• 3D printing
• computational fluid dynamics
• fluid-structure interaction
• imaging
• large vessels
• magnetic resonance
• mechanical properties
• mock circulatory loop
• pulse wave velocity
• uncertainty quantification

Patient-specific vascular modeling represents a powerful tool for the enhancement of diagnosis and treatment of cardiovascular defects including vascular pathologies, from acquired to congenital diseases.
In this work, the fluid dynamics and mechanical properties of large vessels were investigated integrating in-vitro and in-silico methods. The main objective was to provide additional information on hemodynamics and material parameters of vessels otherwise not available at clinical level.
In particular, imaging, 3D printing, mock circulatory loops and numerical methods were used to: (i) generate vessels models, from simplified geometry to patient-specific anatomies, (ii) physically fabricate them and (iii) investigate their fluid dynamics and mechanical properties through experimental test-benches and computational simulations.
Following the selection of the available 3D printing materials, their applicability in the fabrication of vascular models was assessed by means of standard mechanical tests, based on either uniaxial or biaxial traction. The materials were used to manufacture specific vessel phantoms, from rigid to increasingly compliant, based on the final application.
Such models were inserted in properly calibrated mock circulatory loops, to model the fluid dynamics of the cardiovascular system with particular attention to the vessel of interest. Different setups were developed in order to study both systemic and pulmonary circulations. A mock circulatory loop was useful to implement, both experimentally and numerically, the complex flow pattern occurring at the main pulmonary bifurcation of patients affected by the congenital obstruction of right ventricular outflow tract. A second mock circulatory loop was developed to investigate the effect of a compliant aorta model on the resistive and capacitive elements of the rest of the system was evaluated. Then, an imaging acquisition protocol was included in the experiments, to permit the evaluation of phantoms deformation and flow-rate from image analysis. The aim of these in-vitro studies was to evaluate the possibility of extracting mechanical information of the vessel wall from imaging, exploiting the local measurement of pulse wave velocity.
Following the preliminary results, a further investigation was conducted to define a parametric equation able to estimate the elastic modulus of vessel wall uniquely from imaging data. The equation parameters were defined iteratively, running a series of numerical simulations of simplified vascular models. The novel formulation was tested on both in-silico and in-vitro models, to evaluate its predictive capability of the vascular stiffness. Results were promising, confirming a huge reduction of the gap between the target stiffness and its estimation when using the proposed equation, with better outcomes with respect to the standard methodology.
This work opens the door to further investigations to overcome the current limitations of the described image-based method, which still presents crucial uncertainties of the involved parameters. However, this study put strong basis in the modeling of the fluid dynamics and mechanical properties of large vessels, thus increasing the reliability of engineering modeling to be used in the clinical workflow.