ASTM F2606-08(R2021) pdf free download

ASTM F2606-08(R2021) pdf free download.Standard Guide for Three-Point Bending of Balloon-Expandable Vascular Stents and Stent Systems
1. Scope
1.1 This guide provides guidelines for quantitatively char- acterizing balloon-expandable stent and stent system flexibility using three-point bending procedures. Guidelines are provided for characterizing deployed stent flexibility, and for character- izing pre-deployment stent system flexibility in the region of the stent and balloon. 1.2 This guide 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. 1.3 This guide does not provide procedures for characteriz- ing the bending flexibility of self-expanding stents, self- expanding stent systems, endoprostheses (stent-grafts), or en- doprostheses systems. However, some aspects of this guide may be useful for developing appropriate three-point bending characterization procedures for these devices. While this guide 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. 1.4 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 informa- tion only and are not considered standard. 1.5 This international standard was developed in accor- dance with internationally recognized principles on standard- ization established in the Decision on Principles for the Development of International Standards, Guides and Recom- mendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
3. Significance and Use
3.1 This guide 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 guide is not intended to determine material properties, stent system trackability (ability ofa 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) ofvascular tortuosity). While this guide 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 guide 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 guide 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 guide 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.
4. Summary of Guide
4.1 The specimen is loaded onto a three-point bend fixture. The specimen is supported from below by two static supports separated by a known span and bent by a force applied on the top and midway between the lower supports. The bending flexibility of the stent is obtained from force-versus-deflection plots and/or midspan bending moment versus midspan curva- ture plots. Bending flexibility evaluations may be made on balloon-expandable stent systems, and/or on deployed balloon- expandable stents. Bending flexibility ofa delivery system may also be evaluated 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. 4.2 Bending flexibility assessments may be made using a fixed span between the lower supports or by using a span that increases with the specimen length. 4.2.1 The fixed span length method permits force versus deflection comparisons that are independent of stent length. This method may be useful when comparing the flexibility of stents with different diameters or structural designs, and it may permit bending flexibility to be evaluated at multiple longitu- dinal positions along longer test articles. 4.2.2 The variable span length method allows the bending moment arm length to be maximized for any given stent length in order to minimize the potential for non-bending deformation at a given applied load and/or deflection. Bending flexibility comparisons may be made at different span lengths by com- paring midspan bending moments at given midspan bending curvatures. The variable span length approach also permits the study of bending load variation with span length, but the bending loads are not solely dependent on the inherent bending stiffness of the test article.