What is nitinol and where is it used?

August 16, 2024 By Jim Hammerand

Nitinol — a nickel-titanium alloy — is used for medical devices such as stents, heart valves, catheters and orthopedics. [Photo via Adobe Stock]

Nitinol is a nearly equiatomic metal alloy of nickel and titanium with unique properties, including superelasticity (also called pseudoelasticity) and shape memory.

Superelasticity/pseudoelasticity means medical-grade nitinol shows great elasticity under stress and can snap back to its original shape when pressure is released.

Nitinol’s superelastic properties allow medical devices using it to compress to a lower profile when being placed in a patient using a catheter. Implants made of nitinol such as heart valves expand to their intended size and shape at the site of implantation and remain inside the patient, while nitinol therapy devices such as ablation catheters expand inside the body, treat targeted tissue, and then compress again for retrieval.

Shape memory means medical-grade nitinol can remember its original shape and return to it when heated. For example, some catheter-delivered implants are designed to expand to their pre-formed shape at body temperature for permanent placement.

A promising application of nitinol’s shape memory properties is under development by heart failure startup Adona Medical, which is working on a heart shunt device that can be adjusted for variable flow rates.

“With an increasing trend to treat patients using minimally invasive procedures, nitinol has become a popular choice of material due to its ability to return to its original shape after being mechanically deformed or after heat is applied,” the FDA said in a nitinol guidance document. “These properties are due to reversible transformations between the austenite and martensite phases, which may be temperature-induced (shape-memory) or stress-induced (pseudoelasticity). As a result, nitinol can withstand greater amounts of reversible deformations without plastic deformation than conventional metallic alloys, such as stainless steel, titanium, or cobalt-chrome alloys.”

This illustration shows the nitinol frictional elements on Abbott TriClip’ grippers securing a tricuspid heart valve’s leaflets. [Image courtesy of Abbott]

Medtronic’s Affera Sphere-360 pulsed field ablation catheter is adjustable, allowing the nitinol electrode to take different shapes inside a patient. [Illustration courtesy of Medtronic]

The name “nitinol” comes from the metals nickel and tItanium plus “NOL” for Naval Ordnance Laboratory. That’s the U.S military explosives testing facility (now known as the Naval Surface Warfare Center) in White Oak, Maryland, where nitinol was developed. Fun fact: The former NOL facility in White Oak is now the FDA’s headquarters.

Medical nitinol processing turns a solid tube into stents like these — one compressed and the other expanded. [Photo by Zarathustra via Adobe Stock]

Titanium sponge (pictured) is a key ingredient for medical nitinol manufacturing. [Photo by Alexey Rezvykh via Adobe Stock]

Find more information about materials used for medical devices in our Medical Device Handbook.

This post was originally published in 2016 and most recently updated in September 2024.