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Occluder and Closure Device Fatigue Testing

Kent Vilendrer
By Engaged Expert Kent Vilendrer Product Qualification Testing

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Occluder Device Fatigue Testing

Structural heart occluders and closure devices are used to treat congenital heart defects such as atrial septal defect, ventricular septal defect, patent ductus arteriosus (PDA) and patent foramen ovale (PFO). While there are no specific standards for occluder device testing, many of the cardiovascular implant standards such as ISO 5840-1 (2015) cover aspects of occluder testing. Executive summary documents listed by the US FDA from occluder manufacturers for products such as theAMPLATZER™ Patent Foramen Ovale Occluder from St. Jude Medical (now Abbott) and GORE HELEX™ Septal Occluder from W.L. Gore & Associates, Inc. might also be helpful in identifying relevant bench testing.

Test examples listed in these documents include: fatigue testing, tensile strength, stress relaxation,finished device pressure, nickel leachability, particulate testing, and corrosion testing. While Element offers particulate testing, nickel leachability, corrosion testing, and other occluder tests, this paper focuses on pulsatile and axial fatigue testing protocols.

Pulsatile Fatigue

Element excels at pulsatile fatigue testing of cardiovascular medical devices and has developed specialized fixtures for occluders and other closure devices. Devices in the test described were subject to pulsatile radial fatigue for 100M cycles to simulate 2.5 years of implantation; typical tests range from 40Mto 600M cycles.

A frequency sweep is conducted prior to the testing to determine a stable and safe testing frequency to minimize potential artifacts (i.e., diametricexcursions) observed using laser micrometer, strobe light, or high speed video camera. The test is accelerated to obtain results in a shorter time-period than physiological rates would allow and is conducted under simulated physiological environment, in saline at 37 ± 2°C.

Devices were tested to meet the requirements of the FDA Recognized Consensus Standard ASTM F2477 and FDA Guidance 1545 (2010): Non-Clinical Engineering Tests and Recommended Labeling forIntravascular Devices and Associated Delivery Systems.

The image below shows a stent graft tester configured to accommodate two closure devices per station with specialized mounting requirements. The objective of this test is to demonstrate device integrity under mechanical fatigue for 400M cycles to meet the requirements for in vitro mechanical fatigue testing stated in ASTM F 2477 and ISO 25539-1 AMENDMENT 1. Target strain is derived from customer-provided FEA analysis based on worst-case clinical loading conditions.

Pulsatile Durability Device April 2018
Axial Fatigue

The image below is an example of custom-designed fixtures for occluder and closure device tensile fatigue testing. The multi-specimen fixture can accommodate devices of different sizes or diameters. In some cases, wedges are placed between the plates to simulate worst-case scenarios where one or both discs are at an angle with respect to the stem.

A key advantage of the design is that it allows both positive and negative bending through an inflection point for either unidirectional or bidirectional bending fatigue tests. Customer-provided FEA data are used to define the desired angular displacements, and testing can typically be accelerated up to 40Hz.

Pulsatile Durability Axial Fatigue April-2018
Inspections

Inspections are a key component of any well-designed test protocol. Devices are typically inspected prior to testing, during the test at pre-determined intervals and post-testing. Due to the braided design of many of the occluder and closure devices, it is important to look for signs of fretting corrosion that may occur particularly in regions of disc to stem overlapping material.

Additional Testing

Fatigue testing is one type of relevant bench testing for occluders and closure devices. Corrosion testing,particulate testing, nickel leachability and other mechanical tests may also be required depending on your device.

If you would like assistance with your device’s bench testing, contact an expert today to discuss how we can assist with your project.

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