BIOMECHANICAL PROPERTIES OF THE HUMAN VENTRICULAR MYOCARDIUM Sommer G 1 , Schwarz M 2 , Kutschera M 1 , Kresnik R 1 , Regitnig P 3 , Schriefl AJ 1 , Wolinski H 4 , Kohlwein SD 4 , Holzapfel GA 1,5 1 Institute of Biomechanics, Graz University of Technology, Austria 2 Division of Surgical Research, Department of Surgery, Medical University of Graz, Austria 3 Institute of Pathology, Medical University of Graz, Austria 4 Institute of Molecular Biosciences, University of Graz, Austria 5 Department of Solid Mechanics, Royal Institute of Technology (KTH), Sweden sommer@tugraz.at Abstract: In the multidisciplinary field of heart research it is of utmost importance, for the description of phenomena such as mechano-electric feedback or heart wall thickening, to accurately identify the biomechanical properties of the myo- cardium. Hence, this study aims at determining biaxial ten- sile and triaxial shear properties of the passive human myo- cardium. This novel combination of biaxial and shear test- ing, together with the investigation of the myocardial micro- structure, yields new innovative and essential information of the material properties to fulfil the short term goals of con- structing realistic myocardial models. Through such model- ing efforts, capable to capture the biomechanical behaviour of the heart, it is possible to improve some methods of medi- cal treatment, and hence the quality of life for people suffer- ing from heart diseases – at least as a long-term goal. Keywords: passive mechanical behavior, human left ven- tricular myocardium, microstructure, constitutive model- ing Introduction Heart-related diseases are the leading cause of mortality in the world according to the ‘Heart disease and stroke statistics–2013 update’ by the American Heart Associa- tion [1]. It is suggested that shearing of adjacent muscle layers in the left ventricular wall contributes substantially to wall thickening during systole [2]. It is further suggest- ed that the development of realistic finite element models of the mechanical behavior of both healthy and diseased myocardial tissue is dependent on the formulation of appropriate constitutive laws and the accurate identifica- tion of their material parameters [3]. To the authors’ knowledge there is no single biaxial tensile and triaxial shear study on human myocardial tissue yet available in the literature. Therefore, our principal aim of the present study is to characterize the mechanical properties of the human myocardium by biaxial tensile and triaxial shear testing, and the myocardial microstructure, in order to derive new constitutive descriptors and their related pa- rameters for more accurate numerical (finite element) simulation studies of the fundamental mechanisms of human heart mechanics. Fundamental heart mechanisms based on healthy and diseased tissues can be better inves- tigated and understood if material parameters are based on sophisticated and well-determined experimental data. Methods Preparations and mechanical testing. For the biaxial tests, squared specimens with the dimensions 25x25x2mm were prepared from the regions of the lateral left ventricular wall, with one side aligned with the fiber and cross-fiber axes. Several suitable specimens were extracted through the myocardial wall from the epicardi- um to the endocardium. During the experiments, the spec- imens, see Fig. 1(a), were submerged in a cardioplegic solution at physiological conditions. Different stretch levels (5, 7.5, 10, 12.5, 15, 17.5 and 20%) were applied consecutively. For the triaxial shear testing, three adjoin- ing cubic specimens (4x4x4mm) were prepared with their sides aligned according to the fiber axis, sheet axis and sheet-normal axis, see, e.g., Fig. 1(b). Figure 1: Biaxial tensile (a) and triaxial shear (b) specimens inserted in the testing setup, ready for testing. Three cycles of sinusoidal simple shear (0.1-0.5 in 0.1 steps of specimen thickness) were applied to each cubic specimens in two orthogonal directions. Consequently, for the six possible modes of simple shear for an ortho- tropic material three different specimens are needed. Resulting forces in three axes (x, y, z) were measured. On completion of shear testing, relaxation tests (‘step test’) at 0.5 shear strain were performed in the x- and y-directions Biomed Tech 2013; 58 (Suppl. 1) © 2013 by Walter de Gruyter · Berlin · Boston. DOI 10.1515/bmt-2013-4108 Bereitgestellt von | Technische Universität Graz Angemeldet | 129.27.219.131 Heruntergeladen am | 16.12.13 16:05