Constitutive modeling of scaffold materials for implantable heart valves

Description

‘Living’ heart valves made of biodegraded polymers could make a number of heart valve operations superfluous in the future. Although significant advances have been made in the development of novel heart valve devices in recent years, it remains very challenging, costly, time consuming, and rich with obstacles. Advanced computer modeling and simulation technologies have the potential to overcome this limitation by making it possible to test new designs, modified scaffold compositions or other applications in a virtual patient-specific environment – in silico. Biodegradable heart valves consist of a fiber-reinforced polymer scaffold. In order to predict the short-term and long-term behavior of in situ tissue engineered heart valves, simulations need to be developed that precisely describe the behavior of the heart valve devices, in particular the behavior of the scaffold material. According to experimental evidence from several tests, the scaffold
material has several constitutive effects. This includes anisotropy, stress softening, permanent set, and viscoelasticity. A constitutive model must therefore be formulated for in silico studies that takes these properties into account in the setting of large deformations. A continuum modeling approach is presented that describes the short-term material behavior with its nonlinear effects. Several of these effects are interdependent. Moreover, the chosen approach must not only correspond to the experiments, but also apply to all other possible deformations. Therefore, special attention must be paid to both the generality of the modeling framework and its careful calibration in order to avoid unphysical results in subsequent in silico studies. The anisotropy of the scaffold material introduced by the inherent microstructure of the fibers is described by structure tensors. Thus, a polyconvex strain-energy function is formulated, which contains a structure tensor for the preferred directions as well as for all perpendicular directions, inspired by the work of Schröder et al., e.g. [1]. A pseudo-elastic formulation is the used to model the loading-unloading dependent damage of the material, see Dorfmann et al. [2]. This approach also takes into account the permanent set that is visible during the material characterization and is particularly suitable for large scale applications due to its simplicity and computational efficiency. Using an approach by Holzapfel et al. [3], the model is extended to include viscoelasticity. Finally, we show that the constitutive model framework developed reflects the results of the material characterization of the scaffold material model with sufficient accuracy. After implementing the approach in the commercial finite element software Abaqus, we also validate the framework for a realistic boundary-value problem.

Period	4 Jul 2022 → 8 Jul 2022
Event title	11th European Solid Mechanics Conference: ESMC 2022
Event type	Conference
Location	Galway, IrelandShow on map
Degree of Recognition	International