This benchtop test provides empirical evidence for the continued structural integrity of the devices when subjected to mechanical fatigue replicating in vivo conditions. The test is designed to simulate the device radial fatigue due to expansion and contraction of the surrounding vessel. Physiological strain of a healthy vessel is first modeled using mock arteries implanted with the device. The test is then accelerated to obtain results in less time than physiological rates would allow. The test is conducted under simulated physiological conditions with saline at 37°C.
Commonly tested devices include:
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 10 years post-implantation. A device failure is defined by the device manufacturer (for example, any broken or cracked strut visible at 30x magnification during or at the end of the test). The device manufacturer will also examine the devices post-testing against the acceptance and/or failure criteria.
MDT uses ElectroForce 9100 Series Stent Testers which operate on the principle of fluid displacement. The SGTs are fitted with custom fittings to accommodate tubes with a customer-defined radius to simulate the device's physiological deployment site. Electrodynamic linear motors on each end of the tester apply a sinusoidal pumping 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. The laser heads are mounted on a multi-axis micrometer to accommodate measurements along the radius.
|Device OD||Mock Artery #||Radius||*Frequency|
|1.5mm- 5.0mm||8 - 12||1.0cm - 3.5cm||45Hz - 55Hz|
|> 5.0mm||4- 8||Device-dependent||Up to 45Hz|
*estimates based on 3% - 5% physiological compliance
MDT tests are conducted in accordance with ANSI/ISO/IEC 17025-2005. Testing schedules and resource needs are determined during project kickoff meetings with MDT engineers and the customer. The services are performed in accordance with standard operating procedures and test protocols specific to the service. Standard tests do not begin without a protocol signed by both the customer and an MDT representative. For feasibility or non-standard tests, MDT will develop a method and protocol with customer input and will review the final process with the customer prior to initiation of the test.
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.
MDT offers several inspection methods including:
MDT tests are conducted in accordance with ANSI/ISO/IEC 17025-2005. In compliance with this standard, MDT test reports include comprehensive documentation and summary of the test protocol and results. All reports are GLP compliant and can be submitted directly to regulatory agencies. 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, and other information collected during the test (see example test reports).
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