This benchtop test provides empirical evidence for the continued structural integrity of peripheral stent devices when subjected to mechanical fatigue replicating in vivo conditions. The test is designed to simulate the device radial fatigue due to squeezing, twisting and stretching of the surrounding vessel. The test is accelerated to obtain results in less time than physiological rates would allow and is conducted with saline at 37°C.
The testing objective is to meet the appropriate requirements, as identified by the device manufacturer, for in vitro mechanical fatigue. The test demonstrates the device integrity when subjected to torsional, axial, and bending mechanical motion for a minimum of 10 years post-implantation. A device failure may be defined as any broken or cracked strut visible at 30x magnification during or at the end of the test. The devices are also examined after the test against other acceptance and/or failure criteria.
The test system utilizes a gait fixture designed by MDT that is integrated with an ElectroForce® 3300 Axial-Torsion Test Instrument. The test instrument operates using linear and rotary motors. MDT’s gait motion fixture converts the linear/rotary motion into a simulated gait motion. The fixture first applies tension to 16 devices and then compresses (squeezes), bends and twists them simultaneously. The process is then reversed and the cycle repeated at a 2-3Hz typical frequency to provide a full 10 million cycle test (10 years post-implantation) in less than 2 months.
|Device OD||Mock Artery #||Axial Displacement||Rotation||Bend Radius||Frequency|
|3mm - 10mm||16||1mm - 25mm||1° - 100°||10mm - 50mm||1Hz - 3Hz|
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. Services are performed in accordance with standard operating procedures and test protocols specific to the project. 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.
WinTest software monitors parameters such as the cycle count and displacement throughout the duration of the test. MDT engineers monitor tests daily and record various system parameters, as well as other customer-identified parameters such as: load, displacement, and rotation. 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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