Biocorrosion and biomechanical analysis of explant devices
Date Issued
March 26, 2011
Abstract
Introduction: Preliminary studies have revealed that stents undergo corrosion in vivo, with
significant release of metallic ions into surrounding tissues. It is believed that high
concentrations of metal ions from stents are toxic to vascular smooth muscle cells and
stimulate both inflammatory and fibrotic reactions leading to neointimal formation and a
predisposition to device failure. To separate the mechanical effects from the local
environmental effects on the stent surface, in-vitro mechanical studies were performed on
various combinations of stents under low and high curvature and in overlapping positions to
compare the results of surface corrosion with the explanted stents.
Materials and Methods: Accelerated biomechanical studies were performed on Stainless
Steel (SS), Nickel Titanium (NiTi) and Cobalt-Chromium (CoCr) stents using
Bose®ElectroForce®9110 Stent/Graft mechanical testing instrument. The tested stents
underwent surface evaluation by Scanning Electron Microscope (SEM) to identify locations
of pitting, fretting and cracking phenomena due to interfacial conditions.
Results: Wear features were observed on mechanically tested stents, in single and
overlapping cases, in both straight and curved modes. Surface alterations predominantly due
to fretting had occurred in the overlapping cases where we observed localized fret features in
the areas where there is significant crossing of the wire from both stents. Crevices and
fractures were observed in the presence of geometric curvature.
Discussion and conclusion: Wear features from cadaver specimens were similar to the
surface alterations from some of the mechanical studies. The key finding was that mechanical
factors such as arterial curvature combined with stent overlapping enhanced surface
alterations, increased the corroded regions and the degree of corrosion in comparison to the
single stent-straight artery configuration. The effect of metal corrosion on the arterial wall,
the vascular responses and possible cause-effect relationships for biological reactions leading
to restenosis are unknown and need further investigation.
significant release of metallic ions into surrounding tissues. It is believed that high
concentrations of metal ions from stents are toxic to vascular smooth muscle cells and
stimulate both inflammatory and fibrotic reactions leading to neointimal formation and a
predisposition to device failure. To separate the mechanical effects from the local
environmental effects on the stent surface, in-vitro mechanical studies were performed on
various combinations of stents under low and high curvature and in overlapping positions to
compare the results of surface corrosion with the explanted stents.
Materials and Methods: Accelerated biomechanical studies were performed on Stainless
Steel (SS), Nickel Titanium (NiTi) and Cobalt-Chromium (CoCr) stents using
Bose®ElectroForce®9110 Stent/Graft mechanical testing instrument. The tested stents
underwent surface evaluation by Scanning Electron Microscope (SEM) to identify locations
of pitting, fretting and cracking phenomena due to interfacial conditions.
Results: Wear features were observed on mechanically tested stents, in single and
overlapping cases, in both straight and curved modes. Surface alterations predominantly due
to fretting had occurred in the overlapping cases where we observed localized fret features in
the areas where there is significant crossing of the wire from both stents. Crevices and
fractures were observed in the presence of geometric curvature.
Discussion and conclusion: Wear features from cadaver specimens were similar to the
surface alterations from some of the mechanical studies. The key finding was that mechanical
factors such as arterial curvature combined with stent overlapping enhanced surface
alterations, increased the corroded regions and the degree of corrosion in comparison to the
single stent-straight artery configuration. The effect of metal corrosion on the arterial wall,
the vascular responses and possible cause-effect relationships for biological reactions leading
to restenosis are unknown and need further investigation.
Subjects
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