Structural inhomogeneity and fiber orientation in the inner arterial media

Abstract

The microstructural orientation of vascular wall constituents is of interest to scientists and clinicians because alterations in their native states are associated with various cardiovascular diseases. In the arterial media, the orientation of these constituents is often described as circumferential. However, it has been noted that, just below the endothelial surface, the vascular wall constituents are oriented axially. To further study this reported change in orientation, and to resolve previous observations (which were made under conditions of no load), we used nonlinear optical microscopy to examine the orientation of collagen and elastin fibers in the inner medial region of bovine common carotid arteries. Images were obtained from this part of the arterial wall under varying degrees of mechanical strain: 0%, 10% axial, 10% circumferential, and 10% biaxial. We observed that close to the endothelium these components are aligned in the axial direction but abruptly change to a circumferential alignment at a depth of approximately 20 mum from the endothelial surface. The application of mechanical strain resulted in a significantly greater degree of fiber alignment, both collagen and elastin, in the strain direction, regardless of their initial unloaded orientation. Furthermore, variations in strain conditions resulted in an increase or a decrease in the overall degree of fiber alignment in the subendothelial layer depending on the direction of the applied strain. This high-resolution investigation adds more detail to existing descriptions of complex structure-function relationships in vascular tissue, which is essential for a better understanding of the pathophysiological processes resulting from injury, disease progression, and interventional therapies.

Prefailure and Failure Mechanics of the Porcine Ascending Thoracic Aorta: Experiments and a Multiscale Model

“…Previous studies have shown that collagen fibers within the arterial media have strong preferential orientation in the circumferential direction (X hh ) while some percentage of fibers are mainly oriented in the axial direction (X zz ) and even smaller percentage in the radial direction (X rr ) [19][20][21][22][23]. Based on those studies, the average orientation for collagen fiber networks in the media [X hh X zz ] was extrapolated to be [0.62 0.37] [20]. The initial network orientation tensor components [X hh X zz X rr ] were, therefore, specified to be [0.6, 0.3, 0.1] 6 [0.039, 0.040, 0.006]-an orientation state close to that measured in Ref.…”

“…The initial network orientation tensor components [X hh X zz X rr ] were, therefore, specified to be [0.6, 0.3, 0.1] 6 [0.039, 0.040, 0.006]-an orientation state close to that measured in Ref. [20] and with a small amount of alignment in the r direction to maintain the integrity of the network. A single network was used to represent the combined contribution of the collagen and elastin components, with a volume fraction of 5% [15].…”

Failure of the Porcine Ascending Aorta: Multidirectional Experiments and a Unifying Microstructural Model

“…Collagen fibers within the elastin-collagen sheet were generated such that they exhibited strong circumferential orientation, based on the known tissue structure [47][48][49][50][51]. Histological and compositional studies [2,[47][48][49][50][51] show more elastin than collagen within each lamina of the ascending aortic wall. Based on the histological observations of Sokolis et al [51], the overall ratio of elastin-to-collagen within the 2D sheet was set to $1.6.…”

Fibrin Network Changes in Neonates after Cardiopulmonary Bypass: Erratum

“…Quantification of clot fiber alignment was achieved through application of an algorithm based on a fast Fourier transform (FFT) that we have previously employed 17 . Briefly, each confocal image was padded with redundant data, a Gaussian decay (standard deviation = 0.25) and two-dimensional Hann window function were applied to minimize edge effects, and the images were transformed into the frequency domain using a two-dimensional FFT (Supplemental Figure 1A-E).…”