Biaxial mechanical properties of the natural and glutaraldehyde treated aortic valve cusp - Part I: Experimental results

To date, there are no constitutive models for either the natural or biopros thetic aortic valve (AV), in part due to experimental complications related to the AV's small size and heterogeneous fibrous structure. In this study, we developed specialized biaxial testing techniques for the AV cusp, inclu ding a method to determine the local structure-strain relationship to asses s the effects of boundary tethering forces. Natural and glutaraldehyde (GL) treated cusps were subjected to an extensive biaxial testing protocol in w hich the ratios of the axial tensions were held at constant values. Results indicated that the local fiber architecture clearly dominated cuspal defor mation, and that the tethering effects at the specimen boundaries were negl igible. Due to unique aspects of cuspal fiber architecture, the most unifor m region of deformation was found at the lower portion as opposed to the ce nter of the cuspal specimen. In general, the circumferential strains were m uch smaller than the radial strains, indicating a profound degree of mechan ical anisotropy. and that natural crisps were significant more extensible t han the GL treated cusps. Strong mechanical coupling between biaxial stretc h axes produced negative circumferential strains under equibiaxial tension. Further, the large radial strains observed could nor be explained by uncri mping: of the collagen fibers, hut may? be cine to large rotations of the h ighly aligned, circumferential-oriented collagen fibers in the fibrosa. In conclusion, this study provides new insights into the AV cusp's structure-f unction relationship in addition to requisite data for constitutive modelin g. [S0148-0731(00)00901-8].