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Research Papers

Numerical Study of the Uniformity of Balloon-Expandable Stent Deployment

[+] Author and Article Information
P. Mortier1

Cardiovascular Mechanics and Biofluid Dynamics Research Group, Institute Biomedical Technology (IBiTech), Ghent University, De Pintelaan 185, 9000 Gent, Belgium

M. De Beule

Cardiovascular Mechanics and Biofluid Dynamics Research Group, Institute Biomedical Technology (IBiTech), Ghent University, De Pintelaan 185, 9000 Gent, Belgiump.mortier@ugent.be

S. G. Carlier

 Colombia University Medical Center, 111 East 59th Street, New York, NY 10022-1202; Cardiovascular Research Foundation, 630 West 168th Street, New York, NY 10032

R. Van Impe

Laboratory for Research on Structural Models, Ghent University, Technologiepark-Zwijnaarde 904, 9052 Zwijnaarde, Belgium

B. Verhegghe

Department of Mechanical Construction and Production, Ghent University, Sint-Pietersnieuwstraat 41, 9000 Gent, Belgium

P. Verdonck

Cardiovascular Mechanics and Biofluid Dynamics Research Group, Institute Biomedical Technology (IBiTech), Ghent University, De Pintelaan 185, 9000 Gent, Belgium

http://www.ugct.ugent.be

http://engineershandbook.com.

http://bumps.ugent.be/bumper.

1

Corresponding author.

J Biomech Eng 130(2), 021018 (Apr 04, 2008) (7 pages) doi:10.1115/1.2904467 History: Received January 16, 2007; Revised November 22, 2007; Published April 04, 2008

Stents are small tubelike structures, implanted in coronary and peripheral arteries to reopen narrowed vessel sections. This endovascular intervention remains suboptimal, as the success rate is limited by restenosis. This renarrowing of a stented vessel is related to the arterial injury caused by stent-artery and balloon-artery interactions, and a local subsequent inflammatory process. Therefore, efforts to optimize the stent deployment remain very meaningful. Several authors have studied with finite element modeling the mechanical behavior of balloon-expandable stents, but none of the proposed models incorporates the folding pattern of the balloon. We developed a numerical model in which the CYPHER™ stent is combined with a realistic trifolded balloon. In this paper, the impact of several parameters such as balloon length, folding pattern, and relative position of the stent with respect to the balloon catheter on the free stent expansion has been investigated. Quantitative validation of the modeling strategy shows excellent agreement with data provided by the manufacturer and, therefore, the model serves as a solid basis for further investigations. The parametric analyses showed that both the balloon length and the folding pattern have a considerable influence on the uniformity and symmetry of the transient stent expansion. Consequently, this approach can be used to select the most appropriate balloon length and folding pattern for a particular stent design in order to optimize the stent deployment. Furthermore, it was demonstrated that small positioning inaccuracies may change the expansion behavior of a stent. Therefore, the placement of the stent on the balloon catheter should be accurately carried out, again in order to decrease the endothelial damage.

FIGURES IN THIS ARTICLE
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Copyright © 2008 by American Society of Mechanical Engineers
Topics: stents , Catheters
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References

Figures

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Figure 1

3D model of the CYPHER™ stent and delivery system

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Figure 2

Numerical inflation of cylindrical balloon (only half of the balloon was simulated because of symmetry)

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Figure 3

Meshed section of the catheter-balloon-stent model

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Figure 4

Comparison of a trifolded (left) and a sixfolded (right) balloon. Both folding patterns are based on the same initial balloon diameter, namely, D0=2.85mm.

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Figure 5

Expansion of the reference model (trifolded balloon with a length of 10.5mm): before inflation (top); transient phase (middle) corresponding to a pressure between 0.3N∕mm2 and 0.4N∕mm2 (during the transient expansion phase, the balloon unfolds and the stent diameter rapidly increases); situation after this transient expansion (pressure >0.4N∕mm2, bottom)

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Figure 6

Quantitative validation of the reference model: the maximum percent difference in diameter between the numerical results and the compliance chart provided by the manufacturer is 4.1% and occurs at a pressure of 1.4N∕mm2. The steep part (pressure between 0.3N∕mm2 and 0.4N∕mm2) of the curve obtained by simulation corresponds to the transient central shape from Fig. 5.

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Figure 9

Comparison of the transient expansion shape for the reference model (top) and Model K (bottom). The reference model with a trifolded balloon leads to an asymmetric expansion, as the diameter of the left stent end is larger than the diameter of the right stent end. In contrast to the reference model, Model K with the sixfolded balloon shows an approximately symmetric stent deployment.

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Figure 10

Transient expansion shape for Models L and M. A noncentrally placed stent results for both folding patterns in a strongly asymmetric expansion.

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Figure 8

Relationship between the balloon length and the maximum of the dogboning coefficient during the transient expansion phase. A more uniform expansion is obtained by decreasing the balloon length.

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Figure 7

Transient expansion shape for Model J (top), Model E (center), and the reference model (bottom). A shorter balloon length results in a decreased dogbone effect.

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