Biaxial tensile and triaxial shear measurements and modeling of human myocardium

In the multidisciplinary field of heart research it is of utmost importance, for the description of phenomena like mechanoelectric feedback or heart wall thickening, to identify accurate myocardium material properties. To understand highly nonlinear mechanics of complex structures, such as the passive myocardium under different loading conditions, a rationally-based material model is required. Unfortunately today, there is insufficient or no experimental data of human heart tissues available for material parameter estimation and the development of such an adequate material model. This research project aims at determining biaxial tensile and triaxial shear properties of the passive human myocardium. Moreover, the underlying microstructure of the myocardial tissue will be determined and existing material models will be fitted to the experimental data. Remarkably, the only true biaxial experiment ever performed on myocardium was conducted over 23 years ago, and only one shear experiment on one type of myocardial tissue exists in the literature today. Using new state of the art equipment, planar biaxial extension tests will be performed to determine the biaxial tensile properties of passive left and right ventricular human myocardium. The shear properties of myocardium will be examined by triaxial shear tests on cube specimens excised from an adjacent region of the biaxial tensile specimens. A polarized light microscope with a universal stage will be used to study the 3D microstructure of the tissue emphasizing the 3D orientation and dispersion of the muscle fibers and adjacent collagen fabrics. The novel combination of biaxial tensile test data with different loading protocols and shear test data at different specimen orientations allows to adequately capture the direction-dependent material response. With these complete sets of mechanical data, combined with structural data, a better material model and associated material parameters can be defined for the description of the mechanical behavior of the ventricular myocardium in humans. This model is used in numerical (Finite Element) simulations to better understand the fundamental underlying ventricular mechanics, a step needed in the improvement of medical treatment of heart diseases. Moreover, mechanical characterization of the passive human myocardium will lead to a greater understanding of the mechanical deformation of the heart during the cardiac cycle, and in particular, how diseased/ischemic regions can impair pumping ability. Furthermore, it will lead to accurate computer simulations of the cardiac mechanical function to be used to test novel surgical procedures restoring mechanical function of the heart failure following infarction.

In the multidisciplinary field of heart research it is of utmost importance, for the description of phenomena like mechanoelectric feedback or heart wall thickening, to identify accurate myocardium material properties. Furthermore, in order to understand the highly nonlinear mechanics of the complex structures such as the passive myocardium under different loading conditions, a rationally-based material model is required. Remarkably, before we conducted this study, there were insufficient or no experimental data of human heart tissues available for material parameter estimation and the development of an adequate material model. Therefore, the research project Biaxial Tensile and Triaxial Shear Measurements and Modeling of Human Myocardium aimed at determining material properties of the human myocardium by realistic biomechanical experiments. Moreover, the underlying microstructure of the myocardial tissue was determined, and existing material models were fitted to experimental data. In particular using new state of the art equipment, both biaxial tensile properties and direction-dependent shear properties were determined through planar biaxial extension tests and triaxial shear tests, respectively. In summary, more than 30 human heart samples, originating from the left and right ventricular myocardium, were investigated. The novel approach of second harmonic generation microscopy combined with optical tissue clearing allowed a fast, non-destructive, and automated analysis of the cardiac tissues microstructure with high resolution. Thereby, the focus was on the determination of the 3D orientation and dispersion of the muscle fibers and the adjacent collagen fabrics. The combination of biaxial tensile test data with different loading protocols, and shear test data at different specimen orientations allowed to adequately capture the direction-dependent material response. With this set of mechanical data, combined with structural data, a novel material model and associated material parameters were defined for the description of the mechanical behavior of the ventricular myocardium in humans. This model will lead to more realistic computer simulations to better understand the fundamental underlying ventricular mechanics, a step needed to improve medical treatments of heart diseases. For example, accurate computer simulations of the cardiac mechanical function can be used to test novel surgical procedures restoring mechanical function of the heart failure following infarction. Moreover, the mechanical characterization of the passive human myocardium will lead to a greater understanding of the mechanical deformation of the heart during the cardiac cycle, and, in particular, provide more insights why diseased/ischemic regions impair the pumping ability of the heart.