Changes in the mechanical properties of chemically treated bovine pericardium after a short uniaxial cyclic test.

The mechanical behavior of calf pericardium, a biomaterial utilized in the manufacture of cardiac bioprostheses, in response to a short tensile cyclic test has been evaluated. The trial involved 120 samples cut longitudinally or transversely, subjected to 10 cycles until a stress of between 1 and 3 MPa was reached. Tests of hardness and tear propagation were performed, and the results were compared with a control series. The energy loss was also computed, and it was approximately 10-fold greater in the first cycle than the loss in the subsequent nine cycles. Despite this singularity, they correlated very precisely. The effect of the direction in which the tissue is cut on energy loss was not significant nor the difference between hardness prior to and after testing. The results of the tear propagation tests gave no statistical differences prior to and after testing. From the obtained results, it seems that the test carried out does not affect significantly the mechanical properties of calf pericardium.

Fatigue behaviour of young ostrich pericardium.

Young ostrich pericardia (biomaterial under study for manufacturing cardiac valve leaflets), has been subjected to biaxial tension fatigue until breakage. Supraphysiological values of pressure (1 to 6 atm) have been employed to accelerate damage and, therefore, to reduce testing time but at physiological frequency in order to avoid viscoelastic behaviour changes. The lifetime fatigue curves have been obtained and large scatter has been observed in the results but this can be strongly reduced with adequate material selection. The thickness-based selection of samples has proved to be ineffective both in reducing scatter or improving strength, but the energy-based selection aided with statistical decision techniques has been shown to be very successful. The energy loss (energy under the hysteresis loop of each load and unload cycle) appears to be a very accurate predictor of the expected fatigue lifetime of the tissue.