A cohesive model of dissection in arterial layers Anna Ferrara 1 , Anna Pandolfi 1 1 Dipartimento di Ingegneria Strutturale, Politecnico di Milano, Italy E-mail: aferrara@stru.polimi.it, pandolfi@stru.polimi.it Keywords: Cohesive fracture, arterial wall, dissection, finite elements. SUMMARY. In medical terms and referring to aortic arterial damage, dissection is the separation of intra-medial tissue induced by a radial tear cutting the intima and a portion of the underling media. Pressurized blood pervading the tear usually progresses the intramural process of dissection and may later induces formation of clots. The purpose of this study is to setup a mechanical model of arterial dissection, based on cohesive theories of fracture, able to detect the critical mechanical conditions leading to the tissue damage. 1 INTRODUCTION The arterial wall consists of three concentric layers of a laminated-like tissue, reinforced by col- lagen fibers: the intima (inner layer), the media, and the adventitia (outer layer). Arterial dissection is a pathological state which refers to the separation of two layers along their interface or to the delamination within a layer of the arterial wall. Dissections may cause narrowing of the vessel channel (stenosis) and even its entire closure, de- creasing the blood flow to vital organs. Dissection also weakens the artery wall and may lead to their rupture, or to the formation of a balloon-like expansion known as aneurysm. In the aorta, dissection is characterized by the formation of a tear in the intima. Due to the lami- nated structure of arterial wall, intimal tears often have sharp edges and are oriented transversally or vertically in relation to the long axis of the artery. In the dissection, the pressurized blood enters at the site of the tear and splits the middle layer (media) of the artery. Following the material lam- inated microstructure, the tear expands parallel to the original vessel lumen, both circumferentially and longitudinally, creating an additional passage called false lumen [1, 2]. The false lumen varies from a few millimeters to the larger classic false lumen of several centimeters, with an associated flap or septum. A combination of transverse and longitudinal dissections may produce T or cross shaped tears. In some circumstances, adjacent elastin lamellae may converge and fuse together, offering a barrier to dissection. Thus, interlamellar material and fused lamellae may prevent the ini- tiation of dissection, or may contrast its propagation within the media [3]. Less common intramural hematoma-type dissections of the aortic wall have been identified, in which dissection is filled with blood clot without a detectable intimal tear. Unlike aortic dissection, spontaneous coronary artery dissection is often not associated with an in- timal tear. The coronaries are muscular arteries and do not contain a relevant amount of elastic laminae. The preferential surface of dissection for coronary arteries lies therefore between the ad- ventitia and the media. The purpose of this research is to study the process of dissection in the artery walls from the mechanical point of view, by using a finite element model, where the tissue damage is treated by using cohesive theories of fracture. The knowledge of the mechanical factors that affect and drive the arterial dissection may provide important information and useful data for the design of prevention or treatment systems. The present analyses focus on the influence of the cohesive strength and of the mesh size on the dissection evolution process. The cohesive strength, difficult to evaluate and to 1