Biomechanical study of large blood vessels using fluid - structure interaction simulations

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Ζησιμόπουλος, Σπήλιος
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Cardiovascular diseases are one of the major causes of mortality in the modern world. A possible method of treating such conditions is the replacement of a blood vessel’s pathological segment with an artificial one. Dacron and ePTFE are the main materials currently used in the manufacturing of artificial vessels. A great disadvantage of theirs is their low compliance in relation to biological vessels, which may lead to additional pathologies. State-of-the-art research focuses on the production of artificial vessels with increased compliance. The manufacturing of artificial vases from PCL using the electrospinning method is a potential solution. In this Master Thesis we performed a biomechanical study of blood vessels, covering the various theoretical aspects involved in cardiovascular problems. Then, a combined experimental and FEM computational study was carried out. A PCL/PVA carotid caliber vessel was produced by the method of electrospinning and tested under various operating conditions using a physiological flow apparatus. A finite element FSI model was developed in order to simulate and assess the experimental results, as well as to predict the vascular compliance and other mechanical properties. The simulations were performed at pressure intervals between 0 to 150 mmHg. For the modeling of the PCL vessel wall, various elastic and hyperelastic material models were examined. All material models showed errors less than 16% when comparing the calculated vascular compliance to the experimentally measured one and less than 7% compared with bibliographic values at the physiological 80-125 mmHg pressure interval. In this interval, the FEM calculated compliance ranged from 4.7 to 5.1 %/100 mmHg×104, while the experimental one had a mean value of 4.4%/100 mmHg×104 with the corresponding bibliographic value being 5 %/100 mmHg×104. Moreover, at least one material model had an error less than 12% for operating pressures up to 150 mmHg. In addition, the maximum values of the 1st principal stress at 100 kPa and fluid velocity at 0.93 m/s were validated by relevant studies for carotid caliber arteries. The importance of deformable wall analysis provided by the FSI methods was highlighted by the rigid model’s wall shear stress overestimation up to 45% compared to compliant models. In conclusion, the FEM simulations showed that the FSI modelling can yield more realistic results than rigid wall simulations. Although no wall material model can fully describe the PCL vessel’s response for every pressure interval, a hyperelastic constitutive model such as an Ogden material is more appropriate for the modelling of arterial walls, compared to elastic materials. On the other hand, a linear elastic material model is better suited for less compliant artificial vessels. Overall, the FEM model developed in this study was validated by both experimental and bibliographic data and has the potential to be used in predictive models in the future.
Biomechanics, Artificial vessels, Electrospinning, Compliance, FSI