1 Scope
This standard provides guidelines for quantitatively characterizing balloon-expandable stent and stent system flexibility using three-point bending procedures. Guidelines are provided for characterizing deployed stent flexibility, and for characterizing pre-deployment stent system flexibility in the region of the stent and balloon.
This standard is not recommended for test articles that cannot be appropriately evaluated using a span length to stent outer diameter (as tested) ratio of at least 4:1. Test articles that do not meet this requirement are likely to exhibit appreciable deformation by modes other than bending.
This standard does not provide procedures for characterizing the bending flexibility of self-expanding stents, self-expanding stent systems, endoprostheses (stent-grafts), or endoprostheses systems. However, some aspects of this standard may be useful for developing appropriate three-point bending characterization procedures for these devices. While this standard was developed with vascular stents and stent systems in mind, it may be useful for characterizing the bending flexibility of balloon-expandable stents and stent systems used in non-vascular applications.
The values stated in SI units are to be regarded as the standard. The values given in parentheses are mathematical conversions to inch-pound units that are provided for information only and are not considered standard.
2 Terms and Definitions
For the purposes of this document, the following terms and definitions apply.
2.1
bending flexibility
a measure of the ability of a test specimen to bend
2.2
bending stiffness
a measure of the ability of a test specimen to resist bending
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2.3
conformability
the degree to which a stent or stent system matches the native curvature of the vasculature
2.4
deflection
displacement of the dynamic support (loading anvil) at any point in the test
2.5
delivery system
catheter that is used to deliver and deploy a stent at the target site. A delivery system for balloon-expandable stents may be similar to a balloon-dilatation (angioplasty) catheter
2.6
midspan bending moment
a linear estimate of the bending moment at the center of the span (see 8.5)
2.7
midspan curvature
a linear estimate of the curvature of the center of the span (see 8.5)
2.8
span length
distance between the centers of the supports
2.9
stent system
delivery system with a pre-mounted stent
2.10
vascular stent
synthetic structure that is permanently implanted in the native or grafted vasculature and that is intended to provide mechanical radial support to enhance vessel patency
3 Significance and Use
3.1 This standard can be used to obtain force versus deflection or midspan bending moment versus midspan curvature curves for stents and stent systems subjected to three-point bending conditions. Bending flexibility of a stent system may be a factor in its ability to track through the vascular anatomy, and may be a factor in vascular trauma along the delivery pathway distal to the guide catheter. Bending flexibility of a deployed stent may be one measure of its ability to flex with a vessel, or to conform to the natural curvature of a vessel. Bending flexibility of a delivery system may also be of interest if it is desired to assess the separate contributions of the delivery system and the mounted stent to the overall flexibility of the stent system.
3.2 This standard is not intended to determine material properties, stent system trackability (ability of a stent system to follow a guide wire and/or guide catheter through vascular tortuosity), or stent system deliverability (ability of a stent system to deliver a stent to the implantation site(s) or through particular level(s) of vascular tortuosity). While this standard does not determine stent system trackability or deliverability, it can provide quantitative insight into how stent system bending flexibility affects trackability and deliverability. Similarly, while this standard does not determine conformability of a deployed stent, it can provide quantitative insight into how stent and/or stent system bending flexibility affects deployed stent conformability. Since this standard quantifies bending flexibility, it may be useful in determining the magnitude of bending flexibility effects on bending-related performance differences between the test article and control devices.
3.3 The three-point bending procedures provided in this standard are intended to be used to characterize balloon-expandable stent and stent system flexibility during product development. They may not necessarily satisfy any particular requirements of national or international regulatory bodies.
Foreword II
1 Scope
2 Terms and Definitions
3 Significance and Use
4 Summary of Standard
5 Apparatus
6 Test Specimens
7 Procedure
8 Calculation and Interpretation of Data
9 Report
Annex A (Informative) Bending Comparisons Using Variable Span Lengths
