oa Contribution of Specific Glycosaminoglycans to the Relaxation Properties of the Aortic Valve

The aortic valve (AV) is characterized by a complex mechanical behavior which is closely linked to its structural components. The central layer of the AV is rich in glycosaminoglycans (GAGs) which play an important role in the biomechanics of the AV. In this study the effect of selective GAGs depletion on time dependent mechanical behavior of porcine AV was analyzed. Fresh strips of porcine AV cusps were cut in either in the radial or in the circumferential direction and mounted on a tensile testing system (Bose Electroforce) for mechanical testing. Three groups of valves were treated enzymatically, in order to remover either all the GAGs (group 1), the sulphated GAGs only (group 2) or the non-sulphated GAGs only (group 3). Each group had a control group. Mechanical tests were performed on each strip and stress relaxation kinematics as well as relaxation percentage were compared between treated and untreated specimens. Tensile and stress relaxation tests were performed on the strips under physiological load levels. The reduced stress relaxation function was fitted to the experimental data using a two phase (τ1 and τ2) exponential decay model. Relaxation percentage was significantly lower in group 1 for both circumferential (group 1: 20.58% vs control 28.34%, p = 0.004) and radial strips (group 1: 18.89% vs control 28.85%, p = 0.006). In this group, the early relaxation value (τ1) markedly decreased in the radial direction (group 1: 7.86s vs control: 10.35s, p = 0.0041) while no statistical difference was achieved in the circumferential direction. When looking at selective GAGs depletion, an effect of the hyaluronic acid depletion (group 3) was seen on the excursion of circumferentially oriented strips (group 2: 23.15% vs control: 27.76%, p = 0.049). No major effect was seen comparing the results of group 2 with its control. No effect on t2 was found. Histology confirmed the successful GAGs depletion. The presence of GAGs influences the biomechanics of the AV in terms of time dependent mechanical properties. The presence of hyaluronic acid has a distinctive effect on the relaxation excursion of the cusps while no effect was apparent for sulphated GAGs. These results provide further insight into the relationship between structure and fuction in the AV.