Stent Corrosion Testing: Measured parameters
- Degradation rate during corrosion testing (µg/cm²/h)
- Electrochemical behavior curves
Stent Corrosion Testing: Scope
- Identifying and quantifying degradation products from finished metallic medical devices during corrosion testing
Stent Corrosion Testing: Applicable standards
- ISO 10993-15:2000 Biological evaluation of medical devices Part 15: Identification and quantification of degradation products from metals and alloys
- ASTM: F2129-08: Standard test method for conducting cyclic potentiodynamic polarization measurements to determine the corrosion susceptibility of small implant devices
Stent Corrosion Testing: Test Method Description
The procedure includes three steps, and provide a comprehensive approach to corrosion testing: 1) a combination of a potentiodynamic test, 2) a potentiostatic test and 3) a quantitative and qualitative analysis of the electrolyte. The potentiodynamic test is used to determine the general electrochemical behavior of the material under consideration and to determine certain specific points (in particular breakdown potential) on the potential/current density curve. It is (nearly) identical to the “corrosion cyclic”.
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The potentiostatic test is used afterwards to electrochemically degrade the medical device. The sample is holded at a constant electrode potential during a defined test time (Potential = Breakdown potential (Ep) defined in the first test + 50mV – Duration = 5h ). The current density / time curve is recorded.
The degradation products will be lastly identified and quantified.
- A sample of 20 μL of the potentiostatic test electrolyte is taken to perform a qualitative analysis of the electrolyte using the ICP method. (ICP = inductively coupled plasma). This qualitative method allows the determination of presence of trace metal at levels above 1 μg/L.
- A sample of 20 μL of the potentiostatic test electrolyte is taken to perform a quantitative analysis of some elements, as requested by the sponsor (see the test protocol), using the AAS method (AAS = Atomic absorption spectroscopy). The used material offers a typical sensitivity in the parts per billion range.
- The results of analysis of degradation elements in the electrolyte is converted in degradation rate, reported in micrograms per square centimeter per hour (μg/cm²/h).