Time-dependent mechanical properties of aortic valve cusps: Effect of glycosaminoglycan depletion

Aortic valve (AV) performance is closely linked to its structural components. Glycosaminoglycans (GAGs) are thought to influence the time-dependent properties of living tissues. This study investigates the effect of GAGs on the viscoelastic behaviour of the AV. Fresh porcine AV cusps were either treated enzymatically to remove GAGs or left untreated (control). The specimens were tested for stress relaxation and tensile properties under equibiaxial load conditions. The stress relaxation curves were fitted using a double exponential decay equation and the early relaxation constant (τ1) and late relaxation constant (τ2) calculated for each specimen. Immunohistochemistry confirmed the successful depletion of both sulphated and non-sulphated GAGs from the AV cusps. A statistical increase in τ1 was found for both the radial and circumferential directions between the control and –GAGs group (radial, control 17.37 s vs. –GAGs 25.65 s; circumferential, control 21.47 s vs. –GAGs 27.37 s). It was also found that τ1 differed between the two directions for the control group but not after GAG depletion (control, radial 17.37 s vs. circumferential 21.47 s; –GAGs, radial 25.65 s vs. circumferential 27.37 s). No effect on stiffness was found. The results showed that the presence of GAGs influences the mechanical viscoelastic properties of the AV but has no effect on the stiffness. The natural anisotropy, which reflects the relaxation kinematics, is lost after GAG depletion.