GLUTARALDEHYDE FIXATION ALTERS THE INTERNAL SHEAR PROPERTIES OF PORCINE AORTIC HEART-VALVE TISSUE

Glutaraldehyde fixation noticeably alters the mechanical properties of porcine aortic valve tissue, subsequently affecting the function and durability of these tissues when used as prosthetic heart valves. Traditional uniaxial tensile testing techniques do not fully define the mechanical properties and we have devised a new approach to examine the important shear properties of the tissue. Altered shear properties would change the response of the valve tissue as it flexes open and closed. An apparatus combining a high-precision linear actuator with a gram-sensitive load cell was used to measure the shear characteristics of circular punch specimens taken from the center of each valve cusp. The tissue parameters measured showed significant differences between the fixed and fresh tissues. Glutaraldehyde-fixed tissue (n = 16) was about 100 times as stiff as fresh tissue (n = 32) between shear strain values of 0 and 0.2. The fixed tissue also had stress relaxation rates about 60% those of the fresh cusps and had about 70% of the hysteresis loss seen in fresh tissue. These results demonstrated the significant effects of glutaraldehyde fixation on the properties of porcine aortic valve cusp when tested in shear. Such changes could lead to altered tissue function and may increase internal stresses during opening and closing, contributing to valve fatigue.