An experimental evaluation of the mechanics of bare and polymer-covered self-expanding wire braided stents

McKenna, Ciara G.; Vaughan, Ted J.

doi:10.1016/j.jmbbm.2019.103549

“…In theory, covered stents promise reduced restenosis [12], with the cover acting as a mechanical barrier to tissue in-growth, yet this doesn't consistently translate into reliable clinical outcomes in small-diameter applications [39]. While numerous clinical studies have investigated the superiority of bare-metal or covered stents [13,14,16,40], relatively few experimental or computational studies have attempted to explain the mechanical implication of stent covering to give more context to this problem [26][27][28]. Previously, it was shown that the addition of thin polymer covers to wire braided stents resulted in substantially stiffer radial and axial responses (up to ten-fold for a 25μm cover) [28].…”

Section: Discussionmentioning

confidence: 99%

A computational framework examining the mechanical behaviour of bare and polymer-covered self-expanding laser-cut stents

McKenna¹,

Vaughan²

2021

Preprint

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Polymer covered stents have demonstrated promising clinical outcomes with improved patency rates compared to traditional bare-metal stents, however little is known on the mechanical implication of stent covering. In the present work, a combined experimental-computational investigation was carried out to determine the role of a polymeric cover on the biomechanical performance of self-expanding laser-cut stents. Experimental bench top tests were conducted on bare and covered versions of a commercial stent to evaluate the radial, axial and bending response. In parallel, a computational framework with a novel covering strategy was developed that accurately predicts stent mechanical performance, and provides further insight into covered stent mechanics by considering different stent geometries and polymer materials. Results show that stent covering causes increased initial axial stiffness and substantial radial stiffening at small crimp diameters as the cover folds and self-contacts. It was also shown that use of a stiffer polymeric covering material caused significant alterations to the radial and axial response, highlighting the importance of considering the mechanical properties of the combined cover and stent.

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“…Axial compression was performed on each stent using a Zwick uniaxial test machine with a 10N load cell (Zwick Roell, GmbH & Co., Germany) at a displacement rate of 0.5mm/s. Each end of the stent was secured with cylindrical supports and spring clamps, described previously in [27], with a grip-to-grip separation of 25mm. The bottom support was fixed, while the top support was displaced downwards by 5mm to compress the stent to 20% strain (see Figure 2 (b)).…”

Section: Axial Compressionmentioning

confidence: 99%

“…Our recent studies on covered braided stents showed that the addition of a cover led to substantial increases in both radial and axial stiffness, by altering the fundamental deformation mechanisms involved in these wire-based stent configurations [27,28]. Other studies on the mechanics of covered stents are limited, with research in this area mainly focussing on large stent-grafts with separated wire rings intended for abdominal artery aneurysms [29][30][31][32].…”

Section: Introductionmentioning

confidence: 99%

A Computational Framework Examining the Mechanical Behaviour of Bare and Polymer-Covered Self-Expanding Laser-Cut Stents

McKenna

¹

,

Vaughan

²

2021

Cardiovasc Eng Tech

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Polymer covered stents have demonstrated promising clinical outcomes with improved patency rates compared to traditional bare-metal stents, however little is known on the mechanical implication of stent covering. In the present work, a combined experimental-computational investigation was carried out to determine the role of a polymeric cover on the biomechanical performance of self-expanding laser-cut stents. Experimental bench top tests were conducted on bare and covered versions of a commercial stent to evaluate the radial, axial and bending response. In parallel, a computational framework with a novel covering strategy was developed that accurately predicts stent mechanical performance, and provides further insight into covered stent mechanics by considering different stent geometries and polymer materials. Results show that stent covering causes increased initial axial stiffness and substantial radial stiffening at small crimp diameters as the cover folds and self-contacts. It was also shown that use of a stiffer polymeric covering material caused significant alterations to the radial and axial response, highlighting the importance of considering the mechanical properties of the combined cover and stent.

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“…Finite Element (FE) modelling has been used over the past two decades to investigate cardiac mechanics, hemodynamics and device design [20]. In particular, patient-specific FE models have been used to investigate cardiovascular device performance, optimal sizing, placement and optimization of device design [3,4,21–23]. Li et al previously used FE methods to optimize the design of coronary stents to reduce the stent dog-boning effect [23].…”

Section: Introductionmentioning

confidence: 99%

An Investigation into Patient-Specific 3D Printed Titanium Stents and the use of Etching to Overcome Selective Laser Melting Design Constraints

Om

¹

,

Geraghty

²

,

Hughes

³

et al. 2021

Preprint

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There is currently a clear clinical need in the area of stenting for paediatric patients, whereby currently commercially available adult stents are often required to be used off-label for paediatric patients resulting in less than optimal outcomes. The increasingly widespread use of CT and/or MR imaging for pre-surgical assessment, and the emergence of additive manufacturing processes such as 3D printing, could enable bespoke devices to be produced efficiently and cost-effectively. However, 3D printed metallic stents need to be self-supporting leading to limitations in the design of stents available through additive manufacturing. In this study, we investigate the use of etching to overcome these design constraints and improve stent surface finish. Furthermore, using a combination of experimental bench testing and finite element methods we investigate how etching influences stent performance and using an inverse finite element approach the material properties of the printed and etched stents were calibrated and compared. Finally, using patient-specific finite element models the stent performance was tested to assess patient outcomes. Within this study, etching is confirmed as a means to create open-cell stent designs whilst conforming to additive manufacturing rules and concomitantly improving stent surface finish. Additionally, the feasibility of using an in-vivo imaging to product development pipeline is demonstrated that enables patient-specific stents to be produced for varying anatomies to achieve optimum device performance.

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An experimental evaluation of the mechanics of bare and polymer-covered self-expanding wire braided stents

Cited by 38 publications

References 27 publications

A computational framework examining the mechanical behaviour of bare and polymer-covered self-expanding laser-cut stents

A computational framework examining the mechanical behaviour of bare and polymer-covered self-expanding laser-cut stents

A Computational Framework Examining the Mechanical Behaviour of Bare and Polymer-Covered Self-Expanding Laser-Cut Stents

An Investigation into Patient-Specific 3D Printed Titanium Stents and the use of Etching to Overcome Selective Laser Melting Design Constraints

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