Biomechanics of Arterial Walls under Supra-Physiological Loading Conditions

Unknown TEM images: (a) various tissue components including collagen fibrils coming in and out of the imaging plane at various angles; (b) subdomain of (a) highlighting cross-sectioned collagen fibrils (green circles) and their nearest neighbors (white lines) that were automatically identified by a custom made ImageJ plugin. Scale bars: (a) 500 nm; (b) 200 nm.

Unknown 3D reconstruction of the arterial microstructure of a human media through electron tomography. The orange strings indicate the orientations of collagen fibrils, while the green structures correspond to proteoglycans (PGs). Such 3D images are used to extract and quantify angular distributions between collagen and PGs, and to investigate their potential changes as a function of supra-physiological loading conditions.

This DACH project deals with the analysis and modeling of traumatic degenerations of overstretched arterial walls that occur in therapeutical interventions ("DACH" stands for Germany, D; Austria, A; and Switzerland, CH). For example, clinical interventions for treating atherosclerotic degeneration resulting in luminal narrowing often include balloon angioplasty. This invasive procedure involves the inflation of a catheter with the aim of increasing the lumen dimensions by pushing the obstructing plaque into the vessel wall. Naturally, for this procedure a much higher pressure than the physiological blood pressure is required, and this causes microscopic-level tissue damage and results in stress-softening of the collagenous tissue.

A database for the qualitative and quantitative description of arterial tissues will be obtained from uniaxial and biaxial extension tests performed on the tissue components of individual arterial layers loaded far beyond the physiological domain. Towards this end cyclic tension-tests will be carried out on healthy as well as on collagenase and elastase treated arterial tissues to investigate component-specific stress softening behavior. Such tests enable the analysis of the macroscopic mechanical tissue response. In addition, structural analysis techniques such as Fourier transform infrared spectroscopy, scanning electron microscopy and nano-tomography will be used to study damage at the microscopic length scale, with a special focus on damage induced changes in the interfibrillar collagen distances and angular proteoglycan distributions.

The macroscopic response of the fiber-reinforced tissues will be described by a formulation based on micro-mechanical models characterizing the individual tissue components. These models take into account alterations of stochastic distributions of fiber properties as a consequence of the tissue overstretch. In order to obtain a quantitative prediction of the material response, the model parameters will be adjusted to so as to fit data from the performed experiments based on least-squares minimization.

Finally, the models will be validated by comparing finite element calculations with experiments performed on whole arterial wall segments.

Funding: DACH Project support by Austrian Science Fund (FWF) and German Research Foundation (DFG)