T. Doehring, D. Einstein, A. Freed, M.-J. Pindera, A. Saleeb, and I. Vesely (USA)
Computational modelling, heart valves, viscoelasticity, micromechanics, composite materials.
The objective of this study was to develop new, more accurate computational models of soft tissues, particularly the aortic valve. Aortic valve tissue is a complex composite material, consisting of multiple layers of collagen, elastin and glycosaminoglycans. Computational models of such a material must thus scale with the structure, depending on what aspects of valve function require modelling. Thus far, we have pursued a three pronged approach to modeling soft biological tissues. (i) Firstly, we have developed a new, more robust method for estimating viscoelastic material parameters from real-life experiments that may suffer from testing machine artifacts, such as overshoot during ramp-and-hold. The techniques involves the direct fitting of a constitutive function to the point-wise experimental data, and makes use of global optimization methods. (ii) We have advanced an existing high-fidelity micromechanical technique for the response of multi-phase materials with arbitrary periodic microstructures making use of the Generalized Method of Cells. This model can now handle material non-linearities and large strains, and is expected to provide insight into the fibril and macromolecular-level behavior of soft connective tissues. (iii) We have also developed a fully 3D theory to model the large deformations of viscoelastic solids and implemented it in a computational platform making use of the commercial code ABAQUS. This theory represents the viscoelastic behavior of soft tissues as a multi-mechanism viscoelastic solid. We thus have a collection of computational tools with which we can simulate the time-dependent viscoelastic response of different types of soft tissues at both the micro and macro-scale levels.
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