Stent Fatigue Testing: Measured parameters
- Strain: Direct periodic strain measurement performed with ultrasonic (US) dynamic diameter measuring system
- Struts and Diameter integrity – Periodic visual inspection and final SEM inspection
- Cyclic system pressure difference
- N° of Cycles
- Test Frequency
Stent Fatigue Testing: Scope
- Accelerate Fatigue Testing – Coronary and peripheral stent
- Accelerate Fatigue Testing – Aortic, Thoracic and Heart Valves Stent
- Accelerate Fatigue Testing – CrCo, SS, NiTi, Bioresorbable, Bioabsorbable, Covered, Coated stent
Stent Fatigue Testing: Applicable standards
- ISO 25539-2 – CARDIOVASCULAR IMPLANTS – ENDOVASCULAR DEVICES – PART 2: VASCULAR STENTS
- FDA GUIDELINES – GUIDANCE FOR INDUSTRY AND FDA STAFF NON-CLINICAL ENGINEERING TESTS AND RECOMMENDED LABELING FOR INTRAVASCULAR STENTS AND ASSOCIATED DELIVERY SYSTEMS
- GLP STUDIES PER CODE OF FEDERAL REGULATIONS CFR21, PART 58 – GOOD LABORATORY PRACTICE FOR NONCLINICAL LABORATORY STUDIES
Stent Fatigue Testing: Associated tests
- Device pre-conditioning – Simulated use on IDTE 2000
- Optical Inspection
- Scanning Electron Microscopy (SEM)
Stent Fatigue Testing: Test method description
ProtomedLabs’ proprietary thin tube fatigue tester design does not require deriving any specific tube compliance relationship between tube OD and ID. Up to 21 stents can tested simultaneously in one machine. Stent are positioned in transparent silicon tubes with thin walls. Tubes are filled with relevant test solutions depending on stent type and test requirements. A cyclic or a static differential pressure can be directly applied on the silicone tubes.
The differential pressure generates a uniform periodic stress of physiologic magnitude at frequencies of up to 60 Hz. Standard tester operating mode can generate operating stress levels with max peripheral pressure difference of 40 mmhg and 0 mmhg minimal pressure. Standard tests are performed with distilled water and under thermo regulated 37+2 °c conditions if required. Other test fluid can be used for biological tissue covered and biodegradable stent designs.
Stent dynamic displacement is directly measured in-line by ultrasound (us) system in compliance with standard requirement and in order to ensure that dynamic amplitude levels are meeting specifications limits. Applied pressure difference, test frequency, number of cycles and stent positions within the mock artery models are monitored daily. A visual inspection is also performed daily to detect visible stent failure.
Dynamic stent diameters and displacement are measured directly on the device at periodical intervals and at both the beginning and the end of the test. In order to detect early onset of failure and fracture, periodical diameter and displacement monitoring and measurement can be performed to assess stent behavior. Stent preparation, cycle counting, test frequency measurements, calibration of the pressure transducers are performed in compliance with and controlled by proper operating procedures.