PMC

Schematic representation of the mechanism of fretting corrosion and metal ion release in the titanium–cobalt alloy couple. A) initial state of the tribosystem, with the loading and fretting directions marked. B) early stage where the titanium oxide wear debris ploughs the titanium alloy surface to form a chip that remains on the surface due to a folding mechanism. The debris and chips formed on the titanium alloy surface can microplough the cobalt alloy surface, thus damaging the passivation layer of the cobalt alloy. C) final stage of the fretting test where the chips formed on the titanium alloy surface pile up on each other during successive fretting strokes and are laminated together to form raised shelves. The shelves contribute to microploughing of the cobalt alloy surface. When the passivation oxide layer of the cobalt alloy is compromised, dissolution of cobalt, chromium, and molybdenum into the interfacial medium takes place. The metal ions from the corroding cobalt alloy, the oxide‐particle laden liquid fraction of the tribomaterial formed between the surfaces as well as refined grains from the titanium alloy are all incorporated into the shelf during the folding process.

Examples of metallic particle types. (A–C) Titanium Alloy; (D–F) Stainless steel; (G–I) Cobalt chromium alloy (pink arrow identifies the specific cobalt chromium alloy particle)

Visibility bench test comparison of distinct stent alloys.
Notes: Radiopacity of distinct stents with variable alloy composition is shown. The lower row indicates stent strut thickness (in mm and inch).
Abbreviations: PtCr, platinum chromium; CoCr, cobalt chromium; CoNi, colbalt nickel; SS, stainless steel.

SCAAR stent thrombosis rates with various bare-metal stents.
Notes: The graph presents cumulative adjusted risk of definitive stent thrombosis with frequently used bare-metal stents in Sweden between 2007 and 2013. Coroflex Blue, Multilink Vision, and Multilink 8 use a cobalt chromium alloy (CoCr); Titan: titanium stent with nitric oxide coating; Integrity uses cobalt nickel alloy (CoNi); Omega uses the platinum chromium alloy (PtCr). Modified with permission from SCAAR. Swedish Coronary Angiography and Angioplasty Registry. 2015. Available from: http://www.ucr.uu.se/swedeheart/index.php/forskning-scaar/in-english/stent-reports. Accessed April 1, 2015.