McCredie, A.J.; (2010) Ultrasound elastography for the characterisation of cartilage. Doctoral thesis , UCL (University College London).

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Abstract

Articular cartilage is a layered porous fibril-reinforced biological composite which performs essential load bearing and shock absorption in mammalian joints; however it is unable to satisfactorily self-repair and is therefore of interest to tissue engineers. Engineering functional tissue requires full mechanical characterisation of the target tissue. ‘Elastography’ is an ultrasonic method which can be used to find depth-dependent strains in a material following the application of a global strain. In this thesis, ultrasonic elastography are applied to determine the importance of the specialised structure of articular cartilage. Existing ultrasonic elastography techniques are adapted in terms of experimental accuracy, protocol variation and signal-processing to allow experimental comparisons to be made with native articular cartilage, a native non-layered cartilage and engineered tissue constructs at different stages of tissue development. A one-dimensional axisymmetric phenomenological model is constructed, allowing extraction of further material properties from articular cartilage experimental data. The results of these novel comparisons demonstrate the importance of the structure of the tissue in determining the global and depth-dependent elastic properties of the tissue. The global elastic modulus of articular cartilage is dependent on the strain applied, which was not the case for the non-layered sample. Depth-dependent moduli of articular cartilage samples match those previously reported, whereas the cartilage with the non-layered structure has an approximately homogeneous modulus. The changes occurring in the engineered tissue with respect to culture time are small but quantifiable. The suitability of this elastography technique for application to engineered tissue is examined and discussed. The implications of the results demonstrating the importance of the depth-dependent structure for tissue engineering are also addressed and further work suggested.

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