Aortic Biological Prosthetic Valve for Open-Surgery and Percutaneous Implant: Procedure Simulation and Performance Assessment - Cardiovascular and Cardiac Therapeutic Devices - page 155

Fig. 13 Different frames of balloon expansion and stent apposition: a initial configuration; b the
balloon starts to deploy the stent; c the balloon is fully expanded and the stent is fully deployed;
d final configuration after balloon deflation
catheter is virtually reproduced by constraining the displacements in each direction
of the proximal and distal balloon tips. Since the compliant chart of the Edwards
SAPIEN balloon is not available, a reasonable pressure value which leads to a
smooth stent expansion has been used.
The complex contact problem of the balloon interacting with itself and the stent
is described by a Coulomb friction model with a friction coefficient of 0.2. The
whole assembly and the result of the simulation of balloon inflation and stent
expansion is shown in Fig. 13 .
4.2.6 Simulation of Valve Closure
Once the simulation of balloon expansion has been completed and the stent is
placed within the aortic root, we perform a quasi-static simulation to map the valve
onto the implanted stent. In particular, we compute the displacement field of two
different sets of valve nodes: (i) the nodes lying on the line of attachment with the
stent and (ii) the nodes of the circular base of the valve, which are, in the real
device, sewn onto a cylindrical fabric skirt attached to the stent. Finally, the
overlapping nodes of the stent-valve system are tied together.
The last step of the procedure to simulate TAVI consists in the simulation of
valve closure with the aim of evaluating its performance. The diastolic phase
of valve closure has been reproduced by gradually applying a uniform pressure of
0.01 MPa to the leaflets. The nodes of the VAJ and of the STJ belonging to the
patient-specific aortic root model have been constrained; the displacements of the
nodes at the base of the valve are constrained as well.
4.2.7 Results
The described simulation procedure has been performed in two different cases to
evaluate the impact of positioning on the post-implant device behavior: moving