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Research Papers

Finite Element Analysis of the Implantation Process of Overlapping Stents

[+] Author and Article Information
Jiang Xu

School of Mechanics and Engineering,
Southwest Jiaotong University,
Chengdu 610031, China
e-mail: xujiang0123@163.com

Jie Yang

School of Mechanics and Engineering,
Southwest Jiaotong University,
Chengdu 610031, China
e-mail: yangchenjie@home.swjtu.edu.cn

Salman Sohrabi

Department of Mechanical
Engineering and Mechanics,
Lehigh University,
Bethlehem, PA 18015
e-mail: sas713@lehigh.edu

Yihua Zhou

Department of Mechanical
Engineering and Mechanics,
Lehigh University,
Bethlehem, PA 18015
e-mail: yiz311@lehigh.edu

Yaling Liu

Bioengineering Program,
Lehigh University,
Bethlehem, PA 18015;
Department of Mechanical
Engineering and Mechanics,
Lehigh University,
Bethlehem, PA 18015
e-mail: yal310@lehigh.edu

1Corresponding authors.

Manuscript received July 31, 2016; final manuscript received March 15, 2017; published online May 3, 2017. Assoc. Editor: Marc Horner.

J. Med. Devices 11(2), 021010 (May 03, 2017) (9 pages) Paper No: MED-16-1286; doi: 10.1115/1.4036391 History: Received July 31, 2016; Revised March 15, 2017

Overlapping stents are widely used in vascular stent surgeries. However, the rate of stent fractures (SF) and in-stent restenosis (ISR) after using overlapping stents is higher than that of single stent implantations. Published studies investigating the nature of overlapping stents rely primarily on medical images, which can only reveal the effect of the surgery without providing insights into how stent overlap influences the implantation process. In this paper, a finite element analysis of the overlapping stent implantation process was performed to study the interaction between overlapping stents. Four different cases, based on three typical stent overlap modes and two classical balloons, were investigated. The results showed that overlapping contact patterns among struts were edge-to-edge, edge-to-surface, and noncontact. These were mainly induced by the nonuniform deformation of the stent in the radial direction and stent tubular structures. Meanwhile, the results also revealed that the contact pressure was concentrated in the edge of overlapping struts. During the stent overlap process, the contact pattern was primarily edge-to-edge contact at the beginning and edge-to-surface contact as the contact pressure increased. The interactions between overlapping stents suggest that the failure of overlapping stents frequently occurs along stent edges, which agrees with the previous experimental research regarding the safety of overlapping stents. This paper also provides a fundamental understanding of the mechanical properties of overlapping stents.

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Copyright © 2017 by ASME
Topics: stents , Pressure
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References

Figures

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Fig. 1

Schematic diagram of overlapping distance and angle. The left stent is referred to as stent 1 and the right one is referred to as stent 2.

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Fig. 2

The model of balloon deflation and folding: (a) the unfolded balloon, (b) the folded balloon, and (c) detail of the folded balloon

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Fig. 3

Stent structure and finite element mesh

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Fig. 4

The processes of modeling stent overlap: (a) summarizes the simulation steps, (b) summarizes the displacement applied on the outer surface of the stent in step 1, and (c) is the pressure applied on the inner surface of balloon in steps 2–5

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Fig. 5

Deformation of overlapping stents upon completion of all the simulation steps

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Fig. 6

Edge-to-edge contact pattern of overlapping stents. Contact pressure results shown in (b) and (c). A concentration of pressure is predicted on both edges of the contact pairs.

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Fig. 7

Edge-to-surface contact pattern of overlapping stents. Contact pressure is shown in (b) and (c). Pressure concentrations were predicted on one edge of the contact pairs.

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Fig. 8

Overlapping stents with no contact pattern

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Fig. 9

Statistics of stent contact number for different contact pressure ranges. The shaded zone represents the number of edge-to-edge contacts and the solid zone represents the number of edge-to-surface contacts.

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Fig. 10

Schematic diagram of tubelike structure of stents. (a) and (b) A portion of overlapping stents, the red stent is stent 1 and the blue stent is stent 2, (c) and (d) schematic diagram of the interaction of stent struts whose section is not rectangular but fan-shaped, and (e) SEM picture of an actual stent strut cross section.

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Fig. 11

Diagrams of the “dog bone” effect and “local dog bone” effect. (a) The “dog bone” effect during stent expansion, (b) the “dog bone” effect as viewed along the axial direction, (c) the “local dog bone” effect during stent expansion, (d) the “local dog bone” effect from 1 to 1 section view, (e) the contact pressure distribution after the load has been released, and (f) the nonuniform deformation of the overlapping stent as viewed from the axial direction.

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Fig. 12

The statistics of stent contact number at different load ranges applied on balloon 2. The shaded zone represents the number of edge-to-edge contacts and the solid zone represents the number of edge-to-surface contacts.

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Fig. 13

The evolution of edge-to-surface contact changing into edge-to-edge contact during implantation of an overlapping stent

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Fig. 14

The evolution of edge-to-edge contact changing into edge-to-surface contact during implantation of the overlapping stent

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