Anisotropic elasticity of bovine pericardial tissues

Artificial heart valves fashioned from bovine pericardial tissues appear to perform favourably when compared to those fashioned from other biological materials. Tissue mechanical properties have been implicated as a possible factor in determining the success or failure of the materials used for constructing tissue valve substitutes. In this study, strips of bovine pericardial tissues, cut in three different directions (along the base-apex axis of the heart, perpendicular to this axis and at an angle of 45 degrees to this axis), were subjected to uniaxial tensile tests using an Instron machine, at strain rates of 666.7, 166.7, 66.7, and 6.7% X min-1. The pericardial tissues were found to have non-linear stress-strain curves. Anisotropy was also observed, in that the tissue was most extensible when stretched along the vertical direction and least extensible when stained along the horizontal direction. The tissues also exhibited viscoelastic properties, as the extensibility was found to decrease with the increasing strain-rate. The strain at rupture for these tissues, however, were found to be independent of the strain rates and the direction in which they were stretched. On the other hand the stress at rupture was largest when stretched in the horizontal direction and least when stretched in the vertical direction. Stresses at rupture also increase with the strain rate. The implications of the observed tissue properties, when these are used in the fashioning of tissue valve substitutes, will be discussed.