Age-Related Changes in Mechanical Properties in Porcine Heart Valves

Mechanical and bioprosthetic valves work relatively well in adults, but have complications in children. Even if the complications could be resolved, neither of these valve replacements can grow with the child, which a tissue engineered heart valve (TEHV) is expected to do. Recent studies in valve structure and composition showed significant agerelated changes. This indicates that there are likely also age-specific differences in mechanical properties, which have not been thoroughly investigated. This was investigated in this study. Uniaxial tensile tests were used on porcine aortic valve leaflets and mitral valve anterior leaflets of three different ages; 6 weeks, 6 months and 6 years. Samples were taken radially and circumferentially. Thickness, stiffness, percentage stress relaxation (%SR) and extensibility were determined. The thickness and stiffness increased with age. Samples were stiffer circumferentially than radially. The %SR increased with age circumferentially and showed no trend radially. The %SR was higher circumferentially than radially. Mainly extensibility increased with age. The increase in stiffness corresponded with an increase in collagen content and crosslinking with aging. Increased %SR with age could be explained with an increase in hyaluronan (HA) with aging. With more HA, there would be more slippage and thus more %SR. The %SR was higher circumferentially than radially. The reasoning behind this remains unknown. Combining increased extensibility and increased thickness of the leaflets with aging, it was implied that the increased extensibility was not caused by the tissue being stretched out. This information on age-related changes in mechanical properties could be used to incorporate in making TEHVs.