Anisotropic Mechanical Response of Bovine Pericardium Membrane Through Bulge Test and In-situ Confocal-laser Scanning.

In this work, we present a new experimental setup for the assessment of the anisotropic properties of Bovine Pericardium (BP) membranes. The chemically fixed BP samples were subjected to a bulge test with in-situ confocal laser imaging at increasing applied pressure. The high resolution topography provided by the confocal laser scanning allowed to obtain a quantitative measure of the bulge displacement; after polynomial fitting, principal curvatures were obtained and a Degree of Anisotropy (DA) was defined as the normalized difference between the maximum and minimum principal curvatures. The experiments performed on the BP membranes allowed us to obtain pressure-displacement data which clearly exhibited distinct principal curvatures indicating an anisotropic response. A comparison with curvatures data obtained on isotropic Nitrile Buthadiene Rubber (NBR) samples confirmed the effectiveness of the experimental setup for this specific purpose. Numerical simulations of the bulge test with available constitutive equations for anisotropic biological tissues were performed with the purpose of identifying a range of parameters which well describes the obtained range of DA on the BP membranes. The DA values have been partially validated with biaxial tests available in literature and with suitably performed uniaxial tensile tests.