Micromechanics-based numerical analysis of failure in calcified abdominal aortic aneurysm

Abdominal aortic aneurysms (AAAs) are a critical medical concern characterized by the dilation of the abdominal aorta, with the potential for life-threatening rupture. Calcification of AAAs in varying amount is identified as one of the factors affecting their mechanical and failure behaviour. However, reasons behind the same are not clear. The current work presents a micro-mechanics based numerical method to analyse the effect of calcification on the rupture behaviour of aneurysmatic tissue. An anisotropic material model suitable for modelling biological tissues is used and it is calibrated against available experimental data under bi-axial loading. To model failure in tissues, an energy-based failure criterion is used and failure parameters are identified from available experimental data. Calcified tissues are modelled as a composite material with tissue as a matrix and calcium (Ca) particles as an inclusion. Multiple representative volume elements are generated and used for simulation to capture the effect of morphology and amount of calcification. Contact conditions between the tissue and Ca particles are also assumed for the investigation. Thus, failure envelopes of calcified tissues are generated under different conditions. Our findings reveal that calcification affects the aneurysm rupture significantly. Amount of calcification is more critical than its morphology. Highly calcified tissues fail at lower stretches and the failure initiates in the ligaments joining Ca particles. Failure location could be correlated with available experimental observations. With higher calcification, tissues also become more isotropic in nature. The study also emphasizes that stretch-based criterion is a better candidate for predicting the failure of the aneurysm than a stress-based criterion. Further, parameters for constitutive model and failure model are identified for homogenized calcified tissue with low calcification.