Sep 22, 2017

Medtronic Tries To Unlock New Secrets of A Remarkable Material

Nitinol is 10 times more flexible than ordinary metal and a key ingredient in new, innovative devices.

In labs all around the world, Medtronic scientists and engineers are trying to unlock new secrets of an extraordinary metal alloy.

“There is no other material like nitinol,” said Medtronic scientist Carl Schu.

Nitinol stands for Nickel, Titanium, and Naval Ordnance Laboratory (where the alloy was first created). Nitinol is essentially equal parts nickel and titanium and is a key material in some of Medtronic’s newest and most innovative medical devices.

“If we didn’t have nitinol, some of these devices would just not have been possible,” said Dr. Narendra Simha, a Medtronic engineer and a leading expert in the study and use of nitinol in medical devices.

“If we didn’t have nitinol, some of these devices would just not have been possible.'

-- Dr. Narendra Simha

Nitinol is special for two reasons: It possesses a remarkable “shape memory,” so even when it has been crushed or deformed, heating the material can trigger its memory and help return it to its original shape; and it’s considered to be “superelastic,” meaning it can be stretched up to 10 times more than ordinary metals, and under the correct conditions, can also be squeezed or crimped and recover its shape, without heating.

That property in particular – superelasticity – helped in the development of a revolutionary method of replacing heart valves without the typical open heart surgery.

Thanks to nitinol, those new heart valves can be squeezed into a thin delivery device, inserted into a vein in the leg and guided directly to a diseased valve inside the heart.

“In some ways it might look like magic when you see it deploying.'

Cynthia Clague, research director, the Coronary and Structural Heart group 

Expanding treatment to more patients

“In some ways it might look like magic when you see it deploying,” said Cynthia Clague, research director in the Coronary and Structural Heart group at Medtronic. “This technology lets physicians treat patients they couldn’t treat before, patients who weren’t well enough to undergo highly invasive open heart surgery.”

Nitinol is also remarkably durable. Well-designed nitinol stents can withstand hundreds of millions of heartbeats over many years without breaking, making it well-suited for implantable devices.

It’s now common in many other medical devices such as stents and shunts and even has dental applications. 

But that wasn't always the case.

Developed in the mid-20th century, nitinol was, for many years, an amazing material without real-world usefulness.

“In the 1950's there were articles saying ‘Oh great material. What's the application?’” Simha said. “Until medical devices came along, we didn't really know what to do with this fantastic material.”

But Simha says the learning has just begun. 

“If we could get up to, say, 10 floors with this technology, we're probably only at the second or third floor,” Simha said.

Unlocking new potential

For example, unlike most other metal alloys, which expand when heated, Nitinol contracts. And it does so with remarkable strength. Nitinol can easily “lift” more than 4,000 times its own weight. “Essentially, it’s like the engine in your car. It makes things move. But here, you don't need an engine. The material itself is able to do the work. So Nitinol is behaving like an actuator,” Simha said.

Other companies have used nitinol’s actuator property in making insulin pumps for diabetes, and Medtronic is exploring whether that actuator property can be applied in the future to a next generation of implantable medical devices. 

Medtronic teams are actively working to understand other aspects of nitinol, right down to its atomic structure. They’re examining how different nickel/titanium ratios change its behavior; they’re devising new models to test and manufacture it; and they’re trying to figure out what else nitinol can do.

“There are emerging capabilities that are coming with nitinol which we don't even know how we could use yet,” Simha said.

“I probably couldn’t list all of the things Medtronic has going because of nitinol – we’re always playing with it in new applications and new areas,” Clague said. “But certainly, it’s a mainstay of our next generation devices. It’s going to be around for a long time and we’re just going to keep pushing the limits of what we can do with it.”

Because what we don’t yet know about nitinol might someday be even more impressive than what we know today.