Effects of material non-symmetry on the mechanical behavior of arterial wall.

Arteries are commonly assumed as symmetric cylindrical tubes with axisymmetric geometry and mechanical properties. However, their wall stress, structure and mechanical properties may become nonsymmetric when subject to torsion or complex mechanical loading. The objective of this study was to explore the nonsymmetric two fiber family constitutive models for arterial walls and examine the impact of this non-symmetry on the deformation and stress in arteries under mechanical loads. Our results demonstrated that nonsymmetric collagen fiber properties and alignment lead to interesting phenomena such as vessel twisting associated with axial stretch or pressurization. There are "magic" nonsymmetric fiber angles at which a vessel would not twist under given pressure and axial stretch. The nonsymmetric fiber properties and alignment (mean angle and dispersion) affects the torque-twist angle relationship as well as the axial stretch and pressurized inflation. These results illustrate the effects of nonsymmetric collagen fiber distribution and suggest that the Holzapfel-Gasser-Ogden models could be generalized to incorporate the nonsymmetric two fiber families for broader applications, especially when there is shear or torsion.