title: Multi-scale mechanical investigation of stainless steel and cobalt-chromium stents.
abstract: In-stent restenosis (ISR) remains a significant limitation despite the considerable previous clinical and investigative emphasis on the problem. Complications arising from the interaction of stent materials with the surrounding vessel wall as well as from the mechanical forces developing after implantation, play an important role in the development of ISR. To investigate the relation between mechanical factors and stent structural integrity, and to identify any structural weakness points on the geometry of commercially available Stainless Steel and Cobalt-Chromium stents, accelerated pulsatile durability tests were carried out in a simulated physiological environment. Potential spatial variations in the mechanical properties on stent struts and their role in the observed premature failures of the stent devices during operation were also examined. Fretting wear and fatigue-induced fractures were found on stent surfaces after exposure to cyclic loading similar to that arising in vivo. Nanoindentation studies performed on various locations along the stent struts have shown that the hardness of specific stent locations significantly increases after mechanical expansion. The increase in hardness was associated with a reduction of the material's ability to dissipate energy in plastic deformations, therefore an increased vulnerability to fracture and fatigue. We conclude that the locations of fatigue fractures in stent struts are controlled not only by the geometrically-driven stress concentrations developing during cyclic loading but also by the local material mechanical changes that are imparted on various parts of the stent during the deployment process.
authors.affiliation: Department of Mechanical Engineering and Materials Science and Engineering, Cyprus University of Technology, Limassol 3036, Cyprus. Electronic address: k.kapnisis@cut.ac.cy.
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Kapnisis
authors.affiliation: Department of Mechanical Engineering and Materials Science and Engineering, Cyprus University of Technology, Limassol 3036, Cyprus.
authors.forename: Georgios
authors.initials: G
authors.lastname: Constantinides
authors.affiliation: Department of Mechanical Engineering and Materials Science and Engineering, Cyprus University of Technology, Limassol 3036, Cyprus.
authors.forename: Harry
authors.initials: H
authors.lastname: Georgiou
authors.affiliation: Department of Materials Science, Transilvania University of Brasov, Brasov 500036, Romania.
authors.forename: Daniel
authors.initials: D
authors.lastname: Cristea
authors.affiliation: Department of Materials Science, Transilvania University of Brasov, Brasov 500036, Romania.
authors.forename: Camelia
authors.initials: C
authors.lastname: Gabor
authors.affiliation: Department of Materials Science, Transilvania University of Brasov, Brasov 500036, Romania.
authors.forename: Daniel
authors.initials: D
authors.lastname: Munteanu
authors.affiliation: Department of Medicine, University of Alabama at Birmingham, Birmingham, AL 35294-0111, USA.
authors.forename: Brigitta
authors.initials: B
authors.lastname: Brott
authors.affiliation: Department of Pathology, University of Alabama at Birmingham, Birmingham, AL 35294-0111, USA.
authors.forename: Peter
authors.initials: P
authors.lastname: Anderson
authors.affiliation: Department of Prosthodontics, University of Alabama at Birmingham, Birmingham, AL 35294-0111, USA.
authors.forename: Jack
authors.initials: J
authors.lastname: Lemons
authors.affiliation: Department of Mechanical Engineering and Materials Science and Engineering, Cyprus University of Technology, Limassol 3036, Cyprus.
authors.forename: Andreas
authors.initials: A
authors.lastname: Anayiotos
mesh_terms: D002857:Chromium; D003035:Cobalt; D003251:Constriction, Pathologic; D008422:Materials Testing; D013193:Stainless Steel; D015607:Stents; D013314:Stress, Mechanical
chemical_list: D002857:Chromium; D013193:Stainless Steel; D003035:Cobalt
keywords: Fracture; In-stent restenosis (ISR); Mechanical properties; Nanoindentation; Stents