Significance and Use
4.1 Upon deployment, at the site of the vascular stenosis, the stent establishes the patency of the lumen until vascular remodeling occurs. The radial load acting upon the stent is imparted by vessel and lesion stretch. Additionally, the vessel might be affected by excursions due to pulsation (systolic and diastolic variation), muscle-skeletal interactions due to patient movement, as well as external sources (e.g., patient is struck in the neck during a car accident). The excursions vary in magnitude and type based on the location of the vessel.
4.2 In order to maintain vessel patency, the stent has to withstand the forces acting on it without experiencing excessive deformation, migration, or sustained collapse; therefore, it is required that the stent possess adequate resistance to these loads.
4.3 Depending on the type of device and the clinical concern, the resistance to these loads can be presented through multiple test outputs: radial strength, collapse pressure, or chronic outward force.
4.4 The guidelines presented here can be used in the development of test methods to determine the radial loading properties of stents. This guide provides examples of different test apparatus (equipment and tooling), radial loading curves, and calculations. Although the apparatus and methods presented can be used as a reasonable simulation of actual clinical use, they have not been demonstrated to predict the actual in vivo clinical performance of any stent.
Scope
1.1 This document provides guidance for developing in vitro test methods for measuring the radial strength or collapse pressure of balloon-expandable vascular stents and chronic outward force of self-expanding vascular stents.
1.2 This guide is applicable to balloon-expandable and self-expanding stents of tubular geometry. It covers both stent and stent grafts. It does not cover bifurcated stents. It does not cover stents with non-circular cross-sections or tapered stents.
1.3 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 This guide does not recommend any specific test method or apparatus for measuring the radial strength, collapse pressure, or chronic outward force. Instead, this guide provides examples of test methodologies and equipment that could be used and recommends the format for presenting test results.
1.5 This guide covers only in vitro bench testing methods. In vivo behavior might be different.
1.6 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.
