Biomedical Engineering Reference
In-Depth Information
rial. A three-dimensional computational model of artery and balloon is formulated
to simulate the artery-balloon interaction during cerebral angioplasty. Due to the ex-
tensive computational requirements for contact analysis with nonlinear materials, an
axisymmetric geometry and simplified balloon model are used. We do not consider
the role of SMC or of residual stresses. The loading is broken into multiple load
steps including vessel inflation-tension, balloon deployment, artery-balloon contact
and balloon deflation. Future experimental work is needed to provide guidance in
the selection of damage parameters.
Arterial wall model
To represent the heterogeneous histological structure of cerebral arteries [29], we
consider the wall as composed of three distinct layers: the IEL, media and adventitia,
Fig. 6.13. The unloaded geometry is idealized as a circular cylinder with constant
wall thickness.
Based on the histology studies of cerebral arteries [28, 91], it is assumed that all
elastin is concentrated in the IEL, the fibres in the media are near the circumferential
direction while the fibre families in the adventitia are dispersed about two fibre di-
rections. All layers will be modelled as incompressible. The intima will be assumed
to be composed solely of an isotropic mechanism. Since we expect that in cerebral
arteries, the mechanical properties of this layer will be dominated by the response
of the IEL, we simply refer to this layer as the IEL. In diseased arteries with intimal
thickening, it may be appropriate to generalize the model to include intimal collagen
fibres. The medial and adventitial layers will be modelled fibre-reinforced compos-
ites with an isotropic mechanism arising from the ground matrix and an anisotropic
mechanism arising from the collagen fibres. The anisotropic mechanism is assumed
to arise from a pair of helically wound fibres oriented symmetrically with respect
to the circumferential direction, Fig. 6.13. A two fibre model will be used for the
media and a generalized structure tensor approach with two fibre directions will be
used for the adventitia. In both cases, it is assumed the two families are oriented
symmetrically with respect to the circumferential direction of the artery, Fig. 6.13.
Fig. 6.13.
Cylindrical multi-layer arterial wall model with the IEL, media and adventitia layers
