Biomedical Engineering Reference
In-Depth Information
is consistent with endothelium and elastic laminae providing a diffusion barrier. Interestingly, athero-
sclerotic lesions contained large amounts of labeled collagen. Based on these studies, van Zandvoort
and colleagues suggest that CNA can be used to detect atherosclerotic lesions in the arterial wall. CNA
has also been used to reveal platelet binding to exposed subendothelial collagen in a mouse model of
atherothrombosis [46].
Sulforhodamine B has recently been reported to specifically stain elastic fibers intravitally in blood
vessels, and to improve elastin fiber detection as a result of the high cross section and quantum yield of
the dye with two-photon excitation [47]. The spectral properties of sulforhodamine B allows for simul-
taneous detection of collagen SHG or other vital dyes.
13.5 investigations of Vessel Mechanics
13.5.1 Residual Strain
Several studies have investigated the residual strain present in the microstructural components in the
arterial wall. Under conditions where no pressure is applied to the arterial vessel wall, the fibers are
thicker, resulting in a greater overall thickness of the vessel wall. Residual strain in dissected vessels
presents as longitudinal folds, which reflect the residual circumferential stress, or residual strain within
the intimal-medial layers (see Figure 13.7). With no intraluminal pressure, the surface of dissected
murine aorta is compressed in the radial direction into longitudinal wavy folds, indicating that both
radial and longitudinal strains occur in the elastin lamellae [39]. Coiled collagen fibers were arranged
radially within the compressed inner folds of the elastin lamellae and between each lamellar collagen
unit. Individual collagen fibers were coiled with a mean periodicity of 2-5 μm [39].
Arteries at different anatomical sites and species reveal different spacings in the longitudinal folds
[39]. In the mouse, the spacing of the lamellar folds was ~50-100 μm in the upper thoracic aorta and
30-50 μm in the lower abdominal aorta. The porcine carotid artery was compressed in the radial direc-
tion into longitudinal wavy folds spaced ~40-80 μm apart. Similar to the murine aorta, collagen fibers
in the porcine carotid artery were radially arranged within the inner folds of the elastin layer and coiled
with a mean periodicity of 5-10 μm. Residual strain in the porcine coronary artery resulted in longitu-
dinal folds with a spacing of 30-50 μm, implying a dominant radial stress.
FIgurE 13.7
(
See color insert
.) Collagen and elastin microstructure of the porcine carotid artery. Two-photon
image 24 mm below the surface of the porcine carotid intima. Elastin autofluorescence is red; collagen SHG is
green. A wavy sheet of elastin with circular holes throughout envelops the luminal surface of the artery. Individual,
bunched-up collagen fibrils are radially arranged within the inner folds of the elastin lamellae. Scale bar = 20 μm.
