Particle image velocimetry measurement of haemodynamics in compliant phantoms of healthy and stented arteries.

In-vitro measurements potentially can provide a clearer insight into the haemodynamic state and performance of vascular implants. The in-vitro studies presented in this thesis contribute to different aspects of measurement of haemodynamics using particle image velocimetry (PIV). Previous compliant phantom fabrication techniques lead to significant variation of the wall thickness, which affects the compliance and ability to capture physiological haemodynamics. A novel fabrication technique developed to generate a thin wall, compliant model of artery. The fabrication technique utilised a male and two-piece female mould 3D printed for casting the phantom. The aortic arch phantom wall thickness was biased 0.1 mm from the intended value of 1 mm and was suitable for PIV analysis. Although various numerical studies investigated haemodynamics in the aortic arch, most of them required experimental validation or ignored the wall elasticity reducing the clinical value of results. Stereoscopic-PIV measurements of haemodynamics was conducted for the first time in-vitro within compliant and rigid phantoms of the aortic arch artery. During the deceleration of systole and diastole, recirculation and reverse flow was observed at the proximal wall of the brachiocephalic artery (BCA) branch and inner wall of the arch in the compliant phantom. These flow patterns were not evident in the rigid phantom. The region of flow recirculation and reverse flow were correlated to the high-risk regions reported for CVD development. In addition, the flow disturbance observed in the pulsatile experiment near the inner wall of the arch, was not found for identical flow rate in steady flow analysis. Endovascular aortic repair (EVAR) intervention is common treatment for the abdominal arotic aneurysm (AAA). The effect of the EVAR graft on haemodynamic disturbances and its influence on limb occlusion was investigated for the first time in-vitro. The results showed that the compliance mismatch between the graft and parent artery caused a high core velocity at the graft outlet with a low-velocity magnitude near the wall. Flow recirculation observed at the trailing edge of the graft near the walls and caused oscillation of the near-wall shear rate. This was assumed to be caused by the compliance mismatch across the compliant artery and rigid graft. Recirculation and oscillating shear stress are risk factors for intimal thickening and stenosis formation. The effect of gradual compliance transitioning between the stent and the parent artery on haemodynamics was examined for the first time in-vitro. Two novel compliant idealised models of the carotid artery including simplified rigid and compliance transitioning stents designs were fabricated. The compliance mismatch between the stent and artery induced haemodynamics disturbances and shear rate oscillation at stent ends which is a risk factor for restenosis after surgery. The compliance transitioning stent reduced flow disturbances at near-wall stent’s ends and the risk of occlusion. However, due to sudden changes in shear rate between the struts in both models, there is a risk of intra-stent occlusion even for compliance transitioning stent mitigating the clinical outcomes post-treatment. The in-vivo arterial wall can exhibit nonlinear anisotropic mechanical behaviour. Chapter 8 investigated the effect of wall anisotropy on luminal expansion and associated haemodynamics for the first time in-vitro using isotropic material. To mimic the wall anisotropy, two novel phantoms with longitudinal and circumferential exterior patterns were fabricated. The results showed the expected difference in strain across the phantoms. However, the haemodynamics patterns were similar in both phantoms. It was concluded that while the phantom expansion is within the physiological range, the anisotropic effect is negligible and mimicking this effect unnecessarily increases the burden of the experimental setup