Abstract

Computational modeling of the cardiovascular system plays an increasingly important role in biomedicine, as it allows for non-invasive investigations of the status-quo and studying the influence of different treatment options available. The goal is to incorporate patient-specific datasets to obtain socalled digital twins to increase relevance of virtual surgery and support clinical decision making. In this context, aortic dissection is particularly challenging, since the overall system behavior strongly depends on the interplay between tissue deformation and blood flow, giving rise to a fully coupled fluid-structure interaction problem. To account for the complex physics, several additional modeling aspects such as prestress, advanced constitutive models respecting fibre orientation and suitable boundary conditions for the fluid and solid phases have to be considered. Within this study, these special techniques are applied to a patient-specific dataset, for which first results are presented highlighting their relevance.

Abstract

Soft materials, and especially soft biological tissues, have a complex highly nonlinear behavior both for quasielastic (slow) and viscous loading. In partiular, the cyclic behavior is different depending on the loading speed, number of cycles, and their magnitude. Furthermore, different soft materials and soft tissues have different particularities in their behavior. Therefore, a phenomenological proposal capable of accurately capturing all these singularities with few, easy to obtain parameters based on experimental data, is valuable. In this study, a visco-hyperelastic one-dimensional formulation to characterize different biological tissues is proposed, which has proven to be capable of capturing the response of numerous soft biological tissues (brain tissue, coronary arteries, tendons, tongue tissues, abdominal muscle, cells...) under pure and combined loading modes, including tension, compression, simple shear and the combination of the latter one with tension and compression. One of the main advantages of the proposed model is its simplicity, being that the formulation is calibrated with four simple parameters (two of them for the hyperelastic component and four for dealing with the different viscous aspects) obtained from the uniaxial loading. The formulation, based on a combination of Maxwell and Kelvin-Voigt rheological models has proven to represent to very good accuracy the behavior of a wide range of materials under different types of loadings, including effects like preconditioning and cycle stabilization. In all these cases, under different monotonic and cyclic loading, all aspects of the viscous and elastic behavior are accurately captured. Thanks to its structure, this model incorporates strain-level dependent nonequilibrium viscoelasticity and it may be easily incorporated to 3D nonlinear finite strains formulations.

Abstract

In order to understand the mechanisms in degenerative disc disease and support the design of robust disc prothesis, accurate modelling of the intervertebral disc's (IVD) dynamics is necessary. Many experimental studies relate changes in the mechanical properties of the disk to the degenerative state of the IVD. However, further studies are necessary to better assess the influence of parameters which may affect those mechanical properties on the dynamic behaviour of the IVD, especially its dissipative behaviour. The goal of this work is to investigate the effect the static preload and the frequency of excitation through numerical simulations.