Flexibility / Kink Resistance

Medical device may be subjected to tight angulations in tortuous vasculature during use. Inability to withstand flexural forces that are typical of clinical use could lead to device failure or vessel damage.  The ability of a delivery system or a catheter to bend in order to accommodate the predetermined clinically relevant radius or angles is critical during vascular access. The ability of a stent like structure to bend without lumen narrowing plays a critical role in maintaining stent patency

This test is also known as Kink diameter or Kink radii.

Test Procedure

There are 2 main methods to study a kink radius:

1) Using a cone mandrel with decreasing diameter to determine when the kink occurs (without measure of sample diameter).

The sample is wrapped (over 180°) around a cone-shaped mandrel with successively smaller radii until the device kinks or the lumen collapses. When the device is kinked, the test advancement is stopped and the diameter of cone-shaped (where the kink occurs) is measured with a caliper to determine the kink radius. Test is performed on the location(s) defined in the protocol. If required in protocol, guide wire is inserted inside the tested sample.

2) Using several decreasing diameter gauges successively to determine when the kink occurs and measuring the diameter of sample and residual angles.

This cone/mandrel method can also be used to determine the kink radius of a stent in a mock vessel. The stent is deployed in a straight silicone tube, the assembly is wrapped around the mandrels as described above. The stent sample is deployed in a straight silicone tube. Cylindrical mandrels are inserted at each end of the tube to avoid collapse of the silicone tube extremities. A distance d (of 1 to 2 tube internal diameters) is let between stent extremities and cylindrical mandrels. The tube is wrapped around the gauge. For each radius gauge, it is observed if the stent kinks or exhibits a diameter reduction of greater than 50 % and if the stent recovers its original geometry after force release.

Test Sample Preconditioning (If applicable)

Balloons should undergo accelerated and real-time aging.

Stent should undergo simulated use testing before deployment.

Biores devices should undergo accelerated and real-time aging.

 

Equipment

  • Graduated cone-shaped mandrel
  • Calibrated Pin Gauges
  • Calibrated Contactless optical measurement system
  • Calibrated Caliper
  • Temperature controlled test chamber
  • Calibrated thermometer

Measured Parameters

Kink Diameter

Kink Location

Stent Diameter

 

Scope

Catheter and Delivery Systems

  • PTA, PTCA, coronary and peripheral stent delivery systems – functional performance during simulated use
  • TAVI and TMVR delivery systems – functional performance during simulated use
  • Thrombectomy devices — functional performance during simulated use
  • Guidewires testing – functional performance during simulated use
  • Endoscopic devices – functional performance during simulated use
  • RF ablation catheters testing – functional performance during simulated use
  • Any interventional delivery systems – functional performance during simulated use

Stent, Stent/graft and stent like devices

  • Balloon expandable stent: CrCo, SS, Biores
  • Self-expanding stent: NiTi, SS
  • Coronary stent
  • Peripheral stent: Carotid, renal, ilio-femoral
  • Stent-Graft: AAA, TAA, PE covered, PTFE covered, tissue covered
  • TAVI stent structure
  • TMVR stent structure
  • Vena Cava filters
  • Oesophageal Stent
  • Any stent like structure

Service Levels

Applicable Standards

  • ISO 25539-2:2020
    Cardiovascular implants — Endovascular devices — Part 2: Vascular stents

  • FDA-1545
    FDA Guidance: Non-Clinical Engineering Tests and Recommended Labeling for Intravascular Stents and Associated Delivery Systems – Guidance for Industry and FDA Staff

  • FDA-1608
    FDA Guidance: Certain Percutaneous Transluminal Coronary Angioplasty (PTCA) Catheters – Class II Special Controls Guidance for Industry and FDA

  • FDA-1658
    FDA Guidance: Coronary and Carotid Embolic Protection Devices – Premarket Notification [510(k)] Submissions

Related Tests

OLE0810, OLE1413


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