This benchtop test provides empirical evidence for the continued structural integrity of the devices when subjected to mechanical bending replicating in vivo conditions. The test is accelerated to obtain results in less time than physiological rates would allow. The test may be conducted under simulated physiological conditions with saline at 37°C.
The testing objective is to meet the appropriate standard requirements, as identified by the device manufacturer and may include ISO guidelines (25539-1, 7198:1998, and 99128), for in vitro mechanical fatigue. The test demonstrates the device integrity when subjected to bending for an appropriate post-implantation time period. Fatigue tests will be conducted for minimum of 10 years post-implantation while feasibility or strength characterization tests may be shorter. 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 vertical bending fixtures are designed to apply cantilever bending across all samples at a customizable angle and displacement. The fixture pictured (right) is particularly useful for renal stent testing or for testing any device that requires simulation of the breathing cycle.
The test system utilizes a bend fixture designed by MDT that is integrated with an ElectroForce® 3200 Test Instrument. The ElectroForce tester operates using a linear motor rated at +/-450N (100lbs). MDT's bend fixture makes the single axis vertical motion available to all 12 mock arteries. General guidelines for the vertical bend fixture pictured (right) are specified below.
|Device OD||Mock Artery #||Bend Radius||Frequency|
|3mm - 10mm||12||10mm - 40mm||30Hz - 40Hz|
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. Depending on the fixture, MDT may configure a laser micrometer to measure the bend displacement of each stent at predetermined positions. 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 and monitoring 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 by MDT are clearly marked as such. Any 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).