Mechanics of native bovine pericardium. II. A structure based model for the anisotropic mechanical behaviour of the tissue.

A constitutive law to describe the mechanical behaviour of native bovine pericardial samples is proposed. The model is based upon an idealization of the tissue structure and in particular makes use of the preferential orientation of the collagen and elastin fibres in the plane of the tissue along a mechanically predominant direction. This non-axisymmetric layout of the tissue fibres has been shown in the past to cause a systematic variation of the tensile strength and the stiffness with the angle of orientation. The proposed constitutive relation provided a very good fit for results collected along two orthogonal principal directions in the past in uniaxial and biaxial tensile testing modes. It also allowed a better understanding of the interaction of the various load bearing elements and was able to describe some strange features of the tissue's anisotropic mechanical behaviour.