Biomedical Engineering Reference
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model may be suitable for the other types of damage, cyclic fatigue and enzymatic
degradation. Evidence of a uniform frayed appearance has been observed in aged
arteries [30]. We are currently conducting cyclic fatigue studies to further explore
this damage mode. Similar to the acute rupture tests presented here, resulting data
will be fit to the continuum damage model described above.
6.5 Applications of the damage model to cerebral angioplasty
Cerebral percutaneous transluminal angioplasty (PTA) is an important interventional
neurovascular technique for the treatment of atherosclerotic obstructions and va-
sospasm in cerebral vessels. During this procedure, a balloon is inflated within the
cerebral vessels in an attempt to improve cerebral perfusion and as a result reduce
long-term stroke and death [48, 57, 116]. The primary mechanical mechanism of
lumen enlargement by PTA is explained as the overstretching of the arterial wall
[17]. Vessel wall damage is observed at the site of PTA including intimal damage
(endothelial damage, subendothelial destruction, fractured IEL) and medial changes
(damaged myocytes, loss of dense bodies, gap in the extracellular matrix, disorga-
nized collagen fibres) [16, 18, 21, 57, 122]. In addition to local structural damages
such as areas of disruption and dissection throughout the vessel layers, larger scale
structural damage can occur including partial tears of the intima or media and even
vessel rupture [21, 57].
Arterial wall damage caused by angioplasty was studied in common carotid, iliac,
and femoral arteries of mongrel dogs, [122]. Damage was found to be dose depen-
dent. After 25 % inflation, the wall exhibited localized fractures and stretching of
the IEL and damage to the inner one third of the media. At 50 % inflation, exten-
sive damage to the IEL, dissection of the media, distorted SMC and disorganized
collagen fibres through more than one-half of the media were reported. Damage was
largest in the inner layers and increased outwards. While the repair of smooth muscle
cells and collagen in the media was visible at six months, the IEL showed no signs
of recovery.
It is important to develop realistic computational tools for studying this disease.
Sidorov [106] simulated balloon angioplasty with a homogeneous and isotropic
multi-mechanism arterial model developed by [119]. Material anisotropy, dam-
age and heterogeneity were not included in that study. Gasser and Holzapfel [34]
modelled plaque fissure and dissection during angioplasty using an anisotropic and
elastoplastic material formulation with two arterial layers [36, 52]. Arterial injury
was analyzed indirectly via the distribution of a plastic hardening variable.
The damage to the arterial wall following PTA has not been rigorously inves-
tigated theoretically and numerically. In this section we summarize recent results
using the multi-mechanism framework discussed in Sect. 6.3 with the damage the-
ory in Sect. 6.4 to model cerebral angioplasty, [71, 74]. An extension of the theory
is made to include anisotropic damage to collagen fibres so medial injury can be
modelled, [70, 72, 73, 75]. A three-layer heterogeneous vessel wall model is used
in which each layer of the wall is defined as a structural multi-mechanism mate-
