Biocorrosion and biomechanical analysis of explant devices
Date Issued
July 8, 2010
Abstract
Introduction: Preliminary studies have revealed that stainless steel (SS) and nickel titanium (NiTi) stents
undergo corrosion in vivo, with significant release of metallic ions into surrounding tissues. It is
believed that high concentrations of metal ions from both SS and NiTi 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 fretting,
pitting and gouging with the explanted stents.
Methods: Accelerated biomechanical studies were performed on SS, NiTi and Cobalt-Chromium
(CoCr) stents using Bose®ElectroForce®9110 Stent/Graft Test (Bose Corporation, Bethel, WA)
mechanical testing instrument. The stents were deployed in latex tubing mock arteries and the system
was exposed to flow of saline representative of coronary flow under physiologic wall motion 5-10% and
was programmed to perform several million of cycles to simulate several years of operation. The tested
stents underwent surface evaluation by Scanning Electron Microscope (SEM) and optical microscope
Keyence to identify locations of pitting, fretting and cracking phenomena due to interfacial conditions.
Results: Wear features were observed on the stents surface in both straight and low curvature modes
especially in the overlapping cases where we observed localized fret features in the areas where there is
significant crossing of the wire from both stents. Fracture was also observed in addition to fretting
features on both the NiTi and CoCr stents placed in a curved latex tube at 40% overlap under 104
million cycles. Fracture surfaces show a fatigue mechanism.
Discussion and conclusion: In some occasions the fretting features from cadaver specimens were similar
to the fretting features from the mechanical studies. High curvature and the factor of stent overlap
increased the corroded regions and the degree of corrosion. This will provide insights into the
mechanisms of stent corrosion and vascular responses and indicate possible cause-effect relationships
for biological reactions leading to restenosis.
undergo corrosion in vivo, with significant release of metallic ions into surrounding tissues. It is
believed that high concentrations of metal ions from both SS and NiTi 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 fretting,
pitting and gouging with the explanted stents.
Methods: Accelerated biomechanical studies were performed on SS, NiTi and Cobalt-Chromium
(CoCr) stents using Bose®ElectroForce®9110 Stent/Graft Test (Bose Corporation, Bethel, WA)
mechanical testing instrument. The stents were deployed in latex tubing mock arteries and the system
was exposed to flow of saline representative of coronary flow under physiologic wall motion 5-10% and
was programmed to perform several million of cycles to simulate several years of operation. The tested
stents underwent surface evaluation by Scanning Electron Microscope (SEM) and optical microscope
Keyence to identify locations of pitting, fretting and cracking phenomena due to interfacial conditions.
Results: Wear features were observed on the stents surface in both straight and low curvature modes
especially in the overlapping cases where we observed localized fret features in the areas where there is
significant crossing of the wire from both stents. Fracture was also observed in addition to fretting
features on both the NiTi and CoCr stents placed in a curved latex tube at 40% overlap under 104
million cycles. Fracture surfaces show a fatigue mechanism.
Discussion and conclusion: In some occasions the fretting features from cadaver specimens were similar
to the fretting features from the mechanical studies. High curvature and the factor of stent overlap
increased the corroded regions and the degree of corrosion. This will provide insights into the
mechanisms of stent corrosion and vascular responses and indicate possible cause-effect relationships
for biological reactions leading to restenosis.