FDA has finalized its guidance on the nonclinical assessment of medical devices containing nitinol after reviewing feedback from groups including AdvaMed and Cook Medical. The agency has been looking at the alloy as part of a broader look at metals that can cause inflammatory or other reactions once inside the body.
The final guidance issued Thursday features multiple changes from the 2019 draft, including a rewritten section on computational analyses and new advice on corrosion testing. FDA made the changes after the industry called for clarity in feedback on the draft.
- Separately, FDA published draft guidance on the biocompatibility of devices that come into contact with the skin. The draft proposes using specific material information rather than animal testing to show the biocompatibility of certain widely used materials.
FDA last year outlined testing and labeling information it wants to see in companies' premarket submissions for products containing nitinol, an alloy of nickel and titanium commonly used to manufacture medical devices.
The draft guidance proposed premarket applications for devices containing the material should include testing to evaluate susceptibility to corrosion, overall biocompatibility and performance under various stress and temperature conditions.
The alloy was the subject of an FDA advisory committee and part of a broader examination by the agency as to how metals behave inside the body.
Nitinol’s superelastic properties enable it to maintain shape memory characteristics while performing under fatigue and stress. Those properties have led companies to develop medical devices including stents and heart valves that would be impossible to create using conventional materials, according to FDA.
Yet, the complex properties of nitinol also pose challenges. In assessing the safety and effectiveness of nitinol-based devices, researchers and regulators need to consider how manufacturing affects the transformation temperatures and mechanical performance of products.
The final guidance features changes to some of the sections highlighted by AdvaMed and device manufacturer Cook Group in submitted feedback.
For example, FDA has reworked a section on computational stress/strain analyses. The section, which AdvaMed pushed for changes to, now states analyses should include the effect of any shape setting steps in the manufacturing process and features an expanded discussion of fatigue analysis.
Elsewhere, FDA has changed aspects of its position on corrosion testing. That section now features extra details of when further testing may be unnecessary, explaining that the reduced requirements apply to devices made with surface finishing that has no history of adverse events linked to corrosion or nickel ion release.
FDA released the final guidance on the same day as publishing a draft on the biocompatibility of certain devices that come into contact with the skin. The draft applies to devices made from common polymers and fabrics that have a long history of safe use in devices that touch the skin. As it stands, FDA said it expends "significant ... review resources" on obtaining information to justify the omission of biocompatibility testing for such devices.
Given the history of safe use of the materials, FDA is proposing a different approach. If enacted, the new approach would enable companies to include specific material information such as a statement about the safe use of the materials in premarket filings in lieu of biocompatibility testing data.
FDA is accepting feedback on the draft until Dec. 14.