title: Quantification of Shear Deformations and Corresponding Stresses in the Biaxially Tested Human Myocardium.
abstract: One goal of cardiac research is to perform numerical simulations to describe/reproduce the mechanoelectrical function of the human myocardium in health and disease. Such simulations are based on a complex combination of mathematical models describing the passive mechanical behavior of the myocardium and its electrophysiology, i.e., the activation of cardiac muscle cells. The problem in developing adequate constitutive models is the shortage of experimental data suitable for detailed parameter estimation in specific functional forms. A combination of shear and biaxial extension tests with different loading protocols on different specimen orientations is necessary to capture adequately the direction-dependent (orthotropic) response of the myocardium. In most experimental animal studies, where planar biaxial extension tests on the myocardium have been conducted, the generated shear stresses were neither considered nor discussed. Hence, in this study a method is presented which allows the quantification of shear deformations and related stresses. It demonstrates an approach for experimenters as to how the generation of these shear stresses can be minimized during mechanical testing. Experimental results on 14 passive human myocardial specimens, obtained from nine human hearts, show the efficiency of this newly developed method. Moreover, the influence of the clamping technique of the specimen, i.e., the load transmission between the testing device and the tissue, on the stress response is determined by testing an isotropic material (Latex). We identified that the force transmission between the testing device and the specimen by means of hooks and cords does not influence the performed experiments. We further showed that in-plane shear stresses definitely exist in biaxially tested human ventricular myocardium, but can be reduced to a minimum by preparing the specimens in an appropriate manner. Moreover, we showed whether shear stresses can be neglected when performing planar biaxial extension tests on fiber-reinforced materials. The used method appears to be robust to quantify normal and shear deformations and corresponding stresses in biaxially tested human myocardium. This method can be applied for the mechanical characterization of any fiber-reinforced material using planar biaxial extension tests.
authors.affiliation: Institute of Biomechanics, Graz University of Technology, Kronesgasse 5/I, 8010, Graz, Austria. sommer@tugraz.at.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Sommer
authors.affiliation: Institute of Biomechanics, Graz University of Technology, Kronesgasse 5/I, 8010, Graz, Austria.
authors.forename: Daniel Ch
authors.initials: DCh
authors.lastname: Haspinger
authors.affiliation: Division of Cardiac, Thoracic and Vascular Surgery, Klinikum Klagenfurt am Wörthersee, Klagenfurt, Austria.
authors.forename: Michaela
authors.initials: M
authors.lastname: Andrä
authors.affiliation: Department of Cardiology, Medical University Graz, Graz, Austria.
authors.forename: Michael
authors.initials: M
authors.lastname: Sacherer
authors.affiliation: Institute of Pathology, Medical University Graz, Graz, Austria.
authors.forename: Christian
authors.initials: C
authors.lastname: Viertler
authors.affiliation: Institute of Pathology, Medical University Graz, Graz, Austria.
authors.forename: Peter
authors.initials: P
authors.lastname: Regitnig
authors.affiliation: Institute of Biomechanics, Graz University of Technology, Kronesgasse 5/I, 8010, Graz, Austria.
authors.forename: Gerhard A
authors.initials: GA
authors.lastname: Holzapfel
mesh_terms: D000368:Aged; D006801:Humans; D008875:Middle Aged; D009206:Myocardium; D033081:Shear Strength; D013314:Stress, Mechanical
keywords: Biaxial extension test; Mechanical property; Passive human left ventricular myocardium; Shear deformation; Shear stress