A Multi-Scale Collagen Turn-Over Model for Soft Biological Tissues With Application to Abdominal Aortic Aneurysm Growth

Collagen is a structural protein responsible for the mechanical strength, stiffness and toughness of biological tissues like skin, tendon, bone, cornea, lung and vasculature. In the present study we considered the enlargement of the aneurysm as a consequence of a pathological degradation and synthesis of collagen, i.e. malfunction of collagen turn-over. Consequently, the vascular wall is modeled by an (inert) matrix material representing the elastin, which is reinforced by a dynamic structure of bundles of collagen. Specifically, collagen is formed by a continuous stress-mediated process: deposited in the current configuration and removed by a constant degradation rate. Finally the micro-plane concept is used for the Finite Element implementation of the constitutive law. The model proposed within this study has a strong biological motivation and is able to capture both non-linear mechanics of aortic tissue and saline feature of AAA growth. Besides that, the micro-plane approach allows a straight forward FE implementation and preliminary results indicate its numerical robustness.