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  • 1.  New FDA guidance for Nitinol (SMST Newswire)

    Posted 04-15-2021 11:17
    Hello Everyone,
    Don't miss a chance to learn more about the FDA's new guidance for Nitinol used in medical devices (April_AMP_Digital).  Do you want to see additional technical considerations? You can start that conversation here....

    Othmane

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    Othmane Benafan
    Materials Research Engineer
    NASA Glenn Research Center
    Cleveland OH
    (216) 433-8538
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  • 2.  RE: New FDA guidance for Nitinol (SMST Newswire)

    Posted 05-25-2021 12:09
    Thank you for sharing!

    Below are two points from the FDA guidance that stood out to me, followed by a "thinking out loud" bit. Feel free to add or share ideas you would like to discuss.

    I am always interested in learning more about the corrosive response especially with biocompatible materials. The FDA guidance had very interesting points such as: processing helps to form protective layers; however the composition of the matrix may change by forming precipitates thus changing the material properties. Ni ions are an issue too. 

    Reading articles such as this is very exciting to see how much SMAs have progressed even in the few years I have been in research.

    "Thinking out loud" portion
    Considerations with biomaterials are to use resorbable alternative such as Zn for bone or stents. I wonder if Zn would be something to viable for a Ni substitute. In a NiTi pourbaix diagram, Ni+ leaches around pH 6 at 0V. Veins/arteries are usually closer to pH 7; however the composition may shift the diagrams I'm using as a reference. In the same environment and comparing NiZn, Zn would leach into ZnCl. ZnCl is a salt and very soluble in water. I'm not sure if there are other factors to consider it to be safe or how Zn would be in a NiTi-based SMA. It was/is researched for Cu-based. 

    References:
    https://doi.org10.1002/adfm.202005361
    https://doi.org/10.1016/j.commatsci.2017.11.033
    DOI: 10.1039/C8RA04650F

    Thanks for listening.

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    Faith Gantz
    University of North Texas
    Denton TX
    (208) 518-8336
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  • 3.  RE: New FDA guidance for Nitinol (SMST Newswire)

    Posted 05-26-2021 02:37
    NiTi is in use for medical devices for more than two decades now and well established as an implant material and regarding biocompatibility. The new FDA guidance is not really requiring additional testing. Only in cases, where the standard corrosion tests according to ASTM F2129 (pitting & crevice corrosion) and F3044 (galvanic corrosion) are showing unexpected results, Ni ion release testing based on ASTM F3306 has to be conducted. Due to the very well defined passive oxide layer, following the standard electropolishing process, there is no issue regarding Ni ion release and the values are typically orders of magnitude below any critical threshold values.

    Besides, NiTi is normally used in clinical indications with large mechanical deformations (e.g. usually not in coronary arteries but in the periphery, veins or for structural heart applications), where it can survive the expected lifetime of the implant. However, so far no known absobable alloy is available being able to survive there for a single day and off course not for 400 or more million cycles. The indication is limited by the inferior mechanical properties, especially regarding multiaxial dynamic loading, but also due to certain static values.

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    Matthias Frotscher
    Senior Manager Stent & Material Testing
    Cortronik GmbH
    Rostock-Warnemuende
    49 381 81737251
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    Original Message
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