Biomedical Engineering Reference
In-Depth Information
Fig. 6.14.
Balloon and multi-layer artery model for cerebral angioplasty simulation. 3D solid 185
elements are used to discretize the artery and balloon. The arterial inner surface and balloon outer
surface are meshed with surface-surface contact elements, 170 and 173
A three-dimensional axisymmetric angioplasty model is created to simulate the
interaction between a balloon and the multi-layer artery wall. Due to fore-aft sym-
metry of the model, only part of the arterial segment and balloon are included in
the model, Fig. 6.14. A clinically relevant choice of intracerebral single-lumen an-
gioplasty catheters is 2 mm in diameter by 10 mm in length [21]. Most angioplasty
lesions treated by PTA are less than 10 mm long (usually 2 to 4 mm), so very short
balloons are necessary. In the computational model, the unloaded internal diameter
of the artery is set to 2.5 mm (3.816 mm at the physiological loading state), with a
thickness of 125
m and a length of 10 mm. The balloon has a external diameter of
1.8 mm and a length of 5 mm. The IEL, media and adventitia occupy 1/10, 6/10 and
3/10 of the wall thickness respectively.
A surface contact strategy is used to simulate the interaction between artery and
balloon during PTA. The axisymmetric model includes 17000 3D solid elements,
2600 surface-surface contact elements and four solid materials for the balloon, IEL,
media and adventitia.
μ
Loading states
Four representative deformation states are considered, Fig. 6.15. In State A, the
artery is inflated to a transmural pressure
Δ
p
=
13
.
33
KPa
with an axial stretch
λ
Z
=
1. This generates the arterial physiological deformation state before PTA
which is in a purely elastic regime. In State B, the balloon is deployed to contact and
then further deployed to State C, where the internal diameter has been increased by
130 % from its value in State A. Radial displacement loads were applied on the bal-
loon to reach States B and C. The inelastic damage and injury of arterial tissues take
place during this oversized dilatation process from State B to C. Finally, the ballon
is unloaded to bring the artery back to the physiological state after PTA (State D).
At this final unloading state, a residual unloaded deformation is observed, extend-
ing beyond the area contacted by the PTA. This non-homogeneous residual strain
arises from nonrecoverable inelastic damage of the IEL and media induced by the
supraphysiological dilatation loads.
1
.
