VII. NON-CLINICAL TESTS

A. Material Characterization

3. Stent Corrosion Resistance

Significance
Stent corrosion can cause or contribute to premature stent failure. In addition, corrosion byproducts may be toxic or cause other adverse biological and tissue responses.

Recommendation
We recommend that you address the corrosion properties of your device described below. If some of these characteristics do not apply to your device, we recommend that you explain this in your application.

Pitting and Crevice Corrosion Potential
We recommend that you characterize the corrosion potential of your finished stent using a method such as ASTM F2129.

You may use literature citations or previous experience with stents; however, the materials, design, and fabrication processes specific to your stent may reduce or eliminate the applicability of generic literature. For example, the pitting corrosion resistance of nitinol is sensitive to processing variables such as heat treatment and electropolishing; therefore, for a nitinol stent, you should characterize the corrosion potential of the finished stent.

Fretting Corrosion
We recommend that you address the potential for fretting corrosion in designs that allow micro-motion between components, such as woven wires, that may disrupt an associated coating or passive film. If you expect that your stents will be overlapped during clinical procedures, then we recommend that you address the possibility of the additional risk of stent failure caused by fretting corrosion. If you believe that overlapping your stents does create an additional risk, then we recommend that you test overlapping stents as part of the corrosion experiment.

Galvanic Corrosion
If your stent contains more than one type of metal, such as a base stent material with added marker bands, we recommend that you demonstrate the design’s resistance to galvanic corrosion. If you expect that your stents will be overlapped during clinical procedures, and the contacting or overlapping stents may be made of different materials, we recommend that you address the potential for galvanic corrosion between stents. We recommend the methods described in ASTM G71 or their equivalents. These methods may be modified to provide for testing of finished stents, for example, by incorporating the experimental setup described in ASTM F2129.

A copy of the original document can by found on the FDA website, http://www.fda.gov.