The biomechanical properties of arteries are conferred by the rearrangement under load of the collagen and elastin fibers making up the arterial microstructure. Their kinematics under deformation is not yet characterized for all fiber networks. In this respect we have submitted samples of arterial tissue to uniaxial tension, simultaneously to confocal imaging of their microstructure. Our method allowed identifying for the first time the remarkable ability of adventitial collagen fibers to reorient in the direction of the load, achieving reorientation rotations that exceeded those predicted by affine kinematics, while all other networks followed the affine kinematics. Our results highlight new properties of the microstructure, which might play a role in the outcomes of vascular pathologies like aneurysms.

a b s t r a c tIn this paper, we introduce a new scale called the meso-scale in order to define an appropriate local scale for multi-scale kinematic analysis in granular materials. The proposed meso-scale corresponds to subdomains obtained by subdividing a 2D granular assembly taking into account load-bearing contacts. For each sub-domain, a strain tensor is defined and a description of its structure is proposed. Our analysis, carried out on a biaxial compression test, reveals that strain is significantly related to the structure at the meso-scale: (1) strain in the major (respectively, minor) principal compression direction is largest within the sub-domains which are elongated in the minor (respectively, major) principal compression direction, and (2) contractancy takes place within the sub-domains which are elongated in the minor principal compression direction whereas dilatancy takes place within the sub-domains which are elongated in the major principal compression direction. Furthermore, we emphasize a relation between strain at the meso-scale and the induced anisotropy of granular materials during deviatoric loading.