Scope:
These benchtop tests provide empirical evidence for the continued structural integrity of percutaneous heartvalves when subjected to mechanical fatigue replicating in vivo conditions. The tests are designed to simulate the physiological strain due to the expansion and contraction of the surrounding vessel. The test is accelerated to obtain results in less time than physiological rates would allow. Two tests are used to simulate these strains:
Stent Strut Fatigue (SN Curve Generation)
The stent strut fatigue tests the high strain portion of the stent. This portion is determined through Finite Element Analysis Modeling. This piece (or apex) is then placed on an axial fatigue tester using special fixturing to apply cyclic axial tension/compression. The test fixture can be customized to accommodate a wide range of designs and can typically test 12 to 16 samples simultaneously. Additionally, monitoring instrumentation can be added to obtain real time data to monitor the apex condition throughout testing.
Full Device Fatigue
This test is designed to simulate the device radial fatigue due to expansion and contraction of the surrounding vessel. The device is implanted in a physiologically relevant mock vessel (or within a model of the physiological application site). The applied physiological strain of the healthy vessel/device combination is measured at a normal heart rate and slightly elevated blood pressure (normally 72 bbm and 150/50mm-Hg). The test is then accelerated to obtain results in less time than physiological rates would allow. The test is conducted under the observed physiological strains with saline at 37C.
Objective:
The testing objective is to meet the requirements for in vitro mechanical fatigue testing stated in ASTM F2477-07 “Standard Test Methods for in vitro Pulsatile Durability Testing of Vascular Stents” as well as ISO 25539-1, 7198:1998, and 99128. The test demonstrates the integrity of the device under mechanical fatigue for a minimum of 15 years post-implantation. A device failure is defined by the device manufacturer; for example, loss of continuity for the stent strut test or any broken or cracked strut visible at 30x magnification during or at the end of the full device test. The device manufacturer will also examine the devices post-testing against the defined acceptance and/or failure criteria.
Equipment:
For the stent strut fatigue test, MDT uses the ELectroForce® 3000 Series test instruments, which operate using a linear motor. For the full device test, MDT uses ElectroForce 9100 Series Stent Testers which operate on the principle of fluid displacement. Linear motors on each end of the tester apply a sinusoidal action which forces fluid into and out of mock arteries causing them to expand and contract. A laser micrometer measures the radial strain by scanning the outside diameter of the arteries at 1200 scans per second.
Test Protocol & Set Up:
MDT tests are conducted in accordance with ANSI/ISO/IEC 17025-2005. Schedules and resource needs are determined during project kick off meetings with MDT engineers and the customer. The services are performed in accordance to standard operating procedures and test protocols specific to the service. For feasibility or non standard tests MDT will develop a method and protocol with the customers input and will review the final process with the customer prior to initiation of the test. The customer will be notified of the final method prior to test start to align expectations before the test is initiated. Click here for a sample Test Protocol.
Mock Arteries:
To satisfy recent regulatory body requests, MDT provides custom mock arteries for percutaneous heartvalves in a range of sizes, geometries and materials. Mock arteries may be fabricated in either latex or silicone and their design is determined at the time of order.
Inspections & Services Offered:
MDT offers several inspection methods including:
Test Monitoring & Weekly Updates:
The test equipment software monitors the cycle count, displacement, and pressure throughout the duration of the test. MDT engineers monitor the test daily and record the temperature and pressure for the system, as well as the outside radial strain at predetermined positions for each device being tested. MDT sends weekly updates to ensure customers are apprised of the status of their test. Updates include raw data collected throughout the week for the customer’s analysis.
Test Reports:
MDT tests are conducted in accordance with ANSI/ISO/IEC 17025-2005. In compliance with this standard, MDT test reports include comprehensive documentation of the test protocol and results. Any test method deviations, additions or exclusions are documented and reviewed with the customer prior to beginning the test. Information within the report includes the specific test conditions, statements of compliance with test protocol and the estimated measurement uncertainty. The reported results only relate to the items tested. Any opinions and interpretations provided will be clearly marked as such in the test report. Additional information required by customer specific methods will also be noted. At the conclusion of the test MDT provides the customer with a Microsoft Windows formatted CD containing copies of all raw data, inspection results, or other information collected during the test. Click here to view a sample Test Report.
Please take a few moments to tell us more about your device and test requirements in our short questionnaire, and we will be happy to provide you with a quote.
