Turnover of fibrillar collagen in soft biological tissue with application to the expansion of abdominal aortic aneurysms

Abstract

A better understanding of the inherent properties of vascular tissue to adapt to its mechanical environment is crucial to improve the predictability of biomechanical simulations. Fibrillar collagen in the vascular wall plays a central role in tissue adaptation owing to its relatively short lifetime. Pathological alterations of collagen turnover may fail to result in homeostasis and could be responsible for abdominal aortic aneurysm (AAA) growth at later stages of the disease. For this reason our previously reported multiscale constitutive framework (Martufi, G. & Gasser, T. C. 2011 J. Biomech . 44 , 2544–2550 ( doi:10.1016/j.jbiomech.2011.07.015 )) has been enriched by a collagen turnover model. Specifically, the framework's collagen fibril level allowed a sound integration of vascular wall biology, and the impact of collagen turnover on the macroscopic properties of AAAs was studied. To this end, model parameters were taken from the literature and/or estimated from clinical follow-up data of AAAs (on average 50.7 mm-large). Likewise, the in vivo stretch of the AAA wall was set, such that 10 per cent of collagen fibres were engaged. Results showed that the stretch spectrum, at which collagen fibrils are deposed, is the most influential parameter, i.e. it determines whether the vascular geometry grows, shrinks or remains stable over time. Most importantly, collagen turnover also had a remarkable impact on the macroscopic stress field. It avoided high stress gradients across the vessel wall, thus predicted a physiologically reasonable stress field. Although the constitutive model could be successfully calibrated to match the growth of small AAAs, a rigorous validation against experimental data is crucial to further explore the model's descriptive and predictive capabilities.

A Bioreactor to Identify the Driving Mechanical Stimuli of Tissue Growth and Remodeling

“…Yet, the mechanisms through which this mechanical homeostasis is maintained remain largely unknown. An improved knowledge of these mechanisms is key to better understand pathologies where adverse growth and remodeling occur, such as dilated and hypertrophic cardiomyopathy 3 , valvular disease 4,5 , and aneurysm formation 6,7 . Moreover, a fundamental understanding of growth and remodeling is essential in the fields of regenerative medicine and tissue engineering.…”

Goal Function Approach to Growth and Remodeling of Arteries

“…Here, we look only at the two-constituent model. That is, we divide the blood vessels wall into two components: an isotropic part which does not grow or remodel (elastin, which has a much longer degradation time than other relevant materials, [16]), and an anisotropic part that grows and remodels (collagen and smooth muscle have shorter degradation time [31,32]). Stability analysis is performed by changing the parameters CE 2 0 /ν 1 and b 1 C/ν 1 and then letting the dynamical system evolve toward a target homeostatic state.…”

Computational Growth and Remodeling of Abdominal Aortic Aneurysms Constrained by the Spine

“…Computational G&R models provide time-dependent evolution of biomechanical characteristics of the AAA [20][21][22][23], and hence, allow for incorporation of contact due to the aneurysm growth. In our recent studies, we developed a framework for the simulation of AAA expansion initiated by elastin degradation and continuous stress-mediated collagen turnover using realistic geometries [7,24].…”