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.