A modeling pipeline and parametric study to estimate the biomechanical behaviour of bio-engineered fibrous caps

Abstract

Background: Atherosclerosis is a progressive arterial disease that gives rise to plaque. Rupture thereof is a main cause of myocardial infarction and ischaemic stroke. A plaque can have a fibrotic layer between its lipid pool and the arterial lumen, which is termed a fibrous cap (FC). Rupture of this FC can expose thrombogenic plaque content to the bloodstream. From a mechanical viewpoint, the FC is hypothesized to rupture when its strength is exceeded by the structural stresses imposed thereupon. Stresses in the FC can not be measured and are generally approximated by using digital analogs such as finite element models. Such models require among other things a definition of the FC its in-vivo composition. However, this is still poorly understood as it can presently not be measured in-vivo. To investigate the relations between a FC its composition and its mechanical properties, bio-engineered FCs (BE-FC) have been developed by researchers. These BE-FCs are reported to bear resemblance to human FCs in terms of bulk mechanical properties. This study aims to aid in the comprehension of the biomechanical behaviour of these BE-FCs.
Methods: A finite element modeling pipeline has been developed for BE-FCs. Following the pipeline provides a 2D BE-FC model and a total of 16 BE-FCs were modeled. Material behaviour is defined using the Holzapfel-Gasser-Ogden model. The BE-FC models their geometry and material parameters are acquired using geometry and collagen images in combination with self-developed and data-scaleable scripts. Model simulation results provide an approximation of the BE-FC its biomechanical behaviour. This study includes an investigation of the BE-FC models their global biomechanical behaviour as well as their stress and strain peak values, peak value locations, and distributions. In addition a parametric study has been performed; 1260 idealised BE-FC models were created. These models differ in geometry and composition, allowing a more in-depth investigation of the BE-FC models their stress and strain peak values and distributions.Results: The global biomechanical behaviour of the BE-FC models satisfyingly approximates that of their respective BE-FC. Peak stresses and strains in the BE-FC models are considerably higher than those found in the literature for ex-vivo uni-axially tensile tested FCs as well as compared to FC sections of finite element models. To the same extent the locations of the peak stresses and strains in the BE-FC models could not be co-localized to the rupture initiation locations of the BE-FCs. The stress and strain distributions are thoroughly examined using the simulation results of the idealised models. Depending on the specific stress and strain metric, each is contingent on different model characteristics and/or behaviours. In general however the most crucial of these are the collagen fibre dispersion \(\kappa\), the collagen fibre mean angle \(\Theta\), the degree of model compaction, and the model its soft inclusion shape and size.Conclusion: With this study, a novel modeling pipeline has been developed for 2D BE-FC finite element models. Results from simulations therewith give insight into the biomechanical behaviour of BE-FCs. In addition a parametric study has been performed, resulting in numerous idealised BE-FC models. The simulation results of these models aid considerably in the understanding of the BE-FCs their biomechanical behaviour. Taking everything in consideration, a contribution has been made to the comprehension of BE-FCs and along with that it therefore assists current research invested in answering how, why and when a FC ruptures.