Experimental and numerical techniques for characterising catheter-induced blood vessel damage: towards tools for improvement of intravascular catheter design

Cardiovascular diseases are a significant health risk worldwide, being the largest contributor to deaths in most developed and developing countries. For physical testing of new medical devices, diseased tissue specimens are desirable. However, these are difficult to obtain in quantity. The first phase of the work therefore focused on emulating effects of disease on artery mechanical response, using enzyme and chemical treatment of healthy tissue. Porcine aorta was partially digested by elastase and collagenase treatments to remove constituent proteins, and exposed to low concentration glutaraldehdye to partially cross-link proteins. Uniaxial tension testing and controlled peel testing were then performed in the artery axial and circumferential directions to assess the changes in mechanical and failure behaviour. The treatments successfully altered the wall tensile and peeling response with effects varying by the loading type and direction. Multiphoton microscopy was also performed to allow visualisation of the changes to fibre structure and density. Finally, tensile test results were fitted to the Gasser-Ogden-Holzapfel constitutive model and a continuum damage model, and the fitted curves were best matched with the circumferential direction results. The latter phase of the work focused on development of methods for characterising and simulating catheter-induced dissection processes. An experimental procedure was developed, wherein a catheter was forced between layers of arterial media, propagating a dissection, while reaction force was measured. The various approaches utilised to model this process within FEA are presented and the subsequent difficulties explored. The inherent complexity of the process being modelled resulted in difficulty drawing out the underlying problems. To rectify this, the experiment was simplified such that a metal wedge with a rounded front was used to dissect the tissue. This was successfully modelled and insights from this were considered with regard to numerical difficulties in the catheter dissection model.