Significance and Use
5.1 It is important to consider the durability of stent designs in deformation modes that are intended to model in vivo conditions. The appropriate amplitude and number of cycles in each of the modes has to be determined independently for the particular clinical use proposed for the stent. These tests do not replicate all varieties and aspects of the deployment process and the in vivo mechanical environment so they cannot be proofs of durability. Instead, the tests provide evidence of durability. The durability tests can also provide a means of assessing design, material or processing changes.
5.1.1 This guide might be useful for development testing, specification acceptance testing, and regulatory submission testing and filings as it provides a basic assurance that the tests are designed, executed, and reported in a suitable fashion.
5.1.2 If the tests are conducted using a well-defined FTF methodology, they can be useful in:
5.1.2.1 Potential design improvement through identification of better and worse geometries, materials, and manufacturing processes;
5.1.2.2 Understanding product durability by estimating the effects of changes in geometry, materials, or manufacturing processes;
5.1.2.3 Estimating the safety factor relative to the amplitudes and other factors in use conditions; and
5.1.2.4 Validating finite element analysis (FEA) and fatigue life models.
5.1.3 As stated in the scope, this guide is not intended to provide the in vivo physiologic deformation conditions that a vascular stent can be subjected. Reliable clinical data characterizing cyclic vascular deformation may be lacking for some indications. The user should develop and justify the boundary conditions (e.g., literature review, in vivo studies, cadaver studies, or modeling of stent vessel interaction) for the chosen durability bench tests. Additional conditions that may be considered include vessel calcification, vessel taper, eccentric lesions, deformation excursions (e.g., exercise), and vessel remodeling.
5.1.4 Test methods other than those provided in the annexes of this document might be appropriate, depending upon stent design. However, these methods are beyond the scope of this guide.
Scope
1.1 This guide includes three separate cyclic deformation durability guides related to vascular stents: bending, axial, and torsional.
1.2 This guide does not address flat plate, local crush durability, or multi-mode testing.
1.3 This guide applies to balloon-expandable and self-expanding stents fabricated from metals and metal alloys. It does not specifically address any attributes unique to coated stents (i.e., stent with a surface layer of an additional material(s)), monolithically polymeric stents, or absorbable stents, although the application of this standard to those products is not precluded.
1.4 This guide is applicable to testing of stent(s) (or a representative portion of a stent). While durability testing of coupon samples (e.g., a scaled-up portion of the stent structure) can provide useful information, it is not within the scope of this guide.
1.5 This guide applies to endovascular grafts (“stent-grafts”) and other conduit products commonly used to treat aneurismal disease, peripheral vessel trauma, or to provide vascular access. The information provided herein does not address all issues related to testing of these devices.
1.6 This guide applies to in vitro modeling of stent durability from non-radial arterial motions. Such motions may arise from musculoskeletal activities, including walking and breathing, and cardiac motion. ASTM F2477 addresses pulsatile (i.e., radial) durability of vascular stents.
1.7 This guide does not provide the in vivo physiologic deformation conditions for a vascular stent. It is incumbent upon the user of the standard to develop and justify these boundary conditions (e.g., literature review, in vivo studies, cadaver studies, or modeling of stent vessel interaction) in these durability bench tests. Additional conditions that may be considered include vessel calcification, vessel taper, eccentric lesions, loading excursions (e.g., exercise), and vessel remodeling.
1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
