Corroded nitinol wires in explanted aortic endografts: an important mechanism of failure?
OBJECTIVE
To analyze surface alterations and fractures observed in the nitinol stent wires of explanted endovascular grafts used for treatment of abdominal aortic aneurysm.


METHODS
Twenty-one explanted Stentor devices and 1 Cragg stent were received from investigators in Germany and France. After macroscopy and photography, the explants were cleaned and the polyester coating removed. The frame was examined completely by stereomicroscopy, and irregularities were assayed by scanning electron microscopy and energy dispersive x-ray analysis (EDAX). The observed alterations were classified according to stereomicroscopic and electron microscopic morphology.


RESULTS
The mean implantation interval for the endografts was 29.1 +/- 13.2 months (range 5-46). All examined explants, even those retrieved after only a few months in situ, showed pitlike surface damage 10-25 microm in diameter. Larger, irregularly shaped surface alterations were observed in approximately 70% of the explants. Older explants (age >32 months) presented vast regions of decay, with bending of the wire and stress cracks in some areas. EDAX examination revealed decreased nickel concentration in the corroded regions.


CONCLUSIONS
Corrosion of the nitinol wire in endovascular grafts is confirmed. Presumably, the observed pitting and irregularly shaped corrosion defects are the precursors of material failure. They weaken the thin wire, which leads to stress cracks and eventually fracture of the stent wire under circulatory pulsation. Cell-induced electrochemical corrosion and active cellular destruction of surfaces are well-known mechanisms that must be investigated for their possible roles in the corrosion of stent metals.
Heintz
C
C
Department of General, Vascular and Thoracic Surgery, General Hospital of Hamburg-Harburg, Hamburg, Germany. heintz@tuhh.de
Riepe
G
G
Birken
L
L
Kaiser
E
E
Chakfé
N
N
Morlock
M
M
Delling
G
G
Imig
H
H
D000497:Alloys / Q000009:adverse effects*; D017544:Aortic Aneurysm, Abdominal / Q000601:surgery; D019917:Blood Vessel Prosthesis Implantation / Q000295:instrumentation; D003343:Corrosion; D019544:Equipment Failure Analysis / Q000295:instrumentation; D006801:Humans; D008855:Microscopy, Electron, Scanning / Q000295:instrumentation; D009532:Nickel / Q000032:analysis; D015607:Stents; D013997:Time Factors; D019737:Transplants; D014656:Vascular Surgical Procedures / Q000295:instrumentation
D000497:Alloys; C013616:nitinol; D009532:Nickel