Biaxial Tensile and Triaxial Shear Measurements of the Human Myocardium, and Related Continuum Modeling

Unknown Prepared myocardial specimen, clamped into a biaxial testing device.

Unknown (a) Ellipsoidal geometrical model representing the left ventricle of the heart. The orientation of the fiber directions are in red; (b) contour plots of the fiber stress component of the strain-energy function for 116mmHg.

In the research area of cardiac mechanics and electrophysiology it is of utmost importance to identify accurate material properties of the myocardium. This is important for the description of various phenomena such as mechanoelectric feedback or heart wall thickening. To better understand the highly nonlinear mechanics of complex structures such as the passive myocardium under different loading conditions, a rationally-based material model is required. Unfortunately, there are insufficient experimental data of the human myocardium available for material parameter estimation and for the development of adequate material models.

This project aims at determining the biaxial tensile and triaxial shear properties of the passive human myocardium. Moreover, the underlying microstructure of tissues will be determined, and structurally-based material models will be fitted to experimental data. Using new state-of-the-art equipment, planar biaxial extension tests will be performed to determine the biaxial tensile properties of the human myocardium. Shear properties will be examined using triaxial shear tests on cubic specimens excised from an adjacent region of the biaxial tensile specimens. Multiphoton microscopy will be used to study the 3D microstructure of the tissue to emphasize the 3D orientation and dispersion of the muscle fibers and the adjacent collagen fabrics.

The novel combination of biaxial tensile test data with different loading protocols and shear test data at different specimen orientations will facilitate capture of the direction-dependent material response. With these mechanical data sets, combined with structural data, a better material model can be constructed. Such a model will then be used in numerical simulations to better understand ventricular mechanics, a step that is needed for the improvement of the medical treatment of heart diseases. An improved mechanical characterization may also lead to a better understanding of the mechanical deformation of the heart during the cardiac cycle, and, in particular, of how diseased/ischemic regions can impair pumping ability.

Funding: Austrian Science Fund (FWF)