Crosslinking of bioprostheses under minimal stress: Effects on the extensibility of the fibrosa and the ventricularis

Glutaraldehyde fixed porcine aortic valves are commonly used for the construction of bioprostheses. While fixation pressures have decreased over the years to improve leaflet mechanics, little is known about the effects of pre-stressing on the function of the two major components of the valve leaflet, the fibrosa and ventricularis. To investigate the effects of low levels of pre-stress during fixation on the mechanics of the leaflet components, we measured the elastic response of 120 fresh and glutaraldehyde-fixed fibrosa and ventricularis, and also tested the individual layers from leaflets fixed while intact. In the both the radial and circumferential directions, the fibrosa from intact-fixed valves was more extensible than the fresh (39.2% vs. 29.2% strain to high modulus phase, at p <; 0.0122, and 12.7% vs. 8.1% strain, at p <; 0.0001 respectively). The ventricularis from intact-fixed valves, however, was less extensible than when fresh (35.4% vs. 63.7% strain, at p <; 0.00001 in the radial direction). This demonstrates that even zero pressure fixation will affect the mechanics of bioprosthetic heart valves.