Nitinol biocompatibility
Biomedical applications that utilize nitinol include stents, heart valve tools, bone anchors, staples, septal defect devices and implants.
In alloys, such as nitinol, the formation of an oxide layer not only protects against corrosion, but also removes Ni atoms from the surface of the material.
Mechanical polishing removes many surface impurities and crystal structure breaks that may promote corrosion.
In order for nitinol to have the desired superelastic and shape memory properties, heat treatment is required.
After heat treatment, the surface oxide layer contains a larger concentration of nickel in the form of NiO2 and NiO.
[6] The decrease in nickel concentration in the surface layer of nitinol is correlated with a greater corrosion resistance.
After passivation in a nitric acid solution, nitinol stent components showed significantly higher breakdown potentials than those that were unpassivated.
[citation needed] Thrombogenicity, a material’s tendency to induce clot formation, is an important factor that determines the biocompatibility of any biomaterial that comes into contact with the bloodstream.
It has been suggested that fibrinogen may cause platelet activation due to a breakdown of the protein structure as it interacts with high energy grain boundaries on certain surfaces.
By the time the drug therapy has ceased, ideally, a layer of endothelial cells, which line the inside of blood vessels would coat the outside of the stent.
New advances with micro laser welding have vastly improved the quality of medical devices made with nitinol.
[citation needed] Nitinol is an important alloy for use in medical devices, due to its exceptional biocompatibility, especially in the areas of corrosion resistance and thrombogenicity.
Corrosion resistance is enhanced through methods that produce a uniform titanium dioxide layer on the surface with very few defects and impurities.
This research involves producing a coating that is very much like biologic material in order to further lessen the foreign body reaction.
