Crush Resistance – Radially Applied Load

Using a constant displacement a radial load is applied to the sample. Force-diameter curves of stent like structures are determined while loading and unloading the sample according to a specified profile.

Test Procedure

RX550 temperature is set to the defined test temperature

Before and after testing, test samples length and diameter are measured with a micrometric gauging machine

The test samples are selected randomly.

The sample is introduced in the head and profile is started: the RX bench decreases and/or increases the diameter according to specified loading and unloading profile and the radial force vs diameter is recorded.
Pictures of the sample during the test are taken if required by the sponsor
At the end of the test, RX head is opened and the sample is retrieved from the system then placed within its corresponding container.

For balloon expandable devices, the radial strength is calculated in compliance with ASTM F3037.

For self expandable devices, the minimum and maximum chronic outward forces are calculated in compliance with ASTM F3067.

In order to obtain the result ‘by unit of length’, the force is divided by the measured length (in mmThis procedure describes 5 possible ways of generating a radial force-diameter curve according to a desired loading and unloading profile:

1- Measurement in compression only: the device is compressed from an initial diameter to smaller diameter at a set head speed (balloon expandable or self-expanding structures).
2- Measurement in expansion only: the device is either deployed in the RX head preset at a small initial diameter, or compressed, at a low speed, from an initial diameter at rest to a smaller final diameter. Then, the diameter is gradually increased at a set speed to the final target diameter (self-expanding structures).
3- Measurement over one or more compression / expansion cycles: The device is compressed and released over several cycles to assess its hysteresis behavior (for self-expanding devices).
Note: ASTM 3067 recommends to test balloon expandable stent over a complete cycle (initial balloon deployment and RX compression)
4- Measurement according to customized loading and unloading profiles: Compression and expansion measurement are conducted using a user predefined diameter variation profile generated from specific file (time; diameter)
5- Force measurement: The maximum force to be reached is specified and the head of the RX closes on the device until it reaches a set force.

Equipment

The RX550/650 from Machine Solutions Inc. is used to measure both the radial force and the diameter while loading or unloading the device according to a specified crushing profile. The RX head is composed of 12 segments which compress the sample uniformly, with very low friction force.

Measured Parameters

• Load under constant displacement
• Radial force vs. time
• Radial force vs. diameter
• Stent Hoop force
• Stent Radial force
• Stent Diameter
• Stent length
• Temperature

Scope

• 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
• Occluders- LAA closure, PFO closure
• Oesophageal Stent
• Any stent like structure

Service Levels

• Fast Track
• Standard Service
• Full Service

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

Related Tests

• Crush Resistance – Pressure Control
• Crush Resistance – Parallel Plates
• Radial Force Measurement

OLE0906, OLE1311