Corrosion Testing and Surface Characterization Requirements for Intravascular Stents
This guidance addresses self-expanding and balloon expandable extracranial intravascular stents and their associated delivery systems used in coronary or peripheral arteries and saphenous vein grafts. It provides updates on specific aspects: pitting corrosion potential, galvanic corrosion, surface characterization, and nickel ion release testing.
What You Need to Know? 👇
What are the key updates in the FDA’s 2015 guidance for intravascular stent testing?
The guidance updates four main areas: pitting corrosion potential testing (with less burdensome sample conditioning), galvanic corrosion testing (with justification options for omission), surface characterization requirements, and new nickel ion release testing methods for nickel-rich alloys.
When is surface characterization testing required for intravascular stents?
Surface characterization is recommended when pitting corrosion results don’t meet acceptance criteria, when no final passivation step is used, when not using commonly used surface finishing processes, or when the surface finishing differs from marketed devices with good clinical history.
What are the acceptance criteria for pitting corrosion potential testing in stents?
Acceptance criteria should be determined by comparison to legally marketed devices with good clinical history (no corrosion-related fractures or nickel release adverse events), or alternatively using conservative guidelines published by Rosenbloom and Corbett for in vitro corrosion testing.
How long should nickel ion release testing be conducted for stent devices?
Testing should be conducted for at least 60 days. However, if testing demonstrates surface stability (release rate falls below predetermined toxicological risk levels), testing may conclude earlier with a minimum duration of 30 days, requiring justification for reduced duration.
What device conditioning is required before corrosion testing of stents?
Devices must undergo simulated use testing including crimping, tracking, and deployment through an in vitro fixture mimicking in vivo anatomic conditions. Alternatively, stents may be subjected to expected strains during simulated use (e.g., bending) without tracking fixtures, with justification.
Which stent product codes are covered by this FDA guidance?
The guidance covers Class III stents with product codes: MAF (Coronary Stent), NIM (Carotid Stent), NIN (Renal Stent), NIO (Iliac Stent), and NIP (Superficial Femoral Artery Stent). These devices require premarket approval (PMA) applications before marketing.
What You Need to Do 👇
Recommended Actions
- Develop test protocol for pitting corrosion testing according to ASTM F2129
- Assess need for galvanic corrosion testing based on material combinations
- Evaluate surface finishing process and determine if surface characterization is needed
- For nickel-rich alloys:
- Plan nickel ion release testing if required
- Develop risk assessment for nickel release
- Document justifications for:
- Sample selection and size
- Test duration
- Any deviations from recommended methods
- Establish acceptance criteria based on predicate devices or published guidelines
- Validate analytical methods for nickel ion release testing
- Consider implementing a testing flow following the provided flowchart in Appendix 1
Key Considerations
Non-clinical testing
- Pitting corrosion testing should be performed on as-manufactured stents after simulated use testing
- Test setup should meet ASTM G5-14 criteria
- Test worst-case device sizes in terms of corrosion susceptibility
- Use samples from multiple lots
- Galvanic corrosion testing may be replaced by justification if coupling potentials are small and surface ratios are low
Biocompatibility
- For nickel-rich alloys, quantify nickel ion release over minimum 30-60 days if corrosion resistance results don’t meet criteria
- Use buffered solution at physiologic temperature and pH
- Perform sampling at adequate intervals to capture initial bolus release
- Conduct validation testing of analytical instrumentation
- Perform risk assessment for nickel release considering toxicological risks
Safety
- Intravascular metallic stents should have polished, passive and clean surface
- Surface characterization required if:
- Other test results don’t meet acceptance criteria
- No final passivation step is used
- Non-standard surface finishing process is used
- Oxide layer should be less than 50nm and consist primarily of TiO2 for nitinol
Other considerations
- Test devices should be representative of final sterilized devices
- Consider manufacturing variations in sample selection
- Provide justification for sample sizes and selection criteria
Relevant Guidances 🔗
- Non-Clinical Testing and Labeling Requirements for Extracranial Intravascular Stents and Delivery Systems
- Technical Considerations for Nitinol-Containing Medical Devices
- Coronary, Peripheral, and Neurovascular Guidewires - Performance Testing and Documentation Requirements
- Use of ISO 10993-1 for Biological Evaluation and Testing of Medical Devices
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 G5-14: Standard Reference Test Method for Making Potentiostatic and Potentiodynamic Anodic Polarization Measurements