Technical Considerations for Nitinol-Containing Medical Devices
This guidance outlines technical considerations for medical devices containing Nitinol, focusing on devices with at least one patient-contacting component made of Nitinol. It provides recommendations for non-clinical assessment of these devices, particularly addressing the unique properties of Nitinol compared to conventional metals.
What You Need to Know? 👇
What are the key transformation temperatures I need to measure for nitinol medical devices?
You should measure austenite finish (Af) temperature for pseudoelastic devices, and austenite start (As), martensite start (Ms), and martensite finish (Mf) temperatures for shape memory devices. Use ASTM F2004 or F2082 methods with samples from at least three production lots.
How should I conduct pitting corrosion testing for nitinol devices?
Use ASTM F2129 after subjecting devices to simulated assembly and implantation conditions. Test at least 6 samples from multiple lots in final finished form. Include corrosion potentials, breakdown potentials, and polarization curves in your report with justified acceptance criteria.
What nickel ion release testing is required for nitinol devices?
If pitting corrosion testing fails or you don’t use established surface finishing, conduct ASTM F3306 testing for 60 days (permanent implants) or 30 days minimum. Sample frequently initially, then bi-weekly, reporting cumulative release per device and daily release rates.
What biocompatibility risk assessment should I perform for nickel release?
Compare nickel release to the tolerable intake value of 0.5 µg/kg/day for parenteral exposure (35 µg/day for 70kg adult). If exceeded, provide alternative TI justification or modify device design. Follow ISO 10993-1 guidance for comprehensive biocompatibility assessment.
What labeling warnings are required for nitinol-containing devices?
Include warnings about nickel allergy potential for prolonged and permanent contact devices. Recommend stating the device contains nitinol (nickel-titanium alloy) and that patients with metal allergies may experience allergic reactions. Advise pre-implantation patient counseling on materials and allergy risks.
How should I validate computational models for nitinol device analysis?
Use appropriate constitutive laws specific to nitinol’s unique thermomechanical behavior. Obtain material parameters from ASTM F2516 testing on representative samples. For fatigue analysis, generate device-specific constant life curves rather than using generic data, and justify validation activities relative to context of use.
What You Need to Do 👇
Recommended Actions
- Determine device contact duration category (limited, prolonged, or permanent)
- Document material composition and manufacturing processes
- Characterize transformation temperatures of final finished form
- Conduct appropriate mechanical testing based on device design
- Perform corrosion testing following the recommended testing paradigm
- Complete biocompatibility assessment including nickel release risk assessment
- Develop appropriate labeling with required warnings
- Consider early engagement with FDA through Q-Submission process for specific feedback
- Prepare comprehensive test reports with appropriate justifications for test parameters
- Document any deviations from recommended testing with scientific rationale
Key Considerations
Non-clinical testing
- Mechanical testing should be performed under displacement control unless otherwise justified
- Testing should be conducted at clinically relevant temperatures
- Fatigue testing should be performed in liquid test solution rather than air
- For shape memory devices, cyclic shape memory testing at clinically relevant temperature range is recommended
- Computational stress/strain analyses should use appropriate material models for Nitinol
Labelling
- Warning statement required for prolonged and permanent contacting devices about Nitinol containing nickel and potential allergic reactions
- Patients should be counseled on device materials and potential allergies/hypersensitivity
Biocompatibility
- Follow ISO 10993-1 guidance for biocompatibility assessment
- Risk assessment comparing nickel release to Tolerable Intake (TI) value of 0.5 µg/kg/day for parenteral exposure
- Alternative TI may be derived for shorter exposure duration with appropriate justification
Safety
- Pitting corrosion testing per ASTM F2129 for prolonged exposure and permanent contacting devices
- Nickel ion release testing if corrosion resistance criteria not met
- Galvanic corrosion testing if Nitinol contacts dissimilar metals
Other considerations
- Material composition should be provided and conform to recognized standards
- Manufacturing process flow chart required, including thermal processes and surface processing steps
- Transformation temperatures of final finished form should be provided
- Surface processing effects on corrosion/nickel leach performance should be evaluated
Relevant Guidances 🔗
- Use of ISO 10993-1 for Biological Evaluation and Testing of Medical Devices
- Q-Submission Program: Strategic Framework for FDA Interactions in Medical Device Development
- Recommended Format and Content for Non-Clinical Bench Performance Testing in Medical Device Premarket Submissions
Related references and norms 📂
- ASTM F2129: Standard Test Method for Conducting Cyclic Potentiodynamic Polarization Measurements to Determine the Corrosion Susceptibility of Small Implant Devices
- ASTM F2063: Standard Specification for Wrought Nickel-Titanium Shape Memory Alloys for Medical Devices and Surgical Implants
- ASTM F2004: Standard Test Method for Transformation Temperature of Nickel-Titanium Alloys by Thermal Analysis
- ASTM F2082: Standard Test Method for Determination of Transformation Temperature of Nickel-Titanium Shape Memory Alloys by Bend and Free Recovery
- ASTM F3306: Standard Test Method for Ion Release Evaluation of Medical Implants
- ASTM F3044: Standard Test Method for Evaluating the Potential for Galvanic Corrosion for Medical Implants
- ISO 10993-1: Biological evaluation of medical devices - Part 1: Evaluation and testing within a risk management process
- ISO 10993-17: Biological evaluation of medical devices - Part 17: Establishment of allowable limits for leachable substances