EFFECT OF DYNAMIC GLUTARALDEHYDE FIXATION ON THE VISCOELASTIC PROPERTIES OF BOVINE PERICARDIAL TISSUE

We have previously proposed dynamic fixation as an alternative method Co fix a porcine aortic heart valve xenograft with better tissue fixat ion and better preservation of its natural biomechanical properties. B ovine pericardium was fixed under dynamic conditions, low pressures (< 4 mmHg) and low vibration rate (1.2 Hz) in a 0.5% glutaraldehyde phos phate buffer (pH 7.4, 0.2 M). After fixation, tensile testing (i.e. re laxation and stress-strain curves) was performed at low and high exten sion rates (3 and 30 mm s(-1)) and tissue denaturation temperatures we re determined by the hydrothermal isometric tension method. Convention al fresh and statically fixed pericardium were used as controls. In th is instance, we found no significant biomechanical differences between the dynamically and statically fixed pericardial tissue (e.g. moduli and stress relaxation). However, differences in tissue extensibility w ere delineated, since the extensibility of the dynamically fixed tissu e was closer to that of the fresh tissue compared to that of the stati cally fixed tissue. The final relaxation rate of the dynamically fixed tissue (-3.5 +/- 1.0% of stress remaining per log(second)) was simila r to that of the statically fixed tissue (-3.2 +/- 0.6% log(s(-1))) an d significantly lower than the fresh tissue(-9.5 +/- 1.2% log(s(-1))). The denaturation temperatures of the dynamically fixed pericardial ti ssue (mean +/- SD) (86.0 +/- 1.2 degrees C) and the statically fixed ( 85.2 +/- 1.6 degrees C) were similar but significantly higher than tha t of the untreated (fresh) valves (69.3 +/- 0.4 degrees C). The result s suggest a similar degree of internal cross-linking for both statical ly and dynamically fixed pericardium. Although fundamental structural differences exist between both porcine and bovine xenograft tissue, ho w these differences contribute to biomechanical differences in the eff ects of dynamic versus static fixation remain to be explained. (C) 199 8 Elsevier Science Ltd. All rights reserved.