ended indenters) were integrated with ultrasound for assessing functional properties of articular cartilage during loading/unloading, i.e. deformation and recovery.

In these frameworks, articular cartilage osteochondral samples were subjected to loading/unloading while the response of the tissue at the middle was captured by ultrasound at the same time. The mechanical response of a wider continuum of articular cartilage in the loaded area and its surrounding region was captured in these frameworks, leading to the investigation of two parameters, L and TS, related to the surrounding tissue of the loaded area for functional assessment of cartilage. L is the distance between the ultrasound transducer and articular cartilage surface and TS is the transient thickness of articular cartilage during loading and unloading.

The capacity of the two mechanical indentation frameworks and new parameters (L and TS) to distinguish mechanically intact from proteoglycan-depleted tissue during loading/unloading was investigated. The ring-shaped flat-ended indenter, integrated with an ultrasound transducer, was shown to be capable of distinguishing normal from enzymatically degraded bovine osteochondral samples.

Then, the potential of the ring-shaped flat-ended indenter integrated with an ultrasound transducer for functional assessment of normal and different types of cartilage degeneration models (proteoglycan loss and collagen disruption) during deformation/recovery, was investigated. This was also used to investigate the interrelationship between cartilage matrix components with deformation and recovery. Classification Analysis based on Principal Component Analysis was used to investigate the capacity of the new parameters (L and TS) to assess the functionality of the tissue. Multivariate statistics based on Partial Least Squares regression was employed to identify the correlation between the response of the tissue in the indented area and its surrounding cartilage.

The results of this research indicate that there is a significant correlation between the responses of cartilage in the directly-loaded area with its surrounding region. While the deformation data was ineffective in distinguishing between normal and proteoglycan-depleted samples, the recovery data was more reliable for this degeneration model. For cartilage degenerated samples where the tangentially aligned collagen fibres at the cartilage surface were disrupted, deformation data was more efficient than recovery data for tissue integrity assessment. Therefore, it is concluded that both aspects of the cartilage biomechanical response, deformation and recovery, should be considered for a more reliable and efficient characterisation of the tissue’s integrity.