Artificial textile reinforced tubular aortic heart valves - multi-scale modelling and experimental validation

Valvular heart disease is characterized by damage to or a defect in one of the four heart valves: the mitral, aortic, tricuspid or pulmonary. Patients with a malfunctioning valve often must undergo valve replacement surgery. Prosthetic heart valves deployed in the left heart (aortic and mitral) are subjected to harsh hemodynamical conditions causing durability concerns in existing prostheses. Therefore, self-healing tissue-engineered valvular prostheses that can replace damaged native valves are in development as an alternative to available prostheses. Most of the tissue engineered heart valves have been developed for the low-pressure pulmonary position because of the difficulties in fabricating a mechanically strong valve which is able to withstand the higher loads of the systemic circulation of the left heart. Ergo, engineered soft tissues can greatly benefit from reinforcements to attain mechanical properties comparable with that of the native organs. Complex interactions at various levels between the reinforcements and engineered tissue make the selection of the most optimized reinforcing scaffold difficult and subject to an enormous amount of experimental evaluation. Also, to better design these implants, material behaviour of the composite, valve kinematics and its hemodynamical response need to be evaluated. Experimental assessment can be immensely time consuming and expensive, paving way for numerical studies. Hence, to reduce the extent of prototyping, it is prudent to develop a simulation-based development approach. In the presented example of valvular prostheses (aortic valve) which are textile-tissue composites, we test a simulation approach based on multi-scale modelling, often used for evaluating/predicting the behaviour of composites. The current study seeks to predict the behaviour of textile reinforced artificial heart valves along with its hemodynamical behaviour. The complex textile structure was divided into simplified models at different scales. Virtual experiments were conducted on each of these models and their response was fitted by appropriate isotropic and anisotropic hyperelastic material models. The textile response was then used in a macro scale heart valve model, which was subjected to dynamic cardiac loading in a pure mechanical (finite element method - FEM) and multi-physics fluid-structure interaction (FSI) simulation. An in-silico immersed boundary (IB) fluid-structure interaction (FSI) simulation emulating the in-vitro experiment was set-up to evaluate and compare the geometric orifice area and flow rate for one beat cycle. Results from the in-silico FEM & FSI simulation were found to be in good coherence with the in-vitro test during the systolic phase while deviating slightly in the FSI study during the diastolic phase of a beat cycle. Overall the modelling technique provided a good correlation with experimental results, laying the pathway to further study the complex interaction between the engineered tissue and their reinforcing scaffolds. This method can further form the basis for evaluating the mechanical bio-compatibility of scaffolds and their interaction with engineered tissues at various scales and levels