From a general point of view, the project was marked by the development of unique, original and relevant experimental approaches, along with their analyses.
• Experiments combining multi-photon microscopy and a bulge inflation test were developed to observe deforming microstructure under increasing load, focusing on the rupture of the adventitial layer;
• a setup was designed to measure thickness maps of arterial samples with very high accuracy, in order to answer the crucial question of the role of thickness in assessing areas which are more at risk of rupture;
• a complete approach based on tension-inflation testing of tubular arterial segments in a X-ray microtomography setup was developed to study in vitro the onset of dissection in the medial layer of arterial tissue and the influence of intimal defects’ characteristics;
• a study of the effect of propylene-glycol (a chemical used to make tissue more transparent in optical observations like Optical Coherence Tomography, OCT) was performed to evaluate its effects on elastic and rupture properties of tissues. Similarly, the effect of other chemical specifically degrading mechanically-essential components of the extracellular matrix (elastin, collagen) is being investigated to assess the influence of these components if the failure properties of arterial tissue;
• an OCT experiment was developed to observe the progress of dissection-like cracks in the media of an arterial sample, by investigating the 3D deformation state around medial cracks.
In addition to these experimental investigations, numerical analysis methodologies were developed to provide quantitative data in relationship with common models, and deeper understanding than what could be observed in the experiments. They include:
• numerical reconstruction of discrete fiber networks to model and study adventitial rupture, in order improve the understanding of the mechanics of such networks, and to quantify fiber-based adventitial rupture criteria using our experimental data;
• numerical modeling of dissection onset and propagation in the medial layer, in order to understand the influence of mechanical or geometrical properties on the critical pressure triggering dissection and its early propagation, and to identify medial rupture model parameters based on our experiments;
• development and implementation in a Finite Element code of a multi-scale homogenization model taking into account microstructural information in order to include the micro-scale physics and mechanics in a model describing the macroscopic mechanical response of arterial tissue. It was used to elucidate and quantify micro-scale deformation and mechanical state of tissues, and in patient-specific simulation applications where micro-scale information may be the key for remodeling or rupture-risk estimates.
In terms of results, the implementation of these methodologies proved successful and led to results which are of high importance for the community, and for future research.
