Material properties and residual stress of individual layers in the arterial wall

We have obtained thickness, circumferential residual stress and material properties for the entire wall and for individual layers of dilated human ascending aortas (n = 13). Opening angle measurements and biaxial tests were performed on the full wall and again after removing the adventitial layer. Biaxial test data was fit to an exponential constitutive law to obtain material properties for each layer. The adventitia comprised 30 ± 11% of the total wall thickness. The opening angle increased significantly after removal fo the adventitia from 232 ± 87° to 270 ± 89° (p<0.5, paired t-test). The material parameters indicate that the media is stiffer than the adventitia at low strains, while the adventitia becomes stiffer than the media at high strains. The strain at which this crossover occurs decreases with age.